Research On Precoding And Joint Transmit-Receive Processing In Multi-Cell Coordinated System

As one of the key technologies in the wireless communication system, multi-cell coordinated technology plays an important role for suppressing the inter-cell interference, improving the cell-edge user throughput and the average system throughput. The precoding and joint tx-rx processing technologies are used to handle the transmit and receive signal, which can simultaneously impove the multiplexing and diversity gain. However, the introduction of multi-cell coordinated technology has brought in some changes for the communication system, such as the feedback information by receivers, the exchange information among base stations (BSs) and the transmit power constraint. These results in that the precoding and joint tx-rx processing can not be directly extended from single-cell system to multi-cell coordinated system, but should be improved and redesigned.The research work is sponsored by open projects from National Key Laboratory of Wireless Mobile Communication (Innovation Technological Centre of Wireless Mobile), named as "The signal processing and resource scheduling of distributed joint processing systems" and "Nonlinear precoding and interference alignment technology in LTE-A system". The work has made in-depth study about the precoding and joint tx-rx processing technology in multi-cell coordinated system. The main research work and achievements of this thesis are as follows:(1) The precoding and joint tx-rx processing technologies in multi-cell coordinated system are summarized and analyzed. Firstly, the multi-cell coordinated system and MIMO signal processing technologies are summarized. Then, the challenges and research contents are analyzed emphatically. Finally, the research situation of precoding and joint tx-rx processing technology in multi-cell coordinated system is classified. The issues which have not been studied are also proposed.(2) The channel quantization methods affect the performance of the multi-cell coordinated system. The existing researches have analyzed the quantization errors brought by the channel quantization methods, which, however, cannot reflect its effect to the performance of precoding. In the thesis, the performance of linear precoding with difference channel quantization methods are analyzed and compared. There are two channel quantization methods, joint codeword selection (JCS) and independent codeword selection (ICS). Firstly, the theoretical system throughput with linear precoding are derived for these two channel quantization methods. Then, the feedback overhead and selection complexity of these two methods are analyzed. Additionally, a codebook compression scheme is proposed to reduce the complexity of JCS, and a bit allocation scheme is proposed to improve the performance of ICS. Finally, the simulation results prove the correction of the theoretical analysis.(3) As the unfairness is an inherent character of THP, the existing research proposed the sort algorithms, wich, however, introduce the additional complexity. In this thesis, by maximizing the minimum the signal to interference plus noise ratio (SINR) of streams, a nonlinear joint tx-rx processing algorithm is proposed to improve fairness among streams. Considering the backhaul link capacity difference among systems, the algorithms are proposed for the centralized coordinated system and the decentralized coordinated system, respectively. Feasibility and computational complexity of the proposed algorithms are also analyzed. Simulation results prove that the proposed algorithm can achieve the fairness among streams without using additional sort algorithms, which reduces the complexity.(4) As the harvested energy from different BSs varies in space and time, energy cooperation among BSs is considered for designing the nonlinear tx-rx processing matrices to improve the system energy utilization. In the proposed algorithm, the tx-rx processing matrices are designed to maximize the minimum the SINR for each stream of all users, subjecting to the transmit power constraint determined by energy cooperation among BSs. The proposed algorithm guarantees the balance performance among all users and all streams of each user, and improves the system performance. Compared with the algorithm with non-energy cooperation among BSs, the proposed algorithm makes full use of the energy, achieving higher system rate and lower BER.(5) The terminal battery power limits the maximum received rate. However, the existing alogrithms have not considered it into the designing of the tx-rx processing matrices, which results in the waste of the transmit power and against the sustainability of the communication. In this thesis, terminal battery power constraint is considered for designing the nonlinear tx-rx processing matrices to avoid the transmit power waste. In the proposed algorithm, the tx-rx processing matrices are designed to maximize the minimum the SINR for each stream of all users, subjecting to the terminal battery power constraint and the per-BS transmit power constraints. Compared with the algorithm without considering terminal battery power constraint, the proposed algorithm leads to little performance loss, but gurantees the sustainability of the communication.