Techniques for simplifying some near-maximum-likelihood detectors

The paper studies some novel techniques for simplifying a near-maximum-likelihood detector that operates on a sequence of received samples, each of which carries two new data symbols. The new techniques are studied for a particular application in a land-mobile-radio system, which introduces flat fading into the transmitted QPSK data signals. The receiver employs an arrangement of combined detection and estimation. The arrangement enables two QPSK signals to be transmitted simultaneously over any one channel, leading to a more efficient use of bandwidth. The paper shows how substantial simplifications may be introduced into the detection process without, however, significantly changing its resultant operation. The new techniques are of quite general application to many near-maximum-likelihood detectors, in applications over flat fading or frequency-selective fading channels, or over time invariant channels that introduce intersymbol interference.<>