Comparison of Multi-Connectivity Schemes on Different Layers for Reliable Low Latency Communication

Wireless communication systems which provide low latency with high reliability are required for emerging industrial applications such as closed-loop control systems or mobile robotics. Multi-Connectivity (MC), i.e., using multiple communication paths simultaneously, can be a measure to enhance latency and reliability performance of wireless communication systems. MC schemes can be applied on different layers of the communication stack. While Physical (PHY) Layer MC schemes combine the paths at signal or symbol level, in higher layer schemes, i.e., MC schemes on MAC Layer or above, the paths are combined at packet level. Higher layer schemes provide more degrees of freedom for dynamic scheme adaptation, while PHY MC schemes have more information available. MC schemes on different layers need to be compared to evaluate their suitability to enhance latency and reliability performance in different scenarios. In this work system level simulations are performed with the network simulator ns-3 to compare PHY Layer MC schemes, i.e., selection combining (SC), maximum ratio combining (MRC) and joint decoding (JD), with higher layer MC schemes, i.e., MP-UDP with packet duplication (PD). Our results suggest that the gain of PHY Layer MC schemes increases with decreasing SINR. The higher layer MC schemes provide diversity not only on PHY but also on MAC and higher layers and could thus decrease access and queuing latency. The gain of MP-UDP increases with increasing network load. The insights obtained in this work can be used to develop dynamic MC schedulers that activate or deactivate certain MC schemes or switch between MC schemes on different layers based on the scenario.