inimize the signal-to-interference ratio by transmit- ting a single tone at the frequency of the transmitter spectrum's peak. However, this is not the best jamming strategy if the receiver has an addi- tional notch filtering capability, or if the designer is interested in the more significant bit-error-rate (BER) design criterion. 2. The above SIR improvement calculation is valid even if mi(t) = mT(t), randomization by time shift t being enough to make mT(t - t1) and mT(t) quite distinct on the average. This suggests that several systems could use identical SS waveforms, provided the probability that they arrive in near synchronism at a receiver (for any reason, natural or jam- motivated) is virtually zero. 3. Cross-correlation functions and cross-spectra between asynchronous interference and desired signal are not a specific factor in the signal-to- interference ratio improvement based on long-term averages. Clearly the use of long-term averages in a SIR-based figure-of-merit has led to these simple results. Similar results can be achieved for other forms of SS modulation. the DS example was particularly simple because the receiver used only one corre- lator. Corresponding analyses of SS systems using higher dimensional sig- nal sets, e.g., FH/FSK, must consider the total signal energy and total interference energy collected in a set of correlators. 1.5.3 High-Resolution Time-of-Arrival (TOA) Measurements Not all interference waveforms satisfy the independence and randomly asynchronous assumptions used in Section 1.5.2 to reaffirm the energy gain capability of SS systems. Here are some examples which are illustrated pic- torially in Figure 1.5. 1. Multipath: Additional propagation paths from transmitter to receiver may produce undesirable interference in a correlator synchronized to a signal arriving via a specified path. For example, a single additional path may produce an interfering signal of the form (1.64) with m1(t) = mT(t), (1.82) A Spread-Spectrum Overview FRIENDLY REPEATER MULTIPATH DIRECT TRANSMITTER R