Estimation of Timing Offsets and Phase Shifts Between Packet Replicas in MARSALA Random Access

TL;DR

This paper presents a method to estimate and correct timing offsets and phase shifts between packet replicas in MARSALA, improving coherent combining and overall performance in satellite random access systems.

Contribution

It introduces a novel approach for estimating synchronization errors in MARSALA, enhancing its robustness under realistic channel conditions.

Findings

The proposed estimation method effectively reduces synchronization errors.

Correcting timing and phase shifts improves packet decoding success.

MARSALA outperforms CRDSA in simulated realistic scenarios.

Abstract

Multi-replicA decoding using corRelation baSed LocALisAtion (MARSALA) is a recent random access technique designed for satellite return links. It follows the multiple transmission and interference cancellation scheme of Contention Resolution Diversity Slotted Aloha (CRDSA). In addition, at the receiver side, MARSALA uses autocorrelation to localise replicas of a same packet so as to coherently combine them. Previous work has shown good performance of MARSALA with an assumption of ideal channel state information and perfectly coherent combining of the different replicas of a given packet. However, in a real system, synchronisation errors such as timing offsets and phase shifts between the replicas on separate timeslots will result in less constructive combining of the received signals. This paper describes a method to estimate and compensate the timing and phase differences between the replicas, prior to their combination. Then, the impact of signal misalignment in terms of residual timing offsets and phase shifts, is modeled and evaluated analytically. Finally, the performance of MARSALA in realistic channel conditions is assessed through simulations, and compared to CRDSA in various scenarios.