A Study On QoS Guarantee Schemes Based On Cross-layer Design In WiMAX System

Worldwide interoperability for microwave access (WiMAX) based on IEEE 802.16 standards is a rising broadband wireless access technique for wireless metropolitan area networks. Due to its high performance of efficiency, flexibility and setting convenience, WiMAX will become one of the mainstream access technologies in the future. How to provide many subscribers with high speed and good quality of various multimedia communication services in time-varying wireless environment is one of the WiMAX technology problems needed to be solved urgently, and the volatility of communication conditions and diversity of communication services determine the necessity of adopting cross-layer ideology when designing quality of service (QoS) guarantee schemes.In this dissertation, QoS guarantee schemes based on cross-layer design in WiMAX system is studied intensively in four aspects:protocol architecture model, joint control strategy, scheduling algorithm and adaptive modulation and coding (AMC) transmission mode selection algorithm. The main research contents and innovative results are listed as follows:1. In order to solve challenge problems on QoS guarantee caused by the traditional layering structure of wireless networks, this dissertation proposed a cross-layer architecture based on the existing WiMAX layering structure. The whole protocol structure model was divided into two sub-planes vertically:one was data flow delivery sub-plane which could provide data processing and delivering layer-by-layer for multimedia communication service flows based on IEEE 802.16 standards, the other was QoS resource management sub-plane which could cooperate all manage modules from low protocol layer to high protocol layer by various manage signalings and implement QoS joint control adaptively. This proposed architecture is full cross-layer architecture for QoS guarantee with simple structure and clearly defined functions, and very suitable for practical engineering design.2. Based on the proposed WiMAX cross-layer architecture, this dissertation provided a QoS joint control strategy and its proper algorithms. This dissertation also proposed a QoS performance priority algorithm for QoS priority control strategy. Simulation results show that the QoS joint control strategy based on the WiMAX cross-layer architecture can provide flexible QoS guarantees according to the practical requirements. On the constraints of the same QoS outage probability, the second QoS joint control strategy with QoS performance priority algorithm can provide multimedia communication services for more subscribers when compared with the first QoS joint control strategy with weighted round robin algorithm.3. This dissertation proposed a subscriber fair oriented two-level scheduling algorithm for QoS guarantee which could be used in the proposed WiMAX cross-layer architecture. On the support of the QoS joint control strategy, the first level scheduler adopted the existing QoS priority algorithm for QoS guarantee of multimedia communication service flows and implemented QoS priority control. The second level scheduler adopted the proposed subscriber rate fair oriented scheduling algorithm. Simulation results show that the proposed two-level algorithm can meet various QoS requirements of multimedia communication service flows well with better subscriber's rate fairness when compared with the multi-weight scheduling algorithm. Moreover, the proposed algorithm can obtain better performance in low signal-to-noise ratio (SNR) region in terms of system throughput, QoS service traffic throughput and QoS outage probability, which is more suitable for wireless communication environment.4. This dissertation proposed an AMC transmission mode selection algorithm with alterable SNR switch threshold intervals for the proposed WiMAX cross-layer architecture. When base station sent various multimedia communication service flows to subscriber station, the proposed algorithm made the decision of AMC transmission mode selection which was not only decided by channel state information from physical layer, but also related to an important QoS parameter, namely target packet error ratio provided by multimedia communication service flows from upper layer. Through performance evaluation, the results show that the proposed algorithm satisfies the target packet error ratio requirements of each class of multimedia service flow, and also obtains higher effective data transfer rate at the same time when compared with the traditional AMC transmission mode selection algorithm and its modified one.