Frequency Synthesizer Effects in FSK-FH Communications

A frequency hopped (FH) digital communication system requires a receiver to generate a frequency hopping pattern in synchronization with a received carrier hopping pattern. Receiver hopping patterns are typically generated from frequency synthesizers, in which a reference frequency is multiplied up to the desired frequency sequence. In this paper the effects of frequency synthesizer anamolies on the performance of a noncoherent FSK-FH link is presented. The objective of the study is to derive degradation factors that can easily be examined and evaluated for the various types of synthesizer distortion. An important consideration in the design of any frequency hopping synthesizer is the relation between its frequency resolving capability, its frequency range, and its loop bandwidth. While high resolution tends to improve the steady state decoding capability, high resolution synthesizer design is usually accompanied by low synthesizer loop bandwidths, which lead directly to long transient (settling) times and increased phase noise problems. A study of the type presented here is necessary to evaluate the trade-offs leading to the most efficient communication performance.