Decorrelation receivers for unresolved multipath Ricean fading channels

This paper considers specular coherent and non-coherent optimal, as well as sub-optimal detection structures for unresolved multipath Ricean fading channels with known delays. Specular coherent receiver structures require carrier phase estimation of the Ricean specular component. Non-coherent structures, on the other hand, do not make use of the specular coherent carrier phase. It is shown that both detection techniques include a multipath decorrelation stage before diversity combining, generalizing the Rake receiver. It is also shown that for high SNR, the specular coherent structure converges to the non-coherent structure. A sub-optimal technique based on a quadratic decorrelation receiver (QDR) that is easier to implement than the optimal non-coherent structure is also presented. Based on single pulse performance analysis, this paper shows that the decorrelation stage is essential in eliminating error floors. The results demonstrate that diversity gains over unresolved multipath fading channels can be obtained if multipath decorrelation is performed before diversity combining. This work also shows that while specular coherent detection performs in general better than non-coherent, in many cases the advantages for high SNR are very small.