天线极化和阵元间距对地铁隧道MIMO性能的影响

Antenna polarization and array spacing on MIMO performanceinfluence in subway tunnel

在上海地铁隧道环境中对5.6 GHz多输入多输出系统开展了基于伪随机序列的信道测量。通过相关运算获得了子信道冲激响应,分析了不同天线极化和阵元间距对2×2 MIMO信道条件数、等效自由度和信道容量的影响。结果表明,当交叉极化天线的条件数均值约为10时,分别比垂直同极化和水平同极化约低5和8。当交叉极化的等效自由度均值约为1.6时,分别比垂直同极化和水平同极化约高0.3和0.2。当交叉极化的信道容量均值约为5.8 bit/s/Hz,分别比垂直同极化和水平同极化约高0.7 bit/s/Hz和0.8 bit/s/Hz。3个结果都一致表明交叉极化天线有利于MIMO性能的提高。另外,天线阵元间距对于同极化MIMO的信道容量影响较大,而对于交叉极化MIMO的信道容量影响较小,表明采用交叉极化能以较小的阵元间距获取较大的信道容量,这些结果对于地铁隧道狭小空间中减少天线尺寸提升信道容量有参考意义。

The channel measurement based on pseudo-random sequence was carried out for 5.6 GHz Multiple Input Multiple Output(MIMO)system in Shanghai metro tunnel environment.The impulse response of subchannel is obtained by correlation operation.The effects of antenna polarization and array element spacing on the condition number,equivalent degree of freedom and channel capacity of MIMO channels are analyzed.The results show that when the average number of cross polarization conditions of the antenna is about 10,it is about 5 and 8 lower than vertical polarization and horizontal co polarization respectively.When the mean value of cross polarization equivalent degree of freedom is about 1.6,it is about 0.3 and 0.2 higher than that of vertical polarization and horizontal homopolarization respectively.When the average cross polarization capacity is about 5.8 bit/s/Hz,it is about 0.7 bit/s/Hz and 0.8 bit/s/Hz higher than that of vertical polarization and horizontal polarization respectively.All three results agree that the cross polarization of antenna is beneficial to the improvement of MIMO performance.It is also found that the antenna array element spacing has a greater impact on the channel capacity of co polarized MIMO.The channel capacity of cross polarized MIMO is less affected.It shows that cross polarization can obtain larger channel capacity with smaller array element spacing.These results have reference significance for reducing antenna size and increasing channel capacity in narrow space of subway tunnel.