Research On Channel Estimation Used In WiMAX &Channel Equalization Used In Single-Carrier System

World interoperability Microwave Access is a standard technology providing services from immobile mobile and handhold wireless Broad-Band connection to motive wireless Broad-Band connection under NLOS. With high spectrum usage and immunity to multi-path fading, orthogonal frequency division multiplexing (OFDM) technology has been widely used in many advanced digital communication systems。One of this thesis's tasks is the research of the channel estimation technology used in OFDM system and proposal of the channel estimator available for WiMAX system based on 802.16 Protocol. On the other hand, high-order single-carrier communication system is another important communication method widely used in china, especially in mountainous areas. Due to its high bits rate, channel distortion has a severe affect on the constellation. Another question for discussion in the thesis is the channel equalizer used in digital microwave system.The channel estimate in OFDM can be divided into estimate based on pilot and estimate based on preamble. The former technology includes estimation on pilot sub-carrier and interpolation algorithms; ordinary interpolation such as Linear, Gauss, and Transform cannot be used in WiMAX directly for its uneven arrangement of the pilot. In this thesis, improved time-zone estimation method is proposed which makes good use of the pilot message in WiMAX system. In the proposed structure, firstly, the time-zone channel impulse is obtained through matrix calculation; then the negative effect of noise is reduced by passing prediction filer, which can be either linear filter or adaptive filter. Simulations indicate that improved algorithms can acquire 1dB increased for BPSK, 2dB increased for QPSK and 4dB increased for 16QAM, compared to the original algorithm under SUI-3 channel model. Estimate algorithms based on preamble consists of LS, MMSE, FFT, SVD and so on. It is discovered that the least square (LS) channel estimation algorithm has low complexity but its performance decays when signal noise ratio (SNR) is low; while others have good performance, but the high computational complexity limits the application. This thesis proposed an effective channel estimator scheme for WiMAX , which uses LS algorithm on preamble for initialization, then make use of improved time-zone eatimation methods on pilot for information tracking and DDCE method as complementary method when the maxim dalay time is larger than the number of pilot.The channel equalizer used in single-carrier system includes initial equalizer and decision directed part. The decision-directed algorithms are comparatively developed; simulation results indicate that mean-gradient algorithms can get best performance. The initial part mainly uses blind equalization technology. But the convergence of the Constant-modulus algorithm widely...