tribution to behave like a Gaussian distribution. Arguments similar to the above were made in Chapter 1 in connection with the evaluation of the performance of pulse-jammed direct-sequence spread-spectrum systems. A more rigorous treatment of the validity of the Gaussian assumption for CPN has been examined in [6] for a variety of PN and Gold codes, with sufficient evidence that it holds, at least approximately, for a wide class of such codes. Let us now return to (1.91). Conditioned on the (0, 2)-uniformly dis- tributed phase 0j, ZI is, according to the above, a Gaussian random variable whose conditional variance is (1.93) Hence, when the jammer is present, the average bit error probability for the I channel (identically for the Q channel) is given by (1.94) where (1.18), (1.87), (1.90), and (1.93) have been used in arriving at this result. Finally, multiplying (1.94) by p gives the average bit error probabil- ity of FH/PN/QPSK in the presence of partial-band multitone jamming, namely, (1.95) Although (1.95) can be used in assessing the effect of a spread tone jam- mer on system performance, we shall now indicate an even simpler way of evaluating the tone interference effect by means of converting the spread tone jammer to an equivalent AWGN interference, where the equivalence is understood in terms of its effect on bit error probability. Let No, repre- sent the one-sided power spectral density of AWGN interference whose sta- tistical characteristics remain the same after the PN despreader. Clearly, the bit error probability in this case is given by (1.96) Coherent Modulation Techniques Equations (1.94) and (1.96) have been plotted in Figure 1.16. The abscissa is the signal-to-jammer power ratio SJR in decibels where, for the spread tone case (SJR)' = EbIN1 while, for the noise case, (SJR)" = Eb/No, A careful examination of Figure 1.16 reveals that, for values of (SJR) up to approximately 12 dB, the difference (SJR)(dB) - (SJR)(dB) between the signal-to-jammer ratios which achieve the same performance is, to a h