Delay Analysis of Multi-Link Devices Coexisting with Single-Link Devices in Wi-Fi 7

Multi-Link Operation (MLO) introduced in the IEEE 802.11be standard represents a significant advancement by facilitating high data rates and supporting latency-sensitive applications in Wi-Fi 7 via simultaneous utilization of multiple wireless interfaces. Nevertheless, newly-introduced multi-link devices (MLDs) will continue to coexist with a large number of legacy single- link devices (SLDs). In this paper, we propose a novel analytical model for multi-link Wi-Fi 7 networks with coexisting MLDs and SLDs, and study the end-to-end delay performance of MLDs under various traffic conditions. The analysis is verified by simulation results using the open-source simulator ns-3, which shows that the impact of SLDs on MLDs' delay depends on whether SLDs are saturated or unsaturated. Moreover, the analysis underscores the pivotal role of the link traffic allocation policy at the upper medium access control layer of MLDs for delay optimization, particularly when the multiple links are asymmetric due to distinct link conditions or different contention levels due to varying coexisting SLDs, which sheds important light for practical network design of multi-link Wi-Fi 7.