Early Spread-Spectrum and Automatic Equalization - NOMAC and Rake

Today, both spread spectrum and automatic equalization of randomly varying linear channel distortions are well-worn tools underlying cellular telephony, high-speed modems and other workhorse practices. But in the early 1950s, attempts to build communication links in which the signal alphabet consisted of wideband pseudorandom waveforms were frustrated by two problems: (1) how to store at physically separate locations clean, synchronized copies of the same waveform, and then (2) how to mitigate the big problem with short-wave communication, the arrival at the receiver of many variously-delayed copies of the transmission, when only one of them was wanted. The answers we developed at M.I.T. Lincoln Laboratory, namely NOMAC and Rake, respectively, were analyzed, prototyped and then placed into operational U.S. Army service for antijam purposes. Roughly speaking, the eight relay racks of NOMAC/Rake have been replaced today by the chip in your wireless computer mouse or cellphone. Bob Scholtz´ and Bob Price´s classic Communications Transactions papers on the early history of spread spectrum [1, 2] also detail all the many studies in programs other than Lincoln´s. Yet it was Lincoln´s F9C that first saw true operational use, and Rake was the earliest practical automatic channel adapter.