The NOMACand Rake Systems
نویسنده
چکیده
• In the 1950s, Lincoln Laboratory developed the spread-spectrum Noise Modulation and Correlation (NOMAC) system for improved high-frequency radio communications. The production version of NOMAC, named the F9C, generated a pseudonoise (PN) sequence at the receiving terminal in synchronism with the PN modulation of the transmitted signal. The F9C achieved as much as 17 dB of jamming protection. Obtaining an additional 6 dB ofprotection (the original NOMAC design had promised 23 dB) required addressing the effects of multipath propagation. Lincoln Laboratory solved the multipath problem by adding a Rake receiver to the NOMAC system. The Rake receiver synthesized an adaptive matched filter corresponding to the collection of linear propagation paths that produced the actual received signal. The insights that led to Rake ultimately found application to sonar problems, the analysis of seismic signals, the radar mapping of the moon and nearby planets, and the radar imaging of orbiting satellites.
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