Miso Precoding for Temporal and Spatial Focusing

Time reversal precoding accomplishes matched-filtering of the channel in wireless communication systems by precoding before every transmit antenna with the time reversed complex conjugate of the wireless channel impulse response. While time reversal maximizes the received signal energy at a single time instant (as with matched filtering) it does not eliminate intersymbol interference. This is equivalent to saying that the combined precoder/channel response has significant temporal sidelobes and thus, not sufficiently temporally focused. We propose a method of multiple-inputsingle-output (MISO) precoding for lowering sidelobe levels to improve temporal focusing. Through simulations, we analyze and show improved spatial focusing properties of the developed method in correlated and uncorrelated frequency selective channels. Although equalizer design is absent in this paper, we include equalizer length into the optimization, using a methodology similar to channel shortening, such that flexible communication system solutions easily follow.