ay be further apart to support FSK data and maintain the orthogonality of all possible waveforms. Assuming that the pulse shape is rectangular, the corresponding ambiguity func- tion (1.97) can be overbounded by (1.104) Now define the integer ko such that (1.105) or equivalently (1.106) Noting that there are MF - ko frequency pairs (f',f', each from F, for which f' f" = ko/T it can be shown that f'-f"=k/Th ko)T' (1.107) k1-k2#k The last inequality in (1.107) follows from (1.105) and (1.106), and worst case choice of 8. The weakest bound (1.107) occurs when V is close to zero and ko = 0, and hence, considering that case and letting m = k1 Design Issues k2, gives (1.108) The resolution capability of FH/SS communication system can now be esti- mated by noting from (1.102) and (1.108) that (1.109) This is the basis for stating that a high energy gain FH/FSK communication system has TOA resolution on the order of Th That is, (1.109) indicates that frequency-synchronous correlation detectors should be able to reject the desired FH/FSK signal, if it arrives out of time synchronism by more than Th seconds. 1.6 DESIGN ISSUES Based on the analyses presented in this chapter, spread-spectrum techniques promise an attractive approach to the design of communication systems which must operate in an interference environment. However, major design issues have been obscured thus far by the apparent simplicity of the concept. 1. How does the receiver acquire and retain synchronization with the received signal's clocks, especially in the presence of interference? 2. Can the appearance of randomness in modulation selection be achieved deterministically by a stored-reference SS system? 3. In what ways does the communication VS. jamming game change when the payoff function is bit-error rate? 4. What are the effects of imperfect system operation/modelling (e.g., syn- chronization errors, non-uniform channel characteristics across the com- munication band) on performance estimates? 5. How should data detectors be designed when the nature