Multi-Dimensional Resource-Based Hybrid QoS Massive Grant-Free Random Access

Future wireless communications require higher reliability, lower latency, and greater connectivity. In this paper, we mainly investigate a multi-dimensional resource-based hybrid quality of service (QoS) massive grant-free random access (GFRA) in the massive MIMO system. First, inspired by the advanced access protocol [1], we develop an extended multi-dimensional resource-based hybrid QoS massive GFRA scheme to address the differentiated requirements of various services, which not only meets the stringent reliability and low latency demands of URLLC users, but also supports the massive concurrent connectivity of mMTC users. Then, based on the extended multi-dimensional resource access scheme, we analyze the access failure probability of URLLC users by comprehensively considering the pilot collision and decoding error in the finite blocklength regime. To achieve massive concurrent connectivity and reliable access for mMTC users, we further propose a multi-slot replica access scheme that leverages time diversity, and investigate the access failure probability of mMTC users by considering the pilot collision and outage probability across multiple slots. Furthermore, by integrating GFRA mechanism and multi-slot replica access scheme, we model the massive access of mMTC users as a Markov state transition process and analyze the access latency of mMTC users from a frame-level perspective. Finally, the effectiveness of the proposed scheme is demonstrated through simulations. The proposed scheme not only meets the differentiated requirements of URLLC and mMTC users, but also further reduces latency of mMTC users compared with repetition transmission.