Stability and Delay of Network-Diversity Multiple Access with Backlog Retransmission Control

摘要

This paper proposes two strategies for retransmission control of backlog traffic in the family of algorithms known as Network Diversity Multiple Access (NDMA). This type of algorithm has been shown to achieve (in ideal conditions) the following aspects: 1) collision-free performance for contention-based traffic, 2) low latency values, and 3) reduced feedback complexity. These features match the machine-type traffic, real-time, and dense object connectivity requirements in 5G. This makes NDMA a candidate for contention traffic support in 5G systems. However, existing analysis ignores the effects of backlog traffic generated by the imperfect detection conditions that arise in settings with finite Signal-to-Noise Ratio (SNR). This paper aims to partially fill this gap, by providing analytic expressions for the performance of symmetrical training-based NDMA protocols with two different types of backlog traffic retransmission schemes. In the first strategy, all terminals involved in an unsuccessful resolution period retransmit immediately in the subsequent resolution periods or epoch slots. This procedure is repeated continuously (persistent retransmission) by inducing the same collision event under different channel outcomes until all the contending signals are correctly detected and received. In the second retransmission strategy, the terminals in backlog state retransmit at a randomly selected time-slot with a probability that that is assumed (for simplicity) to match the transmission rate of the system. In both strategies, expressions are here obtained of the maximum stable throughput and the average delay experienced by any packet to be correctly received by the destination. This allows us to determine the capabilities of NDMA for achieving low-latency, reduced feedback complexity, as well as highly stable and real-time throughout performance. The results shown here suggest that NDMA can achieve attractive low latency and high throughput figures mainly at high SNR values and moderate traffic loads.