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

高速数字移动的无线电被广泛地要求用于各种新业务的增长的需求，诸如对语音信号、数字数据和可视信息的本地和全国范围的通信。本研究的目的是确认本研究开发的使用天线方向图分集接收（APDR）的原型系统所实现的多径衰落的减少和传输带宽性能的改善。作为现场测试的结果在城市地区进行，已经发现原型系统的衰落减少接近于理想的四分支选择分集接收系统的衰落减少。然而，传输带宽性能的改善不如测试前预期的那么好。然后，四个方向的天线本身的传输带宽的改善进行了实验评估，并发现总是可以获得的，如果最佳的传输带宽性能的天线方向图可以通过一个适当的分支切换算法选择。采用支路切换算法的APDR系统的计算机模拟结果表明，在100 kHz带宽内，APDR系统的信号强度平坦度小于1.5 dB，累积概率为95%。研究结果表明，APDR系统可以减小衰落和频率失真。选择性衰落在数字移动的无线电中引起严重的误码，它扩展了抗多径调制/解调系统的适用范围，从而为高速数字移动的无线电提供了可能。

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.