Basic Study on Radio Propagation Structure of Nountain Reelection in Digital Mobile Radio Communication

在数字移动无线电中，延迟多径波会导致误码率的严重下降。山反射会产生很长的延时，影响系统性能。然而，目前还没有办法预测山脉反射的强度。我们的研究旨在阐明山反射信号的基本特征，以及如何预测山反射信号的强度。在Takushoku大学的校园里，使用指向山的一部分的定向天线，测量了1.2GHz的山脉反射。在电视信号中插入尖锐脉冲，将山反射信号分离，在CRT显示器上观察接收到的脉冲模式，并由计算机记录和处理，得到接收机输入信号中反射信号分量的电平。同时，对以反射山为吸收散射面计算反射信号强度进行了理论分析。根据测量到的反射信号强度，可以计算出山体表面的吸收系数。根据测量，在这种情况下，由于吸收引起的波衰减约为26.5dB。在测量中，观察到反射信号强度随时间变化。例如，在降雪后的几个小时内，反射增加了几个dB，最终也出现了快速波动。结果表明，在已知山面对无线电波的吸收衰减的情况下，在任意传播条件下，提出了一种山面反射信号强度的理论预测方法。对于更广义的环境，需要进一步的研究来证明基本方程和吸收因子值的有效性。

In digital mobile radio, delayed multipath waves cause serious degradation in error rates. Reflection by mountains can produce very long delay which influences the system performance. However, there has been no way of predicting the strength of mountain reflection. Our study aimes to clarify the fundamental characteristics of mountain-reflected signals and how to predict the strength of the signals reflected by a mountain.Measurements of mountain-reflection have been made at 1.2GHz on the campus of Takushoku University, using directive antennas directed to a part of a mountain. The mountain-reflected signal was seperated by a sharp pulse inserted in a TV signal, and received pulse pattern was observed on CRT display and recorded and processed by a computer to give the receiver input signal level of the reflected signal component.In parallel, theoretical analysis was made to calculate the reflected signal strength taking a reflecting mountain as an absorbing scattering plane. The absorption factor at a mountain surface can be calculated from the measured reflected signal strength. According to the measurement, the wave attenuation due to absorption is obtained to be about 26.5dB in this case. In the measurements, the reflected signal strength was observed to vary with time. For example, the reflection increased by several dB in a few hours after snowfall, and also rapid fluctuation was eventually observed.As the results, a method of theoretical prediction of the mountain-reflected signal strength has been proposed for arbitrary propagation conditions, if the absorption attenuation of radio wave by the reflecting mountain surface is known. Further studies are necessary to prove the validity of the fundamental equation and the value of absorption factor for more generalized environments.