Research On High-order Modulations Signal Transmitting Performance For One-Bit Massive MIMO Systems

Massive MIMO technology is a key technology to improve the spectrum efficiency and throughput of the fifth-generation wireless communication system.However,when deploying massive MIMO systems,equipping base station antennas with high-precision quantizers will greatly increase the hardware cost and energy consumption.In order to solve this problem,the combination of 1-bit quantization with the massive MIMO has become a current research hotspot.Since 1-bit quantization will cause serious distortion of the amplitude of high-order modulation signals,in this thesis,we aims at the performance of the signal in the transmission of high-order modulation in a massive MIMO system with a 1-bit analog-to-digital converter(ADC)at the base station antenna.The main work of this thesis is summarized as follows:To address the serious distortion of the 16-QAM modulated signal in 1-bit single-user uplink SIMO system transmission under the condition of high signal-to-noise ratio(SNR),we firstly derived the mutual information of the system approximately through theoretical analysis.Then we compared the theoretical analysis results with the simulation results,which verified the correctness of the theoretical analysis.The analytical and simulation results showed that the mutual information of the system will decrease and tend to a constant value in the area of high signal-to-noise ratio.The mutual information of the 1-bit massive MIMO system decreases in the area of high SNR,a non-subtractive dithering method is designed.For the purpose,a minimum mean square error SNR estimation algorithm based on Bussgang theory is proposed.This algorithm takes into account the impact of 1-bit quantization on the received signal.Then,the estimated SNR and the mutual information SNR turning threshold are compared to determine whether a dither signal is added or not.When the estimated SNR is greater than the mutual information SNR turning threshold,the dither signal is added to the 1-bit ADC.The simulation results show that the non-subtractive dithering method greatly improves the performance of the system in transmitting high-order modulated signals in the region of high signal-to-noise ratio.The 1-bit single-user uplink SIMO system scenario is extended to the 1-bit multi-user uplink massive MIMO system.Considering that the base station have no ideal channel state information,by using the LS channel estimation algorithm to estimate the system channel,a pilot length optimization problem with the goal of maximizing the system's achievable rate is formulated,and a direct exhaustive algorithm is used to solve it.The simulation results show that the achievable rate of the system based on pilot optimization can be increased by nearly 40% for a given SNR and the number of antennas.