Open-Loop Communications for Up-Link URLLC Under Clustered User Distribution

Abstract

To achieve ultra-low latency for ultra-reliable and low latency communications (URLLC) in fifth-generation (5G) systems, open-loop communications (OLC), which removes the time-consuming feedback procedure, has been proposed as a promising technique, especially for uplink transmission (UL). The performance of the OLC has been commonly analysed under a uniform user distribution model. Since the users are commonly clustered around highly populated areas, a clustered or non-uniform user distribution model is more realistic. However, the performance analysis under a clustered user distribution model is not trivial. In this paper, we therefore aim to analyse the OLC network performance under a clustered user distribution. We also investigate how to achieve URLLC by jointly employing the OLC mode, short packet transmission, multi-cell association and diversity schemes such as selection combining (SC) and maximum ratio combining (MRC). We provide a tractable approach to analyse the UL reliability and its approximated closed form. The simulation results show that the derived closed form can provide a reasonable approximation for the UL reliability when the SC algorithm is employed. Moreover, for the case of MRC, the analytical results can provide a tight approximation on the uplink reliability when the number of the associated BSs is lower than 2, while serving as a corresponding upper bound when the number of the associated BSs is larger than 2.