Channel Characteristic Analysis And Optimal Transmission Scheme For Millimeter Wave Wireless Communications

With the rise of internet of things and mobile internet,wireless communication technology is devel-oping at a faster pace.The connection between people is more closely and the intelligent interconnection between both people and things and objects and things will be realized soon.As a result,more barriers of information exchange will be removed gradually.The establishment of 'the integration of heaven and earth'network involves the transformation of various fields,making the data traffic crowded and the requirements of the wireless communication improved.It is imperative to develop high frequency spectrum resources.With the demand of high speed,low latency,large density and wide coverage,the combination of millimeter wave transmission and massive multiple input multiple output(MIMO)technology is the key to improve the quality of communications.Determining the transmission characteristic of millimeter wave channels is the fundamental of the communication system design.Therefore,the transmission characteristic of the millime-ter wave channel,the analog beam training scheme and the antenna array structure design of the line of sight(LoS)MIMO system are studied under the background of the development of the next generation mobile communication system.The main work of this thesis are summarized as follows:Firstly,the frame format,bandwidth resource allocation,synchronization and channel estimation schemes of millimeter wave communication systems are specified in detail.Two methods based on subchan-nel division and resource block group aggregation respectively can be used to allocate bandwidth resources flexibly and efficiently.The integer frequency offset(IFO)and fraction frequency offset(FFO)can be esti-mated simultaneously by means of frame timing and synchronization algorithm based on synchronization se-quences.The channel estimation scheme based on pilot sequence is applicable to channels with time-varying and frequency-selective characteristics.The following research is conducted based on these schemes.Secondly,the propagation characteristic of millimeter wave channels is analyzed and the rank adapta-tion scheme is proposed.The statistical spatial channel model is evaluated from the perspective of model parameters and statistics.In general,the delay and angle spread in the non line of sight(NLoS)environment is larger than the LoS environment.The measured data of the LoS MIMO channel can match the theoretical curve well,which indicates that the antenna spacing and transmission distance have important influence on the channel state.The proposed rank adaptation transmission scheme can dynamically adjust the number of data streams based on the channel state and signal to noise ratio(SNR)condition.Thirdly,an efficient beam training scheme is proposed for the partially connected subarray structure.The codebook based beam training procedure is conducted when explicit channel state information(CSI)is unavailable.According to the spatial position of the beam,the codewords in the initial codebook is screened and combined to reconstruct subcodebooks which are used for the iterative training.Compared with traversing the codebook,the proposed algorithm with a low complexity utilizes only part of the codewords during the whole procedure and thus greatly reduces the time and energy consumption for beam training.The simulation results show that the proposed scheme can achieve the performance close to the exhaustive algorithm with lower computational complexity.Finally,the millimeter wave LoS MIMO channel is considered and the antenna subarray structure is optimally designed to maximize effective degrees of freedom(EDoF).A specific analytic relation between the parameters of antenna configuration and transmission distance is further obtained for codebook based phase shifters.Compared to previous structures,the subarray structure can provide both array gains and spatial multiplexing gains.Based on the millimeter wave channel model,the sensitivity of the system is studied by taking more realistic deployments and propagation conditions into consideration.The simulation results indicate that the optimally designed structure is robust to the geometrical change and misplacement and thus it is a feasible solution for millimeter wave LoS MIMO applications.