异构网中大规模MIMO场景下波束赋形设计

Beamforming in heterogeneous networks with Massive MIMO

近年来,人们对于无线通信系统的数据传输速率的需求越来越大.大规模多输入多输出技术(MIMO)与小小区技术是能够满足人们高速增长的无线通信需求的关键技术.研究在一个异构网中的波束赋形问题,其中宏小区基站的配置为Massive MIMO,同时宏小区中包含小小区.在这样的场景下,宏基站配置大量天线,小小区基站配置少数天线,用户配置单天线.研究在这样的场景下,通过波束赋形设计,最大化所有用户的传输速率.该问题的目标函数是一个非凸的问题.通过运用半正定松弛(SDR)方法以及基于泰勒展开的一阶近似方法,将原问题转化为一个凸的近似问题,然后运用迭代方法求解.仿真结果证明,方案可以有效地提高包含Massive MIMO的异构网场景下的系统吞吐率以及能量效率.

The wireless communication system is now facing an astounding data traffic increase in a decade. Massive multiple-input multiple-output（ MIMO） and small cell（ SC） networks are two promising technologies to meet the increasing data traffic demand. This paper studies the beamforming design problem in a two-tier network consisting of a massive MIMO macro tier overlaid with a second tier of SCs. In this scenario,the Base Station（ BS） uses a large excess of base station antennas（ up to a few hundred antennas） while the SC is equipped with only a small number of antennas. Possible improvements of energy efficiency is investigated. The object is to maximize the transmission rate of the network under the sum power constraint. This object leads to a nonconvex complicated structure,and makes the considered beamforming design problem difficult to handle. To solve this problem,a beamforming design scheme is proposed to transform the original problem into a convex approximation problem,by employing semidefinite relaxation（ SDR） and first-order approximation technique based on Taylor expansion. Numerical results show that the strategy can improve system throughput.