the PN sequence generator. Consider a jammer that transmits many tones each of energy ST. With total power J there are at most Ni-11 (3.81) jammer tones randomly scattered across the band. The probability that any given signal tone position is jammed with a jammer tone is, thus, S,W.T. (3.82) Here p is also a fraction of the signal tone positions that are jammed. Assume that the jammer has exact knowledge of the N possible signal tone positions and places the N jamming tones in some subset of these N posi- tions, where N , N is always assumed. During the transmission of a data bit, one of two possible adjacent tone positions is used by the transmitter. An error occurs if the detected energy is the alternate tone position not containing the transmitted signal tone is larger than the detected energy in the transmitted tone position. This can occur only if a jammer tone occurs in this alternative tone position. Here, ignore the smaller probability of a jammer tone in both positions and assume an error occurs if and only if a jammer tone with power SJ S occurs in the alternative tone position. Thus, the probability of a bit error is (3.83) provided SJ > S. From the communicator's standpoint, the worst choice of SJ is S = S resulting in the maximum bit error probability (3.84) This bit error probability is slightly larger than the worst partial-band noise jammer performance; the results are essentially the same. Figure 3.25 shows the bit error probabilities for broadband noise jamming, worst partial-band noise jamming, and worst multitone jamming. Part 2, Chapter 2, will exam- ine these cases in greater detail. Basic Concepts and System Models 3.7 CODED FREQUENCY-HOPPED BINARY FREQENCY-SHIFT-KEYING Figure 3.25 illustrates the up to 45 dB of degradation at 10-6 bit error prob- ability that a jammer can cause to an uncoded FH/BFSK system using the same average power J. As was done for the DS/BPSK system, we show next how a simple repeat code can effectively neutralize the degradation because of multitone jamming. This s