Bayesian Learning Aided Simultaneous Row and Group Sparse Channel Estimation in Orthogonal Time Frequency Space Modulated MIMO Systems

Abstract

A sparse channel state information (CSI) estimation model is proposed for reducing the pilot overhead of orthogonal time frequency space (OTFS) modulation aided multipleinput multiple-output (MIMO) systems. Explicitly, the pilots are directly transmitted over the time-frequency (TF)-domain grid for estimating the delay-Doppler (DD)-domain CSI that leads to a reduction of the pilot overhead, training duration and pre-processing complexity. Furthermore, it completely avoids placing multiple DD-domain guard intervals corresponding to each transmit antenna within the same OTFS frame, while keeping the training duration flexible, hence increasing the bandwidth efficiency. A unique benefit of the proposed CSI estimation model is that it can efficiently handle fractional Dopplers also. The resultant DD-domain CSI becomes simultaneously row and group (RG)-sparse. To exploit this compelling property, an orthogonal matching pursuit (OMP)-based RG-OMP technique is developed, conveniently complemented by an enhanced Bayesian learning (BL)-based RG-BL framework, both of which substantially outperform the state-of-the-art methods. Furthermore, low-complexity linear detectors are designed for the ensuing data detection phase, which directly employ the estimated DD-domain sparse CSI, without assuming any further knowledge concerning the number of dominant multipath components. Finally, simulation results are provided to demonstrate performance improvement of the proposed BL-based schemes over the OMP and the state-of-the-art schemes.

Delay-Doppler and Angular Domain 4D-Sparse CSI Estimation in OTFS Aided MIMO Systems

“…The existing treatises, which address channel estimation in OTFS systems, can be broadly classified into two categories: 1) Approaches that exploit the 2-dimensional (2D)-circular convolution based relationship [1], [9], [11] between the transmit symbols and the channel in the DD-domain; 2) Alternative schemes that benefit from the limited number of dominant multipath components, i.e., the DD-domain sparsity [10], [12], [13]. The initial solutions of [1], [11] developed impulse-based CSI estimation techniques for SISO OTFS systems, which were then extended to MIMO OTFS in [14].…”

“…Furthermore, they need both a high pilot signal-to-noise ratio (SNR) and high pilot overheads for estimating the CSI accurately. By contrast, only a few recent authors [10], [12], [13] have formulated the CSI estimation problem as a compressive sensing (CS) problem, which also exploit the DD-domain sparsity for attaining an enhanced CSI accuracy at low pilot overheads. Furthermore, as described in [10], [15], [16], the MIMO wireless channel also exhibits sparsity in the angular domain due to the presence of only a few non-negligible angles of arrival (AoAs) and departure (AoDs).…”

“…By contrast, only a few recent authors [10], [12], [13] have formulated the CSI estimation problem as a compressive sensing (CS) problem, which also exploit the DD-domain sparsity for attaining an enhanced CSI accuracy at low pilot overheads. Furthermore, as described in [10], [15], [16], the MIMO wireless channel also exhibits sparsity in the angular domain due to the presence of only a few non-negligible angles of arrival (AoAs) and departure (AoDs). However, to the best of our knowledge, the existing OTFS treatises have not exploited this 4D-sparsity arising in the delay, Doppler and angular (DDA)-domain.…”

“…where blkmtx(•) formulates a block-matrix having H DD,r,t in the rth row and tth column block. Now, upon substituting H DD,r,t from ( 8) into (10), we have…”

“…wireless channels, orthogonal time frequency space (OTFS) signalling [1], [5]- [8], has gained popularity over conventional multicarrier modulation techniques. However, accurate knowledge of the DD-domain channel state information (CSI) is the key to achieving a superior performance in OTFS systems [9], [10]. Therefore, novel CSI estimation techniques specifically tailored for achieving a high CSI accuracy at a low pilot overhead are required for reaping the advantages of OTFS.…”