## 1 Introduction  
The rapid growth in mobile user equipment (UE) and advanced applications has led to a significant rise in the demand for data traffic [1]. As a result, the telecommunication industry, the 3 rd generation partnership project (3 GPP), and the international telecommunication union (ITU) require assistance in upgrading their infrastructure to meet these demands. Modern tools such as the internet of things (IoT), device-to-device (D2D), vehicle-to-vehicle (V2V), and the COVID-19 pandemic have considerably increased the demand for content-of-interest services. Additionally, online services such as telemedicine, telemarketing, online conferences and meetings, and online shopping have necessitated the development of high-capacity, improved spectral efficiency (SE), and low-latency wireless communication systems (WCS) [2]. The 5G technology is regarded as the best solution to provide high coverage, higher data rates and capacity, extremely low latency, improved energy efficiency and SE, and support for a wide range of devices and services [3, 4, 5, 6, 7, 8]. To provide better coverage, higher throughput, and excellent connectivity for both indoor and outdoor users, the 5G network utilizes enabler solutions such as network densification or heterogeneous network (HetNet) [9; 10], millimeter wave (mm-Wave) [11; 12], and massive multiple-input-multiple-outputs (M-MIMO) [13]. In 5G and beyond-5G (B5G) networks, quality of service (QoS) and quality of experience (QoE) are the important factors for improving handover (HO) and mobility performance to provide seamless and uninterrupted service to users. QoS guarantees that a network satisfies the service requirements of its users, while QoE measures how well the user perceives the service. Factors such as bandwidth, network coverage, received signal strength (RSS), latency, jitter, packet loss, HO performance, and UE capabilities impact QoS and QoE in 5G/B5G HetNet. The consideration of these both in the optimization of HO and mobility management processes can empower network operators to provide a superior and satisfactory user experience [14; 15; 16; 17]. Since sub-6 GHz is no longer sufficient to accommodate the vast number of UEs and ensure the best QoS and QoE for IoT devices within a 5G system, a new frequency band, i.e., mm-Wave, needs to be utilized [11]. The mm-Wave operates at very high frequencies, ranging from 24 GHz to 84 GHz for 5G, and it may be increased up to 100 GHz in the future. Due to the wider bandwidth, mm-Wave can resolve the issue of capacity requirements in 5G. However, it significantly suffers from higher path loss and cannot penetrate walls or other obstacles due to its shorter wavelength. Increased frequencies can cause a severe issue, strengthening the HO problem [18]. Similarly, HetNet deploys different kinds and sizes of small cells such as micro, pico, and femtocells over the macro base station (MBS) to provide service to UEs. HetNet has the ability to enhance system capacity in terms of user density, improving the coverage area, and providing uninterrupted connectivity to users with higher data rates [9; 10]. Massive MIMO is also considered a potential technique for the NG-5G cellular networks since it can dramatically increase SE [19; 20]. Massive MIMO technology, in which the BS is equipped with a large number of transmitting and receiving antennas, can serve multiple users and entertain a maximum number of UEs simultaneously [13]. Seamless HO is one of the significant challenges in 5G ultra-dense HetNet (UD-HetNet) to control the mobility of high-speed users [21]. Efficient HO is required for mobility management in WCS to switch UE from one cell to another without any interruption or disconnection. However, in 5G HetNet, transferring UE data between cells or networks results in computational complexity and signaling overhead, leading to significant HO implications. The problem of mobility becomes more challenging with frequent HO (FHO) among small cells.