Hybrid NOMA User Grouping for Short Packet Communications in IoT Network with Different Types of Devices

Abstract

Short packet communications are widely used for sixth generation (6G) mission-critical applications, which also bring challenges such as the transmission error caused by uncertainty noise and channel fading. In this context, age of in-formation (AoI) and throughput are two important performance metrics to evaluate information freshness and transmission capacity influenced by the short packet model, which are supposed to be considered for time-sensitive devices and throughput-sensitive devices, respectively. Our work aims to optimize the system per-formance of a NOMA-enabled IoT uplink network with different types of devices in the finite blocklength regime. Traditionally, NOMA user grouping mainly takes the channel state information of each user's communication link into consideration. However, from our observations, we have that different device types subject to different performance requirements will also affect the NOMA user grouping. Therefore, to simultaneously improve the AoI and throughput performance of different types of devices, we propose both Mixed Block Strategy (MBS) and Uniform Block Strategy (UBS) for NOMA user grouping in our investigated short packet communication scenario, where MBS makes one resource block (RB) shared by two different types of devices while UBS requires the RB shared by the same type of devices. Then, we formulate the joint optimization problem in terms of NOMA user grouping and transmit power under MBS and UBS, respectively. Finally, numerical results demonstrate that MBS-based NOMA transmission performs much better than UBS-based NOMA transmission.