平坦衰落环境中多输入多输出系统衰落相关与信道容量研究

On Fading Correlation and Channel Capacity of MIMO Systems under Flat Fading

为分析模型物理参数和天线排列方式对多输入多输出系统信道容量的影响,提出了一种平坦衰落环境中信道容量的研究方法。该方法基于接收均匀圆阵和均匀线阵分别构建了蕴含模型物理参数的相关矩阵,并利用 Wishart分布的性质推导了信道容量上下限。该方法回避了求取衰落相关矩阵特征值的概率密度函数,降低了运算量;可被推广到多天线-频分复用系统。仿真结果表明,天线间距较小时,采用均匀圆阵比均匀线阵的系统信道容量要高;天线间距增大到一定程度后,系统信道容量达到饱和。散射角越大,信道容量的增长速率越快且采用均匀线阵比均匀圆阵系统的信道容量高。接收信噪比较大时,平均信道容量上下限基小接近其实际值。

In order to study the impacts of array configuration and channel model parameters including antenna spacing and scattering angle on the channel capacity of a MIMO （Multiple Input Multiple Output） system, a novel method is proposed to explore the channel capacity under fiat fading. Fading correlation matrix is constructed based on uniform circular antenna and uniform linear antenna at the receiver side, respectively. And then using the properties of Wishart distribution, closed-form expressions for the upper and lower bounds on the ergodic capacity of N by M MIMO system are presented in detail. The problem of calculating the probability density function of eigenvalues of the fading channel matrix is avoided and the computational complexity is lower in contrast to the previous methods. The novel method also could be generalized to MIMO-OFDM systems with any number of transmit and receive antennas. Computer simulation results show that for small spacing the UCA yields higher channel capacity than ULA. The channel capacity is maximized when the antenna spacing increases to a certain point, and further more, the larger the scattering angle, the quicker the channel capacity converges to its maximum. And at high SNR, the upper and lower bounds on the ergodic capacity are close to its true value.