Enhanced Collision Resolution for the IEEE 802.11 Distributed Coordination Function

The IEEE 802.11 standard relies on the Distributed Coordination Function (DCF) as the fundamental medium access control method. DCF uses the Binary Exponential Backoff (BEB) algorithm to regulate channel access. The backoff period determined by BEB depends on a contention window (CW) whose size is doubled if a station suffers a collision and reset to its minimum value after a successful transmission. BEB doubles the CW size upon collision to reduce the collision probability in retransmission. However, this CW increase reduces channel access time because stations will spend more time sensing the channel rather than accessing it. Although resetting the CW to its minimum value increases channel access, it negatively affects fairness because it favours successfully transmitting stations over stations suffering from collisions. Moreover, resetting CW leads to increasing the collision probability and therefore increases the number of collisions. % Quality control editor: Please ensure that the intended meaning has been maintained in the edits of the previous sentence. Since increasing channel access time and reducing the probability of collisions are important factors to improve the DCF performance, and they conflict with each other, improving one will have an adverse effect on the other and consequently will harm the DCF performance. We propose an algorithm, \gls{ECRA}, that solves collisions once they occur without instantly increasing the CW size. Our algorithm reduces the collision probability without affecting channel access time. We also propose an accurate analytical model that allows comparing the theoretical saturation and maximum throughputs of our algorithm with those of benchmark algorithms. Our model uses a collision probability that is dependent on the station transmission history and thus provides a precise estimation of the probability that a station transmits in a random timeslot, which results in a more accurate throughput analysis. We present extensive simulations for fixed and mobile scenarios. The results show that on average, our algorithm outperformed BEB in terms of throughput and fairness. Compared to other benchmark algorithms, our algorithm improved, on average, throughput and delay performance

Study of QoS Management In IEEE 802.11 and 802.11e MAC Layer Protocols

Wireless networks have become increasingly popular in recent times and it has become a pressing need to ensure that the various applications using it get the necessary Quality of service. Wireless networks being inherently different from wired networks and pose a unique set of challenges . Quality of Service(QoS) is dened as the performance oered by a network to its users in terms of providing resource assurance and service dierentiation to dierent kinds of trac ows .Due to scarcity of bandwidth and high rate of packet loss in wireless networks providing QoS to time critical applications is a challeng- ing task .In this thesis we attempt to study the QoS management strategies applied by the wireless networks at the MAC layer .The most common QoS provisioning strategy is to prioritize the dierent classes of trac and make sure that the high priority trac gets preferential access to the channel .In this thesis ,a study of the binary exponential back-o algorithm which is used by the wireless MAC protocols has been done and an improvement has been proposed in which the Contention Window(CW) is varied in a non-uniform manner for dierent access categories with an aim to improve the performance parameters. The CW denes the range[0,CW] from which a random no of slots are chosen by a station in case of a failure in transmission for backing o before attempt- ing to transmit again. To demonstrate the eect of the modied contention window variation scheme simulations have been carried out using the Qualnet Simulator designed by Scalable Network Technologies, Inc. After implementing the proposed modication a performance comparison has been carried out for parameters such as packet delivery ratio, throughput and jitter

STUDY OF MOBILITY AND QoS OF 802.11 AND 802.11e WIRELESS LAN STANDARDS

Quality of service (QoS) is a key problem in wireless environments where bandwidth is scarce and channel conditions are time varying and sometimes implies highly packet losses. IEEE 802.11b/g/a wireless LAN (WLAN) are the most widely used WLAN standards today, and the IEEE 802.11e QoS enhancement standard exists and introduces QoS support for multimedia applications. This paper presents a class based admission control algorithm for 802.11e based wireless local area networks . The strengths of our admission control is dynamicity and flexibility of the algorithm, which adapts to the situation of the BSS, like global load, number of best effort AC, and position of QSTA by report of QAP. Thus it achieves higher throughput than other admission control for 802.11 e. A summary of many good solutions on admission control for 802.11e is be done, and the model of our admission control is presented. The 802.11e standard starves the low priority traffic in case of high load, and leads to higher collision rates, and did not make a good estimate of weight of queues, so there is an unbalance enters the flows with high priorities. A discussion is presented in detail using simulation-based evaluations, with an aim of comparing results of our admission control algorithm, with the 802.11e standard and the FHCF algorithm. Results reveal an improvement of the network load and a decrease of the number of collisions

WLAN performance evaluation in different wireless access techniques (DCF, PCF, HCF)

IEEE 802.11x Wireless Local-Area-Network (WLAN) considered a powerful solution for the last mile wireless broadband(BB) access. WLAN becomes important element in 4G and 5G mobile networks because it can provide services to mobile users in areas not covered by eNBs. However, the 802.11 legacy protocol doesn’t support delay-sensitive services like VoIP because it adopts the best-effort method. In 2001 IEEE 802.11e standard was proposed to deploy QoS with new access techniques introduction. There are many parameters related to MAC layer which affect the WLAN network performance from the prospective of delay, and throughput. This study presents performance evaluation of voice traffic and FTP traffic in IEEE802.11 legacy protocol WLAN and IEEE802.11e WLAN via OPNET computer simulation. Network performance will be tested against different MAC access protocols and different MAC parameters

IMPROVING QoS OF VoWLAN VIA CROSS-LAYER BASED ADAPTIVE APPROACH

Voice over Internet Protocol (VoIP) is a technology that allows the transmission of voice packets over Internet Protocol (IP). Recently, the integration of VoIP and Wireless Local Area Network (WLAN), and known as Voice over WLAN (VoWLAN), has become popular driven by the mobility requirements ofusers, as well as by factor of its tangible cost effectiveness. However, WLAN network architecture was primarily designed to support the transmission of data, and not for voice traffic, which makes it lack ofproviding the stringent Quality ofService (QoS) for VoIP applications. On the other hand, WLAN operates based on IEEE 802.11 standards that support Link Adaptive (LA) technique. However, LA leads to having a network with multi-rate transmissions that causes network bandwidth variation, which hence degrades the voice quality. Therefore, it is important to develop an algorithm that would be able to overcome the negative effect of the multi-rate issue on VoIP quality. Hence, the main goal ofthis research work is to develop an agent that utilizes IP protocols by applying a Cross-Layering approach to eliminate the above-mentioned negative effect. This could be expected from the interaction between Medium Access Control (MAC) layer and Application layer, where the proposed agent adapts the voice packet size at the Application layer according to the change of MAC transmission data rate to avoid network congestion from happening. The agent also monitors the quality of conversations from the periodically generated Real Time Control Protocol (RTCP) reports. If voice quality degradation is detected, then the agent performs further rate adaptation to improve the quality. The agent performance has been evaluated by carrying out an extensive series ofsimulation using OPNET Modeler. The obtained results of different performance parameters are presented, comparing the performance ofVoWLAN that used the proposed agent to that ofthe standard network without agent. The results ofall measured quality parameters hav

Impact of Background Traffic on Speech Quality in VoWLAN

This paper describes measurements of the impact of background traffic on speech quality in an environment of WLANs (IEEE 802.11). The simulated background traffic consists of three types of current traffics in telecommunication networks such as data transfer service, multimedia streaming service, and Web service. The background traffic was generated by means of the accomplished Distributed Internet Traffic Generator (D-ITG). The impact of these types of traffic and traffic load on speech quality using the test sequence and speech sequences is the aim of this paper. The assessment of speech quality is carried out by means of the accomplished Perceptual Evaluation of Speech Quality (PESQ) algorithm. The proposal of a new method for improved detection of the critical conditions in wireless telecommunication networks from the speech quality point of view is presented in this paper. Conclusion implies the next application of the method of improved detection of critical conditions for the purpose of algorithms for link adaptation from the speech quality point of view in an environment of WLANs. The primary goal of these algorithms is improving speech quality in the VoWLAN connections, which are established in the competent link