The Research On Channel Estimation Algorithms In Relay OFDM Based Systems

Orthogonal Frequency Division Multiplexing (OFDM) technology, due to its efficiency of combating the multi-path fading of wireless channel, has been proposed as one of the physical key technologies in the next generation wireless systems. Relay system, due to its functions of extending the cell coverage and improving the system capacity, also has been a hot research filed in LTE-Advanced. In the system of combination of OFDM and relay techniques, obtaining the accurate multi-link channel state information (CSI) is a key factor that influences the whole system performance. In the thesis, the main work is about the research on the channel estimation algorithms in Relay OFDM based systems, and this thesis achieves the following three part results.1,Research on channel estimation in Amplify-and-Forward (AF) relay systems. In this research field, most existing works only estimate the CSI of the cascaded link Source-Relay-Destination (S-R-D), and the individual information of S-R and R-D link cannot be separated. To overcome the problem, the thesis proposes a channel estimation scheme for destination to disintegrate the CSIs of S-R and R-D links from the cascaded S-R-D link in AF relay networks. Taking the channel estimation mean square error (MSE) as the performance evaluation indicator, the thesis verifies the efficiency of the proposed scheme from the theoretical aspect. Furthermore, the theoretical deduction results are validated by computer simulation.2,Research on channel estimation in Decode-and-Forward (DF) relay systems. The pilot overhead in LTE specification is too much for the S-R link transmission environment. The S-R link is separated from UE, so changing the S-R link design will not cause any compatibility problem to UE. Therefore, the pilot pattern in S-R link could be re-designed for lower pilot overhead and higher spectral efficiency, meanwhile, the system performance is still kept. The thesis evaluates the required pilot overhead in S-R link and takes the channel estimation MSE and bit error rate (BER) as the performance indicator. The efficiency of the designed pilot pattern is validated by computer simulation.3,Research on the optimal receiver design with the channel estimation error. Because of the time variation of wireless channel and the existing of noise, it is impossible to obtain the ideal CSI in realistic systems. Ignoring the CSI error in system design will bring the performance degradation. The research of the thesis focuses on the minimum mean square error (MMSE) receiver design in AF relay systems, when the CSI error exists and the statistic characteristic is pre-known at receiver. Taking the signal-to-noise ratio (SNR) as the performance evaluation, the thesis from the theoretical aspect verifies that the MMSE receiver considering the CSI error could obtain better performance than that of the MMSE receiver non-considering the CSI error. Furthermore, the theoretical deduction is validated by the computer simulation.