Research On Several Key Technologies In Wireless Broadband Access WiMAX System

WiMAX named as Worldwide Interoperability for Microwave Access is an emergingbroadband wireless communications technology, it can provide high-speed connection for Internetas well as a larger wireless coverage. As WiMAX becomes the world’s fourth3G standardfollowing the CDMA2000, WCDMA and TD-SCDMA, WiMAX technology is being extensivelystudied and applied. Compared with the other3G technologies, WiMAX technology has technicaladvantages such as longer transmission distance, higher-speed wireless broadband access, and canprovide QoS-based wireless multimedia communication services. It can be well applied forwireless communication in some areas of frequent disasters and sudden events. In addition, itpromotes the generic certification of WiMAX equipment and ensures the interactive use of devicesfrom different manufacturers with the establishment of the global WiMAX Forum organization,thus WiMAX technology is further used. One of the application difficulty of wireless broadbandaccess WiMAX system is the development of the protocol algorithms.The dissertation firstly analyze the related techniques of WiMAX protocol and present analysismodels. The main problems of the application of WiMAX technology are call admission controlmechanism, classification&compression mechanism and cooperation relay, which is foundationin the whole dissertation.According to the problem of resource constraints when the system is busy, this dissertationproposed an income/expenditure ratio based call admission control algorithm. CustomerSatisfaction Index model was used to calculate system income, system’s total bandwidthconsumption was used as expenditure, thus the system used this income/expenditure ratio to judgewhether or not to accept a new business. The proposed scheme can not only ensure business’sservice quality effectively, but also be easily implemented with low complexity. Four-dimensionaltime discrete MMPP (Markov Modulated Poisson Process) queuing model was used to simulatebusiness load. Compared with the classic Cutoff priority algorithm, our scheme has higheracceptance rate and throughput, and improves system’s efficiency when it is busy.For existing classification algorithms can not be directly applied to the WiMAX system, anaddress block XOR and Hash look-up based packet convergence sub-layer classification algorithmwas proposed, realizing the quick lookup and classification of higher-layer protocol data. Addressblock was used to improve searching speed, block XOR effectively suppressed the memory space explosion. The proposed algorithm can support range matching and realize quick dynamic updatewith low complexity, and its storage performance and delay meet the system’s QoSrequirement.Simulation results proved that the proposed scheme has higher search speed comparedwith the typical AQT (Area-based Quad Tree) algorithm and HiCuts (Hierarchical IntelligentCuttings) algorithm.Aiming at the problems of high complexity in present compression algorithms, the header andsub-header format of segmented protocol data unit were analyzed in media access control layer,and connection identifier field was innovatively compressed using the reserved bits of header andsub-header to decode in segmented protocol data unit. The scheme can realize adaptivecompression according to wireless channel environment. The simulation results verified that thepacket loss rate of proposed compression algorithm is low with high compression efficiency, andachieves satisfactory compression effect.According to low power efficiency in average power algorithm, an optimized power allocationalgorithm was proposed based on cooperative relay AF (Amplify-and-Forward) network. Thescheme used a fixed threshold as adaptive modulation, channel adopted water-filling methodaccording to the number of bits contained in the modulation symbol, reducing the complexity ofthe algorithm and improving bandwidth performance. On this basis, power was trimmed accordingto channel quality in sub-carrier, reducing power’s uneven distribution caused by the difference ofsub-carrier’s signal-to-noise ratio. Compared with the average power algorithm, the optimizedpower allocation algorithm can not only enhance power efficiency, but also improve the system’sBER performance.This dissertation focuses on key technologies of the call admission control mechanism,classification&compression mechanisms and cooperative relay in WiMAX system, someimproved algorithms are proposed. The proposed algorithms and solutions are helpful in WiMAXsystem.