In NDMA (network diversity multiple access), protocol-controlled retransmissions are used to create a virtual MIMO (multiple-input multiple-output) system, where collisions can be resolved via source separation. By using this retransmission diversity approach for collision resolution, NDMA is the family of random access protocols with the highest potential throughput. However, several issues remain open today in the modeling and design of this type of protocol, particularly in terms of dynamic stable performance and backlog delay. This paper attempts to partially fill this gap by proposing a Markov model for the study of the dynamic-stable performance of a symmetrical and non-blind NDMA protocol assisted by a multiple-antenna receiver. The model is useful in the study of stability aspects in terms of the backlog-user distribution and average backlog delay. It also allows for the investigation of the different states of the system and the transition probabilities between them. Unlike previous works, the proposed approach considers the imperfect estimation of the collision multiplicity, which is a crucial process to the performance of NDMA. The results suggest that NDMA improves not only the throughput performance over previous solutions, but also the average number of backlogged users, the average backlog delay and, in general, the stability of random access protocols. It is also shown that when multiuser detection conditions degrade, ALOHA-type backlog retransmission becomes relevant to the stable operation of NDMA. 1. Introduction 1.1. NDMA and Cross-Layer Design in Random Access The last two decades have witnessed the proliferation of advanced random-access protocols assisted by signal processing tools [1]. In these novel algorithms, spatial, code, or frequency resources are conveniently exploited in order to enable the simultaneous reception of more than one packet at the physical layer (PHY). Random-access protocols based on this innovative PHY layer have been termed multipacket reception (MPR) protocols [2]. In the design of MPR protocols, the conventional collision model (where collisions imply the loss of all the contending packets) is no longer useful [2]. A new approach that considers the co-design of medium access control (MAC) and PHY layers (MAC-PHY cross-layer design) is thus required [3, 4]. A breakthrough in the literature of MAC-PHY cross-layer design was the work in [5], which proposed a new approach to achieve diversity in random access by exploiting retransmissions in the time domain. The new protocol, coined network diversity
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