A Two-State Markov-Based Wireless Error Model for Bluetooth Networks

Data transmission over wireless networks is challenging due to the occurrence of burst errors, and packet loss caused by such errors seriously limits the maximum achievable throughput of wireless networks. To tailor efficient transmission schemes, it is essential to develop a wireless error model that can provide insight into the behavior of wireless transmissions. In this study, we investigate the wireless error model of Bluetooth networks. We study the FHSS feature of Bluetooth using both ordinary hopping kernels and Adaptive Frequency Hopping (AFH) kernels, and design analytical error models accordingly to capture the channel behavior of Bluetooth networks. We evaluate the proposed models by comparing the analytical results to the simulation results obtained by Markov Chain Monte Carlo (MCMC) algorithms. The results show that our analytical models can represent the channel behavior of Bluetooth networks in all test cases.     

E-BEB: Enhanced Binary Exponential Backoff Algorithm for Multi-hop Wireless Ad-hoc Networks

Binary exponential backoff algorithm is the de-facto medium access control protocol for wireless local area networks, and it has been employed as the standard contention resolution algorithm in multi-hop wireless ad-hoc networks. However, this algorithm does not function well in multi-hop wireless environments due to its several performance issues and technical limitations. In this paper, we propose a simple, efficient, priority provision, and well performed contention resolution algorithm called enhanced binary exponential backoff (E-BEB) algorithm for impartial channel access in multi-hop wireless ad-hoc networks. We also provide a simple and accurate analytical model to study the system saturation throughput of the proposed scheme. Simulations are conducted to evaluate the performance of E-BEB algorithm. The results show that the E-BEB algorithm can alleviate the fairness problem and support multimedia transmission in multi-hop wireless environments.     

Wireless Adaptive Framed Pseudo-Bayesian Aloha (AFPBA) Algorithm with Priorities

In this paper, we propose a new priority algorithm to control the access to the wireless ATM MAC uplink frame, for multimedia traffic like wireless ATM, similar to the Pseudo-Bayesian algorithm presented in [1]. The adaptive framed Pseudo-Bayesian Aloha (AFPBA) algorithm ensures minimum access delay for high priority traffic classes with small delay degradation to low priority traffic classes. Control packets are transmitted in each slot according to transmission probabilities based on the history of the channel and in contention with other packets of the same priority class. The number of contention slots assigned for each priority class, on a given frame, changes adaptively according to its priority index and the estimated arrival rate on each frame using an adaptive slot assignment mechanism. Finally, the throughput analysis of the algorithm is presented and the delay performance is evaluated by simulation on a wireless channel in the presence of shadowing, Rayleigh fading and capture. Results show that the wireless channel offers significant delay improvements to all priority packets, especially in the presence of fast fading.     

A study of deadlock models for a multiservice medium accessprotocol employing a slotted Aloha signalling channel

Medium access protocols for HFC and wireless ATM networks often use a collision based capacity request signalling channel which may rely on the slotted Aloha multiaccess principle. This paper studies the performance of a p-persistence slotted Aloha contention resolution algorithm (CRA), subject to extreme interstation correlation, by means of a discrete-time Markov chain analysis. We examine in detail the conditions leading to a deadlock-a situation where the time to collision resolution becomes unacceptably high and the system is practically unstable. We analyze two disaster scenario deadlock models, and study the effect of channel error probability, signalling traffic load, and the contention resolution algorithm used. We show that the key factor of the CRA is the collision rate and not channel errors. We propose and test three signalling channel capacity allocation schemes. We identify the best-performing of these three schemes as the cyclic contention mini-slot (CMS) sharing employing multiple CMSs per data slot. Finally, we demonstrate the need for implementation of an added scheme, which dynamically adjusts the p-persistence parameter     

A Markov-Based Channel Model Algorithm for Wireless Networks

Techniques for modeling and simulating channel conditions play an essential role in understanding network protocol and application behavior. In [11], we demonstrated that inaccurate modeling using a traditional analytical model yielded suboptimal error control protocol parameters choices. In this paper, we demonstrate that time-varying effects on wireless channels result in wireless traces which exhibit non-stationary behavior over small window sizes. We then present an algorithm that extracts stationary components from a collected trace in order to provide analytical channel models that, relative to traditional approaches, more accurately represent characteristics such as burstiness, statistical distribution of errors, and packet loss processes. Our algorithm also generates artificial traces with the same statistical characteristics as actual collected network traces. For validation, we develop a channel model for the circuit-switched data service in GSM and show that it: (1) more closely approximates GSM channel characteristics than traditional Markov models and (2) generates artificial traces that closely match collected traces' statistics. Using these traces in a simulator environment enables future protocol and application testing under different controlled and repeatable conditions.     

Z-MAC: A Hybrid MAC for Wireless Sensor Networks

This paper presents the design, implementation and performance evaluation of a hybrid MAC protocol, called Z-MAC, for wireless sensor networks that combines the strengths of TDMA and CSMA while offsetting their weaknesses. Like CSMA, Z-MAC achieves high channel utilization and low latency under low contention and like TDMA, achieves high channel utilization under high contention and reduces collision among two-hop neighbors at a low cost. A distinctive feature of Z-MAC is that its performance is robust to synchronization errors, slot assignment failures, and time-varying channel conditions; in the worst case, its performance always falls back to that of CSMA. Z-MAC is implemented in TinyOS.     

Contention-Aware Performance Analysis of Mobility-Assisted Routing

A large body of work has theoretically analyzed the performance of mobility-assisted routing schemes for intermittently connected mobile networks. But the vast majority of these prior studies have ignored wireless contention. Recent papers have shown through simulations that ignoring contention leads to inaccurate and misleading results, even for sparse networks. In this paper, we analyze the performance of routing schemes under contention. First, we introduce a mathematical framework to model contention. This framework can be used to analyze any routing scheme with any mobility and channel model. Then, we use this framework to compute the expected delays for different representative mobility-assisted routing schemes under random direction, random waypoint and community-based mobility models. Finally, we use these delay expressions to optimize the design of routing schemes while demonstrating that designing and optimizing routing schemes using analytical expressions which ignore contention can lead to suboptimal or even erroneous behavior.     

Free access stack algorithms for microcellular radio systems

We evaluate the data traffic performance of a centralized packet access protocol for microcellular radio systems supporting both speech and data users. A time-slotted radio channel is assumed. Speech contention is decoupled from data contention to give speech priority over data. A free access stack algorithm is used for handling data contention. An out-slot access scheme is used in which the slots are divided into user-information transmission slots and contention slots for sending transmission requests. The contention slots are subdivided in minislots to improve the access capacity. The out-slot algorithm performances are compared with the performances of a previously proposed in-slot one in which all slots can be used for sending user information. A memoryless channel, with capture and errors, is considered. The effects of speech traffic on data performance are evaluated. Moreover, the paper presents a method for evaluating the packet error probability of a packet cellular system. This method is used for evaluating the proposed algorithm in a microcellular system. An access technique with coordinated operation among cochannel cells is studied. The effects of sectorization on data performances and protocol unfairness are investigated. Different frequency reuse factors are taken into consideration     

一种基于子集约束的协议首部纠错算法

针对无线网络数据的协议首部容易出错问题,该文在研究基于循环冗余校验的协议首部纠错算法的基础上,提出一种基于子集约束的纠错算法。该算法利用接收比特的置信度信息以接收向量为中心构建约束子集,从而缩小运算搜索范围,克服此前算法运算复杂度高的缺陷。随后,结合无线信号类型与信道模型,对算法的测试长度参数的取值范围进行了理论分析和实验验证。仿真结果表明,对于不同信噪比的无线信号,该算法可通过改变测试长度来调节约束子集大小,实现在保证较好性能条件下有效地降低运算开销,具有较强的实际应用价值。     

Contention-Based Airtime Usage Control in Multirate IEEE 802.11 Wireless LANs

In a multirate wireless LAN, wireless/mobile stations usually adapt their transmission rates to the channel condition. It is difficult to control each station's usage of network resources since the shared channel can be overused by low transmission-rate stations. To solve this problem, we propose a distributed control of stations' airtime usage which 1) always guarantees each station to receive a specified share of airtime, and 2) keeps service for individual stations unaffected by other stations' transmission rates. Such airtime control enables service differentiation or quality of service (QoS) support. Moreover, it can achieve a higher overall system throughput. The proposed airtime usage control exploits the Enhanced Distributed Channel Access (EDCA) of the IEEE 802.11e standard . Two control mechanisms are proposed: one based on controlling the station's arbitration inter-frame space (AIFS) and the other based on the contention window size. We show how the stations' airtime usage is related to the AIFS and contention window size parameters. Using this relation, two analytical models are developed to determine the optimal control parameters. Unlike the other heuristic controls or analytical models, our model provides handles or parameters for quantitative control of stations' airtime usage. Our evaluation results show that a precise airtime usage control can be achieved in a multirate wireless LAN     

Selfish MAC layer misbehavior in wireless networks

Wireless medium access control (MAC) protocols such as IEEE 802.11 use distributed contention resolution mechanisms for sharing the wireless channel. In this environment, selfish hosts that fail to adhere to the MAC protocol may obtain an unfair throughput share. For example, IEEE 802.11 requires hosts competing for access to the channel to wait for a "backoff" interval, randomly selected from a specified range/before initiating a transmission. Selfish hosts may wait for smaller backoff intervals than well-behaved hosts, thereby obtaining an unfair advantage. We present modifications to the IEEE 802.11 protocol to simplify detection of such selfish hosts and analyze the optimality of the chosen strategy. We also present a penalty scheme for punishing selfish misbehavior. We develop two misbehavior models to capture the behavior of misbehaving hosts. Simulation results under these misbehavior models indicate that our detection and penalty schemes are successful in handling MAC layer misbehavior.     

Physical layer capture aware MAC for WLANs

The physical layer capture (PLC) effect occurs frequently in the real wireless deployment; when two or more nodes transmit simultaneously, a receiver can successfully decode the collided frame if the signal strength of one frame is sufficiently high enough. Although the PLC effect increases the channel utilization, it results in an unfair channel access among the wireless nodes. In this paper, we propose a PLC-aware media access control (MAC) algorithm that employs the average waiting time as a common control reference. It enables the nodes to converge to a fair channel access by changing one of the IEEE 802.11 enhanced distributed channel access parameters: contention window, arbitration interframe space, or transmission opportunity. We then find multiple control references that meet the fair channel access constraint and obtain the near-optimal reference that maximizes the overall throughput. Through ns-2 simulations and real in-door experiments using the universal software radio peripheral platform, we evaluate the fairness and throughput performance of the PLC-aware MAC algorithm.     

Impact of bursty error rates on the performance of wireless local area network (WLAN)

With an increasing popularity of DCF based wireless LAN, the modeling of 802.11 distributed coordination function (DCF) has attracted lots of research attention. Existing analysis of 802.11 DCF has been focused on the determination of the throughput and the packet delay under saturated traffic and ideal channel conditions. Although some recent papers address the saturated performance under a simple uniform error model, they can hardly capture the impact of bursty characteristics of wireless fading on the performance of 802.11 DCF. This paper presents exact formulae for the throughput and the delay in DCF for various traffic conditions when either saturated or unsaturated traffic load is present. A two-state Markov channel model is incorporated to present the bursty characteristics of channel errors. With our analysis, the impact of bursty channel error on unsuccessful transmission probability and the DCF performance can be determined. The results of our analytical framework reveal that the four-way handshaking scheme does not improve throughput substantially for light traffic load. However, for heavy traffic load, the four-way handshaking scheme is advantageous as compared to the basic access scheme. Also, extensive simulation is done to substantiate the accuracy of our analytical model.     

A cross-layer congestion and contention window control scheme for TCP performance improvement in wireless LANs

Neither the current TCP protocol nor the standard backoff algorithm of IEEE 802.11 protocol is able to distinguish corruption loss from congestion or collision loss. Hence, high transmission errors and a varying latency inherent in wireless channel would have a seriously adverse effect on the performance of TCP. In this paper, we propose a novel and pragmatic cross-layer approach with joint congestion and contention window control scheme to improve the performance of TCP in IEEE 802.11 wireless environments. In addition to theoretical analysis, simulations are conducted to evaluate the proposed scheme. As it turns out, our design indeed provides a more efficient solution for frequent transmission loss and enables TCP to distinguish between congestion loses and transmission errors, thus to take proper remedial actions.     

Quality-of-service in ad hoc carrier sense multiple access wirelessnetworks

Carrier sense multiple access (CSMA) is one of the most pervasive medium access control (MAC) schemes in ad hoc, wireless networks. However, CSMA and its current variants do not provide quality-of-service (QoS) guarantees for real-time traffic support. This paper presents and studies black-burst (BB) contention, which is a distributed MAC scheme that provides QoS real-time access to ad hoc CSMA wireless networks. With this scheme, real-time nodes contend for access to the channel with pulses of energy-so called BBs-the durations of which are a function of the delay incurred by the nodes until the channel became idle. It is shown that real-time packets are not subject to collisions and that they have access priority over data packets. When operated in an ad hoc wireless LAN, BB contention further guarantees bounded and typically very small real-time delays. The performance of the network can approach that attained under ideal time division multiplexing (TDM) via a distributed algorithm that groups real-time packet transmissions into chains. A general analysis of BB contention is given, contemplating several modes of operation. The analysis provides conditions for the scheme to be stable. Its results are complemented with simulations that evaluate the performance of an ad hoc wireless LAN with a mixed population of data and real-time nodes     

Contention resolution in random-access wireless networks based on orthogonal complementary codes

This paper proposes a new method for contention resolution in random-access wireless networks. Using orthogonal complementary codes to design access-request packets, users can reserve channel access successfully, even in severe contentions. Collisions among access-request packets can be resolved and exploited, whereas collisions among data packets are avoided. System throughput and delay performance can be enhanced, because random-access contention becomes transparent. Specifically, system throughput approaches the offered load up to the maximum value one with improved average packet delay performance. A joint layer design approach is proposed with both the physical layer signal-detection algorithm and the medium access-control layer random-access protocol. The performance is analyzed with the consideration of signal detection errors. Simulations are performed to demonstrate its superior performance.     

Packet multiple access for channel with binary feedback, capture, and multiple reception

This paper considers the multiple access of mobile users to a common wireless channel. The channel is slotted and the binary feedback (empty slot/nonempty slot) is sent to all accessing users. If a slot was not empty and only one user transmitted in it, the transmission is considered successful. Only the user, which had the successful transmission, receives information about its success. In the Introduction, the paper gives a review of known multiple-access algorithms for such a channel. Then our algorithm is constructed that has none of the weaknesses of the algorithms discussed in the Introduction. The algorithm is stable, in contrast to the ALOHA algorithm. It can work in a channel with capture and multiple reception. Without them, the algorithm has a throughput of 0.2891. It is shown how capture and multiple reception can increase the algorithm throughput to 0.6548 and decrease the packet delay for some fading models. The average packet delay and variance are found for two fading models. The models are Rayleigh fading with incoherent and coherent combining of joint interference power. The accessing traffic is Poisson.     

On Channel Adaptive Multiple Access Control without Contention Queue for Wireless Multimedia Services

As tetherless multimedia computing environments are becoming much desired, broadband wireless communication infrastructures for providing wireless multimedia services will play an important role, and thus, are expected to proliferate. However, despite much research efforts have been expended, the multiple access control of the precious bandwidth remains a challenging problem because of the existence of two common drawbacks in the state-of-the-art protocols: (1) channel condition is ignored or not exploited, and (2) inflexible or biased time slots allocation algorithms are used. Indeed, existing protocols mostly ignore the burst errors due to fading and shadowing, which are inevitable in a mobile and wireless communication environment. A few protocols take into account the burst errors but just handle the errors in a passive manner. Most of the existing protocols employ an inflexible or biased allocation algorithm such that over-provisioning may occur for a certain class of users at the expense of the poor service quality received by other users. In this paper, a new MAC protocol, called SCAMA (synergistic channel adaptive multiple access) is proposed. The proposed protocol works closely with the underlying physical layer in that through observing the channel state information (CSI) of each mobile user, the MAC protocol first segregates a set of users with good CSI from requests gathered in the request contention phase of an uplink frame. The MAC protocol then judiciously allocates information time slots to the users according to the respective traffic types, CSI, urgency, and throughput, which are collectively represented by a novel and flexible priority function. Despite that contention request queue is not used in the protocol, the SCAMA protocol is robust in that it can avoid the congestion collapse which occur in other protocols.     

A deadlock model for a multi‐service medium access protocol employing multi‐slot N‐ary stack algorithm (msSTART)

Many modern multi‐service medium access protocols (MACs) use a collision based capacity request signaling channel as part of a hybrid TDMA frame structure. Multi‐slot Stack Random Access Algorithm (msSTART) is proposed for use in IEEE 802.14 hybrid fiber/coaxial network and will be highly relevant for the S‐MAC development of evolving WATM MAC specifications. This paper studies the performance of msSTART as an example of a Q‐ary tree contention resolution algorithm (CRA) in the wireless environment using the novel Basic Deadlock model. We contrast approximate results for msSTART performance obtained by simulation under extreme inter‐station correlation with analytical results for the more popular p‐persistence CRA used in several testbed WATM implementations. Using three signaling channel schemes designed to provide support for increased system stability, to implement priority in the wireless MAC, and maximise efficiency, we provide comparative results for evaluation of msSTART and p‐persistence ALOHA under what the IEEE 802.14 working group has termed the “disaster scenario”. We find that of the three schemes evaluated the full Contention Mini‐Slot (CMS) sharing scheme employing multiple CMSs per data region extends the protocol's useable load region the furthest. We conclude that Q‐ary tree contention resolution algorithms (in particular msSTART) are best adapted to the wireless environment, providing less case sensitive performance. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation on group based contention bandwidth request in LTE-A networks under high delay spread environment

In this paper, contention bandwidth request has been investigated for long term evolution-advanced (LTE-A) networks under extended typical urban based multipath fading channel that displays high delay spread environment. As the choice of preambles has to provide high detection probability under such environments, at the outset, this paper examines various group based preamble selection mechanisms, namely, Type I, Type II and Type III preamble sets. With suitable type of group based preamble, the challenge during contention bandwidth request is the appropriate choice of contention window during contention resolution. The contention window in this paper is chosen based on the indicators of various failure events, namely, probability of collision due to contention, probability of unavailability of bandwidth, probability of channel error and probability of improper detection of Zadoff–Chu sequences. After suggesting a scheme to account the possible failure events, an analytical model for contention-based bandwidth request has been developed for LTE-A networks. In addition, two backoff mechanisms are proposed to resolve contention among user equipment’s effectively and these mechanisms are compared to the existing techniques, namely, binary exponential backoff and uniform backoff. Further, the contention mechanism has been substantiated for varying depth of channel errors. With Type I grouping, the backoff with optimized contention window improves the efficiency by 13.95 %, reduces the access delay by 18.71 % and decreases the dropping probability by 59.33 % than the existing uniform backoff mechanism.