Intercarrier interference canceling techniques for SISO- and MIMO-OFDM systems

Abstract

In this thesis, the rate-t/k $(t \leq k)$ intercarrier interference (ICI) canceling schemes for single-input single-output (SISO) and multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems in time-varying frequency selective channels are considered. For SISO-OFDM systems, two types of ICI canceling techniques are proposed; frequency-domain coding and time-domain windowing. Based on the observation that a SISO-OFDM system with the proposed schemes can be viewed as a collection of MIMO systems, the capacity lower bound of such an OFDM system is derived. Then, codes and windows maximizing the lower bound are designed numerically. In the simulation, the proposed techniques outperform the conventional frequency- and time-domain ICI cancellation schemes, and provide considerable ICI suppression over a wide range of the Doppler frequency. The simulation results suggest using the proposed rate-2/3 techniques because it can improve the performance while causing only a minor increase in the implementation complexity. In particular, for rate one (t = k) cases, only the frequency-domain coding can mitigate ICI to some degree while time-domain windowing does not at all. Therefore, it is concluded that frequency-domain coding is somewhat better than time-domain windowing. For MIMO-OFDM systems, two types of MIMO techniques are considered; space-frequency block codes (SFBC) obtaining a diversity and coding gain, and spatial multiplexing techniques increasing the capacity. To design a SFBC performing ICI cancellation as well as acquiring a diversity and coding gain, the bound of approximated pairwise error probability for MIMO-OFDM with a SFBC along with a receive code is derived for time-varying frequency-selective channels, and codes are designed to minimize the bound. The simulation results demonstrate that the proposed codes outperform the conventional schemes. In particular, an orthogonal SFBC (OSFBC) is proposed for practic...