Analysis and Design of Tomlinson-Harashima Precoding for Multiuser MIMO Systems

Abstract

The multiuser multiple-input-multiple-output (MIMO) downlink has attracted great research interests because of its potential of increasing the system capacity(Caire & Shamai, 2003; Vishwanath et al., 2003; Viswanath & Tse, 2003; Weingarten et al., 2006). Many transmitter precoding schemes have been reported in order to mitigate the cochannel interference (CCI) as well as exploiting the spatial multiplexing of the multiuser MIMO downlink. Tomlinson-Harashima precoding (THP) has become a promising scheme since the successive interference pre-cancelation structure makes THP outperform linear precoding schemes (Choi & Murch, 2004; Zhang et al., 2005) with only a small increase in complexity. Many THP schemes based on different criteria have been reported in the literature(Doostnejad et al., 2005; Joham et al., 2004; Mezghani et al., 2006; Schubert & Shi, 2005; Stankovic & Haardt, 2005; Windpassinger et al., 2004), in which one is the zero-forcing (ZF) criterion and the other is the minimum mean square error (MMSE) criterion. This chapter will consider the above two criteria based THP schemes’ analysis and design, respectively. For the ZF-THP scheme, initial research mainly focuses on the scenarios that each receiver is equipped with a single antenna (Windpassinger et al., 2004), where there exists only the transmit diversity, but without any receive diversity. Presently, the receive diversity due to multiple antennas at each receiver is taken into account (Stankovic & Haardt, 2005; Wang et al., 2006).In these literatures, it is commonly assumed that the total number of receive antennas is less than or equal to that of transmit antennas. Under this assumption, firstly the layers are divided into groups which correspond to different users, and then the dominant eigenmode transmission is performed for each group. Hereby, this kind of schemes is regarded as per-user processing. Actually, it is more common in the cellular multiuser downlink systems that the number of users is not less than that of transmit antennas at the base station (BS), which is investigated as the generalized case with THP in this chapter. In order to avoid complicated user selection and concentrate on the essential of transceiver filters design, our consideration is limited into a unique case that the number of users equals the number of transmit antennas, denoted as M. Besides, it is assumed that the channels of these M users have the same large-scale power attenuation.1 In this case a so-called per-layer processing can be applied by the regulation that each user be providedwith only one