Channel estimation and transmit power control in wireless body area networks

Wireless body area networks have recently received much attention because of their application to assisted living and remote patient monitoring. For these applications, energy minimisation is a critical issue since, in many cases, batteries cannot be easily replaced or recharged. Reducing energy expenditure by avoiding unnecessary high transmission power and minimising frame retransmissions is therefore crucial. In this study, a transmit power control scheme suitable for IEEE 802.15.6 networks operating in beacon mode with superframe boundaries is proposed. The transmission power is modulated, frame-by-frame, according to a run-time estimation of the channel conditions. Power measurements u…

MAC–Engine: a new architecture for executing MAC algorithms on commodity WiFi hardware

In this demo, we prove that the flexibility supported by off–the–shelf IEEE 802.11 hardware can be significantly ex- tended if we move the control of the MAC programming interface from the driver to the firmware, i.e. from the host CPU to the card CPU. To this purpose, we introduce the concept of MAC–Engine, that is an executor of Pro- grammable Finite State Machines (PFSM) implemented at the firmware level: we show how the card itself can support different protocol logics thanks to PFSM bytecode repre- sentations that can be dynamically injected inside the card memory at run-time without incurring in down time issues or network disconnect events. We provide different PFSM examples in order…

Experimental Assessment of the Backoff Behavior of Commercial IEEE 802.11b Network Cards

It has been observed that different IEEE 802.11 commercial cards produced by different vendors experience different performance, either when accessing alone the channel, as well as when competing against each other. These differences persist also when thorough measurement methodologies (such as RF shielding, laptop rotation, etc) are applied, and alignment of the environmental factors (same laptop models, traffic generators, etc) is carried out. This paper provides an extensive experimental characterization of the backoff operation of six commercial NIC cards. It suggests a relevant methodological approach, namely a repeatable, well defined, set of experiments, for such a characterization. …

Joint routing and per-flow fairness in wireless multihop networks

In wireless multihop networks communication between two end-nodes is carried out by hopping over multiple short wireless links. Traditional CSMA/CA based media access control does not work satisfactory in a multihop scenario, since an intended target of a communication may be subject to mutual interference imposed by concurrent transmissions from nodes which cannot directly sense each other, causing unfair throughput allocation. Although TDMA seems to be a more promising solution, careful transmission scheduling is needed in order to achieve error-free communication and fairness. In our previous work, a TDMA scheduling algorithm has been proposed that schedules the transmissions in a fair m…

Learning from Errors: Detecting ZigBee Interference in WiFi Networks

In this work we show how to detect ZigBee interference on commodity WiFi cards by monitoring the reception errors, such as synchronization errors, invalid header formats, too long frames, etc., caused by ZigBee transmissions. Indeed, in presence of non-WiFi modulated signals, the occurrence of these types of errors follows statistics that can be easily recognized. Moreover, the duration of the error bursts depends on the transmission interval of the interference source, while the error spacing depends on the receiver implementation. On the basis of these considerations, we propose the adoption of hidden Markov chains for characterizing the behavior of WiFi receivers in presence of controlle…

SHARP: Environment and Person Independent Activity Recognition with Commodity IEEE 802.11 Access Points

In this article we present SHARP, an original approach for obtaining human activity recognition (HAR) through the use of commercial IEEE 802.11 (Wi-Fi) devices. SHARP grants the possibility to discern the activities of different persons, across different time-spans and environments. To achieve this, we devise a new technique to clean and process the channel frequency response (CFR) phase of the Wi-Fi channel, obtaining an estimate of the Doppler shift at a radio monitor device. The Doppler shift reveals the presence of moving scatterers in the environment, while not being affected by (environment-specific) static objects. SHARP is trained on data collected as a person performs seven differe…

Efficiency analysis of burst transmissions with block ACK in contention-based 802.11e WLANs

The channel utilization efficiency of the standard 802.11 networks is severely compromised when high data transmission rates are employed, since physical layer headers and control frames are transmitted at low rate, thus wasting more channel time, proportionally. The extensions defined in the emerging 802.11e for quality-of-service (QoS) provisioning include some new mechanisms developed in order to improve the efficiency. Those include data transmission bursting (referred to as TXOP operation) and acknowledgment aggregation (referred to as block ACK). These two features allow it to offer new data transmission services, in which the data delivery and acknowledgment unit is not a single fram…

Impact of Spreading Factor Imperfect Orthogonality in LoRa Communications

In this paper we study the impact of imperfect-orthogonality in LoRa spreading factors (SFs) in simulation and real-world experiments. First, we analyze LoRa modulation numerically and show that collisions between packets of different SFs can indeed cause packet loss if the interference power received is strong enough. Second, we validate such findings using commercial devices, confirming our numerical results. Third, we modified and extended LoRaSim, an open-source LoRa simulator, to measure the impact of inter-SF collisions and fading (which was not taken into account previously in the simulator). Our results show that non-orthogonality of the SFs can deteriorate significantly the perform…

WiSHFUL : enabling coordination solutions for managing heterogeneous wireless networks

The paradigm shift toward the Internet of Things results in an increasing number of wireless applications being deployed. Since many of these applications contend for the same physical medium (i.e., the unlicensed ISM bands), there is a clear need for beyond-state-of-the-art solutions that coordinate medium access across heterogeneous wireless networks. Such solutions demand fine-grained control of each device and technology, which currently requires a substantial amount of effort given that the control APIs are different on each hardware platform, technology, and operating system. In this article an open architecture is proposed that overcomes this hurdle by providing unified programming i…

An architecture Wi-fi and GPRS for efficient management of distribution electrical networks

In this paper, a telecommunication infrastructure for faults management is proposed. The complete automation of the electrical energy distribution requires the implementation of suitable data transmission systems able to easily interface with microprocessor based systems and to handle large amount of data. In particular, reliability and speed of the data transmission system are required in the fault diagnosis and post-fault management procedures, in order to guarantee high quality standards. The proposed diagnostic system indeed works by means of a set of intercommunicating MV/LV dasiaintelligent substationspsila. In this paper, after a brief description of the fault diagnostic system, an o…

MAC design on real 802.11 devices: From exponential to Moderated Backoff

In this paper we describe how a novel backoff mechanism called Moderated Backoff (MB), recently proposed as a standard extension for 802.11 networks, has been prototyped and experimentally validated on a commercial 802.11 card before being ratified. Indeed, for performance reasons, the time critical operations of MAC protocols, such as the backoff mechanism, are implemented into the card hardware/firmware and cannot be arbitrarily changed by third parties or by manufacturers only for experimental reasons. Our validation has been possible thanks to the availability of the so called Wireless MAC Processor (WMP), a prototype of a novel wireless card architecture in which MAC protocols can be p…

The Risks of WiFi Flexibility: Enabling and Detecting Cheating

Flexibility is an important paradigm for future WiFi networks. However, it also opens the possibility for diverse methods of cheating, which users can perform to increase their throughput. Therefore, it is important to develop the necessary tools to mitigate such efforts. In this paper we first discuss the risks of flexibility in terms of misbehaviour. We then propose an architecture to detect misbehaviour and react by punishing the cheaters. The proposed architecture utilizes advanced passive monitoring, flexible WiFi software, and appropriate reasoning to detect cheating. We validate its performance and discuss means of punishment

FLUMO: FLexible Underwater MOdem

The last years have seen a growing interest in underwater acoustic communications because of its applications in marine research, oceanography, marine commercial operations, the offshore oil industry and defense. High-speed communication in the underwater acoustic channel has been challenging because of limited bandwidth, extended multipath, refractive properties of the medium, severe fading, rapid time variation and large Doppler shifts. In this paper, we show an implementation of a flexible Software-Defined Acoustic (SDA) underwater modem, where modulation parameters are completely tunable to optimize performance. In particular, we develop the system architecture following two key ideas. …

On the effects of transmit power control on the energy consumption of WiFi network cards

Transmit power control has been largely proposed as a solution to improve the performance of packet radio systems in terms of increased throughput, spatial reuse and battery lifetime for mobile terminals. However, the benefits of transmit power control schemes on these different performance figures may strongly depend on the employed PHY technology and channel access mechanism. In this paper, we focus on the effects of power control on the energy consumption of WiFi network cards. By means of several experimental tests carried out under different operation conditions and modulation schemes, we try to justify why the reduction of the transmission power has a marginal effect on the overall en…

Achieving Fair Bandwidth Distribution in WiFi Networks: A Game Theoretical Approach

International audience; Achieving fair bandwidth distribution among uplink and downlink ows in IEEE 802.11 infrastructure networks is a complex issue, due to the well-known features of the Distributed Coordination Function (DCF) which regulates the access to the shared medium. Indeed, the dynamic adaptation of the contention windows causes phenomena of short-term unfairness, while the use of homogeneous contention parameters among the contending nodes makes the aggregated downlink bandwidth equal to the uplink bandwidth of a single node. We propose a dynamic tuning of the contention parameters used by the nodes, based on simple network monitoring functionalities and rational strategies. Spe…

What's New for QoS in IEEE 802.11?

Two amendments to IEEE 802.11 have recently been published: 802.11aa and 802.11ae. Both enhance Quality of Service (QoS) provisioning in Wi-Fi networks by providing support for multicast transmission, enhanced audio video streaming, coping with inter-network interference, and improved prioritization of management frames. The proposed solutions either extend mechanisms already existing in the standard or introduce new ones. Therefore, it is important for researchers to understand the new functionalities. To this end we provide the first description of these latest mechanisms: we present the motivation behind them, explain their design principles, provide examples of usage, and comment on com…

Performance of LoRa technology: link-level and cell-level performance

Abstract LoRa is a chirp spread spectrum technology that is becoming very popular for low-power wide-area networks, with high-density devices. In this chapter, we study the capacity of LoRa in rejecting different interfering signals. First, we analyze LoRa modulation numerically demonstrating that channel captures appear easily and that collisions between packets modulated with different spreading factors (SFs) are not uncommon. We validate such findings in experiments based on commercial devices and software-defined radios. Second, we model the network capacity obtainable in a typical LoRa cell: we show that high SFs can be seriously influenced by inter-SF collisions and that fading has a …

Wireless card virtualization: from virtual NICs to virtual MAC machines

Virtualization has been a hot topic in computer science this last 10 years, and a key enabler to the recent advances. By technically enabling the Cloud paradigm, virtualization is becoming an inspiring source for the whole IT industry. At the same moment the virtualization of commodity PC was envisioned, Software Defined Radio started as a huge promise of efficient wireless transmission hardware. Unfortunately, the pace of innovation has still to reach the one of the PC virtualization. Yet, there is a another option. The current state of the art of hardware and software of wireless adapter in standard PC reveals interesting capabilities in terms of unused wireless capacity, processing power…

Learning From Errors: Detecting Cross-Technology Interference in WiFi Networks

In this paper, we show that inter-technology interference can be recognized using commodity WiFi devices by monitoring the statistics of receiver errors. Indeed, while for WiFi standard frames the error probability varies during the frame reception in different frame fields (PHY, MAC headers, and payloads) protected with heterogeneous coding, errors may appear randomly at any point during the time the demodulator is trying to receive an exogenous interfering signal. We thus detect and identify cross-technology interference on off-the-shelf WiFi cards by monitoring the sequence of receiver errors (bad PLCP, bad FCS, invalid headers, etc.) and propose two methods to recognize the source of in…

On the anomalous behavior of IEEE 802.11 commercial cards

Designing the 5G network infrastructure: a flexible and reconfigurable architecture based on context and content information

5G networks will have to offer extremely high volumes of content, compared to those of today’s. Moreover, they will have to support heterogeneous traffics, including machine-to-machine, generated by a massive volume of Internet-of-Things devices. Traffic demands will be variable in time and space. In this work, we argue that all this can be achieved in a cost-effective way if the network is flexible and reconfigurable. We present the Flex5Gware network architecture, designed to meet the above requirements. Moreover, we discuss the links between flexibility and reconfigurability, on the one side, and context awareness and content awareness, on the other; we show how two of the building…

Rethinking the IEEE 802.11e EDCA Performance Modeling Methodology

Analytical modeling of the 802.11e enhanced distributed channel access (EDCA) mechanism is today a fairly mature research area, considering the very large number of papers that have appeared in the literature. However, most work in this area models the EDCA operation through per-slot statistics, namely probability of transmission and collisions referred to "slots." In so doing, they still share a methodology originally proposed for the 802.11 Distributed Coordination Function (DCF), although they do extend it by considering differentiated transmission/ collision probabilities over different slots.We aim to show that it is possible to devise 802.11e models that do not rely on per-slot statis…

Remarks on IEEE 802.11 DCF performance analysis

This letter presents a new approach to evaluate the throughput/delay performance of the 802.11 distributed coordination function (DCF). Our approach relies on elementary conditional probability arguments rather than bidimensional Markov chains (as proposed in previous models) and can be easily extended to account for backoff operation more general than DCF's one.

MAC-Engine

In this demo, we prove that the flexibility supported by off-the-shelf IEEE 802.11 hardware can be significantly extended if we move the control of the MAC programming interface from the driver to the firmware, i.e. from the host CPU to the card CPU. To this purpose, we introduce the concept of MAC--Engine, that is an executor of Programmable Finite State Machines (PFSM) implemented at the firmware level: we show how the card itself can support different protocol logics thanks to PFSM bytecode representations that can be dynamically injected inside the card memory at run-time without incurring in down time issues or network disconnect events. We provide different PFSM examples in order to t…

Optimal Resource Allocation in Multi-Hop Networks: Contention vs. Scheduling

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) is actually the most used method in ad-hoc networks for transmitting on a contending medium, even if it shows poor performance in presence of hidden nodes. To increase performance, we propose an algorithm that combines CSMA and TDMA (Time Division Multiple Access) approaches. The adopted solution consists of grouping contending nodes in non-interfering subsets and granting a different numbers of time slots to different groups, while using the CSMA to manage medium access among nodes belonging to the same subset. An optimization procedure to assign the time slots to each subset of nodes and to find an equilibrium between contention …

A simulation study of load balancing algorithms in cellular packet networks

This paper provides a comparative performance evaluation of various load balancing schemes in cellular packet networks. With respect to traditional schemes, that measure each cell load in terms of number of admitted calls, our schemes use supplementary packet level information, expressed in terms of effective resource consumption of each individual call when retransmission mechanisms are employed. The simulation model adopted is based on a toroidal cellular network topology, to avoid border effects affecting the numerical results.

Data fusion analysis applied to different climate change models: an application to the energy consumptions of a building office

The paper aims to achieve the modelling of climate change effects on heating and cooling in the building sector, through the use of the available Intergovernmental Panel on Climate Change forecasted data. Data from several different climate models will be fused with regards to mean air temperature, wind speed and horizontal solar radiation. Several climatic models data were analyzed ranging from January 2006 to December 2100. Rather than considering each model in isolation, we propose a data fusion approach for providing a robust combined model for morphing an existing weather data file. The final aim is simulating future energy use for heating and cooling of a reference building as a conse…

Understanding 802.11e contention-based prioritization mechanisms and their coexistence with legacy 802.11 stations

The IEEE 802.11e task group has reached a stable consensus on two basic contention-based priority mechanisms to promote for standardization: usage of different arbitration interframe spaces and usage of different minimum/maximum contention windows. The goal of this article is to provide a thorough understanding of the principles behind their operation. To this purpose, rather than limit our investigation to high-level (e.g. throughput and delay) performance figures, we take a closer look at their detailed operation, also in terms of low-level performance metrics (e.g., the probability of accessing specific channel slots). Our investigation on one hand confirms that AIFS differentiation prov…

Demo - MAC learning: Enabling automatic combination of elementary protocol components

Cognition as a way to deal with the challenges of future wireless networks has been largely considered by the recent literature, with a main focus on physical layer adaptability and dynamic spectrum access. In this demo, we show how a simple cognition mechanism can be also applied at the MAC layer, by exploiting the emerging paradigm of programmable wireless cards. The idea is using the formal definition of simple MAC protocol components and platform-independent representation of channel events gathered from the wireless node, for emulating the behavior of protocols which are not currently running on the network, learning about their expected performance, and dynamically reconfiguring the w…

“Vendor-Affected” WLAN experimental results: A Pandora’s Box?

WLC24-1: Dynamic MAC Parameters Configuration for Performance Optimization in 802.11e Networks

Quality of service support in wireless LAN is a theme of current interest. Several solutions have been proposed in literature in order to protect time-sensitive traffic from best-effort traffic. According to the EDCA proposal, which is a completely distributed solution, the service differentiation is provided by giving probabilistically higher number of channel accesses to stations involved in real-time applications. To this purpose, the MAC parameter settings of each contending stations can be tuned dynamically. In this paper, we face the problem of tuning the EDCA MAC parameters in common scenarios in which a given number of low-rate delay-sensitive traffic flows share the channel with so…

Testbed implementation of the meta-MAC protocol

The meta-MAC protocol is a systematic and automatic method to dynamically combine any set of existing MAC protocols into a single higher layer MAC protocol. We present a proof-of-concept implementation of the meta-MAC protocol by utilizing a programmable wireless MAC processor (WMP) on top of a commodity wireless card in combination with a host-level software module. The implementation allows us to combine, with certain constraints, a number of protocols each represented as an extended finite state machine. To illustrate the combination principle, we combine protocols of the same type but with varying parameters in a wireless mesh network. Specifically, we combine TDMA protocols with all po…

Out-of-Band Signaling Scheme for High Speed Wireless LANs

In recent years, the physical layer data rate provided by 802.11 Wireless LANs has dramatically increased thanks to significant advances in the modulation and coding techniques employed. However, previous studies show that the 802.11 MAC operation, namely the distributed coordination function (DCF), represents a limiting factor: the throughput efficiency drops as the channel bit rate increases, and a throughput upper limit does indeed exist when the channel bit rate goes to infinite high. These findings indicate that the performance of the DCF protocol will not be efficiently improved by merely increasing the channel bit rate. This paper shows that the DCF performance may significantly bene…

Differentiation mechanisms for heterogeneous traffic integration in IEEE 802.11 networks

Fake News Spreaders Detection: Sometimes Attention Is Not All You Need

Guided by a corpus linguistics approach, in this article we present a comparative evaluation of State-of-the-Art (SotA) models, with a special focus on Transformers, to address the task of Fake News Spreaders (i.e., users that share Fake News) detection. First, we explore the reference multilingual dataset for the considered task, exploiting corpus linguistics techniques, such as chi-square test, keywords and Word Sketch. Second, we perform experiments on several models for Natural Language Processing. Third, we perform a comparative evaluation using the most recent Transformer-based models (RoBERTa, DistilBERT, BERT, XLNet, ELECTRA, Longformer) and other deep and non-deep SotA models (CNN,…

Channel-dependent load balancing in wireless packet networks

This paper refers to a wireless cellular packet network scenario where fast retransmission of corrupted packets is used to improve the packet error ratio. Since the ‘gross’ packet transmission rate (including retransmission) depends on the channel quality perceived, admitted calls weight unevenly in terms of effective resource consumption. In this paper, we suggest using channel quality information to drive load balancing mechanisms. We propose two novel metrics to determine the best cell to attach to, during handover or new call origination. Extensive simulation results prove the superiority of our proposed schemes with respect to traditional load balancing, which base their operation on t…

In.Line: A Navigation Game for Visually Impaired People

Part 3: Serious Games; International audience; In.line is a novel game based on a navigation system, called ARIANNA (pAth Recognition for Indoor Assisted NavigatioN with Augmented perception, [1]), primarily designed for visually impaired people permitting to navigate and find some points of interests in an indoor and outdoor environment by following a path painted or stuck on the floor. The aim of the game is twofold: (1) let the users learn and familiarize with the system, (2) improve blind people spatial skills to let them learn and acquire an allocentric spatial representation. The impact stands in the possibility of enhancing the social inclusion of a large part of the society that is …

Dynamic MAC Parameters Configuration for Performance Optimization in 802.11e Networks

Quality of service support in wireless LAN is a theme of current interest. Several solutions have been proposed in literature in order to protect time-sensitive traffic from best-effort traffic. According to the EDCA proposal, which is a completely distributed solution, the service differentiation is provided by giving probabilistically higher number of channel accesses to stations involved in real-time applications. To this purpose, the MAC parameter settings of each contending stations can be tuned dynamically. In this paper, we face the problem of tuning the EDCA MAC parameters in common scenarios in which a given number of low-rate delay-sensitive traffic flows share the channel with so…

'Good to Repeat': Making Random Access Near-Optimal with Repeated Contentions

Recent advances on WLAN technology have been focused mostly on boosting network capacity by means of a more efficient and flexible physical layer. A new concept is required at MAC level to exploit fully the new capabilities of the PHY layer. In this article, we propose a contention mechanism based on Repeated Contentions (ReCo) in frequency domain. It provides a simple-to-configure, robust and short-term fair algorithm for the random contention component of the MAC protocol. The throughput efficiency of ReCo is not sensitive to the number of contending stations, so that ReCo does not require adaptive tuning of the access parameters for performance optimization. Efficiency and robustness is …

Remarks on IEEE 802.11 DCF Performance Evaluation, IEEE Communication Letters, Vol. 9, Issue 8, Aug 2005 pp:765 - 767

This letter presents a new approach to evaluate the throughput/delay performance of the 802.11 Distributed Coordination Function (DCF). Our approach relies on elementary conditional probability arguments rather than bidimensional Markov chains (as proposed in previous models), and can be easily extended to account for backoff operation more general than DCF's one

No Reservations Required: Achieving Fairness between Wi-Fi and NR-U with Self-Deferral Only

Wireless technologies coexisting in unlicensed bands should receive a fair share of the available channel resources, even when they use different access methods. We consider the problem of coexistence between Wi-Fi and New Radio Unlicensed (NR-U) nodes, which employ, respectively, a random and scheduled access scheme. The latter typically resorts to reservation signals (RSs), which allow keeping the control of the channel until the start of the next synchronized slot. This mechanism, although effective for increasing the channel access opportunities of scheduled-based nodes, is also a waste of channel resources. We investigate alternative solutions, based on self-deferral only. We built ana…

CADWAN – A Control Architecture for Dense Wi-Fi Access Networks

The growing demands of ubiquitous computing are leading towards the densification of wireless access networks. The challenges of high density deployments can be addressed by network- wide centralized control. To this end we propose CADWAN – a Control Architecture for efficient management of Dense Wi-Fi Access Networks. Its main advantages are: flexibility (it supports software- defined wireless networking), scalability (it uses a three-tier optimization framework), and extendibility (it exploits a unified control interface with support for heterogeneous devices). Furthermore, CADWAN is complementary to ongoing developments in IEEE 802.11, especially 802.11ax.

Interference Estimation in IEEE 802.11 Networks

This article describes a technique for distinguishing and quantifying medium access control (MAC) and physical layer (PHY) interference in error-prone 802.11 networks. This technique, is fully distributed, allowing each station to estimate interference individually. The estimator is based on an extended Kalman filter coupled to a mechanism for revealing abrupt changes in state. The network state is a vector of two components, representing PHY interference, expressed in terms of channel-error rate, and MAC interference. Two distinct state models are considered. When PHY interference can be assumed to be constant for all stations, network congestion is expressed by the number of competing ter…

Multi-party metering: An architecture for privacy-preserving profiling schemes

Several privacy concerns about the massive deploy- ment of smart meters have been arisen recently. Namely, it has been shown that the fine-grained temporal traces generated by these meters can be correlated with different users behaviors. A new architecture, called multi-party metering, for enabling privacy-preserving analysis of high-frequency metering data without requiring additional complexity at the smart meter side is here proposed. The idea is to allow multiple entities to get a share of the high-frequency metering data rather than the real data, where this share does not reveal any information about the real data. By aggregating the shares provided by different users and publishing …

Performance Analysis in Spatially Correlated IEEE 802.11 Networks

Wireless mesh networks are difficult to be characterized, especially under multi-hop traffic streams. The problem is that the local view of the channel and the correlation between the buffers of consecutive nodes in a stream path make complicated the identification of the contention level perceived by each station along the time. Such a figure is used in the models based on the so called decoupling assumption for evaluating the final scheduling of simultaneous channel access grants. In this paper we propose a simplified mesh network model focused on capturing the correlation due to the network topology and traffic routes rather than the access protocol state at each node. To this purpose, w…

Refinements on IEEE 802.11 Distributed Coordination Function Modeling Approaches

With the popularity of the IEEE 802.11 standards, many analytical saturation throughput studies for the distributed coordination function (DCF) have been reported. In this paper, we outline a number of issues and criticalities raised by previously proposed models. In particular, a careful look at backoff counter decrement rules allows us to conclude that, under saturation conditions, the slot immediately following a successful transmission can be accessed only by the station (STA) that has successfully transmitted in the previous channel access. Moreover, due to the specific acknowledgment (ACK) timeout setting adopted in the standard, the slot immediately following a collision cannot be ac…

Rings for Privacy: an Architecture for Large Scale Privacy-Preserving Data Mining

This article proposes a new architecture for privacy-preserving data mining based on Multi Party Computation (MPC) and secure sums. While traditional MPC approaches rely on a small number of aggregation peers replacing a centralized trusted entity, the current study puts forth a distributed solution that involves all data sources in the aggregation process, with the help of a single server for storing intermediate results. A large-scale scenario is examined and the possibility that data become inaccessible during the aggregation process is considered, a possibility that traditional schemes often neglect. Here, it is explicitly examined, as it might be provoked by intermittent network connec…

McRock at SemEval-2022 Task 4: Patronizing and Condescending Language Detection using Multi-Channel CNN, Hybrid LSTM, DistilBERT and XLNet

In this paper we propose four deep learning models for the task of detecting and classifying Patronizing and Condescending Language (PCL) using a corpus of over 13,000 annotated paragraphs in English. The task, hosted at SemEval-2022, consists of two different subtasks. The Subtask 1 is a binary classification problem. Namely, given a paragraph, a system must predict whether or not it contains any form of PCL. The Subtask 2 is a multi-label classification task. Given a paragraph, a system must identify which PCL categories express the condescension. A paragraph might contain one or more categories of PCL. To face with the first subtask we propose a multi-channel Convolutional Neural Network…

One size hardly fits all

This paper casts recent accomplishments in the field of Wireless MAC programmability into the emerging Software Defined Networking perspective. We argue that an abstract (but formal) description of the MAC protocol logic in terms of extensible finite state machines appears a convenient and viable data-plane programming compromise for modeling and deploying realistic MAC protocol logics. Our approach is shown to comply with existing control frameworks, and entails the ability to dynamically change the MAC protocol operation based on context and scenario conditions; in essence, move from the traditional idea of "one-size-fits-all" MAC protocol stack to the innovative paradigm of opportunistic…

Enabling a win-win coexistence mechanism for WiFi and LTE in unlicensed bands

The problem of WiFi and LTE coexistence has been significantly debated in the last years, with the emergence of LTE extensions enabling the utilization of unlicensed spectrum for carrier aggregation. Since the two technologies employ com-pletely different access protocols and frame transmission times, supporting coexistence with minimal modifications on existing protocols is not an easy task. Current solutions are often based on LTE unilateral adaptations, being LTE in unlicensed bands still under definition. In this paper, we demonstrate that it is possible to avoid a subordinated role for WiFi nodes, by simply equipping WiFi nodes with a sensing mechanism based on adaptive tunings of the …

Modeling Energy Demand Aggregators for Residential Consumers

International audience; Energy demand aggregators are new actors in the energy scenario: they gather a group of energy consumers and implement a demand- response paradigm. When the energy provider needs to reduce the current energy demand on the grid, it can pay the energy demand aggregator to reduce the load by turning off some of its consumers loads or postponing their activation. Currently this operation involves only greedy energy consumers like industrial plants. In this paper we want to study the potential of aggregating a large number of small energy consumers like home users as it may happen in smart grids. In particular we want to address the feasibility of such approach by conside…

Performance Study of IEEE 802.11 DCF and IEEE 802.11e EDCA

Wireless MAC processors: programming MAC protocols on commodity hardware

Programmable wireless platforms aim at responding to the quest for wireless access flexibility and adaptability. This paper introduces the notion of wireless MAC processors. Instead of implementing a specific MAC protocol stack, Wireless MAC processors do support a set of Medium Access Control “commands” which can be run-time composed (programmed) through software-defined state machines, thus providing the desired MAC protocol operation. We clearly distinguish from related work in this area as, unlike other works which rely on dedicated DSPs or programmable hardware platforms, we experimentally prove the feasibility of the wireless MAC processor concept over ultra-cheap commodity WLAN hardw…

Allocation algorithms for PRIMO system

A performance analysis of block ACK scheme for IEEE 802.11e networks

The demand for the IEEE 802.11 wireless local-area networks (WLANs) has been drastically increasing along with many emerging applications and services over WLAN. However, the IEEE 802.11 medium access control (MAC) is known to be limited in terms of its throughput performance due to the high MAC overhead, such as interframe spaces (IFS) or per-frame based acknowledgement (ACK) frame transmissions. The IEEE 802.11e MAC introduces the block ACK scheme for improving the system efficiency of the WLAN. Using the block ACK scheme can reduce the ACK transmission overhead by integrating multiple ACKs for a number of data frames into a bitmap that is contained in a block ACK frame, thus increasing t…

A CAPWAP Architecture for Automatic Frequency Planning in WLAN

Recently, the impressive success of the IEEE 802.11 WLAN technology has dramatically changed the role of the wireless connectivity provisioning. Born as a wireless extension of small office or home networks, todays the WLANs are getting more and more popular as a large, even metropolitan, area networks. The deployment of large-scale WLANs has some critical issues, because of the lack of coordinated management functionalities among the network nodes. In this paper we briefly describe the CAPWAP architectural solution, for centralizing some control and maintenance functionalities in large scale WLAN, by guaranteeing the interoperability between network nodes provided by different vendors. We …

1 Hop or 2 hops: Topology analysis in Body Area Network

Wireless Body Area Networks (WBANs) have recently received much attention due to the possibility to be used in healthcare applications. For these applications, link reliability and energy efficiency are critical issues, as in many cases, information carried can be vital for the patient and batteries cannot be easily replaced. The wireless on-body channel experiences significant temporal variation due to body movements and the use of relays is sometimes necessary in order to guarantee reliability or improve lifetime. In this paper, an experimental evaluation is used to give a better understanding about reliability, energy consumption and lifetime in a single hop or a two hops communication. …

Joint Usage of Dynamic Sensitivity Control and Time Division Multiple Access in Dense 802.11ax Networks

It is well known that in case of high density deployments, Wi-Fi networks suffer from serious performance impairments due to hid- den and exposed nodes. The problem is explicitly considered by the IEEE 802.11ax developers in order to improve spectrum efficiency. In this pa- per, we propose and evaluate the joint usage of dynamic sensitivity con- trol (DSC) and time division multiple access (TDMA) for improving the spectrum allocation among overlapping 802.11ax BSSs. To validate the solution, apart from simulation, we used a testbed based on the Wireless MAC Processor (WMP), a prototype of a programmable wireless card.

Demo

We present an innovative smartphone-centric tracking system for indoor and outdoor environments, based on the joint utilization of dead-reckoning and computer vision (CV) techniques. The system is explicitly designed for visually impaired people (although it could be easily generalized to other users) and it is built under the assumption that special reference signals, such as painted lines, colored tapes or tactile pavings are deployed in the environment for guiding visually impaired users along pre-defined paths. Thanks to highly optimized software, we are able to execute the CV and sensor-fusion algorithms in run-time on low power hardware such as a normal smartphone, precisely tracking …

WMPS: A Positioning System for Localizing Legacy 802.11 Devices

The huge success of location-aware applications calls for the quick development of a positioning system alternative to GPS for indoor localization based on existing technologies such as 802.11 wireless networks. In this paper we propose WMPS, the Wireless MAC Processor Positioning System, that is a localization system running on off-the-shelf 802.11 Access Points and based on time-of-flight ranging of users’ standard terminals. We prove through extensive experiments that propagation delays can be measured with the accuracy required by indoor applications despite the different noise components that can affect the result, like latencies of the hardware transreceivers, multi- path, ACK jitters…

Supporting a Pseudo-TDMA Access Scheme in Mesh Wireless Networks

Wireless mesh networks appear a promising solution for pro- viding ubiquitous low-cost wireless access, but cannot rely on simple CSMA access protocols because of the critical inefficiencies that arise in topologies with hidden nodes. To overcome these limitations, some important protocol extensions based on synchronization and reservation mechanisms have been ratified. In this paper we show that an alternative approach to the standardiza- tion of new features and signaling messages for mesh networks can be the utilization of programmable nodes able to execute different MAC protocols programmed on the fly. Signaling messages are used only for disseminating the new protocol among the nodes. …

Kalman filter estimation of the contention dynamics in error-prone IEEE 802.11 networks

In the last years, several strategies for maximizing the throughput performance of IEEE 802.11 networks have been proposed in literature. Specifically, it has been shown that optimizations are possible both at the medium access control (MAC) layer, and at the physical (PHY) layer. In fact, at the MAC layer, it is possible to minimize the channel wastes due to collisions and backoff expiration times, by tuning the minimum contention window as a function of the number n of competing stations. At the PHY layer, it is possible to improve the transmission robustness, by selecting a suitable modulation/coding scheme as a function of the channel quality perceived by the stations. However, the feas…

Performance Analysis of Memory Cloning Solutions in Mobile Edge Computing

This paper deals with the problem of service migration in the emerging scenarios of Mobile Edge Computing. Mobile edge computing is achieved by moving the traditional cloud infrastructures, exploited by many today applications, close to the network edge in order to reduce the response times in the so called tactile-internet. However, because of user mobility, such an application architecture may pose the problem of service migration in case of handover from one server site to another. After introducing the current solutions for dealing with service migration and, in particular, the approaches based on service decomposition into multiple layers, we quantify the migration time and the service…

A CAPWAP-Compliant Solution for Radio Resource Management in Large-Scale 802.11 WLAN

Recently, the impressive success of the IEEE 802.11 WLAN technology has dramatically changed the role of the wireless connectivity provisioning. Born as a wireless extension of small office or home networks, todays the WLANs are getting more and more popular as a large, even metropolitan, area networks. The deployment of large-scale WLANs has some critical issues, because of the lack of coordinated management functionalities among the network nodes. In this paper we briefly describe the CAPWAP architectural solution, for centralizing some control and maintenance functionalities in large scale WLAN, by guaranteeing the interoperability between network nodes provided by different vendors. We …

DEMO: Unconventional WiFi-ZigBee communications without gateways

Nowadays, the overcrowding of ISM bands is becoming an evident limitation for the performance and widespread usage of 802.11 and 802.15.4 technologies. In this demo, we prove that it is possible to opportunistically exploit the inter-technology interference between 802.11 and 802.15.4 to build an unconventional low-rate communication channel and signalling protocol, devised to improve the performance of each contending technology. Differently from previous solutions, inter-technology communications do not require the deployment of a gateway with two network interfaces, but can be activated (when needed) directly between two heterogeneous nodes, e.g. a WiFi node and a ZigBee node. This capab…

A Channel-Aware Adaptive Modem for Underwater Acoustic Communications

Acoustic underwater channels are very challenging, because of limited bandwidth, long propagation delays, extended multipath, severe attenuation, rapid time variation and large Doppler shifts. A plethora of underwater communication techniques have been developed for dealing with such a complexity, mostly tailoring specific applications scenarios which can not be considered as one-size-fits-all solutions. Indeed, the design of environment-specific solutions is especially critical for modulations with high spectral efficiency, which are very sensitive to channel characteristics. In this paper, we design and implement a software-defined modem able to dynamically estimate the acoustic channel c…

Performance Analysis of Sweep-Spread Carrier (S2C) Modulation for Underwater Communications

In the last decades, underwater acoustic communications have seen a growing development with a variety of research as well as commercial applications, dealing with channel distortions, multipath and Doppler effects typical underwater channels. A very robust modulation able to guarantee connectivity in harsh environments (where spectral efficient solutions such as OFDM can be prevented) is the so called sweep-spread carrier (S2C) modulation, which is based on the usage of a linearly time-varying carrier. Underwater modems based on S2C modulations have been patented and successfully adopted in real-world deployments. In this paper, we analyze the performance of S2C both in simulation and infi…

Breaking layer 2: A new architecture for programmable wireless interfaces

This paper introduces a new architecture for programmable wireless interfaces, aiming at responding to the emerging request of wireless access flexibility and adaptability. Instead of implementing a specific MAC protocol stack, the proposed architecture supports a set of programmable services, devised to customize the wireless access operations according to specific network and application scenarios. The services are composed by means of simpler functions, which in turns work on system primitives (i.e. elementary non-programmable functionalities, natively provided by the system) dealing with the physical transmission and reception of the frames. Our approach significantly differs from softw…

The role of the Access Point in Wi-Fi networks with selfish nodes

In Wi-Fi networks, mobile nodes compete for accessing the shared channel by means of a random access protocol called Distributed Coordination Function (DCF), which is long term fair. But recent drivers allow users to configure protocol parameters differently from their standard values in order to break the protocol fairness and obtain a larger share of the available bandwidth at the expense of other users. This motivates a game theoretical analysis of DCF. Previous studies have already modeled access to a shared wireless channel in terms of non-cooperative games among the nodes, but they have mainly considered ad hoc mode operation. In this paper we consider the role of the Access Point (AP…

A Navigation and Augmented Reality System for Visually Impaired People

In recent years, we have assisted with an impressive advance in augmented reality systems and computer vision algorithms, based on image processing and artificial intelligence. Thanks to these technologies, mainstream smartphones are able to estimate their own motion in 3D space with high accuracy. In this paper, we exploit such technologies to support the autonomous mobility of people with visual disabilities, identifying pre-defined virtual paths and providing context information, reducing the distance between the digital and real worlds. In particular, we present ARIANNA+, an extension of ARIANNA, a system explicitly designed for visually impaired people for indoor and outdoor localizati…

Experimental evaluation of privacy-preserving aggregation schemes on planetlab

New pervasive technologies often reveal many sen- sitive information about users’ habits, seriously compromising the privacy and sometimes even the personal security of people. To cope with this problem, researchers have developed the idea of privacy-preserving data mining which refers to the possibility of releasing aggregate information about the data provided by multiple users, without any information leakage about individual data. These techniques have different privacy levels and communication costs, but all of them can suffer when some users’ data becomes inaccessible during the operation of the privacy preserving protocols. It is thus interesting to validate the applicability of such…

Maximizing network capacity in an heterogeneous macro-micro cellular scenario

The problem of resource allocation in cellular networks has been traditionally faced at two different levels: at the network level, in terms of frequency planning and reuse pattern design, and at the cell level, in terms of cell capacity optimizations based on channel-dependent scheduling, link adaptation, power control, and so on. While this second aspect has been deeply investigated in literature, the first aspect has been mainly faced with static or semi-dynamic reuse utilization solutions. In this paper we deal with the problem of multi-cellular resource allocation in heterogeneous OFDMA environments with reuse factor equal to 1, where base stations with different power constraints coex…

Sensor Fusion Localization and Navigation for Visually Impaired People

In this paper, we present an innovative cyber physical system for indoor and outdoor localization and navigation, based on the joint utilization of dead-reckoning and computer vision techniques on a smartphone-centric tracking system. The system is explicitly designed for visually impaired people, but it can be easily generalized to other users, and it is built under the assumption that special reference signals, such as colored tapes, painted lines, or tactile paving, are deployed in the environment for guiding visually impaired users along pre-defined paths. Differently from previous works on localization, which are focused only on the utilization of inertial sensors integrated into the s…

Revealing transmit diversity mechanisms and their side-effects in commercial IEEE 802.11 cards

Service differentiation in WLAN has been traditionally faced at the MAC layer. However, some PHY layer parameters, such as the transmission power, the antenna, and the modulation/coding scheme, have a deep impact on network performance. Since the criterion for selecting these parameters is left to the vendor specific implementations, the performance spread of most experimental results about 802.11 WLAN could be affected by vendor proprietary schemes. The focus of this paper is an experimental analysis of the undisclosed antenna diversity mechanisms employed by some widely used cards (namely, the Atheros and Intel based cards), and a thorough understanding of the optimization goals which gui…

Kata Containers: An Emerging Architecture for Enabling MEC Services in Fast and Secure Way

New coming applications will be only possible through Mobile Edge Servers deployed in proximity of the mobile users. Due to the user's mobility and server's workload, service migration will be an integral part of the services. For this reason, a standardized architecture should be designed to accomplish a workload migration in a secure and timely manner. Most research done to date has focused on the use of either virtual machine (VM) or container or a mix of both recently. A final solution might be an architecture only having the advantages of both technologies as the security of the VM and the speed of the containers. Custom solutions, actually, by using both technologies, need continuous …

SDN@home: A Method for Controlling Future Wireless Home Networks

Recent advances in wireless networking technologies are leading toward the proliferation of novel home network applications. However, the landscape of emerging scenarios is fragmented due to their varying technological requirements and the heterogeneity of current wireless technologies. We argue that the development of flexible software-defined wireless architectures, including such efforts as the wireless MAC processor, coupled with SDN concepts, will enable the support of both emerging and future home applications. In this article, we first identify problems with managing current home networks composed of separate network segments governed by different technologies. Second, we point out t…

Rings for privacy: An architecture for privacy-preserving user profiling

A unified radio control architecture for prototyping adaptive wireless protocols

Experimental optimization of wireless protocols and validation of novel solutions is often problematic, due to limited configuration space present in commercial wireless interfaces as well as complexity of monolithic driver implementation on SDR-based experimentation platforms. To overcome these limitations a novel software architecture is proposed, called WiSHFUL, devised to allow: i) maximal exploitation of radio functionalities available in current radio chips, and ii) clean separation between the logic for optimizing the radio protocols (i.e. radio control) and the definition of these protocols.

Enhancing tracking performance in a smartphone-based navigation system for visually impaired people

In this paper we show how to enhance the tracking performance of Arianna, a low-cost augmented reality system designed to meet the needs of people with problems of orientation, people with sight impairment and blind people. For augmented reality system we mean the design of: i) a set of paths and tags to be deployed in the environment, realized in various ways depending on the context (decorative elements easily identifiable, colorful stripes, QR code, RFID, etc.); ii) an instrument of mediation between the reality and the user (typically a smartphone) to access the information disseminated in the environment by means of a camera and provide a vibration feedback signal to the users for foll…

Random access with repeated contentions for emerging wireless technologies

In this paper we propose ReCo, a robust contention scheme for emerging wireless technologies, whose efficiency is not sensitive to the number of contending stations and to the settings of the contention parameters (such as the contention windows and retry limits). The idea is iterating a basic contention mechanism, devised to select a sub-set of stations among the contending ones, in consecutive elimination rounds, before performing a transmission attempt. Elimination rounds can be performed in the time or frequency domain, with different overheads, according to the physical capabilities of the nodes. Closed analytical formulas are given to dimension the number of contention rounds in order…

A Flexible 4G/5G Control Platform for Fingerprint-based Indoor Localization

In this paper we propose a centralized SDN platform devised to control indoor femto-cells for supporting multiple network-wide optimizations and applications. In particular, we focus on an example localization application in order to enlighten the main functionalities and potentialities of the approach. First, we demonstrate that the platform can be exploited for reconfiguring some operational procedures, based on standard signalling mechanisms, at the programmable femto-cells; these procedures enable customized logics for collecting measurements reports from mobile terminals. Second, assuming that high-density devices such as smart objects are disseminated in the controlled indoor space, w…

An Experimental Testbed and Methodology for Characterizing IEEE 802.11 Network Cards

It has been observed that IEEE 802.11 commercial cards produced by different vendors show a different behavior in terms of perceived throughput or access delay. Performance differences are evident both when the cards contend alone to the channel, and when heterogeneous cards contend together. Since the performance misalignment does not disappear by averaging the environmental factors (such as propagation conditions, laptop models, traffic generators, etc), it is evident that the well known throughput-fairness property of the DCF protocol is not guaranteed in actual networks. In this paper we propose a methodological approach devised to experimentally characterize the IEEE 802.11 commercial …

A Space-Division Time-Division MAC Protocol for broadband wireless access

Privacy-Preserving Overgrid: Secure Data Collection for the Smart Grid

In this paper, we present a privacy-preserving scheme for Overgrid, a fully distributed peer-to-peer (P2P) architecture designed to automatically control and implement distributed Demand Response (DR) schemes in a community of smart buildings with energy generation and storage capabilities. To monitor the power consumption of the buildings, while respecting the privacy of the users, we extend our previous Overgrid algorithms to provide privacy preserving data aggregation (PP-Overgrid). This new technique combines a distributed data aggregation scheme with the Secure Multi-Party Computation paradigm. First, we use the energy profiles of hundreds of buildings, classifying the amount of &ldquo

“Vendor-Affected” WLAN experimental results: A Pandora’s Box?

Experimental results are typically envisioned as the ultimate validation reference for any theoretical and/or simulation modelling assumptions. However, in the case of Wireless LANs, the situation is not nearly as straightforward as it might seem. In this paper, we discuss to what (large) extent measurement results may depend on proprietary undocumented algorithms implemented in the vendor-specific card/driver employed. Specifically, we focus on the experimental study of IEEE 802.11 b/g outdoor links based on the widely used Atheros/MADWiFi card/driver pair. We show that unexpected performance divergences do emerge in two classes of comparative experiments run on a same outdoor link: broadc…

Impact of LTE’s Periodic Interference on Heterogeneous Wi-Fi Transmissions

The problem of Wi-Fi and LTE coexistence has been significantly debated in the last years, with the emergence of LTE extensions enabling the utilization of unlicensed spectrum for carrier aggregation. Rather than focusing on the problem of resource sharing between the two technologies, in this paper, we study the effects of LTE's structured transmissions on the Wi-Fi random access protocol. We show how the scheduling of periodic LTE transmissions modifies the behavior of 802.11's distributed coordination function (DCF), leading to a degradation of Wi-Fi performance, both in terms of channel utilization efficiency and in terms of channel access fairness. We also discuss the applicability and…

A space-division time-division multiple access scheme for high throughput provisioning in WLANs

Directional antennas may dramatically increase the capacity of a Wireless LAN by allowing several stations to simultaneously communicate. Since deployment of directive/smart antennas on the customer's terminals is awkward (for technological, cost, robustness, and convenience reasons) it is of interest to deploy advanced antenna solutions only at the Access Point. When omnidirectional transmissions are used at the Mobile Stations, the asynchronous nature of the 802.11 MAC handshake structurally limits the possibility to exploit spatial reuse. Significant throughput enhancements can be achieved only at the expense of redesigning (part of) the 802.11 MAC protocol: mainly a form of synchronizat…

A secret sharing scheme for anonymous DNS queries

Since its adoption in the early 90's, several privacy concerns have emerged about the Domain Name System (DNS). By collecting the DNS queries performed by each user, it is possible to characterize habits, interests and other sensitive data of the users. Usually, users resolve their {\em url} requests by querying the DSN server belonging to their Internet Service Provider (ISP) and therefore they assume they can trust it. However, different DNS servers can be used, by revealing sensitive data to a partially untrusted entity that can collect and sell this data for several purposes (target advertising, user profiling, etc.). In this paper we address the possibility to integrate tools in the cu…

Data fusion analysis applied to different climate change models: An application to the energy consumptions of a building office

Abstract The paper aims to achieve the modelling of climate change effects on heating and cooling in the building sector, through the use of the available Intergovernmental Panel on Climate Change forecasted data. Data from several different climate models will be fused with regards to mean air temperature, wind speed and horizontal solar radiation. Several climatic models data were analysed ranging from January 2006 to December 2100. Rather than considering each model in isolation, we propose a data fusion approach for providing a robust combined model for morphing an existing weather data file. The final aim is simulating future energy use for heating and cooling of a reference building a…

Exploiting EDCA for Feedback Channels in Hybrid VLC/WiFi Architectures

In this paper, we consider integrating VLC and WiFi technologies in a scenario in which Light-Emitting-Diodes (LEDs), acting as network access points (APs) for ultra-dense Internet of Things applications, are deployed into an indoor lighting infrastructure. In such a scenario, RF-links can be exploited for complementing VLC-links in dealing with mobility and bidirectional communications, which can be problematic due to the limited coverage areas and self-generated interference of VLC APs. In particular, we consider the possibility of supporting a technology-based duplexing scheme, in which downlink and uplink transmissions are performed by means, respectively, of VLC and WiFi interfaces int…

Impact of LoRa Imperfect Orthogonality: Analysis of Link-Level Performance

In this letter, we focus on the evaluation of link-level performance of LoRa technology, in the usual network scenario with a central gateway and high-density deployment of end-devices. LoRa technology achieves wide coverage areas, low power consumption and robustness to interference thanks to a chirp spread-spectrum modulation, in which chirps modulated with different spreading factors (SFs) are quasi-orthogonal. We focus on the performance analysis of a single receiver in presence of collisions. First, we analyze LoRa modulation numerically and show that collisions between packets modulated with different SFs can indeed cause packet loss if the interference power received is strong enough…

Smart plugs: A low cost solution for programmable control of domestic loads

International audience; Balancing energy demand and production is becoming a more and more challenging task for energy utilities. This is due to a number of different reasons among which the larger penetration of renewable energies which are more difficult to predict and the meagre availability of financial resources to upgrade the existing power grid. While the traditional solution is to dynamically adapt energy production to follow the time-varying demand, a new trend is to drive the demand itself by means of Direct Load Control (DLC). In this paper we consider a scenario where DLC functionalities are deployed at a large set of small deferrable energy loads, like appliances of residential…

Decentralized Synchronization for Zigbee wireless sensor networks in Multi-Hop Topology

Abstract The most effective solution for energy saving in low-rate wireless sensor networks is maintaining each node in a doze state as long as possible. In order to guarantee network connectivity, the intervals at which the network sensors are turned on and off have to be coordinated. We analyze the Zigbee MAC performance in sensor networks deployed in multi-hop topologies. For this networks, critical inefficiencies can arise due to transmissions performed by hidden nodes. We evaluate the impact of different synchronization schemes on the network performance, both in terms of network capacity and in terms of energy consumption. We show how the synchronization function can be opportunistica…

A game theoretic approach to MAC design for infrastructure networks

Wireless network operation intrinsically assumes different forms of cooperation among the network nodes, such as sharing a common wireless medium without interfering, relaying frames belonging to other nodes, controlling the transmission power for optimizing spectrum reuse, coding cooperatively multiple frames for improving information redundancy, and so on. For this reason, Game Theory has been extensively employed to model wireless networks. In particular, we propose a game-theoretic approach for defining a generalized medium access protocol for slotted contention-based channels. Contention-based channels are largely adopted in data networks, e.g. in WiFi and WiMax networks and in some em…

Revisit of RTS/CTS Exchange in High-Speed IEEE 802.11 Networks

IEEE 802.11 medium access control (MAC), called distributed coordination function (DCF), provides two different access modes, namely, 2-way (basic access) and 4-way (RTS/CTS) handshaking. The 4-way handshaking has been introduced in order to combat the hidden terminal phenomenon. It has been also proved that such a mechanism can be beneficial even in the absence of hidden terminals, because of the collision time reduction. We analyze the effectiveness of the RTS/CTS access mode, in current 802.11b and 802.11a networks. Since the rates employed for control frame transmissions can be much lower than the rate employed for data frames, the assumption on the basis of the 4-way handshaking introd…

LoRa Technology Demystified: From Link Behavior to Cell-Level Performance

In this paper we study the capability of LoRa technology in rejecting different interfering LoRa signals and the impact on the cell capacity. First, we analyze experimentally the link-level performance of LoRa and show that collisions between packets modulated with the same Spreading Factor (SF) usually lead to channel captures, while different spreading factors can indeed cause packet loss if the interference power is strong enough. Second, we model the effect of such findings to quantify the achievable capacity in a typical LoRa cell: we show that high SFs, generally seen as more robust, can be severely affected by inter-SF interference and that different criteria for deciding SF allocati…

MAC Design for WiFi Infrastructure Networks: A Game-Theoretic Approach

In WiFi networks, mobile nodes compete for accessing a shared channel by means of a random access protocol called Distributed Coordination Function (DCF). Although this protocol is in principle fair, since all the stations have the same probability to transmit on the channel, it has been shown that unfair behaviors may emerge in actual networking scenarios because of non-standard configurations of the nodes. Due to the proliferation of open source drivers and programmable cards, enabling an easy customization of the channel access policies, we propose a game-theoretic analysis of random access schemes. Assuming that each node is rational and implements a best response strategy, we show that…

"MAC Parameters Tuning for Best Effort Traffic in 802.11e Contention-Based Networks"

Cross-layer design of optimized packet scheduling and radio resource allocation algorithms for 4th generation cellular wireless systems

On the Fidelity of IEEE 802.11 commercial cards

The IEEE 802.11 D CF protocol is known to be fair in terms of long-term resource repartition among the contending stations. However, when considering real scenarios, where commercial 802.11 cards interact, very unpredictable as well as sometimes surprising behaviors emerge. Motivation of this paper is to investigate the reasons of the very evident disagreement between the theoretical IEEE 802.11 DCF protocol models and its practical implementations. Inparticular, we try to characterize the card behavior not only in terms of perceived throughput, but also in terms of low-level channel access operations. In fact, the simple throughput analysis does not allow to identify what affecting paramet…

A new approach to model the effect of climate change on the building sector: A climate models data fusion

Several climate models have been developed and used to forecast the effects of the climate changes, however the variability of results due to different models lead to a significant uncertainty on the estimation of the building energy use for the next century. In this context, the paper analyses this uncertainty and combines different climate models in order to improve the robustness of energy consumption predictions. The data of the climate models were then used to generate hourly weather files for the future period 2020-2099 and energy simulations for a case study located in Palermo (Italy) were performed. Results show a wide variability among all models (either alone or combined with our …

Performance of LoRa for Bike-Sharing Systems

Today bike sharing systems are becoming popular in many cities as short-distance transit vehicles. More than 18 million bicycles are available worldwide for public use and one of the main problems that afflicts such sharing systems is the loss of bikes, which can be stolen or simply left in unknown locations. Thus, many bikes are docked or tracked using GPS and costly cellular connections. In this paper, we consider the emerging Long Range (LoRa) technology for use in bike sharing systems. LoRa exploits free ISM bands and has been conceived for low power and low data rate applications. Additionally, LoRa is characterized by large cells and heterogeneous application domains, which may lead t…

Performance analysis of selfish access strategies on WiFi infrastructure networks

In this paper we propose a game-theoretic approach for characterizing WiFi network performance in presence of intelligent nodes employing cognitive functionalities. We assume that a cognitive WiFi node is aware of its application requirements and is able to dynamically estimate the network status, in order to dynamically change its access strategy by tuning the contention window settings. We prove that, for infrastructure networks with bidirectional traffic and homogeneous application requirements, selfish access strategies are able to reach equilibrium conditions, which are also Pareto optimal. Indeed, we show that the station strategies converge toward values which maximize a per-node uti…

An Indoor and Outdoor Navigation System for Visually Impaired People

In this paper, we present a system that allows visually impaired people to autonomously navigate in an unknown indoor and outdoor environment. The system, explicitly designed for low vision people, can be generalized to other users in an easy way. We assume that special landmarks are posed for helping the users in the localization of pre-defined paths. Our novel approach exploits the use of both the inertial sensors and the camera integrated into the smartphone as sensors. Such a navigation system can also provide direction estimates to the tracking system to the users. The success of out approach is proved both through experimental tests performed in controlled indoor environments and in r…

Multi-cloud privacy preserving schemes for linear data mining

This paper presents an approach to privacy-preserving data mining that relies upon a relatively simple secret sharing scheme. Its main feature is that users, sensitive data owners, are engaged in the secret sharing operations that protect their privacy. They are grouped in independent clouds connected to a central unit, the data miner, that only manages the aggregated data of each cloud, therefore avoiding the disclosure of information belonging to single nodes. We propose two privacy preserving schemes, with different privacy levels and communication costs. When designing them, we assume that some users' data might become inaccessible during the operation of the privacy preserving protocol…

Wireless MAC Processor Networking: A Control Architecture for Expressing and Implementing High-Level Adaptation Policies in WLANs

The current proliferation of unplanned wireless local area networks (WLANs) is creating the need for implementing different adaptation strategies to improve network performance under mutating and evolving interference scenarios. In this article, we envision a new solution for expressing and implementing high-level adaptation policies in WLANs, in contrast to the current approaches based on vendor-specific implementations. We exploit the hardware abstraction interface recently proposed by the wireless medium access control (MAC) processor (WMP) architecture and some flow-control concepts similar to the Openflow model for defining MAC adaptation policies. A simple control architecture for dis…

Interference Cancellation for LoRa Gateways and Impact on Network Capacity

In this paper we propose LoRaSyNc (LoRa receiver with SyNchronization and Cancellation), a second generation LoRa receiver that implements Successive Interference Cancellation (SIC) and time synchronization to improve the performance of LoRa gateways. Indeed, the chirp spread spectrum modulation employed in LoRa experiences very high capture probability, and cancelling the strongest signal in case of collisions can significantly improve the cell capacity. An important feature of LoRaSyNc is the ability to track the frequency and clock drifts between the transmitter and receiver, during the whole demodulation of the interfered frame. Due to the use of low-cost oscillators on end-devices, a s…

On the Flexibility of the IEEE 802.11 Technology: Challenges and Directions

The original 802.11 standard, which is the de-facto standard for contention-based wireless data networks, has shown to give poor performance or to be scarcely suitable for dealing with new PHY-layer technologies, networking scenarios, or service contexts, thus boosting the proliferation of projects, technical solutions and dedicated task groups for extending the basic protocol operations. In this paper, starting from the evolution analysis of current 802.11 standard and de- vices, we propose an architectural solution for making the medium access protocol programmable. Our basic idea, pursued within the FP7 EU Project FLAVIA [1], started in July 2010, is changing the role of the wireless net…

A Survey on LoRa for Smart Agriculture: Current Trends and Future Perspectives

This paper provides a survey on the adoption of LoRa in the agricultural field, and reviews state-of-the-art solutions for Smart Agriculture, analyzing the potential of this technology in different infield applications. In particular, we consider four reference scenarios, namely irrigation systems, plantation and crop monitoring, tree monitoring, and livestock monitoring, which exhibit heterogeneous requirements in terms of network bandwidth, density, sensors’ complexity, and energy demand, as well as latency in the decision process. We discuss how LoRa-based solutions can work in these scenarios, analyzing their scalability, interoperability, network architecture, and energy-efficiency. Fi…

Large Scale Control of Deferrable Domestic Loads in Smart Grids

International audience; In this paper, we investigate a realistic and low-cost deployment of large scale direct control of inelastic home appliances whose energy demand cannot be shaped, but simply deferred. The idea is to exploit 1) some simple actuators to be placed on the electric plugs for connecting or disconnecting appliances with heterogeneous control interfaces, including non-smart appliances, and 2) the Internet connections of customers for transporting the activation requests from the actuators to a centralized controller. Our solution requires no interaction with home users: in particular, it does not require them to express their energy demand in advance. A queuing theory model …

Design and performance evaluation of an hybrid reservation-polling MAC protocol for power-line communications

This paper presents an hybrid reservation-polling MAC protocol able to effectively deal with the channel disturbances typical of Power-line communication systems. Channel access is controlled by a scheduler running on a centralized station. Fast retransmission of corrupted packets is employed to achieve high performance on Power-line channels characterized by frequent error bursts due to impulsive noise. The performance of our proposed mechanism are evaluated by means of simulation, for the more challenging case of time-sensitive traffic sources (voice calls). Results show that the system efficiency is virtually not affected by lightly to moderately disturbed PLC channel. Moreover, by sligh…

Performance Analysis of IEEE 802.11 DCF in Multi-Hop Chain Topologies

Resource sharing optimality in WiFi infrastructure networks

In WiFi networks, mobile nodes compete for accessing a shared channel by means of a random access protocol called Distributed Coordination Function (DCF). Although this protocol is in principle fair, since all the stations have the same probability to transmit on the channel, it has been shown that unfair behaviors may emerge in actual networking scenarios. Assuming that a contending node can dynamically change its strategy, by tuning its contention parameters to non-standard values on the basis of channel observations, we prove that, for infrastructure networks with bidirectional traffic and homogeneous application requirements, selfish access strategies are able to reach equilibrium condi…

WhoSNext: Recommending Twitter Users to Follow Using a Spreading Activation Network Based Approach

The huge number of modern social network users has made the web a fertile ground for the growth and development of a plethora of recommender systems. To date, recommending a new user profile X to a given user U that could be interested in creating a relationship with X has been tackled using techniques based on content analysis, existing friendship relationships and other pieces of information coming from different social networks or websites. In this paper we propose a recommending architecture - called WhoSNext (WSN) - tested on Twitter and which aim is promoting the creation of new relationships among users. As recent researches show, this is an interesting recommendation problem: for a …

Leakage Detection via Edge Processing in LoRaWAN-based Smart Water Distribution Networks

The optimization and digitalization of Water Distribution Networks (WDNs) are becoming key objectives in our modern society. Indeed, WDNs are typically old, worn and obsolete. These inadequate conditions of the infrastructures lead to significant water loss due to leakages inside pipes, junctions and nodes. It has been measured that in Europe the average value of lost water is about 26 %. Leakage control in current WDNs is typically passive, repairing leaks only when they are visible. Emerging Low Power Wide Area Network (LPWAN) technologies, and especially IoT ones, can help monitor water consumption and automatically detect leakages. In this context, LoRaWAN can be the right way to deploy…

Moving RTS/CTS to the frequency domain: an efficient contention scheme for 802.11ax networks

In this paper, we propose a contention mechanism based on the execution of multiple contention rounds in the frequency domain (ReCHo), which is designed to offer high throughput performance and robustness with respect to imperfect carrier sensing. The main idea is using narrow tones as signalling messages for performing channel access contentions and allowing the Access Point (AP) to echo these signals, in order to extend the sensing capabilities to all the stations associated to the AP. In particular, we refer to the emerging IEEE 802.11ax standard, showing how our scheme can boost performance of random access with respect to the current version of IEEE 802.11ax OFDMA Back-Off (OBO), even …

MAClets: Active MAC Protocols over hard-coded devices

We introduce MAClets, software programs uploaded and executed on-demand over wireless cards, and devised to change the card's real-time medium access control operation. MAClets permit seamless reconfiguration of the MAC stack, so as to adapt it to mutated context and spectrum conditions and perform tailored performance optimizations hardly accountable by an once-for-all protocol stack design. Following traditional active networking principles, MAClets can be directly conveyed within data packets and executed on hard-coded devices acting as virtual MAC machines. Indeed, rather than executing a pre-defined protocol, we envision a new architecture for wireless cards based on a protocol interpr…

Error-Based Interference Detection in WiFi Networks

In this paper we show that inter-technology interference can be recognized by commodity WiFi devices by monitoring the statistics of receiver errors. Indeed, while for WiFi standard frames the error probability varies during the frame reception in different frame fields (PHY, MAC headers, payloads) protected with heterogeneous coding, errors may appear randomly at any point during the time the demodulator is trying to receive an exogenous interfering signal. We thus detect and identify cross-technology interference on off-the-shelf WiFi cards by monitoring the sequence of receiver errors (bad PLCP, bad PCS, invalid headers, etc.) and develop an Artificial Neural Network (ANN) to recognize t…

Cross-Technology WiFi/ZigBee Communications: Dealing With Channel Insertions and Deletions

In this letter, we show how cross-technology interference can be exploited to set up a low-rate bidirectional communication channel between heterogeneous WiFi and ZigBee networks. Because of the environment noise and receivers' implementation, the cross-technology channel can be severely affected by insertions and deletions of symbols, whose effects need to be taken into account by the coding scheme and communication protocol.

Improving IEEE 802.11 Performance in Chain Topologies through Distributed Polling and Network Coding

Wireless multi-hop networks often rely on the use of IEEE 802.11 technology. Despite of the robustness of the IEEE 802.11 Distributed Coordination Function (DCF) for working in various network scenarios, it has been proven that critical inefficiencies can arise in the case of multi-hop packet forwarding. In this paper, we propose a MAC scheme, based on the virtualization of the Point Coordination Function, optimized for working on chain topologies with bidirectional traffic flows. Our scheme is based on a token-like access mechanism coupled with network coding. The basic idea is the use of multiple Point Coordinators (PCs) along the node chain, which are elected by passing special token fra…

Deploying Virtual MAC Protocols Over a Shared Access Infrastructure Using MAClets

Network virtualization has been extensively researched in the last years as a key enabler for improving the network performance. However, virtualization in wireless networks pose some unique challenges: first, the usual over-provisioning approach for providing isolation between multiple virtual entities is not viable; second, the partitioning criteria are often ambiguous, since the actual resources perceived by each entity depend on many external (and time-varying) factors. In this demo, we show an effective virtualization solution for wireless local area networks, solving the problem of isolation and flexible resource paritioning, based on the concept of MAClets. MAClets are software progr…

Doppler Estimation and Correction for JANUS Underwater Communications

In recent years, underwater communications have seen a growing interest pushed by marine research, oceanography, marine commercial operations, offshore oil industry and defense applications. Generally, underwater communications employ audio signals which can propagate relatively far but are also significantly affected by Doppler distortions. In fact, physical properties of the water and spatial changes due to tides, currents and waves can cause channel variations or unwanted movements of the transmitter or receiver. This study shows how to compensate for the Doppler effect in transmission employing the JANUS standard, a popular modulation scheme for underwater communication. Differently for…

Temporal Fairness Provisioning in Multi-Rate Contention-Based 802.11e WLANs

The IEEE 802.11e extensions for QoS support in WLAN define the transmission opportunity (TXOP) concept, in order to limit the channel holding times of the contending stations in the presence of delay-sensitive traffic. We evaluate the use of TXOP for a different purpose: "temporal fairness" provisioning among stations employing different data rates. We show that the equalization of the channel access times allows each station to obtain its throughput basically (1) proportional to its transmission rate, and (2) independent of the transmitted frame length. This also improves the aggregate throughput of the overall WLAN. For a given TXOP limit, i.e., a granted channel access time, a station is…

BusyBee: Low Rate WiFi-ZigBee Communications without Gateways

Nowadays, the overcrowding of ISM bands is becoming an evident limitation for the performance and widespread us- age of 802.11 and 802.15.4 technologies. In this demo, we prove that it is possible to opportunistically exploit the inter- technology interference between 802.11 and 802.15.4 to build an unconventional low-rate communication channel and sig- nalling protocol, devised to improve the performance of each contending technology. Differently from previous solutions, inter-technology communications do not require the deploy- ment of a gateway with two network interfaces, but can be activated (when needed) directly between two heterogeneous nodes, e.g. a WiFi node and a ZigBee node. Thi…

SDR-LoRa

In this paper, we present SDR-LoRa, a full-fledged SDR implementation of a LoRa transmitter and receiver. First, we reverse-engineer the LoRa physical layer (PHY) functionalities, including the procedures of packet modulation, demodulation, and preamble detection. Based on this analysis, we develop the first Software Defined Radio (SDR) implementation of the LoRa PHY. Furthermore, we integrate LoRa with an Automatic Repeat Request (ARQ) error detection protocol. SDR-LoRa has been validated on (i) the Colosseum wireless channel emulator; and (ii) a real testbed with USRP radios and commercial-off-the-shelf (COTS) devices. Our experimental results demonstrate that the performance of SDR-LoRa …

An explanation for unexpected 802.11 outdoor link-level measurement results

This paper provides experimental evidence that "weird'/poor outdoor link-level performance measurements may be caused by driver/card-specific antenna diversity algorithms unexpectedly supported/activated at the WLAN transmitter side. We focus our analysis on the Atheros/MADWiFi card/driver case, and we observe that the transmit antenna diversity mechanisms remain by default enabled when the available antennas are not homogeneous in terms of gain or, even worse, when only a single antenna is connected. This may cause considerable performance impairments (large frame loss ratio), in conditions frequently encountered in outdoor link deployments. The negative impact of transmit antenna diversit…

Unidirectional probabilistic direct control for deferrable loads

International audience; The idea of harnessing the inherent flexibility in demand of many types of electric loads has been largely discussed in the last years for coping with the need to maintain the energy demand-supply balance. In particular, the fine tuning of the operation conditions of different thermostatic loads (such as air-conditioning, refrigerators, etc.) has appeared as the most natural solution for load control with minimal user discomfort. In this paper we focus on an alternative approach: deploying simple open-loop control strategies for deferrable loads with minimal communication overhead. The idea is to send a multicast control message to a group of users, on the basis of t…

Performance analysis of the Out-of-Band signalling scheme for high speed wireless LANs

Use of ICT to support epidemiological surveillance on a community of university students during SARS-CoV-2 phase 3 pandemic

Populations documenting to date low incidence rates of SARS-CoV-2 infection are immunologically susceptible and at high exposure risk of new COVID-19 outbreaks during phase 3 of the pandemic. Following the experience documented by other countries with regard to the use of Information Communication Technology (ICT) to counteract the current pandemic, Italy has implemented a contact tracing system based on a mobile application. In this work, we describe the proposal of a complementary ICT-based prototypal model of COVID-19 prevention and surveillance system, involving the university students as sentinels acting both in the academic community and the general population.

A flexible and reconfigurable 5G networking architecture based on context and content information

The need for massive content delivery is a consolidated trend in mobile communications, and will even increase for next years. Moreover, while 4G maturity and evolution is driven by video contents, next generation (5G) networks will be dominated by heterogeneous data and additional massive diffusion of Internet of Things (IoT). The current network architecture is not sufficient to cope with such traffic, which is heterogeneous in terms of latency and QoS requirements, and variable in space and time. This paper proposes architectural advances to endow the network with the necessary flexibility helping to adapt to these varying traffic needs by providing content and communication services whe…

Testbed evaluation of optimized REACT over multi-hop paths

REACT is a distributed resource allocation protocol that computes a max-min allocation of airtime for mesh networks. The allocation adapts automatically to changes in local traffic load and in local network views. SALT, a new contention window tuning algorithm, ensures that each node secures the airtime allocated to it by REACT. REACT and SALT are extended to the multi-hop flow scenario with the introduction of a new airtime reservation algorithm. With a reservation in place, multi-hop TCP flows show increased throughput when running over SALT and REACT compared to running over 802.11 DCF. All results are obtained from experimentation on the w-iLab.t wireless network testbed in Belgium.

A decentralized load control architecture for smart energy consumption in small islands

Abstract In this paper we propose the adoption of Overgrid, a new decentralized load control architecture, for balancing the energy production variations introduced with the adoption of renewable sources, facilitating and improving the smart energy retrofit. The system is presented and applied for managing the aggregated daily load profile of a community of domestic end-users in the island of Lampedusa, Italy, exploiting the load profiles gathered in a real measurement campaign. The Overgrid Demand Response (DR) architecture is used for managing the residential flexible loads, estimating the aggregated power demand without any centralized server and creating a virtual “community” of smart b…

The RAMON module: architecture framework and performance results

A design study of a Re-configurable Access Module for Mobile Computing Applications is described. After a presentation of its cross-layered architecture, Control Parameters (CPs) of the module are introduced. The set of CPs both describes the functional state of the communication process in relation to the time-varying transport facilities and provides, as input of suitable Algorithms, the control information to re-configure the whole protocol stack for facing modified working conditions. The paper also presents the structure of the simulator realized to demonstrate the feasibility of the design guidelines and to evaluate reconfigurability performances.

Unidirectional Direct Load Control through Smart Plugs

International audience; Balancing energy demand and production is be-coming a more and more challenging task for energy utilities also because of the larger penetration of renewable energies which are more difficult to predict and control. While the traditional solution is to dynamically adapt energy production to follow time-varying demand, a new trend is to drive demand itself. Most of the ongoing actions in this direction involve greedy energy consumers, like industrial plants, supermarkets or large buildings. Pervasive communication technologies may allow in the near future to push further the granularity of such approach, by having the energy utility interacting with residen-tial appli…

Scalable and Privacy-Preserving Admission Control for Smart Grids

International audience; Energy demand and production need to be constantly matched in the power grid. The traditional paradigm to continuously adapt the production to the demand is challenged by the increasing penetration of more variable and less predictable energy sources, like solar photovoltaics and wind power. An alternative approach is the so called direct control of some inherently flexible electric loads to shape the demand. Direct control of deferrable loads presents analogies with flow admission control in telecommunication networks: a request for network resources (bandwidth or energy) can be delayed on the basis of the current network status in order to guarantee some performanc…

Cross-technology wireless experimentation: Improving 802.11 and 802.15.4e coexistence

In this demo we demonstrate the functionalities of a novel experimentation framework, called WiSHFUL, that facilitates the prototyping and experimental validation of innovative solutions for heterogeneous wireless networks, including cross-technology coordination mechanisms. The framework supports a clean separation between the definition of the logic for optimizing the behaviors of wireless devices and the underlying device capabilities, by means of a unifying platform-independent control interface and programming model. The use of the framework is demonstrated through two representative use cases, where medium access is coordinated between IEEE-802.11 and IEEE-802.15.4 networks.

Performance evaluation of differentiated access mechanisms effectiveness in 802.11 networks

The IEEE 802.11e draft specification aims to extend the original 802.11 MAC protocol by introducing priority mechanisms able to manage bandwidth and resource allocation according to the QoS needs of real-time applications. Different strategies based on MAC parameter diversifications, such as contention window limits, contention window updating factor and silence monitoring time, can be pursued in order to provide service differentiation, also in the case of distributed access. In this paper, we investigate on the behaviour of each differentiation possibility under different load conditions and traffic requirements. Our results show that the most powerful mechanisms which provide service dif…

Method of changing the operation of wireless network nodes

Performance analysis of the out-of-band signaling scheme for high speed wireless LANs

In this paper, we study the performance of our earlier proposed out-of-band signaling (OBS) scheme for high speed wireless local area networks (WLANs). We employ the system approximation technique for modeling of the OBS scheme. An equivalent state dependent single server queue, that describes the OBS scheme, is constructed for the analysis of the throughput and delay performances. Moreover, we study the throughput optimization of the OBS scheme, which provides a means for optimizing the performance of the OBS scheme, given a particular network environment. Finally, we conduct several simulation experiments to validate our analytical results.

Overgrid: A Fully Distributed Demand Response Architecture Based on Overlay Networks

In this paper, we present Overgrid, a fully distributed peer-to-peer (P2P) architecture designed to automatically control and implement distributed demand response (DR) schemes in a community of smart buildings with energy generation and storage capabilities. As overlay networks in communications establish logical links between peers regardless of the physical topology of the network, the Overgrid is able to apply some power balance criteria to its system of buildings, as they belong to a virtual microgrid, regardless of their physical location. We exploit an innovative distributed algorithm, called flow updating, for monitoring the power consumption of the buildings and the number of nodes…

Revealing Transmit Diversity Mechanisms in Commercial IEEE 802.11 Cards

Service differentiation in WLAN has been traditionally faced at the MAC layer. However, some PHY layer parameters, such as the transmission power, the antenna, and the modulation/coding scheme, have a deep impact on network performance. Since the criterion for selecting these parameters is left to the vendor specific implementations, the performance spread of most experimental results about 802.11 WLAN could be affected by vendor proprietary schemes. The focus of this paper is an experimental analysis of the undisclosed antenna diversity mechanisms employed by some widely used cards (namely, the Atheros and Intel based cards), and a thorough understanding of the optimization goals which gui…

Recognizing Video Resolution by Monitoring Memory Metrics in Mobile Clients

Content delivery is one of the most successful applications in mobile networks. Mobile edge servers are significantly contributing to the improvement of this type of applications, by also performing resolution adaptations as a function of the radio link quality observed by the users. In this paper, we face the problem of dynamically tracking the perceived video resolution by mobile clients in a mobile edge environment to guarantee an agreed Service Level Agreement (SLA). To this purpose, we propose a protocol-agnostic approach, based on monitoring some memory metrics of a running video streaming process at the mobile client, for identifying the time-varying resolution of the video content.

Medium access in WiFi networks: strategies of selfish nodes

This article provides a game theoretical analysis of the WiFi MAC protocol to understand the risks or the advantages offered by possible modifications of MAC functionalities implemented at the driver level.

Realizing airtime allocations in multi-hop Wi-Fi networks: A stability and convergence study with testbed evaluation

Abstract REACT is a distributed resource allocation protocol used to negotiate a max–min allocation of airtime for multi-hop ad hoc wireless networks. Two approaches are proposed for a node to realize its REACT allocation in a contention-based MAC protocol. This is achieved by tuning its contention window to a value that corresponds to its allocation. Only a change in the allocation, due to a change in local traffic requirements or local network views, results in re-tuning. The approaches for tuning are implemented in commercial Wi-Fi devices and their stability and convergence are studied experimentally in the w-iLab.t wireless network testbed. These properties are also studied analyticall…

Analysis of the IEEE 802.11e EDCA Under Statistical Traffic

Many models have been proposed to analyze the performance of the IEEE 802.11 distributed coordination function (DCF) and the IEEE 802.11e enhanced distributed coordination function (EDCA) under saturation condition. To analyze DCF under statistical traffic, Foh and Zukerman introduce a model that uses Markovian Framework to compute the throughput and delay performance. In this paper, we analyze the protocol service time of EDCA mechanism and introduce a model to analyze EDCA under statistical traffic using Markovian Framework. Using this model, we analyze the throughput and delay performance of EDCA mechanism under statistical traffic.

Making WiFi work in multi-hop topologies: Automatic negotiation and allocation of airtime

We propose a solution for mitigating the performance impairments of CSMA/CA protocols in multi-hop topologies based on the dynamic adaptation of the contention process experienced by nodes in a wireless network. A distributed protocol is used to negotiate the channel airtime for a node as a function of the traffic requirements of its neighbourhood, taking into account bandwidth reserved for the control operations. A mechanism is provided for a node to tune its contention window depending on its allocated airtime. Different from previous schemes, a node's contention window is fixed in size unless the traffic requirements of its neighbourhood change. The scheme is implemented on legacy commer…

A Low-level Simulation Study of Prioritization in IEEE 802.11e Contention-based Networks

This work deals with the performance evaluation of the IEEE 802.11e EDCA proposal for service prioritization in Wireless LANs. A large amount of study has been carried out in the scientific community to evaluate the performance of the EDCA proposal, mainly in terms of throughput and access delay differentiation. However, we argue that further performance insights are needed in order to fully understand the principles behind the EDCA prioritization mechanisms. To this purpose, rather than limit our investigation on throughput and delay performance figures, we take a closer look to their operation also in terms of low-level performance metrics (such as probability of accessing specific channe…

Architectures and protocols for mobile computing applications: a reconfigurable approach", Elsevier Computer Networks

Coloring-based resource allocations in ad-hoc wireless networks

It is well known that CSMA/CA protocols exhibit very poor performance in case of multi-hop transmissions, because of inter-link interference due to imperfect carrier sensing. We propose to control such an interference by preallocating temporal slots in which different sets of network nodes are allowed to contend for the channel access. The approach is based on distributed coloring algorithms with limited signaling overhead that can be customized as a function of the network topology and traffic load.

On-body and off-body transmit power control in IEEE 802.15.6 scheduled access networks

Wireless Body Area Networks (WBANs) have received much attention due to the possibility to be used in healthcare applications. For these applications, energy saving is a critical issue, as in many cases, batteries cannot be easily replaced. A transmit power control scheme, able to adapt to the variations of the wireless body channel, will allow consistent energy saving and longer battery life. In this paper we propose a transmit power control scheme suitable for IEEE 802.15.6 narrowband scheduled access networks, in which the transmission power is modulated frame by frame according to a run-time estimation of the channel propagation conditions. A simple and effective line search algorithm i…

A Cognitive Tuning of Contention Windows in WiFi Infrastructure Networks

In WiFi networks, mobile nodes compete for accessing a shared channel by means of a random access protocol called Distributed Coordination Function (DCF). Although this protocol is in principle fair, since it should guarantee that all the stations have the same probability to transmit on the channel, it has been shown that unfair behaviors may emerge in actual networking scenarios. These phenomena are due to different reasons, including non-standard configurations of the nodes, critical network topologies, and short-term performance observations. In this paper we propose a game-theoretic approach for defining an enhanced DCF scheme suitable for WiFi intelligent nodes employing cognitive fun…

Demo - Dynamic Adaptations of WiFi Channel Widths Without TX/RX Coordination

Most modern standards for wireless communications support physical layer adaptations, in terms of dynamic selection of channel central frequency, transmission power, modulation format, etc., in order to increase link robustness under time-varying propagation and interference conditions. In this demo, we demonstrate that another powerful solution for extending physical layer flexibility in OFDM-based technologies is the dynamic adaptation of the channel width. Although some standards already define the possibility of utilizing multiple channel widths (e.g. 20MHz, 10MHz, 5MHz for IEEE 802.11a standards), such an utilization is limited to a static configuration of a value defined during the ne…

Supporting Autonomous Navigation of Visually Impaired People for Experiencing Cultural Heritage

In this chapter, we present a system for indoor and outdoor localization and navigation to allow the low vision users in experiencing cultural heritage in autonomy. The system is based on the joint utilization of dead-reckoning and computer vision techniques on a smartphone-centric tracking system. The system is explicitly designed for visually impaired people, but it can be easily generalized to other users, and it is built under the assumption that special reference signals, such as colored tapes, painted lines, or tactile paving, are deployed in the environment for guiding visually impaired users along pre-defined paths. Differently from previous works on localization, which are focused …

Capture Aware Sequential Waterfilling for LoraWAN Adaptive Data Rate

LoRaWAN (Long Range Wide Area Network) is emerging as an attractive network infrastructure for ultra low power Internet of Things devices. Even if the technology itself is quite mature and specified, the currently deployed wireless resource allocation strategies are still coarse and based on rough heuristics. This paper proposes an innovative "sequential waterfilling" strategy for assigning Spreading Factors (SF) to End-Devices (ED). Our design relies on three complementary approaches: i) equalize the Time-on-Air of the packets transmitted by the system's EDs in each spreading factor's group; ii) balance the spreading factors across multiple access gateways, and iii) keep into account the c…

Teletraffic Engineering for Direct Load Control in Smart Grids

International audience; The traditional paradigm for power grid operation is to continuously adapt energy production to demand. This paradigm is challenged by the increasing penetration of renewable sources, that are more variable and less predictable. An alternative approach is the direct load control of some inherently flexible electric loads to shape the demand. Direct control of deferrable loads presents analogies with flow admission control in telecommunication networks: a request for network resources (bandwidth or energy) can be delayed on the basis of the current network status in order to guarantee some performance metrics. In this paper we go beyond such an analogy, showing that u…

MAC learning

Cognition as a way to deal with the challenges of future wireless networks has been largely considered by the recent literature, with a main focus on physical layer adaptability and dynamic spectrum access. In this demo, we show how a simple cognition mechanism can be also applied at the MAC layer, by exploiting the emerging paradigm of programmable wireless cards. The idea is using the formal definition of simple MAC protocol components and platform-independent representation of channel events gathered from the wireless node, for emulating the behavior of protocols which are not currently running on the network, learning about their expected performance, and dynamically reconfiguring the w…

A Kalman Filter Approach for Distinguishing Channel and Collision Errors in IEEE 802.11 Networks

In the last years, several strategies for maximizing the throughput performance of IEEE 802.11 networks have been proposed in literature. Specifically, it has been shown that optimizations are possible both at the medium access control (MAC) layer, and at the physical (PHY) layer. In fact, at the MAC layer, it is possible to minimize the channel waste due to collisions and backoff expiration times, by tuning the minimum contention window as a function of the network congestion level. At the PHY layer, it is possible to improve the transmission robustness, by selecting a suitable modulation/coding scheme as a function of the channel quality perceived by the stations. However, the feasibility…

Demo - A Cell-level Traffic Generator for LoRa Networks

In this demo we present and validate a LoRa cell traffic generator, able to emulate the behavior of thousands of low-rate sensor nodes deployed in the same cell, by using a single Software Defined Radio (SDR) platform. Differently from traditional generators, whose goal is creating packet flows which emulate specific applications and protocols, our focus is generating a combined radio signal, as seen by a gateway, given by the super-position of the signals transmitted by multiple sensors simultaneously active on the same channel. We argue that such a generator can be of interest for testing different network planning solutions for LoRa networks.

Exploiting programmable architectures for WiFi/ZigBee inter-technology cooperation

The increasing complexity of wireless standards has shown that protocols cannot be designed once for all possible deployments, especially when unpredictable and mutating interference situations are present due to the coexistence of heterogeneous technologies. As such, flexibility and (re)programmability of wireless devices is crucial in the emerging scenarios of technology proliferation and unpredictable interference conditions. In this paper, we focus on the possibility to improve coexistence performance of WiFi and ZigBee networks by exploiting novel programmable architectures of wireless devices able to support run-time modifications of medium access operations. Differently from software…

ARIANNA: a smartphone-based navigation system with human in the loop

In this paper we present a low cost navigation system, called ARIANNA, primarily designed for visually impaired people. ARIANNA (pAth Recognition for Indoor Assisted NavigatioN with Augmented perception) permits to find some points of interests in an indoor environment by following a path painted or sticked on the floor. The path is detected by the camera of the smartphone which also generates a vibration signal providing a feedback to the user for correcting his/her direction. Some special landmarks can be deployed along the path for coding additional information detectable by the camera. In order to study the practical feasibility of the ARIANNA system for human users that want to follow …

ErrorSense: Characterizing WiFi Error Patterns for Detecting ZigBee Interference

Recent years have witnessed the increasing adoption of heterogeneous wireless networks working in unlicensed ISM bands, thus creating serious problems of spectrum overcrowding. Although ZigBee, Bluetooth and WiFi networks have been natively designed for working in presence of interference, it has been observed that several performance impairments may occur because of heterogeneous sensitivity to detect or react to the presence of other technologies. In this paper we focus on the WiFi capability to detect interfering ZigBee links. Despite of the narrowband transmissions performed by ZigBee, in emerging scenarios ZigBee interference can have a significant impact on WiFi performance. Therefore…

Downlink channel access performance of NR-U: Impact of numerology and mini-slots on coexistence with Wi-Fi in the 5 GHz band

Coexistence between cellular systems and Wi-Fi gained the attention of the research community when LTE License Assisted Access (LAA) entered the unlicensed band. The recent introduction of NR-U as part of 5G introduces new coexistence opportunities because it implements scalable numerology (flexible subcarrier spacing and OFDM symbol lengths), and non-slot based scheduling (mini-slots), which considerably impact channel access. This paper analyzes the impact of NR-U settings on its coexistence with Wi-Fi networks and compares it with LAA operation using simulations and experiments. First, we propose a downlink channel access simulation model, which addresses the problem of the dependency an…

A cultural heritage experience for visually impaired people

Abstract In recent years, we have assisted to an impressive advance of computer vision algorithms, based on image processing and artificial intelligence. Among the many applications of computer vision, in this paper we investigate on the potential impact for enhancing the cultural and physical accessibility of cultural heritage sites. By using a common smartphone as a mediation instrument with the environment, we demonstrate how convolutional networks can be trained for recognizing monuments in the surroundings of the users, thus enabling the possibility of accessing contents associated to the monument itself, or new forms of fruition for visually impaired people. Moreover, computer vision …

Throughput and Delay Analysis of IEEE 802.1le Block ACK with Channel Errors

Medium access in WiFi networks: strategies of selfish nodes [Applications Corner]

This article provides a game theoretical analysis of the WiFi MAC protocol to understand the risks or the advantages offered by possible modifications of MAC functionalities implemented at the driver level.

A Metaheuristic Bandwidth Allocation Scheme for FiWi Networks Using Ant Colony Optimization

Optical-wireless access networks constitute a quite attractive solution to meet the ever-increasing bandwidth requirements of end-users, offering significant benefits such as ubiquitous coverage in the wireless domain and huge bandwidth in the optical domain. However, converging optical and wireless networking technologies, with Passive Optical Networks (PONs) and 4G wireless standards, such as the Worldwide Interoperability for Microwave Access (WiMAX) and the Long Term Evolution (LTE), entails major challenges that need to be addressed. In this context, designing an efficient and fair bandwidth distribution with Quality of Service (QoS) support is a difficult task due to the interdependen…

Side Effects of Ambient Noise Immunity Techniques on Outdoor IEEE 802.11 Deployments

A very common conclusion of many experimental studies about IEEE 802.11 outdoor network deployments is that their poor performance results derive from the unfavorable interference and multi-path signals in which the WLAN-cards are required to operate. Goal of this paper is to show that this condition does not always hold, and unexpected and inaccurated PHY layer implementations can be a primary cause of packet losses. With the support of extensive measurement campaigns led in our campus, we provide the performance evidence that IEEE 802.11 outdoor performance impairments are strongly affected by proprietary interference mitigation techniques that adaptively adjust the WLAN-card receiver sen…

Control Architecture for Wireless MAC Processor Networking

Abstract: In these years, the proliferation of unplanned WLANs is creating the need of implementing different adaptation strategies for improving the network per- formance under mutating and evolving interference scenarios. Many vendors pro- pose undisclosed MAC/PHY optimization solutions, such as ambient noise immunity schemes, dynamic tuning of operating channels and contention parameters, etc., rely- ing on low-level implementations in the card hardware/firmware. In this paper we envision a new solution for expressing and implementing high-level adaptation policies in WLANs, in contrast to the current approaches based on vendor- specific implementations. We exploit the hardware abstracti…