High Efficiency Multiple Access Communications Through a Signal Processing Repeater

Abstract

This paper describes a signal processing repeater which enhances the performance that can be obtained with random access discrete address (RADA) digital transmission links which operate in a multiple access mode. In general, RADA modulation techniques employ groups of pulses to transmit information. The pulses within a group normally have different carrier frequencies and are separated from each other by one or more time slots. The communication performance capability of a system which uses these techniques is a function of interference between the pulse groups of different users and background noise. A number of RADA techniques were proposed for the U. S. Army to provide communications within field army and divisions. For army application these had the advantages of rapid synchronization and ease of implementation, accompanied by the disadvantage of requiring large amounts of bandwidth. Significant bandwidth reductions can be obtained through the use of efficient data encoding-decoding techniques. Also, the downlink power requirements can be minimized through the use of an antipodal downlink signal. The processing repeater discussed in this paper can convert any number of randomly phased uplink signals to a single antipodal downlink signal which is amenable to phase coherent detection. The required downlink power is thereby minimized. Thus, the use of RADA techniques with efficient encodingdecoding and a processing repeater can provide a multiple access capability which efficiently uses bandwidth and downlink power.