Lattice All-Pass Filter based Precoder Adaptation for MIMO Wireless Channels

Smart vehicles employ multiple-input multipleoutput (MIMO) communication links in conjunction with orthogonal frequency division multiplexing (OFDM) for enhanced data rates and reliability over mobile wireless channels. These systems use a large number of subcarriers, and feeding back the estimated precoder for even a subset of subcarriers from the receiver to the transmitter is prohibitive. Moreover, frequency domain approaches do not exploit the predominant line-of-sight component present in such channels to reduce feedback. In this work, we view the precoder in the time-domain as a matrix all-pass filter, and model the discrete-time precoder filter using a matrix-lattice structure that reduces the overall feedback while maintaining the desired frequency-phase delay profile. This provides an efficient precoder representation across the subcarriers using fewer coefficients, and is amenable to tracking the precoder coefficients over time with much lower feedback than past approaches, which is beneficial for mobile communication links. Compared to frequency domain approaches that depend on approximate discrete-time representation, the proposed method yields higher achievable rates with a much lower feedback burden. Through extensive simulations over mmW channel models, we confirm the effectiveness of our claims, and show that the proposed approach reduces the feedback burden by up to 70%. Index Terms—Precoder, Matrix Lattice Filter, 5G, MIMO, Mobile Communication