Detection techniques for fading multipath channels with unresolved components

In this paper we consider noncoherent detection structures for multipath Ri cean/Rayleigh fading channels. The multipath components are assumed to be u nresolved, with known delays. These delays could have been estimated, for e xample, by using super-resolution techniques or sounding the channel,vith a wide-band pulse. We show that the Rayleigh channel optimum receiver (R OPT ) consists of an "orthogonalization'' (or decorrelation) stage and then it implements an optimum decision rule for a resolved multipath channel. Since the optimum decision rule over Ricean channels is in general too complex f or implementation, we propose several suboptimum structures such as the qua dratic decorrelation receiver (QDR) and the quadratic receiver (QR). The QD R scheme exploits the decorrelation performed on the input samples. The non linear term due to the Ricean specular term is replaced by a quadratic form that is more suitable for implementation Single-pulse performance of these schemes are studied for commonly used binary modulation formats such as FS K and DPSK. This paper shows that it is possible to have diversity-like gai ns over Ricean/Rayleigh multipath fading channels with unresolved component s even if the channel is not fully tracked. Furthermore, this paper demonst rates the importance of using generalizations of RAKE receivers designed to handle the unresolvability condition. For two-path mixed-mode Ricean/Rayle igh channels, it is shown that improved performance can be obtained by usin g receivers that know the strength of the Ricean specular term.