NOMAC and Rake were examples of what came to be called spread-spectrum (SS) systems. Most significantly, the success of modern mobile phones relies heavily on the rake concept, with almost every cell phone implementing a Rake receiver.Īs the rake paper by Price and Green (1958) got more attention, questions were raised about the very large bandwidth of the transmitted signals: A bandwidth of 10 kHz was used to support a single 60-word-per-minute teletype channel! But the reason could not be revealed at the time, because the main purpose of the system was its antijamming function. The Rake receiver concept, first used for ionospheric communications, has been applied in a variety of areas such as underwater communications, analysis of seismic signals, and, as described below, planetary radar astronomy. Of the multiple signals to enhance the signal strength, combining the signals from the different fingers with the right weights to undo the multipath effects. The Rake receiver consists of several “fingers” with different delays, which look like a rake, hence the name. How to mitigate this deterioration was the topic suggested by Fano for Price’s doctoral research. But in the field, it was soon found that NOMAC’s performance was seriously affected by the presence of multipath propagation (signals arriving at the receiver after multiple reflections via a randomly varying fading channel). One of the systems was deployed in Germany at the time of the Berlin blockade. NOMAC was put into service by the Army Signal Corps under the name F9C. Following ideas put forward in information theory by Claude Shannon, Jerome Wiesner, director of the Research Laboratory of Electronics (who later became science advisor to President Kennedy and then president of MIT), proposed building a system that transmitted wideband (pseudo)random signals detected by the use of correlation between the received signal and the transmitted (pseudo)random signal. This now celebrated “estimator correlator” principle has been found to be of value in many problems, but it found relatively quickly an application in the development of the famous “Rake” multipath-embracing receiver, done together with his close friend and colleague Paul Green ( Price and Green 1958).įor years, Price and Green had worked together at Lincoln Laboratory on different aspects of a noise modulation and correlation (NOMAC) system. In actual applications even such an estimate would be difficult to compute, but he pointed out that it would be possible to use intelligent approximations to obtain a useful estimate. This would not work when the signal is random, but studying his formulas, Bob noticed that the computation could be regarded as a cross correlation between the received waveform and a least mean squares estimate of the random Gaussian signal. It was well known that the detection of a deterministic signal in additive white Gaussian noise involved cross correlation between the received waveform and the deterministic signal. The required computations will be fairly complicated in any physical problem but it is aĬharacteristic of Bob’s work that he sought to find a physical interpretation of the mathematical formulas. The main computation requires the evaluation of a double integral of a quadratic function of the received signal, with a weighting function obtained as the solution of an integral equation. The latter material is further developed in Price (1956), where in the (later extensively studied by others) problem of the detection of Gaussian signals in additive white Gaussian noise, Bob made a very important observation. Following his AB degree in physics in 1950 from Princeton, and a short stint at Philco Labs in Philadelphia, he joined the MIT Lincoln Laboratory and simultaneously enrolled at MIT, where Robert Fano suggested the topic that would lead to his ScD dissertation, “Statistical Theory Applied to Communication Through Multipath Disturbances” (MIT RLE Technical Report 266, September 1953).īob’s thesis contains a number of channel capacity calculations and some results on optimal receivers. Washington, north of Philadelphia, and studied at the William Penn charter school, one of the oldest private schools in Philadelphia. ROBERT PRICE, a communications scientist, died December 3, 2008, at the age of 79 in Lexington, Massachusetts, where he had resided for more than 50 years.īob was born on July 7, 1929, in Ft. “For pioneering achievements in applying statistical communication theory to radio communication, radar astronomy, and magnetic recording.” BY THOMAS KAILATH
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