Warakorn Srichavengsup

A Design and Performance Evaluation of a Class of Channel Reservation Techniques for Medium Access Control Protocols in High Bit-Rate Wireless Communications

This paper introduces 12 channel reservation techniques for medium access control (MAC) protocols suitable for high bit-rate wireless communication systems. The first 7 algorithms, namely CFP, CAP, COP, COP+SPL, CFP+SPL, UNI and UNI+LA, are applicable to systems with single-access chance per frame, whereas the other 5 algorithms, namely MT-CFP, MT-CFP+SPL, MT-UNI, MT-UNI+LUA and MT-UNI+LUT are suitable for systems with multi-access attempts per frame. The performance of these techniques are analytically evaluated and compared with the existing known techniques. The analytical model derived here are also validated through Monte Carlo computer simulations. Numerical results show that all proposed techniques are in general more superior to conventional reservation techniques. Finally when comparing between all proposed schemes in terms of both throughput performance and practical feasibility it is found that the MT-UNI+LA scheme are relatively efficient and suitable for practical applications.

Analysis of a Multiple-Token Contention Scheme for Broadband Wireless Access Networks

In this paper, we present a mathematical analysis to evaluate the contention phase of a wireless system in which each contending station transmits multiple copies of the bandwidth reservation/request packet to increase the probability of successful transmissions using multiple slots randomly selected from the pool of available slots at the given moment. Here, we define this type of systems as a multi-token reservation scheme with uniform random backoff (MT-UNI). The proposed MT-UNI mechanism can be used in various broadband wireless access systems including IEEE 802.16, PRMA, C-TDMA and others. The simulation results show that the proposed performance formulae are very accurate, and the MT-UNI mechanism can improve the performance of the system at low load conditions. In addition, when each station uses 2 reservation tokens, the MT- UNI scheme seems to produce the near-optimal performance.

Channel reservation techniques under misbehaved users in high bit-rate wireless communication systems

This paper presents a mathematical analysis of a channel reservation technique referred to as CFP for medium access control protocol in high bit-rate wireless communication systems with two groups of users, i.e. normal and misbehaved users. Two different misbehaving scenarios are investigated, namely cascade fixed prop + 2 group (CFP+2G) and cascade fixed prop + 2 group + multi-token (CFP+2G+MT). The objective is to evaluate the effect of some misbehaved users on the overall system performance. Numerical results show that the probability of success in reservation clearly degrades if some users do not follow the agreed rule.

Efficient Medium Access Control Protocols for Broadband Wireless Communications

Suvit Nakpeerayuth1, Lunchakorn Wuttisittikulkij1, Pisit Vanichchanunt2, Warakorn Srichavengsup3, Norrarat Wattanamongkhol1, Robithoh Annur1, Muhammad Saadi4, Kamalas Wannakong1 and Siwaruk Siwamogsatham5 1Chulalongkorn University 2King Mongkuts University of Technology North Bangkok 3Thai-Nichi Institute of Technology 4University of Management and Technology 5National Electronics and Computer Technology Center 1,2,3,5Thailand 4Pakistan

On Improving WLAN Medium Access Control via Uniform Transmission Cycle and Performance Analysis

In this paper, we propose a modified backoff mechanism that can be used in conjunction with the existing backoff algorithms for medium access sharing among wireless stations via the CSMA protocol. With a proper design, the resulting scheme can achieve better short-term throughput fairness performance without degradation in the average throughput performance. The main idea of the proposed scheme is to virtually create a transmission cycle for each wireless station. After getting a turn to access the medium, each wireless station is not allowed to start the backoff procedure for its next transmission until it has waited for some additional number of backoff slots. Moreover, the average throughput performance of the proposed scheme is analytically evaluated in this work via the Markov chain approach. The simulation results show that the performance analysis model derived here for the proposed scheme is valid and accurate. In addition, the proposed scheme noticeably improves the short-term throughput fairness performance of the conventional backoff scheme.

Design and Performance Evaluation of Contention Resolution Schemes with QoS Support for Multimedia Traffic in High Bit-Rate Wireless Communications

This paper considers the problem of contention resolution algorithm for multi-class with quality of service (QoS) constrained for wireless communication. Five different channel reservation schemes are proposed, namely, UNI+MLA, UNI+DS, UNI+DS+MLA, Partial UNI and Partial UNI+MLA schemes for multimedia traffic, all are extensions of our recently proposed UNI scheme for single-class traffic. The goal is to achieve the highest system performance and enable each traffic type to meet its QoS requirements. We evaluate the performance of each scheme by mathematical analysis. The numerical results show that our proposed schemes are effective in enabling each traffic type to achieve the best successful rate possible in this kind of environment. Finally when comparing between our proposed schemes and conventional technique in terms of both throughput performance and QoS requirements it is found that the UNI+MLA, UNI+DS+MLA and Partial UNI+MLA schemes are relatively efficient and suitable for practical applications.

Performance analysis of modified backoff algorithm in IEEE 802.11 networks

The primary medium access control (MAC) protocol for wireless local area network (WLAN) is distributed coordination function (DCF) for IEEE 802.11. The binary exponential backoff (BEB) scheme used in 802.11 DCF mechanism may suffer from low throughput when the number of stations gets large due to the lack of flexibility in choosing the contention window size imposed by the standard. To improve the system throughput of IEEE 802.11 DCF, in this paper we propose a modification to the conventional BEB. The simulation results show that the modified backoff algorithm helps improve the saturation throughput of the DCF protocol using the same standard parameter settings. In addition, it is shown that the throughput performance of the system depends on the total number of stations and the maximum backoff stage.

Delay Performance Analysis of Two Channel Reservation Algorithms, CFP+SPL and UNI+LA in High-Speed Wireless Communication Systems

This paper presents the time delay analysis of two channel reservation schemes namely CFP+SPL and UNI+LA for system with relatively long round trip propagation delay time. Mathematical models have been formulated for the performance evaluation. The numerical results reveal the delay performance of the CFP+SPL scheme depends on the number of groups whereas the delay performance of the UNI+LA scheme depends on the permission probability, i.e. appropriate number of groups and appropriate permission probability need to be carefully set to achieve minimal delay. Finally when comparing between these schemes it is found that when the number of groups is equal to the number of request slots, the maximum system performance of CFP+SPL scheme is comparatively equal to maximum system performance of UNI+LA scheme

A robustness analysis of a practical contention resolution algorithm under misbehaved users in wireless communication systems

This paper presents an analysis of a practical contention resolution algorithm referred to as UNI for medium access control protocols in high bit-rate wireless communication systems with two groups of users, i.e. normal and misbehaved users. The objective is to examine the robustness of the UNI algorithm when some users (misbehaved) do not conform to the agreed rules by accessing more reservation slots than they are permitted. Mathematical analysis is derived and applied to determine the average success rate of each group of users as well as the overall system performance. Computer simulations are also conducted to confirm and validate the mathematical model. Numerical results on various traffic conditions indicate that misbehaved user could potentially gain some throughput advantages when the number of slots available is relatively much higher than the number of overall users; this is achieved by carefully selecting proper number of tokens. However, when the number of overall users becomes greater than the number of slots the reversed effect is observed

Design and Performance Evaluation of Channel Reservation Schemes for QoS Constrained Multimedia Traffic

This paper considers the problem of contension resolution problems for high bit-rate wireless communication systems where the round trip propagation delay is relatively longer than the slot transmission time. In this scenario, we found that existing channel reservation schemes cannot guarantee the satisfaction to all users regarding different quality of service (QoS). Thus in this paper, we propose 2 new channel reservation schemes which taken into consideration priority service to more delay-sensitive multimedia traffics, namely, Partial UNI and UNI+MT schemes for multimedia traffics, an extension of our recently proposed UNI scheme for single-class traffic. The goal is to achieve the highest system performance and enable each traffic types to meet their QoS requirements. We evaluate the performance of each scheme by mathematical analysis. The numerical results show that our proposed schemes are effective in enabling different traffic users to achieve the best successful rate possible in this kind of environment.