Design Equations for a Specified Bit Error Rate for PCM/FM+FM/FM and Optimum Bandwidths

Abstract

A PCM/FM+FM/FM system combines the bit sequence with the modulated subcarriers at baseband and the resultant modulates the carrier. This paper concerns the design of this composite system. Such a system combines the spectral efficiency of the analog system with the accuracy of a PCM system when needed for specific sensors and allows the direct transmission of binary computer words if necessary. The impact of the subcarriers on the bit error rate of the bit sequence is determined. Equations are given which allow the degradation of the FM/FM channels by the bit sequence to be determined. Further, it is shown in this work that as the IF bandwidth is increased above twice the bit rate, the peak deviation of the carrier by the bit sequence is no longer .35 times the bit rate. An optimum value for IF bandwidths is determined. The developed design equations allow the design of the composite system with a specified bit error rate and a specified signal to noise ratio in the subcarrier channels.