Performance Evaluation of MARSALA with Synchronisation Errors in Satellite Communications

Multi-replicA decoding using correlation baSed LocAlisAtion (MARSALA) is a recent random access method for satellite communications. It follows the multiple transmission and interference cancellation scheme of Contention Resolution Diversity Slotted Aloha (CRDSA). Besides, at the receiver side, MARSALA uses autocorrelation to localise replicas of a same packet so as to combine them. This signal combination increases the decoding probability of the packet, especially in case of collisions. Previous work has shown good performance of MARSALA with an assumption of perfect signal combination. However, phase and timing parameters are unknown at the receiver and they are different for the replicas on separate time slots . In this paper, we describe a method to estimate and compensate the timing and phase differences between the replicas prior to signal combination. We also propose to enhance the signal combination by using the principle of Maximum Ratio Combining (MRC). Then, we evaluate the impact of synchronisation errors on MARSALA using our estimation method. We also assess the performance gain achieved with MRC. Finally we compare the performance of MARSALA and CRDSA in various scenarios.