Search results for "ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS"
showing 10 items of 449 documents
Evaluating the Performance of Real Time Videoconferencing in Ad Hoc Networks Through Emulation
2008
The validation of new video protocols and applications for mobile ad hoc networks in a real environment is an important task. In this work we present Castadiva, a test-bed architecture that allows validating software solutions for ad hoc networks using low-cost, off-the-shelf devices and open source software. We use this tool to test a videocall using the OLSR protocol in different scenarios, varying the number of hops between the caller and the receiver. The results obtained in this paper show that, for an ad hoc network with a large number of hops, the quality of videocalls suffers a significant degradation even in the absence of mobility.
Packet Aggregation in TelosB WSNs: Design, Implementation and Experiments
2016
Master's thesis in Information- and communication technology IKT590 - University of Agder 2016 WSN is an extensive field of research and a core technology which is adopted for monitoring and data assembling, used in various applications. Traditionally in a WSN, communication is performed in the fashion of single packet per transmission which produces high energy consumption and longer delay. Therefore, we introduce a novel approach by designing a system which applies packet aggregation in TelosB sensor motes using Contiki platform. In this approach, we assemble multiple packets together and send them in an aggregated frame towards the sink which can reduce the number of transmissions, energ…
Tracking Mobile Robot in Indoor Wireless Sensor Networks
2014
Published version of an article in the journal: Mathematical Problems in Engineering. Also available from the publisher at: http://10.1155/2014/837050 This work addresses the problem of tracking mobile robots in indoor wireless sensor networks (WSNs). Our approach is based on a localization scheme with RSSI (received signal strength indication) which is used widely in WSN. The developed tracking system is designed for continuous estimation of the robot's trajectory. A WSN, which is composed of many very simple and cheap wireless sensor nodes, is deployed at a specific region of interest. The wireless sensor nodes collect RSSI information sent by mobile robots. A range-based data fusion sche…
Energy Efficient Resource Allocation for OFDMA Two-Way Relay Networks with Channel Estimation Error
2015
In this work, we consider the practical issues of resource allocation problem in OFDMA two-way relay networks: the inaccuracy of channel-state information (CSI) available to the transmitters. Instead, only the estimated channel status is known by the transmitters. In this context, a joint optimization of subcarrier pairing and allocation, relay selection and transmit power allocation is formulated in the OFDMA two-way amplify-and-forward relay networks. Moreover, to ensure the Quality of Service (QoS) requirement, the energy consumption must be minimized without compromising the QoS. Therefore, by applying convex optimization techniques, energy efficient algorithms are developed with the ob…
UMTS radio networks
2006
Publisher Summary This chapter reviews the contributions to the UMTS radio network planning, with the optimization being provided from COST 273 and the real-time tuning, which is related to RRM. The results on UTRAN performance evaluation by the means of simulation tools are also discussed. The UMTS planning includes processes like: the propagation and traffic models, the aspects of parameter planning, and the automatic planning algorithms. An accurate ray-tracing model integrated in a UMTS-capable planning tool allows the radio network planner to reach optimal numbers for the BS deployment and configuration while meeting the service level requirements. Ray tracing can identify the problem …
OLSR Mesh Networks for Broadband Access: Enhancements, Implementation and Deployment
2008
In the context of an EU FP6 project, ADHOCSYS, we have developed a reliable and cost-effective solution for broadband Internet access in rural and mountainous areas. This solution is built based on multi-hop wireless mesh networking technologies and covers many aspects such as routing, reliability, QoS, security, self-configuration, self-healing, remote network monitoring, power management etc. In this paper, we present solely the routing aspect of the developed mesh network, focusing on new routing features that have been designed, implemented, and deployed in a real-life operational network. These new features are developed based on an extended version of the OLSR protocol. The test resul…
Policy-based channel access mechanism selection for QoS provision in IEEE 802.11e
2007
The appearance of the 802.11e standard made the 802.11 wireless local area networks (WLANs) capable of providing different levels of quality of service (QoS). This standard defines two new channel access mechanisms (CAMs), namely the enhanced distributed channel access (EDCA) and the HCF controlled channel access (HCCA). The introduction of two CAMs increases the complexity of traffic management, since now not only the available resources have to be distributed, but also the optimal CAM for each data flow has to be selected. However, the best CAM selection algorithm is still not clear. This paper presents and analyses different CAM selection policies in order to derive the best-suited strat…
A dynamic channel access strategy for underlay cognitive radio networks: Markov modelling and performance evaluation
2015
Unlike in overlay cognitive radio networks, secondary users in underlay cognitive radio networks can access licensed spectrum even at the presence of a primary user, given that the interference caused by the secondary transmission is lower than a pre-specified threshold. Based on this underlay access principle, we propose in this paper a dynamic channel access strategy for multi-channel cognitive radio networks. Different from existing underlay access techniques, channel assembling, spectrum adaptation and restricted channel occupancy are also considered in the proposed strategy in order to achieve better performance in the secondary network. Accordingly, a partial channel occupancy mode, w…
A cooperative lifetime extension MAC protocol in duty cycle enabled wireless sensor networks
2011
To reduce energy consumption in wireless sensor networks, the concept of duty cycle is used in many MAC protocols. Although these protocols provide efficient energy-conservation solutions, they cannot resolve the energy hole problem in a multi-hop network, where a few nodes near the sink must relay the packets from the rest of the network, and consequently exhaust their batteries earlier. The previously proposed REACT forwarding protocol triggers the cooperation of several nodes to extend transmission range and hop over the highly burdened node, thereby allowing it to save its energy and extend the lifetime of the network. However, the previous work lacked a MAC protocol with a duty cycle. …
Sparsity-aware narrowband interference mitigation and subcarriers selection in OFDM-based cognitive radio networks
2016
In this paper, the performance of an orthogonal frequency division multiplexing overlay cognitive radio network with subcarrier selection schemes is investigated. We propose three subcarrier selection techniques that reduce the level of interference at the primary base station based on collected channel state information from the different network nodes. Approximated outage probability expressions are also derived and verified by simulations for the different studied techniques. In addition, we propose and investigate a new approach for asynchronous narrowband interference (NBI) estimation and mitigation in cognitive radio networks. The proposed approach does not require prior knowledge of …