OTFS-Based Massive MIMO with Fractional Delay and Doppler Shift: The URLLC Case

Abstract

This paper considers orthogonal time frequency space (OTFS)-based uplink multiuser multiple-input multipleoutput (MU-MIMO) systems in the ultra-reliable-and-low-latency communication (URLLC) space. The maximum-ratio-combining (MRC) scheme is first applied at the base station (BS) to combine all the received symbols and then the maximum likelihood (ML) decoding metric is employed to decode the intended symbols. To better characterize the system performance, we consider the ideal pulse shape functions at both users and BS side while the effect of fractional delay and Doppler shift (FDDS) is also taken into account. Based on this, we first derive the theoretical refined achievable coding rate under short-packet transmission for both joint and individual decoding at the BS. Subsequently, the corresponding asymptotic results under massive MIMO are presented. Capitalizing on these results, we draw a series of interesting insights: i) when the sampling resolution along the delay domain is not high enough, the achievable coding rate is more accurate than the channel capacity as the performance metric; ii) almost no diversity gain is obtained for the FDDS under the case considered in this paper; iii) the achievable coding rate is agnostic to the users' speed.

Rectangular Pulse-Shaped OTFS with Fractional Delay and Doppler Shift for MU-MIMO Systems

“…The users' speed is set as v u = 300km/h. with rectangular pulse-shaped waveforms and the result in [8] with ideal bi-orthogonal pulse-shaped functions is provided, which is used to show the severe effect of the former on the system performance.…”

“…However, as shown in [6], when the practical case of the fractional Doppler shift and integer delay is considered, the output signal is further contaminated by the inter-Doppler interference. Moreover, from [8], we know that when both the fractional delay and Doppler shift are taken into consideration, the output signal is contaminated by both the inter-delay and inter-Doppler interference. This indicates that the fractional delay will introduce further inter-delay interference whilst the fractional Doppler shift will bring inter-Doppler interference.…”

Profuse Channel Estimation and Signal Detection Techniques for Orthogonal Time Frequency Space in 6G Epoch: A Survey

“…In the context of URLLC, which is a crucial component of 5GB wireless networks, the exploration of OTFS modulation has gained significance. URLLC is designed to offer communication services characterized by high reliability and minimal latency, catering to applications like industrial automation, remote surgery, and intelligent transportation systems in the upcoming 6G era [123]- [125]. OTFS, due to its inherent resilience to delay and Doppler effects, presents itself as a potential solution for scenarios involving multipath propagation and high mobility.…”