Chapter 8
Iterative Joint Channel Estimation and MUD for SDMA-OFDM Systems
8.1 Introduction1
Multiple-Input, Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing (OFDM) systems have recently attracted substantial research interest. On the one hand, the employment of multiple antennas offers an opportunity to exploit both transmitter and receiver diversity, thus significantly increasing the system’s transmission integrity [107]. On the other hand, as a further benefit, OFDM exhibits robustness against both frequency-selective fading as well as the Inter-Symbol Interference (ISI) imposed by multi-path propagation. Specifically, intensive research efforts have been invested both in Bell Labs Layered Space–Time architecture (BLAST) [105,108,452] and in Space-Division Multiple Access (SDMA) based MIMO OFDM [3].More specifically, in SDMA-OFDM 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 Multi-User Detection (MUD) [439] techniques are invoked for detecting the different users’ transmitted signals with the aid of their unique user-specific spatial signature constituted by their Frequency-Domain CHannel Transfer Functions (FD-CHTFs) or, equivalently, Channel Impulse Responses (CIRs). Since the same time– frequency resource is shared by simultaneous users, a higher bandwidth efficiency can be achieved by SDMA systems ...
