Search results for "Medium Acce"

Refinements on IEEE 802.11 Distributed Coordination Function Modeling Approaches

2010

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…

MAC Protocols for Wake-up Radio: Principles, Modeling and Performance Analysis

2018

[EN] In wake-up radio (WuR) enabled wireless sensor networks (WSNs), a node triggers a data communication at any time instant by sending a wake-up call (WuC) in an on-demand manner. Such wake-up operations eliminate idle listening and overhearing burden for energy consumption in duty-cycled WSNs. Although WuR exhibits its superiority for light traffic, it is inefficient to handle high traffic load in a network. This paper makes an effort towards improving the performance of WuR under diverse load conditions with a twofold contribution. We first propose three protocols that support variable traffic loads by enabling respectively clear channel assessment (CCA), backoff plus CCA, and adaptive …

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

2010

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…

Rethinking the IEEE 802.11e EDCA Performance Modeling Methodology

2010

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…

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

2005

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…

Performance Optimization in Wireless Local Area Networks

Wireless Local Area Networks (WLAN) are becoming more and more important for providing wireless broadband access. Applications and networking scenarios evolve continuously and in an unpredictable way, attracting the attention of academic institutions, research centers and industry. For designing an e cient WLAN is necessary to carefully plan coverage and to optimize the network design parameters, such as AP locations, channel assignment, power allocation, MAC protocol, routing algorithm, etc... In this thesis we approach performance optimization in WLAN at di erent layer of the OSI model. Our rst approach is at Network layer. Starting from a Hybrid System modeling the ow of tra c in the net…

Opportunistic Synchronization for Improving IEEE 802.15.4 MAC Performance in Chain Topologies

2010

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. Therefore, synchronization is a very critical function for sensor networks. In this paper, we analyze the IEEE 802.15.4 MAC performance in sensor networks deployed in a chain topology. For this topology, critical inefficiencies can arise in case of multi-hop packet deliveries. We evaluate the impact of different synchronization schemes on the network performance, both in terms of network throughput and in terms of ene…