Chapter 4
Coded Modulation Assisted Multi-user SDMA-OFDM Using Frequency-Domain Spreading
4.1 Introduction
In recent years Orthogonal Frequency-Division Multiplexing (OFDM) [1, 3, 4, 24] has emerged as a successful air-interface technology for both broadcast and Wireless Local Area Network (WLAN) applications, while Wideband Code-Division Multiple Access (WCDMA) has emerged as the winning candidate for 3G mobile systems. Our research therefore includes exploration of the performance versus complexity trade-offs of a generic class of Multi-Carrier Code-Division Multiple Access (MCCDMA) [38] systems, which are capable of supporting the interworking of existing as well as future broadcast and personal communication systems.
Space-Division Multiple Access (SDMA) based OFDM [3, 193, 438] communication invoking Multi-User Detection (MUD) [439] techniques has recently attracted intensive research interests. In SDMA Multiple-Input, Multiple-Output (MIMO) systems the transmitted signals of L simultaneous uplink mobile users – each equipped with a single transmitter antenna – are received by the P different receiver antennas of the Base Station (BS). At the BS the individual users’ signals are separated with the aid of their unique, user-specific spatial signature constituted by their channel transfer functions or, equivalently, Channel Impulse Responses (CIRs). A variety of MUD schemes, such as the Least- Squares (LS) [3, 439, 440] and Minimum Mean Square Error (MMSE) [3, 193, 197, 439, ...
