On signal design and detection in a multi-user channel

Severe congestion of the communications spectrum illustrates the need to seek a communication technique that offers the potential to utilize the spectrum efficiently. Communication efficiency and multiple access capability are the two factors influencing the design of signalling systems. In this paper, a technique is proposed to address this problem. A unique continuous baseband waveform is designed for each of the many users. All users are allowed to access the channel at the same time. A waveform estimator followed by a correlator has been postulated as the detection processor. Based on such a processor, the baseband waveforms for individual users are found by maximizing the correlator´s output signal-to-noise ratio, subject to the constraint of a finite bandwidth. The resulting waveforms are linear combinations of sinusoids or of prolate spheroidal functions, depending on whether the r.m.s. or the Slepian [1] definition of bandwidth is used. The use of unique continuous baseband waveforms for the individual users avoids the use of rectangular code sequences which spreads the spectrum in conventional code division multiple-access systems.