Adaptive QoS Guaranteed Scheduling For Multimedia Traffic In Broadband Wireless Access Systems

Rapid growth in high-speed Internet access and multimedia service applications, along with the ubiquitous availability, especially in hard-to-reach areas has increased the demand for broadband wireless access (BWA) communications. Emerging broadband wireless networks, such as IEEE802.11, IEEE802.16 and IEEE 802.20, are promising solutions to support the rapidly growing demands. However, one of the main challenges in BWA is to provide the quality of service (QoS) for heterogeneous traffic streams requiring various QoS guarantees. On the other hand, it is widely accepted that the scheduling algorithm is the key feature of QoS architecture in BWA networks. Consequently, the design of efficient scheduling algorithms is a critical issue. It is the aim of this dissertation to develop adaptive scheduling algorithms with QoS guarantees for multimedia traffic in broadband wireless networks, such as IEEE802.11 and IEEE 802.16.In the first part of this thesis, a dynamic QoS enabling mechanism in contention-based medium access over wireless local area networks is introduced. Based on dynamic traffic prioritization and transmission delay estimation, not only better throughput and packet delay are obtained but also variations of these parameters become narrower over a timescale. Furthermore, without starving the low priority traffic, the mechanism provides better fair medium sharing among the users and significant improvement in the system performance in comparison to the fixed priority-based method introduced in the standard.Since a lot of multimedia applications have variable bit rate characteristics, designing an efficient scheduling algorithm is a challenging task in polling-based access medium over IEEE802.11e. The simple scheduling algorithm introduced in the draft version of the standard can not satisfy the required QoS guarantees. Next, the operation and evaluation of a new traffic scheduling algorithm for contention-free medium access referred to adaptive transmission opportunity (ATX) are presented. Comparing to the dominant existing algorithms in literatures, the proposed new scheduling algorithm indicates a great performance improvement in term of throughput and delay. Using a dynamic bandwidth selection, according to real queue size and predicted queue size, the bandwidth wastage offered in the fixed transmission opportunity can be reduced.Then, a novel priority analytical model that is useful to analyze and enhance the performance of hybrid coordination function controlled channel access (HCCA) in provisioning required QoS is introduced. The model provides service differentiation between two classes of packets, namely, high priority and low priority packets. In this model, nodes are modeled as Markovian arrival process (MAP)/phase type (PH) distribution/1/k non-preemptive priority queues with vacation model. Using a MAP for packet arrival process, PH distribution for service and vacation processes, and the priority queuing model with the vacation make the analysis tractable.In the succeeding part, an extension of the proposed queuing model is presented. The model supports the multi-rate non-ideal channel using adaptive modulation and coding (AMC), which is the key feature in the wireless networks to increase the effective transmission rate. To analyze the performance of the system, the finite state Markov chain channel model is adopted and nodes are considered as MAP/PH/1 queues with vacation and time-limited. A new concept of non-transmission period, defined in the service period, enables the server to stop the packet transmission if the transmission channel is dirty. Using a powerful Matrix-geometric method, the stationary probability distribution for the system states is obtained. Finally, the performance measures followed by an optimization method to catch the best amount of parameters in the cross-layer design are presented.To provide QoS guarantees for classified traffic streams and to distribute available bandwidth fairly among the users in the WiMAX environment, a two-layer channel-aware scheduling algorithm based on an adaptive credit-based fair queuing (ACFQ) algorithm is presented. The proposed algorithm develops an error-free credit-based fair queuing (CBFQ) for the multi-rate medium with AMC at the radio link layer. The scheduler is adapted in two different scenarios defined in the WiMAX standard. First, the scheduler is applied to the point-to-multipoint (PMP) scenario and the operation of scheduler in the presence of various types of traffic and channel conditions is evaluated. In the next step, the scheduler is extended to apply to centralized scheduling scenario in mesh mode, where some users can be located more than one hop away from the base station. The system performance in terms of fair service and temporal medium access is evaluated. Simulation results show that the channel transmission rate selection scheme and compensation techniques, in both scenarios, provide a fair sharing of bandwidth among the users while excellent system performance is achieved.In conclusion, this dissertation has provided some scheduling algorithms to manage and allocate the system resources fairly in different types of transmission medium, and shows significant positive effect of adaptive schedulers under various system and channel conditions.