Chapter 15
Multi-stream Detection for SDM-OFDM Systems
The principle of sphere decoding as a reduced-complexity near-ML SDMA MUD was first introduced in this volume in Chapter 9, where diverse SDs were studied comparatively. One of the important techniques considered was the OHRSA SDMA MUD. In this chapter no channel coding was employed – indeed, the sphere-decoding philosophy was originally conceived for hard-decision-aided MUDs, rather than soft-decision-assisted channel-coded systems. As a further enhanced SD, the centre-shifting philosophy was developed in Chapter 10 in the context of iterative detection-aided channel-coded SDMA systems. The SD of Chapter 10 was then further exploited throughout Part II of the book in diverse contexts, when a potentially complex detection task arose. For example, the SD was used for reducing the detection complexity of sphere-packing modulation-aided STBCs in Chapter 11 and for the complexity reduction of multiple-symbol differential detection in the cooperative wireless systems of Chapter 12.
By contrast, throughout Part III of the book, the application of SDs such as the OHRSA will be investigated in the context of SDM, rather than SDMA systems. The multi-stream detection task of SDM systems may be deemed to be more challenging than the SDMA MUD task, since in the case of SDM systems the antenna elements are likely to have a lower spatial separation than the geographically dispersed users of an SDMA system. Unless unique user/antenna-specific ...
