Development of Four-branch Antenna Pattern Diversity Reception System with Multi-threshold Branch-switching Strategy for Mobile Radio Communication

高速数字移动对讲机是地方和全国通信对语音信号、数字数据和视觉信息等各种新型业务日益增长的需求。本研究的目的是验证本研究开发的天线方向图分集接收（APDR）原型系统在减少多径衰落和提高传输带宽性能方面所取得的效果。在城市进行的现场测试结果表明，原型系统对衰落的抑制接近理想的四支路选择分集接收系统。然而，传输带宽性能的提升并没有测试前预期的那么好。然后，通过实验评估了四向天线本身对传输带宽的改善，发现只要通过适当的分支切换算法选择传输带宽性能最佳的天线方向图，就总是可以实现的。采用分支交换算法对APDR进行了计算机仿真，直接观察了传输频带内信号强度的平坦度，结果表明，在100khz带宽内，以95%的累积概率可获得低于1.5 dB的平坦度。研究结果表明，APDR系统能够有效地降低数字移动无线电中由于频率选择性衰落而产生的严重误码的衰落和失真，扩大了抗多径调制解调系统的适用范围，从而为高速数字移动无线电的实现提供了可能。

High speed digital mobile radio is widely required for the increasing demands of various kinds of new services, such as local and nation-wide communications on speech signal, digital data and visual information. The purpose of this research is to confirm the reduction of multipath fading and the improvement in transmission bandwidth performance achieved by a prototype system using an antenna pattern diversity reception (APDR), which has been developed in this research.As the results of the field tests conducted in urban areas, the fading reduction by the prototype system has been found to be close to that by an ideal four-branch selection diversity reception system. However, the improvement in transmission bandwidth performance was not so good as expected before the tests. Then, the improvement in transmission bandwidth of a four-direction antenna by itself was evaluated experimentally and was found to be alwawys obtainable if the antenna pattern of the best transmission bandwidth performance can be selected by a proper branch-switching algorithm. A computer simulation of APDR with a branch-switching algorithm directly observing the flatness of the signal strength within the transmission band shows that a flatness below 1.5 dB within 100 kHz bandwidth is obtainable with 95 % of cumulative probability.The results of this research show that APDR system can reduce the fading and the distortion due to frequency-selective fading which causes serious bit errors in digital mobile radio, and that it expands the applicable area of anti-multipath modulation/demodulation system, thus resulting in a possibility of high speed digital mobile radio.