Research On Precoding Technology For Massive MIMO Systems Based On Ideal/Non-ideal DACs

As one of the key technologies of the fifth-generation mobile communication,massive Multiple input multiple output(MIMO)technology has been proven to increase the capacity and reliability of the system without increasing bandwidth.Precoding technology can effectively suppress inter-user-interference,inter-symbol-interference,and inter-streaminterference,so it is indispensable in the downlink of massive MIMO systems.However,in large-scale multi-user MIMO systems,as the number of antennas increases,system power consumption and cost issues become more prominent.Therefore,not only traditional precoding techniques are studied in the paper,but also the performance of precoding using non-ideal Digital to analog converter(DAC)is analyzed.The wireless channel fading model is introduced in this paper first,and the causes of largescale multi-user MIMO systems are also analyzed.Then the massive MIMO channel capacity is calculated.With the increasing number of antennas,the matrix of the small-scale fading channel exhibits progressive orthogonality.In addition,due to the impact of cost and power consumption,communication systems must be predicated on practical deployment,so the downlink of large-scale MIMO systems using non-ideal DACs is analyzed.Secondly,the linear precoding schemes using ideal DACs in the system of massive MIMO are studied in depth.what's more,when the number of base station antennas are changed,the performance of the common algorithms is compared.Aiming at the problem of severe interference between data streams in multiple data streams for precoding schemes,a precoding scheme based on signal-to-leakage-and-noise ratio(SLNR)is proposed,which balances the gain of data streams to make the reliability performance of temminal better.The simulation results show that although the SLNR-based scheme proposed in this paper will have a certain loss in throughput,the overall BER performance of the system can be improved.Finally,for the large-scale MIMO system with non-ideal DACs,the precoding performance using 1-bit quantization DACs is studied in depth.Due to the serious distortion of the system in linear precoding,and the commonly used nonlinear precoding is usually accompanied by high complexity.Therefore,a nonlinear precoding scheme based on alternating direction multiplier method(ADMM)is proposed in this paper.The precoding matrix is solved by alternate iteration.The simulation results show that the proposed algorithm not only greatly controls the complexity,but also improves the convergence speed.