A Multiple Input-Multiple Output (MIMO) Adaptive Decision Feedback Equalizer (DFE) with Cancellation for Wideband Space-Time Communications

Recently it has been shown that by exploiting the fading properties of the wireless environment, a communication structure with multiple transmit/receive antennas can deliver enormous capacities [1]. Several architectures have been proposed to implement space-time systems for the narrowband flat fading wireless environment [2,3]. However, in order to support higher data rates, the concept of space-time communication architecture needs to be extended to frequency-selective wideband channels. Three different space-time structures have been studied for the multiple input-multiple output (MIMO) dispersive channel. The first architecture uses orthogonal frequency division multiplexing (OFDM) to mitigate the effect of the frequency-selective channel and then applies techniques that have been developed for the narrowband space-time system on each OFDM substream [4,5]. Similarly, the second architecture employs directsequence spread spectrum code division multiple access (DSSS-CDMA) instead of OFDM to combat the multipath channel [6]. The third approach, and the one that will be explored in this paper, uses equalization techniques to provide space-time communications over frequency-selective MIMO channels [7,8,9,10]. In this paper, we propose a new framework for the analysis of a modified MIMO minimum-mean-squarederror (MMSE) decision feedback equalizer (DFE). The modified MIMO DFE structure proposed here assumes that decisions for each data stream are made sequentially and available current decisions of detected data streams are used to compute the new estimate of a given data stream. This structure therefore performs an operation similar to interference cancellation and is an extension for the frequency-selective fading channel of the MMSE equivalent of the VBLAST algorithm [2]. This type of A Multiple Input-Multiple Output (MIMO) Adaptive Decision Feedback Equalizer (DFE) with Cancellation for Wideband Space-Time Communications