With the rapid increase in the number of mobile users, wireless access technologies are evolving to provide mobile users with high data rates and support new applications that include both human and machine-type communications. Heterogeneous networks (HetNets), created by the joint installation of macro cells and a large number of densely deployed small cells, are considered an important solution to deal with the increasing network capacity demands and provide high coverage to wireless users in future fifth generation (5G) wireless networks. Due to the increasing complexity of network topology in 5G HetNets with the integration of many different base station types, in 5G architecture mobility management has many challenges. Intense deployment of small cells, along with many advantages it provides, brings important mobility management problems such as frequent handover (HO), HO failure, HO delays, ping-pong HO and high energy consumption which will result in lower user experience and heavy signal loads. In this paper, we provide a comprehensive study on the mobility management in 5G HetNet in terms of radio resource control, the initial access and registration procedure of the user equipment (UE) to the network, the paging procedure that provides the location of the UE within the network, connected mode mobility management schemes and beam level mobility and beam management. Besides, this paper addresses the challenges and suggest possible solutions for the 5G mobility management.

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The massive growth of mobile users and the essential need for high communication service quality necessitate the deployment of ultra-dense heterogeneous networks (HetNets) consisting of macro, micro, pico and femto cells. Each cell type provides different cell coverage and distinct system capacity in HetNets. This leads to the pressing need to balance loads between cells, especially with the random distribution of users in numerous mobility directions. This paper provides a survey on the intelligent load balancing models that have been developed in HetNets, including those based on the machine learning (ML) technology. The survey provides a guideline and a roadmap for developing cost-effective, flexible and intelligent load balancing models in future HetNets. An overview of the generic problem of load balancing is also presented. The concept of load balancing is first introduced, and its purpose, functionality and evaluation criteria are then explained. Besides, a basic load balancing model and its operational procedure are described. A comprehensive literature review is then conducted, including techniques and solutions of addressing the load balancing problem. The key performance indicators (KPIs) used in the evaluation of load balancing models in HetNets are presented, along with the concurrent optimisation of coverage (CCO) and mobility robustness optimisation (MRO) relationship of load balancing. A comprehensive literature review of ML-driven load balancing solutions is specifically accomplished to show the historical development of load balancing models. Finally, the current challenges in implementing these models are explained as well as the future operational aspects of load balancing.

In this study, we design a pair of third‐order conformal Hilbert curve antennas for use in capsule endoscopy at three different bands (Industrial, Scientific, and Medical [ISM]), especially at 433 MHz, 915 MHz, and 2.45 GHz. The antennas are placed orthogonally with respect to each other, offering dual linear polarization characteristics, which have been highlighted in literature as the most robust communication link between a roaming transmitting capsule within the GI tract and the receiver antenna. The robustness of the link depends on (i) invariance of linear polarization with the position and orientation of the roaming transmitter, as well as (ii) tolerance of linearly polarized fields to depolarization effects when penetrated through the body. The antennas were manufactured on polyimide substrate, which was wrapped around a 3D‐printed capsule volume. Both antennas were measured inside bovine muscle tissue and the obtained results have been compared with the simulated results to validate the performance of the propose solution. The presented results showed that, the return loss characteristics and the measured bandwidth, for both antennas inside bovine muscle tissue, have matched with the simulated results. To the best of our knowledge, these demonstrated antennas are the first designed capsule antennas to address three ISM bands with dual linear polarization. The designed antennas can be adapted for clinical use with further development.

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