Iterative List Detection and Decoding for mMTC

TL;DR

This paper introduces an iterative list detection and decoding scheme for massive machine-type communications that jointly detects device activity and signals, improving performance with low complexity in grant-free systems.

Contribution

It proposes a novel list detection technique integrated with iterative decoding, enhancing detection accuracy and efficiency in mMTC scenarios.

Findings

Outperforms existing suboptimal detectors in simulations.

Achieves performance close to the oracle LMMSE detector.

Maintains low computational complexity.

Abstract

The main challenge of massive machine-type communications (mMTC) is the joint activity and signal detection of devices. The mMTC scenario with many devices transmitting data intermittently at low data rates and via very short packets enables its modelling as a sparse signal processing problem. In this work, we consider a grant-free system and propose a detection and decoding scheme that jointly detects activity and signals of devices. The proposed scheme consists of a list detection technique, an $l_0$-norm regularized activity-aware recursive least-squares algorithm, and an iterative detection and decoding (IDD) approach that exploits the device activity probability. In particular, the proposed list detection technique uses two candidate-list schemes to enhance the detection performance. We also incorporate the proposed list detection technique into an IDD scheme based on low-density parity-check codes. We derive uplink sum-rate expressions that take into account metadata collisions, interference and a variable activity probability for each user. A computational complexity analysis shows that the proposed list detector does not require a significant additional complexity over existing detectors, whereas a diversity analysis discusses its diversity order. Simulations show that the proposed scheme obtains a performance superior to existing suboptimal detectors and close to the oracle LMMSE detector.