Time Domain Precoding for MIMO-OFDM Systems

Broadband multiple-input multipleoutput (MIMO) communication systems using spatial multiplexing are facing multi-stream interference (MSI) from the transmit antennas and intersymbol interference (ISI) due to the time-dispersive nature of the channel. Appropriate detection requires the minimization of both sources of interference, usually at the receiver. Orthogonal frequency division multiplexing (OFDM) is a well-known technique implemented in IEEE 802.11a chipsets that can eliminate ISI, and therefore MSI remains the only source of interference in a MIMO-OFDM system. Removal can be realized at the transmitter utilizing channel state information (CSI) in the frequency domain [1]. In some practical cases no signal processing at the sub-carrier (frequency domain) level is possible and MSI removal (equalization) has to be done in time domain. In this paper we consider a MIMO-OFDM system built as a set of signal generating off-the-shelf IEEE 802.11a chipsets connected to a spatial multiplexing convergence layer. We present a time domain based full rate precoding scheme for removing MSI in frequency selective channels under assumption of perfect CSI at the transmitter that is still benefiting from the OFDM ability to remove ISI. The proposed system uses low complexity receivers and can be applied to a multiple-antenna transmitter communicating with several single antenna receivers (downlink scenario).