compute the exact performance. An error will occur whenever the m diversity transmissions are all jammed, the untransmitted symbol is hit each time, and a < 1 ((2.36) raised to the m-th power): (2.75) This is maximized at a = 1. provided EIN is large enough SO that u VI 1; therefore the performance of FH/BFSK signals with diversity m in worst case n = 1 band multitone jamming is exactly specified by (2.76) This is plotted in Figure 2.35 for various values of m, including the uncoded m = 1 case. Note that (2.76) is valid Am 1, and is identical to (2.40) and (2.41) for K = m = 1. The slope discontinuity in these curves is characteristic of band multitone jamming because of the constraint that each jammed M-ary band contain exactly n jamming tones (recall Figures 2.12, 2.18, and 2.19). The horizontal portion of each curve in Figure 2.35 is the "saturation region" where u = 1; that is, each binary (M = 2) band contains its quota of one jamming tone. In this region, the power in each jamming tone exceeds S and continues to rise (awc falls in (2.76)) as Eb/N, decreases. There is somewhat of a paradox here. The n = 1 band multitone scenario is highly structured. It concedes the jammer knowledge of the location of the M-ary bands, information that is used to undermine the receiver's awareness of which hops are jammed by distributing the jamming power SO as to hit the maximum number of hops. Yet, unlike the less structured partial-band noise behavior illustrated in Figure 2.30, the constraint Coding Countermeasures m = 20 Eb/N,,dB Figure 2.35. Performance of FH/BFSK signals with diversity m chips/bit in worst case n = 1 band multitone jamming. In the horizontal regions, the probability u that a binary band is jammed is 1. imposed by n = 1 band multitone jamming ultimately leads to error-free performance as m becomes large. For small values of m, each jamming tone contains the same power as the signal tones, and the Q = J/S jamming tones are less than the number of M-ary bands. However, as m increases SO does the chip rate