多天线终端测试方法的演进、理论与实践

出信号的变化，我们记录到40 分钟最大的信号幅度变化在0.1dB 以下，这证明在同一次测试过程中，功率放大器的信号漂移不会对系统测试结果产生影响。

图13、功率放大器各通道的信号漂移（长期）

3.2.4、多探头之间的耦合情况

对于多探头系统，天线探头之间的互相耦合可能会影响到测试结果，这种影响的评估在尺寸较小的暗室配置中显得更为重要，在ABP MIMO OTA 单簇法系统中使用到了3 个双极化的天线探头，我们分别对3 个天线的两种极化做了测试，测试结果见图14，测试结果表明最大的耦合发生在3 号天线的垂直与水平极化之间，在1.2GHz 约为-18dB，其他耦合一般小于-30dB。

图14、暗室内天线探头之间及各极化方向的信号耦合情况

3.3、信道模型的验证

作为系统信道环境重建成功与否的重要确认，在正式开始测试之前，无论是何种测试方法，均应当对暗室/ 混响室内部的信道模型做一个完整的验证。广播电视规划院对单簇模型的信道验证结果在参考文献[40] 中有详细的介绍，PDP、多普勒频移和空间相关性验证的结果见图15、表6 及图16。

图15、ABP 单簇法信道模型的验证：时延特性

表6、多普勒扩展的验证结果

图16、ABP 单簇法信道模型的验证：空间相关性

3.4、测试区域内的信号功率与SIR 验证

在目前的MIMO OTA 针对吞吐量测试，必须对测试区域内的参考测试信号功率（RS-EPRE）及SIR 值进行验证，否则不同实验室之间的测试数据无法进行统一和比较。参考文献[41]、[42]、[43] 中列举了测试功率及SIR 的定义和验证方法。

广播电视规划院的单簇MIMO OTA 系统的信号功率与SIR 验证结果在参考文献[39] 中已列举，摘录如下：在测试区域中的RS-EPRE 的计算值与实际测试值之间差异为-0.34861 dB ；在UMi、UMa/A、UMa/B 信道模型下，测试区域中的SIR 目标值与实际测试值之间的差异分别为-0.28dB，-0.58dB 及-0.47dB。

3.5、实际测试结果

在CTIA 开展的第二轮比对测试当中，广播电视规划院利用建立的单簇法MIMO OTA 测试系统对送样的3 类天线及其终端进行了测试，测试结果表明单簇法可以很好地将3 个终端进行区分，不同的信道模型对终端吞吐量的影响也清晰可辨（图17） 。

图17、ABP 单簇法实测结果

4、结束语

在本文当中，以多探头方案为主介绍了各种多天线终端的测试方法，并阐述了信道模型及其验证在多天线终端的性能评估方案中的重要意义，对以单簇法为代表的多探头方案在系统校准、信道验证、测试方法等细节进行了详细的论述。

中国的4G 牌照已于2013 年12 月4 日发放，多天线终端和MIMO 技术将逐渐成为主流，与此同时，随着国家地面数字电视的推广和高清多屏互动的应用，以802.11ac 为代表的WiFi 多天线技术也将进入普通家庭。在这个背景下，MIMO OTA 作为保障用户体验的终端性能评估方法，其研究和演进必然对整个无线通信行业及多天线技术的发展产生重要影响。

作者：新浪微博@吴醒峰 来源：广播与电视技术

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