cceptable FH/MFSK performance in worst case jamming, the next recourse is to concatenate an RS outer code with a suitable inner code (usually a convolutional code) as illustrated in Figure 4.21, Part 1. In particular, the RS outer code generates Q-bit code symbols (or char- acters). These are decomposed into L smaller K-bit subsymbols, which are then scrambled by an interleaver. Suppose these subsymbols are then fed to an inner dual-K, rate 1/v convolutional encoder, producing K-bit chips that are transmitted over an FH/MFSK channel. In the receiver, the dual-K Viterbi decoder makes hard K-bit subsymbol decisions based on the soft decision chip energy, linear combining metric with perfect jammer state side information. These subsymbols are then deinterleaved to break up any burst error patterns, and reconstituted into Q-bit RS characters which are input to the outer RS decoder. Suppose we want to achieve a particular Pb out of the RS decoder: this maps into a character error rate PQ [22], which determines the subsymbol error rate PK using (2.153). Even though the inner decoder makes hard sub- symbol rather than bit decisions, its performance is characterized by the Pb of (2.154). Depending on whether we have worst case partial-band noise or multitone jamming, (2.130) or (2.131) is combined with (2.151) to com- pute the required D. If we have an (n,k RS outer code (i.e., each block of k Q-bit data symbols produces n > k code symbols), the concatenated code rate is (2.155) which relates EJN, and Eb/N, via (2.133). Now the required Eb/N, can be determined from D using (2.132) and (2.134), or (2.138) and (2.139), depend- ing on the type of jamming. As shown in Table 2.14 for selected combinations of (n,k) and K, the con- catenated scheme above appears to be quite promising, with significant per- formance advantages over the dual-K or RS codes alone (Tables 2.12 and 2.13). Not too surprisingly, the concatenated systems with the rate 1/3 inner code outperform those with the rate 1/2 code by anywhere from about .5 to 2 