Chapter 16
Approximate Log-MAP SDM-OFDM Multi-stream Detection
16.1 OHRSA-Aided SDM Detection1
As was pointed out in [265], the ‘brute-force’ ML detection method does not provide a feasible solution to the generic SDM detection problem as a result of its excessive computational complexity. Nevertheless, since typical wireless communication systems operate at moderate-to-high SNRs, a Reduced Search Algorithm (RSA) may be employed, which is capable of approaching the ML solution at a complexity considerably lower than that imposed by the ML detector of [265]. The most potent among the RSAmethods found in the literature is constituted by the Sphere Decoder (SD) [333]. The SD was first proposed for employment in the context of space–time processing in [334], where it is utilized for computing the ML estimates of the modulated symbols transmitted simultaneously from multiple transmit antennas. The complex version of the SD, which is capable of approaching the channel capacity, was proposed by Hochwald and ten Brink in [335]. The subject was further investigated by Damen et al. in [336]. Subsequently, an improved version of the Complex Sphere Decoder (CSD) was advocated by Pham et al. in [337]. The issue of achieving near-capacity performance while reducing the associated complexity was revisited by Wang and Giannakis in [343, 629]. Further results on reduced-complexity CSD were published by Zhao and Giannakis in [342]. Finally, CSD-aided detection was considered by Tellambura et al. ...
