Channel Estimation Algorithm For OFDM Modulated Two-Way Relay Networks

Wireless relay networks have been intensively studied duo to their capacity of enhancing the transmission capacity compared to traditional point-to-point type, and providing the spatial diversity for singal-antenna wireless transceivers by employing the relay nodes as "virtual" antennas. Two-way relay networks communication is a popular type of modern communications, in which two terminals simultaneously transmit and receive information. Most existing works have assumed perfect channel state information at the relay node and/or the source terminals. However, under the assumption of coherent detection, the fading channel coefficients need to be first estimated and then used in the detection process. The quality of channel estimates inevitably affects the overall performance of system, and might become a performance limiting factor. Although there have been a lot of studies about One-way relay networks channel estimation, little work has been done for TWRN, recently.In this thesis, the evolution background of two-way relay-assisted communication transmission based AF relaying scheme is firstly introduced, and including current developing and studying state of TWRN. Then the theory of OFDM is simply introduced, and the following is the transmission theory of TWRN based OFDM modulated. After that, the signal process of relay and two source terminals is analysed, deeply the LS channel estimation and the optimal training sequencce for TWRN based OFDM blocks is advanced. Subsequently, another kind of optimal training sequence based Zadoff-Chu sequence is designed so as to decrease the PAPR(peak-to-average power ratio), the simulation results show that this training sequence has the capacity of decreasing PAPR and the similar performace of channel estimation with the optimal training. Follow that, The Dantzig-Selec-tor is forwarded for TWNR in special environment such as underwater acoustic channels, digital TV channels and residential ultrawideband channels based the new theory of estimation with convex optimization knowledge, the performance of DS is apparently better than traditional method in this case. The algrithm of channel estimation based pilot-tones is brought forward due to the concider of bandwidth efficiency, and the pilot training at two source termianls and the power scaling factor at the relay are designed carefully. The simulation results reveal that the performance is worse than block training. Channel identifiability, individual channel recovering and channel reconstruction are investigated under OFDM block transmission and pilots transmission. Reconstructed cascaded channels are more accurate than cascaded channels estimated, and the operation of individual channel recovered from cascaded channels at terminals is prepared for the following studies, terminals can predict the operation of the power allocation at relay, and do power allocation for themselves.