| Multiple Input Multiple Output(MIMO)technology is one of the key technologies in the next-generation wireless communication field because the signal transmission performance can be significantly improved.Space-time coding technology and beamforming technology are two effective means to improve signal quality in an actual communication environment,and both can improve the reliability and data transmission rate of the wireless communication system.At the same time,the relay cooperative forwarding technology,which can effectively extend the communication distance,expand the coverage area of the communication system,and counter various fading in the data transmission process,is currently one of the most popular technologies in current research.This thesis combines the advantages of MIMO and relay cooperative forwarding and constructs a relay cooperation model to forward the soft information in the relay node.This thesis also proposes a parallel multi-relay estimation forwarding scheme and a mutual information forwarding scheme between the sender and the receiver.The received signal is detected at the destination to find the best detection scheme,and finally the performance of the proposed scheme through the generalized SNR is analyzed.The main research work of this thesis is as follows:(1)The theory of MIMO and cooperative communication is introduced,and the performance gains brought by the space-time coding and beamforming techniques are highlighted.By analyzing the respective advantages of MIMO technology and relay cooperative forwarding technology,a cooperative MIMO system model in non-direct path is established to cooperatively forward the received signal at the relay node based on the traditional amplification scheme and decoding scheme.At the same time,the received signal at the destination node is detected using ML,ZF,MMSE,and QP detection schemes.The advantages and disadvantages of each detection scheme are analyzed by simulation,and theQP scheme is verified to be the best detection scheme.(2)The estimation forwarding mechanism suitable for beamforming technology is proposed.Based on the MIMO soft information forwarding,the estimation forwarding function is constructed by using the conditional mathematical expectation of the received signal at the relay node in non-direct path cooperative communication system and the expression of the received signal at the destination node is derived.The advantages and disadvantages of various detection schemes are analyzed to find a suitable detection solution.(3)A mutual information forwarding mechanism suitable for beamforming technology was proposed.Based on the MIMO soft information forwarding,the mutual information forwarding function is constructed by using the conditional mutual information of the received signal at the relay node in non-direct path cooperative communication system and the expression of the received signal at the destination node is derived.The advantages and disadvantages of various detection schemes are analyzed to find a suitable detection solution.(4)The entire cooperating beam system is equated to a new transmission system with only the transmitted signal,the received signal,the multiplicative factors and the additive noise.And the generalized SNR of various schemes is calculated to verify the gains brought by the proposed scheme.The analysis and simulation results show that the two proposed cooperative modes,i.e.,the estimated forwarding scheme and the mutual information forwarding scheme,can significantly improve the performance of the wireless communication system. |
