Enhancing Multi-Connected XR Device Performance With Soft Combining and Joint HARQ Processing in Cooperative Multicast

In this work, we investigate multi-connectivity for Extended Reality (XR) devices, which have stringent requirements in terms of delay, data rate and reliability. This approach employs one direct connection and one indirect connection via a 5th generation-Advanced (5G-A) tethering device. We investigate the Selection Combining Scheme (SCS) and Selection/Soft Combining Scheme (SSCS) between the tethering device and the XR device under point-to-multipoint (PTM) multicast transmission in downlink (DL) in a spatially consistent channel model. The SSCS is particularly effective in enhancing the XR device performance, achieving the maximum potential gain of either selection or soft combining, while limiting cooperative data exchange. This is done through various limited fraction soft bits relaying schemes, including modified ones from existing literature and newly proposed code block (CB) based indexing schemes. Additionally, we propose algorithms for joint processing of hybrid automatic repeat request (HARQ) feedback (FB) in 5G multicast sessions with cooperative users to enhance spectral efficiency by enabling the network to benefit from the cooperation of the users. Our link-level simulations demonstrate that multi-connectivity with joint HARQ enables XR devices to achieve the same spectral efficiency as with unicast but with a 0.8 dB and 4.5 dB lower average signal-to-noise ratio (SNR) with SCS and SSCS, respectively, in non-line-of-sight (NLOS) scenarios. In line-of-sight (LOS) scenarios, multi-connectivity yields a gain of 3 dB with SSCS, though no significant gain is observed with SCS.