Space-Time Detection In MIMO-OFDM Communication Systems: Algorithms And DSP Implementations

The increasing demand for higher data rates, better quality of service, higher network capacity and user coverage calls for innovative technologies to improve spectral efficiency and link reliability. To meet this end, several wirelesss communication advances have been achieved during the past decades. Among these breakthroughs, Multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) have attracted the most attention in both academic and industry field. Space-time signal processing in MIMO-OFDM systems is the main topic of this thesis.We first focus our discussion on signaling and detection over flat fading MIMO channels. A review of researches in spatial multiplexing and space-time coding (STC) is given in chapter 2. When the channel is not static over a space-time coding block, space-time block codes (STBCs) would suffer from an irreducible error floor due to the existence of inter element interference (IEI). To improve the robustness of STBCs against fast fading, we propose an improved algorithm termed ZF-PIC.Chapter 3 and 4 are devoted to space-time signal processing over frequency selective channels. After discussing multi-carrier communications and developing MIMO-OFDM system model, the criterions of designing space-frequency codes are introduced. Two schemes, SFBC-OFDM and STBC-OFDM, are taken as examples to demonstrate the distinction between space-time coding and space-frequency coding (SFC).In chapter 4, we propose a MIMO-OFDM architecture based on linear constellation precoding (LCP), which is termed as Full-Rate SFC. Both space-time signaling at the transmitter and detection at the receiver are treated in detail. In view of the large number of OFDM tones in communication systems, we further propose a simplified detection method for our scheme in order to reduce the computational complexity.Finally, the DSP based implementation of Full-Rate SFC detection algorithm is discussed in chapter 5, where we also show some principles on fixed-point programming using TI's TMS320C6416 DSP.