Soft-decision decoded performance of fast frequency-hopped (FH) M-ary FSK signals over partial band noise jammed binary channels is studied. The effects of metrics conversion, quantization, and the presence of regenerative nodes on the system's cutoff rate performance are investigated. It is found that the conversion from an M-ary metric to a binary one suffers only negligible degradations. For communication links without regenerative nodes, as expected, the infinite-bit soft-decision is the optimal metric, followed by finite-bit soft decision and then hard-decision. For those with regenerative nodes, however, the infinite-bit soft-decision is outperformed by the hard-decision, but the finite-bit soft-decision decoder still keeps its edge over the latter. The issue concerning the order of metric conversion and diversity combining is also analyzed. Numerical results indicate that the conclusion obtained by an earlier simulation report addressing a similar design alternative in fading channels is valid for jammed binary channels, as well. That is, the precombining metric conversion technique gives up only minor performance degradations when compared to the more sophisticated postcombining metric conversion technique. I. INTRODUCTION HE ANTIJAM (AJ) capabilities of various fast T frequency-hopped (FFH) M-ary frequency-shift keying (MFSK) systems have been subjects for quite a few recent publications; see [ 11-[6] and the references therein. Many of the studies concentrate on the uncoded or hard decision decoded performances for a variety of diversity combining techniques. Soft-decision decoding performance was discussed by Stark [lo], Stiiber et al. [ll], [I21 and Simon et al. [5]. In these studies, M-ary symbol codes were used in conjunction with MFSK signals; [5], [11]-[12] assumed zero thermal noise while maximum-likelihood decoding was used in [ 101. The case of MFSK with M-ary codes in AWGN was analyzed by Proakis [4]. As for more practical binary codes, simulation results can be found in [16], [17]. For all these efforts, as far as we know, no analytical work on the behavior of binary coded FFWMFSK signaling with soft-decision decoding has been reported. McGree and Deaett [16] investigated the Paper approved by E. Biglieri, the Editor for Data Communications and Modulation of the IEEE Communications Society.
