基于多参量联合优化的去蜂窝大规模MIMO系统能效研究

Energy Efficiency of Cell-free Massive MIMO System Based on Multi-parameter Optimization

去蜂窝大规模多输入多输出(Multiple-input Multiple-output, MIMO)系统利用低精度模数转换器来降低硬件成本和反向链接负载,从而获得高频谱效率和宏分集增益,但仍产生大量的功耗精度损失。针对在接收端采用低分辨率模数转换器(Analog-to-Digtial Converter, ADC)的去蜂窝大规模MIMO系统的上行链路,本文提出了一种基于fpZF(full-poilt Zero Forcing)检测的交替联合优化能效算法。首先推导出去蜂窝大规模MIMO系统中采用fpZF接收机时系统上行链路能效的近似闭式表达式;其次,根据分数规划的性质,将分数形式转化为等价的减式形式,在确定量化精度和接入点数目的基础上,以导频序列长度、接入点天线数以及发射功率为优化目标的三变量进行交替迭代,得出最优能效值;再进一步通过调整量化精度和接入点数目,对能效和频效进行优化,以达到能效最优值。仿真结果表明,所提算法能够有效提高系统的能量效率和频谱效率,并且保证用户之间的公平性。

Cell-free massive multiple-input multiple-output systems use low-precision analog-to-digital converters to reduce hardware cost and the load on backhaul link,thus achieving high spectrum efficiency and macro diversity gain,but still resulting in a large amount of power consumption loss.In this paper,an alternating joint optimization energy efficiency algorithm based on fpZF(full poilt Zero Forcing)detection is proposed for the uplink of cell-free massive MIMO(Multiple-input Multiple-output)system using a low resolution Analog-to-Digital Converter(ADC)at the receiving ends.Firstly,approximate closed form expression for the uplink energy efficiency of cell-free massive MIMO systems using fpZF receivers is derived.Secondly,according to the properties of fractional programming,the fractional form is converted into an equivalent subtractive form.Based on the determination of quantization accuracy and access points,the optimal energy efficiency value is obtained through alternating iteration of three variables with the optimization objectives of pilot sequence length,access point antenna number,and transmission power.Furthermore,energy efficiency and frequency efficiency are optimized by adjusting quantization accuracy and access points to achieve the optimal energy efficiency value.The simulation results show that the proposed algorithm can effectively improve the energy efficiency and spectral efficiency of the system,and ensure fairness among users.