solution and in the latter, rate of flow of information. A signal that provides good resolution and, hence, has fairly large bandwidth, should be made more complex in nature within this bandwidth for anti-jamming characteristics. Finally, it is important to note that nowhere has The Historical Origins of Spread-Spectrum Communications Figure 2.11. Nathan Marchand, organizer and first chairman of the IRE Information Theory Group, early practitioner of correlation techniques, and codesigner of the WHYN system. He was the lyricist of the classified jingle presented at a Washington meeting where radar correlation-detection methodology was discussed [100]. (Photo courtesy of N. Marchand.) the type of modulation of the signals been specified; the conclusions apply equally to pulse-, frequency-, and phase-modulated signals. Similar views are expressed by Harvey in a companion paper [102]. Ideas and analyses which were prompted by the Sylvania Bayside work appeared in the literature [103]-[106], in two Harvey patents, the first on WHYN [107] and the second on a collision warning radar [108] which could employ noise modulation, and in another patent [109] on spectrum shaping for improving TOA measurement accuracy in correlation detectors. With continued study, the need for bandwidth expansion to improve system performance became even more apparent, and it was declared that [110] Jamming signals which are noise modulated or non-synchronous CW or modu- lated signals are rejected to the same extent that general noise is rejected, the improvement in signal over interference in terms of power being equivalent to the ratio of the transmission bandwidth to the receiver bandwidth. This improvement property of SS systems is usually referred to as pro- cessing gain, which nominally equals the multiplicity factor of the system. By suitably setting these bandwidth parameters, acceptable receiver oper- ation from 40 to 60 dB interference-to-signal ratio was reported in labora- tory tests, and navigation receivers operating at -25 dB S