ncy selected by the hopper for this interval, and A(i-1) is again the transmitted phase in the (i - 1)-st interval. In analyzing the performance of FH/DQASK in the presence of the tone jam- mer (assuming the i-th transmission interval is jammed) (2.83) it is convenient to adopt a vector diagram approach analogous to that taken for MDPSK. As such, the transmitted signal will be represented by a normalized vector with X and y components respectively given by n = by/8 and m = am/8. The jammer is then represented by a normalized vector with phase OJ and amplitude5 (2.84) Recalling that M = K2, then combining (2.18), (2.19), (2.56), and (2.84), (2.85) For example, for FH/DQASK-16 (K = 4), (2.85) becomes (2.86) In the remainder of this chapter, we shall deal specifically with FH/DQASK-16 as a matter of convenience. However, whenever results are obtained in their final form, they shall be given in the generalized form suit- able to FH/DQASK-K2, with arbitrary K. Figure 2.11 is the normalized signal point constellation corresponding to QASK-16. The dashed lines indicate the decision region boundaries appro- priate for coherent or differentially coherent detection of the various signal points. Now suppose that we wish to transmit signal point 1 with differ- entially encoded phase in the i-th interval. The signal transmitted in the (i - 1)-st interval could have been any of the 16 signal points. Thus, the vec- tor representation of Figure 2.12 is adequate for characterizing the signal and jammer in these two intervals. For convenience, we shall always draw the vec- tor representing the signal transmitted in the (i - - 1)-st interval along the positive x-axis. The amplitude A1 corresponds to the normalized envelope of the signal point transmitted in the (i - 1)-st interval and, from Figure 2.11, Note that the normalized vector amplitude B as defined here is not the same as a similar quan- tity denoted by B in Section 2.1 and defined in (2.17). Performance of FH/DQASK in the Presence of Partial-Band Multitone Jamming Figure 