Highly Efficient Customization of 5G NR Sidelink Device-to-Device Synchronization Relay Protocol for 60 GHz WPAN Communication Systems

This study proposes a customized enhancement to the mandatory device-to-device (D2D) synchronization relay protocol specified in the 5G New Radio (NR) sidelink for enabling reliable synchronization in 60 GHz wireless personal area network (WPAN) systems. Existing 60 GHz WPAN standards, such as IEEE 802.15.3c and IEEE 802.11ad, lack mandatory mechanisms for synchronizing frame relaying, making them highly vulnerable to line-of-sight (LoS) blockages. In contrast, the 5G NR sidelink defined as a D2D communication framework over the 5G air-interface mandates support for the relay transmission of synchronization signals, driving a new paradigm of 5G NR sidelink-based 60 GHz WPANs to enable blockage-robust 60 GHz WPAN systems. However, the behavior and suitability of the current 5G NR sidelink synchronization relay protocol under 60 GHz WPAN conditions, characterized by dense device deployments and high susceptibility to LoS blockages, remain under-investigated. Through extensive simulations, this study identifies two critical limitations of the existing protocol in such environments: (i) suboptimal preconfigured slot-timing parameters frequently cause repeated collisions among relayed synchronization transmissions, and (ii) inappropriate preconfigured power thresholds lead to insufficient relay participation, especially in dense scenarios. To address these issues, this study proposes customizations, including a collision-avoidance slot-timing selection mechanism and an optimized relay-selection power threshold to ensure sufficient relay availability. Simulation results confirm that the proposed customization achieves near-perfect synchronization performance (98-99%), whereas the conventional protocol exhibits success rates below 40% in a typical indoor environment.