Research On STBC-OFDM And QoS Scheduling Algorithm In IEEE 802.16e System

With the development of mobile multimedia services, IEEE 802.16e systemneeds to provide the guarantee of QoS for a variety of service types. As wirelesschannel has the characteristics of variability, limited bandwidth and burst errors, howto effectively solve multi path effects and frequency selective fading, and how toimprove the transmission efficiency, capacity of system, availability of frequencyspectrum and reduce the bit error rate in complex wireless communicationenvironment, are important topics of researching IEEE 802.16e system.This paper develops research on STBC OFDM system simulation platform andQoS scheduling algorithms in IEEE 802.16e system. The main works andcontributions are listed as follows.Firstly, this paper studies the STBC OFDM as well as system simulation andimplementation in several channel models. According to the characteristics of IEEE802.16e OFDM system, the STBC OFDM system simulation platform is built withMatlab, and the transmission process is simulated in Gaussian, Rayleigh and 3GPPchannel. After compared with OFDM system, the bit error rate in terms of differentchannel environment is evaluated. It provides effective theoretical basis for correctlyevaluating the actual STBC OFDM system performance.Secondly, this paper explores the QoS scheduling algorithm which is to improvethe resource utilization of the VoIP services. In the algorithm the bandwidth usage ofUGS, rtPS and ertPS is analyzed by considering of the channel state, the ertPSscheduling algorithm is improved, and rationally bandwidth resource is assignedaccording to whether the channel state is good or bad. Simulation results show thatthe algorithm can improve system throughput and resource utilization. However,further studies on fairness of the service flows which channel error occurred will beconducted.Thirdly, this paper studies and points out the QoS scheduling algorithm toguarantee fairness of VoIP services. In this algorithm the priority of the VoIP serviceflows is determined per their state. When the channel is in error state, extra bandwidthcan be allocated in terms of priority. When the channel recovers from error state, thecompensation mechanism will be triggered. Simulation results show that thealgorithm can guarantee long time fairness of the VoIP service flows, meanwhile, theshort time fairness can be improved in a certain degree by adjusting the compensationparameters. Finally, this paper investigates the QoS scheduling algorithm which fits fordifferent services. The strategy of two phase extra bandwidth distribution andcompensation mechanism is proposed. The viewpoint of determining the priority inaccordance with the state of service flows and the weight bases on the type of serviceis put forward. So, the QoS requirements can be satisfied. Simulation results showthat the algorithm has an effective balance of the complexity and fairness, at the sametime, the system capacity and resource utilization can be maximized.