Delay and Utilization Analysis of Roadside 5G NR IAB Deployments With Half-Duplex Constraints

The standardized 3GPP integrated access and backhaul (IAB) technology is expected to provide a cost-efficient densification of 5G New Radio access networks. Relying on multi-hop communications, one of the critical metrics in such a system is latency. In this paper, our objective is to characterize the latency performance of the roadside deployment of an IAB system operating in the millimeter wave band (mmWave). To this end, we first utilize queuing theory tools to capture the dynamics of the buffering process at intermediate nodes with bursty arrival and service processes in the uplink and downlink directions. We then apply stochastic geometry to parameterize the model with radio part parameters. We address both user- and operator-related metrics, including packet latency and resource utilization coefficient. Our numerical results show that in roadside IAB deployment, backhaul is the main bottleneck, as the number of IAB nodes that can be supported by a donor is mainly affected by the number of users and traffic they generate, even for large bandwidths supported by 5G mmWave NR systems. The mean latency in the system scales exponentially as a function of the number of hops supported by the donor, implying that congestion in such a system is partial, affecting only the last few nodes in the chain. We demonstrate that an efficient way to adapt deployment to road traffic conditions is to fix the minimal modulation and coding scheme at the backhaul links by appropriately choosing the inter-IAB node distance. The proposed model provides a ready-to-use tool for estimating the optimal distance between IAB nodes for a given road, system traffic conditions, and number of IAB nodes associated with a single IAB donor. © 2020 IEEE.