Stability and Delay of NDMA-MPR Protocol in Rice-Correlated Channels with Co-Channel Interference

Abstract

This paper investigates backlog retransmission strategies for a class of random access protocols with retransmission diversity (i.e., network diversity multiple access or NDMA) combined with multiple-antenna-based multi-packet reception (MPR). This paper proposes NDMA-MPR as a candidate for 5G contention-based and ultra-low latency multiple access. This proposal is based on the following known features of NDMA-MPR: (1) near collision-free performance, (2) very low latency values, and (3) reduced feedback complexity (binary feedback). These features match the machine-type traffic, real-time, and dense object connectivity requirements in 5G. This work is an extension of previous works using a multiple antenna receiver with correlated Rice channels and co-channel interference modelled as a Rayleigh fading variable. Two backlog retransmission strategies are implemented: persistent and randomized. Boundaries and extended analysis of the system are here obtained for different network and channel conditions. Average delay is evaluated using the M/G/1 queue model with statistically independent vacations. The results suggest that NDMA-MPR can achieve very low values of latency that can guarantee real-or near-real-time performance for multiple access in 5G, even in scenarios with high correlation and moderate co-channel interference.Technologies 2019, 7, 22 2 of 16 presented in [6] where the authors use an adaptive source of diversity via retransmissions to achieve MPR. The algorithm was called NDMA or network diversity multiple access, and in ideal conditions it can achieve almost collision free performance, ultra low latency, and minimum feedback complexity. These features are very attractive for contention-based access in 5G. In NDMA, the MPR capabilities are adaptive and therefore, the algorithm can deal, in principle, with collisions of any size. NDMA is the perfect example of cross-layer algorithm: retransmissions induced by MAC (medium access control) layer create a source of physical (PHY)-layer diversity to resolve a collision.In NDMA, the Base Station (BS) uses signal-processing to estimate the size of a collision. This is used to calculate the number of retransmissions required to achieve MPR and recover the colliding signals (i.e., resolve the collision). Retransmissions are stored in memory and the BS uses MIMO (multiple-input multiple-output) tools to recover and decode the signals in conflict. Training-based versions of NDMA have been proposed in non-dispersive and dispersive channels in [6,7], respectively. Blind versions can be found in [8,9]. Stability analysis with perfect channel and reception conditions were presented in [10]. NDMA with MPR has been investigated in [11] using Markov chains improving data rates and delay. In our work in [12] an addition to NDMA-MPR based on Successive Interference Cancellation (SIC) was shown to surpass the capacity of previous protocols. Hybrid combination of NDMA with Automatic Repeat reQuest (ARQ) was presented in [13]. Feedback free NDMA was presented in [14], and a...