In LTE, the system information (SI) is periodically broadcast to UEs. To improve the utilization of wireless resources and the latency of SI acquisition, SI is categorized into minimum SI and other SI in the 5G NR network. Moreover, a new approach, on-demand SI delivery, is also specified in NR. This enables gNBs to transmit other SI only when the UEs request it. In this paper, the MSG1-based and MSG3- based on-demand SI delivery designs are discussed. Besides, the effects of the beam sweeping and the UE behavior, ‘‘Listen Before Request’’, are also considered. Therefore, up to 10 design options are introduced. The corresponding analytical models of signaling overhead, delay and UE power consumption are also proposed. On the basis of analysis and simulation results, the SI delivery policies for the cases with different arrival rates of SI demands and the number of the base station (BS) beams are also proposed.

Introduction

In recent years, the demand for wireless network applications, including Internet of Things (IoT), virtual reality (VR), augmented reality (AR), unmanned (aerial) vehicle, etc., has exponentially increased. The 5G wireless network targets to satisfy the various requirements, such as low latency, high data rate, high reliability and the enormous number of connections [1]. Third Generation Partnership Project (3GPP) started the standardization work for 5G systems in 2016 and the development of 5G New Radio (NR) in 3GPP Release 15 is provided in [2]. It is obvious that the utilization of the spectrum above 24 GHz, also known as millimeter-wave (mmWave) bands, is inevitable because of the lack of frequency resources. Besides, to enhance the transmission range and eliminate the interference, beamforming is applied in NR systems. This can compensate for the high propagation loss of mmWave links as well [3]. However, the directionality of beamformed mmWave links unfits most existing Medium Access Control (MAC) layer procedures, such as system information (SI) acquisition [4]–[۶]. For example, before a UE in idle or inactive mode transfers to connected mode, it needs the SI to access the network. If the communication links are directional, then the difficulty to acquire the SI is significantly increased.