# Adaptive Handover Decision Using Fuzzy Logic for 5G Ultra-Dense Networks
###### Abstract  
With the explosive increase in traffic volume in fifth-generation (5G) mobile wireless networks, an ultra-dense network (UDN) architecture, composed of highly concentrated millimeter-wave base stations within the fourth-generation (4G) system, has been developed. User equipment (UE) may encounter more frequent handover opportunities when moving in a UDN. Conventional handover schemes are too simple to adapt to the diverse handover scenarios encountered in 5G UDNs because they consider only UE signal strength. Unnecessary handovers aggravate the ping-pong effect and degrade the quality of service of cellular networks. Fuzzy logic (FL) is considered the best technique to unravel the handover problem in a high-density scenario of small cells for 4G/5G networks. In this paper, we propose an FL-based handover scheme to dynamically adjust the values of two handover parameters, namely handover margin (HOM) and time to trigger (TTT), with respect to each UE. The proposed scheme, abbreviated as FLDHDT, has dynamic adjustment of TTT in addition to HOM by using the signal to interference plus noise ratio and horizontal moving speed of the UE as inputs to the FL controller. To demonstrate the effectiveness and superiority of FLDHDT, we perform simulations using the well-known ns-3 simulator. The performance measures include the number of handovers, overall system throughput, and ping-pong ratio. The simulation results demonstrate that FLDHDT improves the handover performance of 5G UDNs in terms of the number of handovers, ping-pong ratio, and overall system throughput compared to a conventional handover scheme, namely Event A3, and an FL-based handover scheme with dynamic adjustment of only HOM. U 2022  
cellular networks, handover occurs when a device moves from one cell to another cell. On the other hand, joint beamforming design and optimization, security, and energy efficiency of mmWave and MIMO are continuously investigated for satellite communications [3; 4; 5]. With the aforementioned explosive growth in traffic volume, cellular network fragmentation and densification have emerged as the most effective technologies for increasing network capacity and improving user experience. In recent years, ultra-dense networks (UDNs) have been developed as a crucial solution to support capacity densities of up to 10 Mbps/m\({}^{2}\) in 5G networks. However, the propagation distance of millimeter radio waves is up to 300 m. Therefore, smaller BSs must inevitably be set up at intervals of a few hundred meters to extend the service coverage, resulting in a UDN-like architecture. In terms of cell coverage, BSs are classified as macro-, micro-, femto-, and picocells depending on their cell radii. Among them, micro-, femto-, and picocells are considered small cells. Several definitions of UDNs have been proposed in terms of cell quantity. In [6; 7], a UDN is defined as a cellular network with a BS density that may be equal to or greater than the user density, which is suitable for describing a scenario in which user traffic increases but the number of users does not. Alternatively, a UDN is defined as a cellular network that offers coverage of a few meters between any two BSs [8]. In addition, a UDN is a cellular network in which the number of BSs increases linearly as the demand for network capacity increases [9]. As depicted in Figure 1, a 5G UDN is typically a heterogeneous network composed of dense mmWave BSs and traditional 4G BSs. Although 5G UDNs can significantly improve network capacity, they are fraught with multiple problems. For instance, inter-cell interference is more severe, optimal utilization of radio resources is more complex, and load distribution among BSs is more unbalanced. Specifically, the UE moving within a UDN are likely to encounter more frequent handover opportunities that lead to handover-related problems, such as premature/late handover decisions and the ping-pong effect. Handover execution at an inappropriate time may interrupt data transmission links.