Multilevel SCPC System Design

A method of assigning carrier levels in an SCPC system with mixed earth station is developed which optimizes system performance for uniformly spaced and randomly assigned carrier frequencies. The optimum transponder backoff is shown to be identical to that for a system of uniform carriers in which the (common) earth station is a weighted average of the different values in the mixed system. With the transponder backoff determined, the carrier level to be transmitted to each station type is simply expressed in terms of the station . Since the carrier frequencies are randomly assigned, the technique described is ideally suited to the design of a demand-assignment system. Alternatively, the same performance can be realized through a pseudorandom choice of frequencies in a system of fixed frequency assignments. In the particular case of two station types with an equal number of large and small carriers, a system employing a random assignment of carrier frequencies is compared with one in which the large and small carriers alternate in frequency. It is shown that, if equal carrier-to-noise ratios are required for the two carrier sizes, the two systems are capable of identical performance. However, the system of alternating carriers requires a lower EIRP per carrier from the smaller stations.