Summary IEEE 802.11 MAC protocol is the de facto standard for wireless local area networks (LANs), and has also been implemented in many network simulation packages for wireless multi-hop ad hoc networks. However, it is well known that, as the number of active stations increases, the performance of IEEE 802.11 MAC in terms of delay and throughput degrades dramatically, especially when each station’s load approaches its saturation state. To explore the inherent problems in this protocol, it is important to characterize the probability distribution of the packet service time at the MAC layer. In this paper, by modeling the exponential backoff process as a Markov chain, we can use the signal transfer function of the generalized state transition diagram to derive an approximate probability distribution of the MAC layer service time. We then present the discrete probability distribution for MAC layer packet service time, which is shown to accurately match the simulation data from network simulations. Based on the probability model for the MAC layer service time, we can analyze a few performance metrics of the wireless LAN and give better explanation to the performance degradation in delay and throughput at various traffic loads. Furthermore, we demonstrate that the exponential distribution is a good approximation model for the MAC layer service time for the queueing analysis, and the presented queueing models can accurately match the simulation data obtained from ns-2 when the arrival process at MAC layer is Poissonian. Copyright # 2004 John Wiley & Sons, Ltd.

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Performance analysis of IEEE 802.11 MAC protocols in wireless LANs

Since the publication of Wireless Video Communications five years ago, the area of video compression and wireless transceivers has evolved even further. This new edition addresses a range of recent developments in these areas, giving cognizance to the associated transmission aspects and issues of error resilience. Video Compression and Communications has been updated and condensed yet remains all-encompassing, giving a comprehensive overview of the subject. Covering compression issues, coding delay, implementational complexity and bitrate, the book also looks at the historical perspective to video communication. New edition of successful and informative text, Wireless Video Communications Substantial new material has been added on areas such as H.264, MPEG4 coding and transceivers Clear presentation and broad scope make it essential for anyone interested in wireless communications Systematically converts the lessons of Shannon's information theory into design principles applicable to practical wireless systems. This book is ideal for postgraduates and researchers in communication systems but will also be a valuable reference to undergraduates, development and systems engineers of video compression applications as well as industrialists, managers and visual communications practitioners.

Video Compression and Communications: From Basics to H.261, H.263, H.264, MPEG4 for DVB and HSDPA-Style Adaptive Turbo-Transceivers

Opportunistic spectrum access and adaptive power management are effective techniques to improve throughput, delay performance, and energy efficiency for wireless networks. In this paper, we consider the joint design of opportunistic spectrum access and adaptive power management under the setting of multi-radio nodes and multi-channel wireless local area networks (WLANs) under the distributed coordination function (DCF) mode. This design problem is particularly challenging due to the conflicting nature of the multi-radio capability of a node, i.e., multiple radios improve throughput and delay performance at the cost of increased energy consumption. To address this problem, we propose a power-saving multi-channel MAC protocol (PSM-MMAC), which is capable of reducing the collision probability and the waiting time in the ‘awake’ state of a node, resulting in improved throughput, delay performance, and energy efficiency. The key ideas of PSM-MMAC are the following: we first estimate the number of active links; given this estimation as well as queue lengths and channel conditions, we appropriately select channels, radios, and power states (i.e., awake or doze state); then we optimize the medium access probability in p-persistent CSMA used in the data exchange. Another contribution of this paper is an analytical model that characterizes the throughput performance. Simulation results validate the accuracy of our analytical model and show that our proposed protocol is able to significantly improve both throughput and energy efficiency.

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A Power-Saving Multi-Radio Multi-Channel MAC Protocol for Wireless Local Area Networks

A superframe lock subsystem includes a correlator which searches for and identifies a first unique word indicative of a frame boundary within a received bit stream during an initial acquisition state. A controller subsequently predicts frame boundaries in accordance with the first unique word. In a tentative frame lock state, the correlator searches for and determines if a second unique word exists at the frame boundary subsequent the frame boundary which corresponds to the first unique word. If the second unique word is determined to exist at the corresponding frame boundary and if a single frame duration separates the first and second unique words, the superframe lock subsystem enters a frame lock state. During the frame lock state, information of the corresponding frames is processed. The correlator searches for and determines if a carrier wave sequence indicative of a superframe boundary exists in the received bit stream at the frame boundary immediately following the frame boundary which corresponds to the second unique word. If the carrier wave sequence exists at the predicted frame boundary, the correlator searches for and determines if a third unique words exists in the received bit stream immediately after the carrier wave sequence. Upon determination that the third unique word exists subsequent the carrier wave sequence, the superframe lock subsystem enters a superframe lock state wherein the correlator searches for and detects only unique words at subsequent predicted frame boundaries to maintain superframe lock.

Mobile telephone single channel per carrier superframe lock subsystem

IEEE 80211 MAC protocol has been the standard for wireless LANs, and also adopted in many network simulation packages for wireless multihop ad hoc networks However, it is well known that, as the traffic goes up, the performance of IEEE 80211 MAC drops dramatically in terms of delay and throughput, especially when the station approaches its saturation state To explore the inherent problems in this protocol, it is important to characterize the probability distribution of the packet service time at the MAC layer In this paper, by modeling the exponential backoff process as a Markov chain, we can use the signal transfer function of the generalized state transition diagram to derive the probability distribution of the MAC layer service time We then present the discrete probability distribution for MAC layer packet service time, which is shown to accurately match the simulation data from network simulations Finally, based on the probability model for the MAC layer service time, we are able to analyze a few performance metrics of the wireless LAN and give better explanation to the performance degradation in delay and throughput at various traffic load

Performance of wireless LANs based on IEEE 802.11 MAC protocols

Four key timing parameters that are used as performance measures are defined; reframe time, false in-frame time, out-of-frame detection time, and misframe time. Several strategies that improve frame alignment performance are considered for the case of a burst frame alignment word (FAW). With a little modification, the same strategies could also be applied to the case of a distributed FAW. The probability generating function is introduced, and its derivation from a state transition diagram is presented. The probability generating function is used in the timing parameters estimation. As an example, the frame alignment of a SONET (synchronized optical network) STS-3 signal is discussed. >

D. Choi

Papers

Frame alignment in a digital carrier system-a tutorial