Research And Simulation On Channel Estimation Algorithm In IEEE 802.16d System

With the development of Internet and multimedia applications, there is an increasing need for large scale deployed broadband wireless access system which can support high-speed data transmission. To satisfy this need. IEEE developed and published 802.16 standard, often referred to as WiMAX. Due to its features of well multipath immunity and high bandwidth efficiency, OFDM (Orthogonal Frequency Division Multiplexing) has been employed by 802.16d systems. While Alamouti space-time coded which can realize space domain transmit diversity is an optional scheme at the downlink in 802.16d systems. In 802.16d systems, CSI(channel state information) is needed by diversity-combine,coherent demodulate and space-time decode, and the receiver's decode correctly depend on correct CSI, it is decided by accurate channel estimation. The thesis mainly focuses on channel estimation algorithm in Alamouti space-lime coded 802.16d-OFDM systems.First, we introduce the wireless communication's channel model. The small-scale time-frequency fading effects of the received signal which caused by radio channel is discussed emphatically. And the SUI (Stanford University Interim) channel model and it's simulation is discussed in detailed which is suggested by 802.16 work group to be used in fixed wireless wideband access.Second, we analyze the specifications of STC preamble and STC comb-type pilot in the 802.16d-OFDM standard. By utilizing the frequency orthogonality of STC preamble and the code orthogonality of STC comb-type pilot, multi-channel estimation in space-time coded 802.16d-OFDM systems can be decoupled into several channel estimations just as in a SISO (single input single output) environment. After carefully analyzing the algorithms in SISO, a near-complete channel estimation scheme in 802.16d-OFDM systems based on Alamouti STC is introduced. Both STC preamble assisted channel estimation and STC comb-type pilot assisted channel estimation are included in this scheme. Then their performance are analyzed and compared through simulation. The simulation results show that the performance of STC preamble assisted channel estimation is better than STC comb-type pilot's, the frequency-domain LS algorithm is simple but the performance is poor, the performance of LMMSE-SVD algorithm almost the same as LMMSE algorithm but is modestly complex, time-domain LS algorithm has the best performance but is more complicated.Finally, owing to frequency-domain LS algorithm is simple but it's performance is tend to affected by noise and ICI, and there are some virtual carrier at OFDM symbol in 802.16d systems, we introduce a iterative algorithm base on time-domain noise suppression, and proof it validity.