A parallel systems approach to universal receivers

A universal approach to the design of communication systems for unknown and time-varying channels is introduced. The true channel is from a known set of channels called the channel class, but the transmitter and receiver do not know which of these channels is actually in effect. One of the goals of this research is to design a universal receiver that provides nearly optimal demodulation for every channel in the class of interest.A parallel implementation is proposed for a universal scheme that deals with such uncertainty. The resulting system consists of a finite number of receivers with the property that, for each channel in the channel class, at least one of the receivers provides nearly optimal performance. A selection mechanism is required for choosing the receiver output sequence that best matches the transmitted sequence, and this mechanism is provided by means of an appropriate coding scheme that utilizes any available side information.Sufficient conditions for the existence of such a universal receiver for a given channel class are established, procedures are developed for the receiver design, and examples are provided to show the applicability of the theory. It is demonstrated by example that even if the sufficient conditions do not hold, a universal receiver design may still be obtained via our approach by exploiting the specific characteristics of a given problem. An information-theoretic characterization is given for the discrete channel that is formed by the cascade of the channel in effect and the universal receiver.It is shown that a coding system that employs Reed-Solomon codes and bounded distance decoding provides a selection mechanism, in addition to correcting errors in the universal receiver output. For binary coding schemes, additional side information may be needed for the selection mechanism, and it is demonstrated that side information obtained from the transmission of test symbols does not provide sufficient reliability. For the Rician fading channel, a method for obtaining side information from the demodulators is developed, and the performance of the resulting universal receiver is shown to be better than that of the traditional noncoherent receiver.U of I OnlyETDs are only available to UIUC Users without author permissio