Exploiting Device Heterogeneity in Grant-Free Random Access: A Data-Driven Approach

TL;DR

This paper introduces a stochastic gradient descent-based algorithm for optimizing slot allocation in grant-free random access networks with device heterogeneity and activity estimation errors, significantly improving throughput.

Contribution

It proposes a novel importance weighted stochastic gradient algorithm that accounts for activity estimation errors, enhancing resource allocation in heterogeneous GFRA systems.

Findings

Up to 66% throughput gain with asymmetric bit flipping errors.

Algorithm converges to a stationary point under activity estimation errors.

Performance varies with error distribution type.

Abstract

Grant-free random access (GFRA) is now a popular protocol for large-scale wireless multiple access systems in order to reduce control signaling. Resource allocation in GFRA can be viewed as a form of frame slotted ALOHA, where a ubiquitous design assumption is device homogeneity. In particular, the probability that a device seeks to transmit data is common to all devices. Recently, there has been an interest in designing frame slotted ALOHA algorithms for networks with heterogeneous activity probabilities. These works have established that the throughput can be significantly improved over the standard uniform allocation. However, the algorithms for optimizing the probability a device accesses each slot require perfect knowledge of the active devices within each frame. In practice, this assumption is limiting as device identification algorithms in GFRA rarely provide activity estimates with zero errors. In this paper, we develop a new algorithm based on stochastic gradient descent for optimizing slot allocation probabilities in the presence of activity estimation errors. Our algorithm exploits importance weighted bias mitigation for stochastic gradient estimates, which is shown to provably converge to a stationary point of the throughput optimization problem. In moderate size systems, our simulations show that the performance of our algorithm depends on the type of error distribution. We study symmetric bit flipping, asymmetric bit flipping and errors resulting from a generalized approximate message passing (GAMP) algorithm. In these scenarios, we observe gains up to 40\%, 66\%, and 19\%, respectively.