# Directional Paging for 5G Communications Based on Partitioned User ID
## 1 Introduction  
Emerging 5G communications is directly attributable to the increasing bandwidth appetite of the wireless industry, majorly driven by the prevalent use of smart devices, advances in realistic Ultra High Definition (UHD) services, the unabated rise of social media and the need for network solutions for connected living, encompassing: smart cities, healthcare, manufacturing, energy, agriculture, transport, tracking and surveillance. While escalating demands for higher data rates and the popularity of the Internet of Things (IoT) are spawning apparent requirements for high network capacity, at the same time, energy-efficient design is gaining momentum as the fundamental requirement of future wireless networks. However, the emerging millimeter wave (mmWave)-driven complex spectrum techniques raise new challenges for the energy-efficient design aspirations. The spectral efficiency of microwave links, responsible for all current wireless communications, is approaching its fundamental limit [1], resulting in the progressively growing research interest towards the mmWave radio spectrum for 5G wireless communications. Large chunks of the radio spectrum at mmWave frequencies promise to bridge the gap between the limited \"sub-GHz\" bandwidth and the desire for high data services and massive connectivity [2]. Although very attractive, the integration of the mmWave spectrum in wireless scenarios is complex, especially in view of high path and propagation losses at higher frequencies. Providentially, small mm wavelengths facilitate embedded antenna array architectures in portable devices. The practical compositions of antenna arrays are capable of focusing electromagnetic energy in desired directions (beams). Beams providea viable solution to path loss impediments at higher frequencies [3]. Thus, beam-based directional communication is an essential proposition for mmWave-based 5G communications [1; 4]. The Third Generation Partnership Project (3 GPP) has already started work on efficient alignment of New Radio access technology (NR) designed to operate in the high frequency spectrum (up to 100 GHz) [5]. Establishing a wireless network using directional beam-based communication is relatively new and different from current omnidirectional wireless communication, as depicted in Figure 1. Directivity changes the way the air interface is processed today, thereby challenging legacy mechanisms designed and optimized for omnidirectional communication. The broadcast transmission of paging messages to User Equipment (UE) in Discontinuous Reception (DRX) mode is one such mechanism that requires redesigning in directional 5G communication. In the LTE/LTE-A wireless system, the DRX mechanism is specified, which reduces the UE's energy expenditure by configuring sleep periods. During the sleep period, most of the UE's circuitry is turned off to save battery power [6]. With rising computational expenses at the UE, due to higher order modulation and coding, beam searching overheads, massive MIMO technologies, raised quality expectations and increasing social/multimedia trends, it would be difficult to ignore DRX for energy conservation at the UE in 5G networks [7]. Recently, 3 GPP also acknowledged supporting the same in NR [8]. Paging is an important mechanism that helps with directing an incoming call to a UE when it is an Idle mode DRX (IDRX) to conserve energy. Network broadcasts the paging messages in the cells to convey an intimation about the incoming call to the UE in IDRX mode [9]. Since the spatial coverage of each Transmission (TX) beam is limited, the paging message broadcast becomes complicated in directional 5G communications. To cover the area of an entire cell, the paging message needs to be transmitted over all TX beams, as shown in Figure 1. However, simultaneous transmission over all the beams is nonviable due to limited number of antenna panels at the gNB (5G base station is known as next generation NodeB (gNB)) [8].