Reserch On Hybrid Space-Time Coding For Air-Ground Communication With Low Elevation Angle

With higher and higher demands on the quality of air-ground communications, it is of vital importance to provide high-speed and reliable data transmissions. VBLAST coding technique in space time coding, has the advantage of improving high data transmission rate, however has low transmission reliability, in this thesis, by using a hybrid space time code combining STBC and VBLAST code, the compromise between diversity gain and multiplexing gain is attained. Channel coding can be cascaded at the transmitter to further optimize the performance of hybrid space time coding; however, traditional convolution coding cannot satisfy the demand of air-ground communication, thus this thesis proposes to combine LDPC with hybrid space time coding system and a detailed research is conducted on how to improve performance of air-ground communication.Firstly, STBC and VBLAST techniques are presented, Alamouti and VBLAST encoding and decoding schemes are mainly investigated; besides, system performances of hybrid space time coding with different antenna grouping are analyzed through simulations; based on the conventional group interference suppression algorithm decoding technique, performing linear transformation on the channel matrix breaks the limit of conventional decoding method on the antenna number at the transceiver.Secondly, the characteristics of air-ground communication are discussed, the parameters which describe air-ground communication channel are mainly presented, with the impact of correlation between antennas on the channel matrix in MIMO transmission, a LOS MIMO channel model and Rayleigh fading channel are built respectively; thus an air-ground MIMO channel modeling scheme which takes the transmit and receive antennas correlation into account is proposed under low antenna elevation angle. BER performance analysis of hybrid space time coding in the channel model built in this thesis is conducted through simulations, which confirms the correctness of the channel model proposed, and the hybrid space time coding scheme is proved to be effective in the air-ground communication.Lastly, LDPC standard specified by CCSDS, which is more appropriated for air-ground communication, is also studied in this thesis; by applying the LDPC to the hybrid space time coding system, the cascading system performance in the air-ground channel built in this thesis is simulated and analyzed. Results show that the schemes proposed in this thesis can remarkably improve the BER performance of air-ground communication.