Abstract
Orthogonal time-frequency space (OTFS) scheme, which transforms a time and frequency selective channel into an almost non-selective channel in the delay-Doppler domain, establishes reliable wireless communication for high-speed moving devices. This work designs and analyzes low-complexity zero-forcing (LZ) and minimum mean square error (LM) receivers for multiple-input multiple-output (MIMO)-OTFS systems with perfect and imperfect receive channel state information (CSI). The proposed receivers provide exactly the same solution as that of their conventional counterparts, and reduce the complexity by exploiting the doubly-circulant nature of the MIMO-OTFS channel matrix, the block-wise inverse, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Schur</i> complement. We also derive, by exploiting the Taylor expansion and results from random matrix theory, a tight approximation of the post-processing signal-to-noise-plus-interference-ratio (SINR) expressions in closed-form for both LZ and LM receivers. We show that the derived SINR expressions, when averaged over multiple channel realizations, accurately characterize their respective bit error rate (BER) with both perfect and imperfect receive CSI. We numerically show the lower BER and lower complexity of the proposed designs over state-of-the-art exiting solutions.
Highlights
Future wireless communication systems are expected to support mobile services in high-speed trains and even in aircrafts [1], [2]
We show that the derived SINR expressions, which can be evaluated with a computational cost of O(M N ) + O(M N log2M N ), accurately characterize bit error rate (BER) of the proposed designs for both perfect and imperfect receive channel state information (CSI)
We propose a low complexity method to calculate the SINR of the proposed LM and low-complexity ZF (LZ) receivers with imperfect CSI using Algorithm 1
Summary
Future wireless communication systems are expected to support mobile services in high-speed trains and even in aircrafts [1], [2]. With the aforementioned gaps in the existing literature, this work focuses on designing low-complexity receivers for MIMO-OTFS systems, and deriving their analytical BER expressions. Towards achieving these aims, the main contributions of this work can be summarized as follows. The challenge is to invert extremely large-dimensional matrices HH H and HH H + ρI in a computationally-efficient manner We tackle this challenge by proposing a novel algorithm which inverts them by exploiting the i) inherent doubly-circulant structure of MIMO-OTFS channel matrix H, ii) block-wise inverse property of block matrices; and iii) a recursive structure which iterates between matrix partitioning and backtracking phases. The notations IN , 0M×N and [m − n]M represent an N × N identity matrix, M × N zero matrix and modulo-M operation, respectively
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