One major influence on the future deployment of cellular networks will be a continuous increase in traffic inside mobile broadband systems. Moreover, traditional macrocell-based mobile communication networks will struggle to keep up with the enormous expansion in the demand for communications services in the future. Densification of networks is required if we are to meet the comprehensive needs for end terminals for a wide range of applications. One of the leading concepts in this competitive environment is the Ultra-Dense Network (UDN) where the access nodes and/or the communication links per unit area are densified, with the aim of improving overall network performance. The location of the UDN nodes meets the criteria for symmetry with a high probability. Ultra-dense cell deployment aims to reduce the physical distance between the transmitter and receiver in order to boost system performance and generally optimize the values of a wide variety of key performance indicators (KPIs). This paper aims to provide a taxonomy of UDNs and specifically of UDN-related KPIs. Initially, we address the complex questions “What is the current understanding of what ultra-dense networks are and what they should be, and how can we measure their performance?” by shedding light on the fundamental characteristics of UDNs.

The 6G communication networks and technologies have to enable the development of wide variety of low latency and ultra-reliable services. Furthermore, the 6G is foreseen to be the era of new devices which integrate our natural human senses in order to create a fully new concept of human-machine interactions. The eXtended Reality (XR) based wearables will surely improve the way we collaborate with modern technologies by merging the real and virtual world in one innovative continuum in order to expand the possibilities of using and interacting with different types of modern or already well-known IT services. In this context, a vital 6G research area is the design of different flexible quality assessment metrics, targets and measures that integrate human perceptions and physical factors from human physiology. This metric design should consider the multisensory nature of XR devices by incorporation of different objective network-related as well as strongly subjective human-related features like sight, touch, smell, taste, body physiology, psychological traits, gestures and even sixth sense. In this paper a conceptual framework incorporating a mixture of new and classical quality assessment constructs like Quality of Service (QoS) and Quality of Experience (QoE) is proposed for 6G networks from human-centric point of view. It considers the development of new types of intelligent XR technologies and give an insight in regard to overall human experience assessment, modelling and prediction.

Nowadays, Low-power Wide Area Networks (LPWANs) hold much promise, due to their low-power, low-cost, and low throughput nature. The very long range of LPWA technologies enables devices to spread and move over large geographical areas, thus creating excellent opportunities for new IoT technologies and for Wireless Sensor Networks (WSNs) in general. In this context, LoRa (Long Range) technology represents a highly important example of wireless technology working in high-density networks. LoRa Wide-Area Networks (LoRaWANs) are characterised by low data rate requirements per device, large cells and heterogeneous application domains, which can lead to extremely high numbers of devices coexisting in the same cell. The coexistence of other technologies operating in the same ISM (Industrial Scientific and Medical) band may lead to increased interference. In this paper an overview of interference management in LoRaWANs is performed, encompassing different approaches, methods and algorithms to deal with interference in the ISM band. We focus on the so-called Co-Spreading Factor Interference (CSFI) and Inter-Spreading Factor Interference (ISFI) occurring when the useful and interference signal use the same or different SFs. We aim to show via link-level simulations the impact of coding rate and bandwidth on this imperfect orthogonality-based CSFI and ISFI.

Ultra-dense Internet of Things (IoT) networks in the unlicensed bands are subject to significant interference due to their high deployment density and attacks from malicious users. The interference has a non-uniform distribution, when examined in 3D space which leads to the need of volumetric monitoring for precise estimation of spectrum utilization. This paper analyzes the indoor spectrum occupancy for two promising IoT standards - LoRa and WiFi, through 3D interference maps and spatial throughput (ST) analysis produced using an automated measurement tool. The system is implemented through software-defined radio (SDR) platforms. Fading impacts the interference distribution not only in a single plane but also in height. In addition, the experimental results show that the received interference power within an area (measured in m ² ) and a volume (in m ³ ), and consequently the ST, vary dynamically. Thus, the worst-case interference rather the mean value, needs to be considered in realistic dense scenarios for beyond 5G IoT networks.

In this paper, a new method for designing orthogonal bicomplex digital signal processing (DSP) algorithms is developed. In contrast to those previously reported on, the method proposed is universal, since it is not affected by the order or the type of the real digital processing algorithm employed as a prototype. The method is based on a transformation starting with either real or complex orthogonal DSP algorithms represented in the z-domain, and transforming them into orthogonal bicomplex algorithms. The proposed new method is applied in the design of bilinear orthogonal bicomplex DSP systems with a canonical number of elements, the main advantage of which is that the order of the digital system is reduced by a factor of four. As well as being canonical, the orthogonal bicomplex digital systems are also symmetrical structures, as a result of which they offer parallelism and subsequent unification. It is experimentally shown that bicomplex orthogonal DSP algorithms acquire the properties of the initial algorithm prototype, irrespective of whether it is real or complex. Since the new design method is universally applicable, it can be used to develop bicomplex orthogonal digital algorithms of any order and type. Being simple, canonical, and symmetrical—and, thus, leading to lower equipment cost, reduced complexity, and higher energy efficiency—these structures may well be appropriate for the enhancement of the implementation of intelligent algorithms in next-generation radio access networks.