Joint MIMO Channel Tracking and Symbol Decoding

The objective of fourth generation (4G) wireless communication systems is to achieve broadband connectivity anytime, anywhere and between anything. It is anticipated that in the next two decades, this is likely to be achieved by employing multiple antennas at the base station (service provider) as well as at the end user devices. In this regard, the past decade has seen an explosion of interest in multi antenna systems, especially, multi-input multi-output (MIMO) communication systems. MIMO communication systems provide a promising approach to deliver higher data throughput without the need for increased power and bandwidth. Space-time coding adds time as another dimension to the diversity, in addition to the spatial diversity achieved by multiple antennas in MIMO system. Among different space-time coding schemes presented in the literature, orthogonal spacetime block codes (OSTBCs, Alamouti, 1998) are of particular interest since they achieve full diversity at a lower receiver complexity. Indeed, many practical systems and standards such as WiFi and WiMAX have already adopted OSTBC for MIMO communications. The primary interest of this Chapter is to delve into the receiver aspect of the MIMO system where continuous interest has been shown in developing blind-adaptive decoding algorithms. Blind decoding algorithms improve data throughput by enabling the system designer to replace training symbols with data. On the other hand, considering the fact that the wireless end user environment is becoming increasingly mobile, adaptive algorithms have the ability to improve the performance of a system regardless of whether it is a blind system or training based one. The difficulty faced by blind and adaptive algorithms is that they are generally computationally intense. Further, the possible use of higher frequency carriers and the appeal of broadband communication for a wide variety of applications as well as the emergence of newer technologies such as cooperative communications have been contributing to the growing interest in a general M N × MIMO system over the 2 1 × Alamouti’s scheme which was the subject of intense research in the past decade. Hence, any blind-adaptive algorithm should be computationally efficient before they can be implemented in practical systems. This Chapter presents blind decoding algorithms that are adaptive in nature as well as computationally efficient for any M N × MIMO system. In (Liu et al., 2002), Kalman filtering has been studied in application to channel tracking for MIMO communication systems. The method proposed in (Liu et al., 2002) is based on two assumptions. First, the underlying space-time coding scheme is based on Alamouti code O pe n A cc es s D at ab as e w w w .in te ch w eb .o rg