MIMO系统和无线信道容量研究

Study on the MIMO System and Wireless Channel Capacity

MIMO(Multiple-Input Multiple-Output)理论试图在Shannon信道容量公式基础上导出正比于收发信天线数的MIMO无线信道容量(WCC)公式.由于MIMO系统同时使用多根天线发送同频信号,在MIMO的物理信道中会包含多个虚拟独立瑞利衰落信道.因此MIMO理论关于独立瑞利衰落信道的定义在实际应用中很难成立,会导致所依据的空分复用(SDM)无法实现,使MIMO理论在数学层面导出的WCC公式在物理实现上会存在很大的不确定性.由于该系统使用不控制相位的多天线同频发射,多波干涉作用的影响是不可避免的,一定会产生方向不确定的定向发送波束,将形成多个电波覆盖盲区和一个不合理的无线通信系统.本文将利用数学分析和多天线发送波束模拟的方法证明上述结论.还将提出在Shannon公式应用原理和相控天线阵理论基础上构建的SHPCA系统,将利用相控天线阵给出的定向窄波束形成功率利用率极高的SDM功能,并给出对应的WCC公式,其容量正比与收发天线数和SDM次数,比Shan-non公式具有更高的效率.

In terms of Shannon formula,multiple-input multiple-output（MIMO） theory tries to derive the formula of wireless channel capacity（WCC）,which is proportional to the number of transmitting and receiving antennas in MIMO system.As multi-antenna is used in MIMO system to transmit signals with the same carrier frequency in the same time,one physical channel in MIMO system will contain multi-virtual independent Rayleigh fading channel.So,the definition in MIMO theory for the independent Rayleigh fading channel is most possibly to be invalid.This will lead space division multiplex（SDM） to be difficult to be realized,and the derived WCC formula in mathematics to be difficult to be established.Moreover,the directional transmission beams with uncertain directions are employed in the MIMO system.The interference among those transmitting signals can not be avoided,which would form a number of blind spots of radio coverage and an unreasonable wireless communication system.In this paper,the above views are firstly proved by mathematical analysis and the simulation of the transmitting radio beam produced by multi-antenna.Then,an SHPCA system is proposed,in which phase-controlled antenna array is used to produce a narrow directional radio beam with very high power efficiency to form SDM.Finally,the WCC formula for SHPCA system is presented in the paper,and its capacity is proportional to the numbers of antennas and SDM.It has higher efficiency for that WCC formula than Shannon formula.