ECEIVER COMMUNICATION PATH SURVEILLANCE RECEIVER JAMMER LONG-TERM INDEPENDENT SIGNAL INTERFERENCE ANALYSIS Figure 1.5. A scenario for SS link operation. at a fixed delay t1 corresponding to the incremental propagation delay between the interference path and the communication signal path. 2. Repeater Jamming: This is a form of artificial multipath, in which the jam- mer attempts to receive the SS signal, somehow alter the data modula- tion, and then broadcast the result. Hence, if the modulation multiplicatively changed, then the signal retransmitted by the jammer may be of the form (1.64) with m/(t) = d'(t)m7(t) (1.83) In this case, t1 corresponds to the additional propagation delay encoun- tered over the propagation path through the surveillance/jamming sys- In both of these cases, the time shift parameter t and freqnecy offset A of (1.64) are nearly constant or slowly varying over restricted ranges. The inter- ference's incremental delay t is a positive quantity when a direct natural propagation path is used for communication. On the other hand, communi- cation via a friendly repeater or an indirect path may result in a negative value for t. The average response of a correlation detector to the above types of signal-related interference can be determined by evaluating (1.66) or (1.71), e.g., (E{|v1(k)|2}) = (1.84) (k-1)T The Advantages of Spectrum Spreading Here it is assumed that the receiver's correlator reference signal MR(t) is syn- chronized to the signal arriving via the communication path, and that t and A are the incremental time and frequency shifts incurred by the interference signal during the k-th correlation interval. At this point, we must depart from the analysis of the previous section, because t is fixed within a limited range in this interference scenario and cannot be used as an averaging variable. The shape of (E{vi(k)|} as a function of t1 and A will indicate the time and freqnecy resolution capability of the SS signal structure, i.e., the abil- ity of the receiver's correlation detector to