Message Errors and Message-Channel Signal-to-Noise Ratios

Basic statistical characteristics of the message-signal channel output signal-to-noise ratio (SNR) are discussed and measured. An explanation and experimental proof are given for the lack of close correlation between the measured median output SNR and the measured average bit-error rate. Also, it is shown that a much higher correlation exists between the fade-level distribution of the output SNR and the average bit-error rate. These results also explain the lack of close correlation between the median of the received RF signal and the average bit-error rate. The measured relationship between the average bit-error rate and the median output SNR was found to be considerably different from the calculated value for quadruple-diversity conditions; this difference is attributed to the fact that the actual distribution of the output SNR does not correspond to the theoretical distribution for quadruplediversity conditions for the FDM-FM type of transhorizon tropospheric radio link.