up to a maximum of 64 [21]. In an unpublished report, L. Deutsch and R. Miller of the Jet Propulsion Laboratory in Pasadena, California, extended Berlekamp's table to include all odd values of k; these results were used in conjunction with (2.176) to derive the per- formance curves of Figure 2.103. We found that for the system under con- sideration, with worst case partial-band noise jamming, the optimum RS code rate k/n = .81, for which Eb/N, < 8.55 dB, Mopt < 5.8, and r .14; for worst case n = 1 band multitone jamming, the optimum k/n = .83, with EbIN1 < 13.19 dB, Mopt < 6.6, and 1rz.12. These results are only marginally better than the (255, 191) RS code in Table 2.19. But, what is really sur- prising is that the system performance is optimized by a weak, high rate RS outer code concatenated with a simple repetition code, rather than a more powerful low rate RS code alone. Thus, although the overall system code rate r is quite low, indicating that a significant amount of redundancy is needed to counter the postulated threats, the RS code by itself with hard decision decoding is apparently poorly matched to the worst case FH/MFSK jamming channel. In general, the traditional codes in use today were designed to provide good performance in stationary, additive Gaussian noise. The worst case jam- ming environment is often neither stationary nor Gaussian, SO we should not be terribly surprised if these codes are vulnerable to this kind of patholog- ical interference. What is really needed is the development of new codes specifically matched to the various anticipated jamming threats. Do such codes exist? To provide some insight into this issue, let us apply random coding arguments to the FH/MFSK channel with worst case noise Coding Countermeasures 13.45 WC n= I BAND MULTITONE 13.35 WC PARTIAL-BAND NOISE AT # = 211 13.25 E IN = 8.55 dE AT 207 p==10-5 13.15 RS CODE BLOCK LENGTH, k Figure 2.103. Required EIN, to achieve Pb = 10-5 for FH/16-ary FSK system with (255, k) Reed-Solomon code and optimum diversity in worst ca