e jamming. The repeat m code is a simple code of rate R = 1/m bits per coded bit. It is also referred to as diversity of order m. Diversity techniques are useful in combatting deep fades in a fading channel. For similar reasons, diversity is effective for multitone jamming and for worst case partial-band jamming. We shall see later, however, that there are more effective codes than simple diversity. Broadband Jammer Multitone Jammer Eb/Ns Figure 3.26. FH/BFSK with diversity-multitone jammer. Basic Concepts and System Models As with the DS/BPSK example, the use of coding here did not change the data rate of the total spread-spectrum bandwidth W SS* Only the instantaneous bandwidth associated with each coded bit or chip became wider. 3.8 INTERLEAVER/HOP RATE TRADEOFF In the coded FH/BFSK example considered above, the hop rate was increased from once every T seconds to once every T = Tblm seconds. Rather than increasing the hop rate by a factor of m, the same result can be achieved with an interleaver and deinterleaver. This is illustrated in Figure 3.27 with an example of m = 3. Assume the frequency hop rate is fixed at once every Tb seconds, but m = 3 chip tones are transmitted during each hop. As illustrated in the fre- quency and time diagram of Figure 3.27, during each hop transmit chip tones corresponding to three different data bits. Thus, in three hop intervals of 3T seconds transmit nine chip tones where chip tones corresponding to the same data bit appear in different hop intervals. This ensures that the transmitted chips for each data bit are hopped independently. The performance achieved with this interleaver and deinterleaver is the same as the case where each transmitted chip is independently hopped at the rate of three times per T seconds. 3.9 RECEIVER NOISE FLOOR In this chapter receiver noise was ignored. A more accurate model of the received signal is y(t)= x(t)+J(t)+n(t) (3.89) where x(t) is the transmitted signal, J(t) is the jammer signal, and n(t) is the receiver noise which is typically modele