A Communication Technique for Multipath Channels

Application of principles of statistical communication theory has led to a new communication system, called Rake, designed expressly to work against the combination of random multipath and additive noise disturbances. By coding the Mark-Space sequence of symbols to be transmitted into a wide-band signal, it becomes possible at the receiver to isolate those portions of the transmitted signal arriving with different delays, using correlation detection techniques. Before being recombined by addition, these separated signals are continuously and automatically processed so as to 1) apply to each an optimum weighting coefficient, derived from a measurement of the ionosphere response, and 2) introduce in each an appropriate delay such that they are all brought back into time coincidence. After a brief introduction, a functional description of the system is presented. There follows a review of the communication theory studies, which indicate that such systems have certain optimal properties. Details of design of an experimental prototype Rake system are followed by the results of limited field tests of this prototype. Conclusions and recommendations for future work are given.