To cope with the unprecedented ubiquity of smart applications, Machine-Type Communication (MTC), the cellular communication backbone of the Internet of Things (IoT), has become an inevitable choice. In this paper, we investigate the achievable performance of MTC in an Ultra-Dense Network (UDN). To fully utilize the available resources in 5G and beyond networks, we exploit the propagation characteristics and excess bandwidth of the Millimeter wave (mmWave) band. Using tools from stochastic geometry, we provide a mathematical framework to evaluate the achievable Signal-to-Interference plus Noise Ratio (SINR) per user and the average capacity per Small Cell (SC) while considering the severe Inter-Cell Interference (ICI) of UDNs and the blockage effect in mmWave. The accuracy of the formu-lated analytical expressions is verified through extensive Monte-Carlo simulations. The obtained results show the existence of an optimal Small Cell (SC) density that maximizes the utilization of the deployed SCs.

The rising era of smart living requires unprecedented advancements in cellular networks to support the communications of the Internet of Things (IoT), referred to as machine-type communication (MTC). Hence, we consider an ultradense network (UDN) environment supported by wireless backhaul links (BHs) and investigate the achievable performance gains for MTC. By doing so, we avoid the complexity, cost, and/or infeasibility of providing fiber BHs for the massive number of small cells (SCs) found in UDNs. We utilize the millimeter wave (mmWave) band to support the communications between the IoT Devices (IoTD) and their serving SCs. By doing so, the excess available bandwidth can be used to support a massive number of IoTDs while the propagation characteristics of the mmWave signals can be exploited to mitigate the severe intercell interference (ICI) found in UDNs. In this regard, we formulate a mathematical framework using tools from stochastic geometry to derive analytical expressions for the density of supported IoTDs and the average capacities per SC on both the access link (AL) and the BH. In addition, we obtain a tight lower bound of the average capacity per SC under the considered wireless limited-capacity BHs. The obtained results show the existence of an optimal active SC density that maximizes SC utilization.

The recent advances and unprecedented ubiquity of computation-intensive applications such as virtual reality and mobile augmented reality force new approaches to handle the accompanying challenges. Ultra-Dense Network (UDN) as a leading direction in 5G and beyond offers an opportunistic degree of freedom to be exploited where a massive number of low-power and low-cost Small Cells (SCs) are deployed. In particular, integrating Edge Computing Servers (ECSs) within the SCs at the edge of the cellular network paves the way to tackle several challenges including the processing of computation-intensive tasks with low latency. To exploit the full potentials of UDNs and ECSs, we deploy multiple associations of SCs to the same user while partitioning and offloading its computation-intensive task to the integrated ECSs therein. In this regard, we formulate a mathematical framework using tools from stochastic geometry to evaluate the average processing delay per user. Extensive Monte-Carlo simulations are conducted to verify the accuracy of our analytical results under different system parameters. Results show the existence of an optimal order of multiple-association. In addition, we propose a novel offline task division approach which significantly reduces the overall delay.

Ultra-Dense Networks (UDNs), where Small Cells (SCs) will be deployed in very high densities, are considered as a leading promising technology in 5G and beyond. Such SCs being equipped with multiple antennas can further enhance the achievable performance. In particular, significant gains can be obtained in securing the wireless data transfer through Physical Layer Security (PLS) protocols. In this paper, we study the combined effects and trade-offs between densifying the SCs and increasing the number of antennas per SC on the achievable downlink secrecy rate per user. Using tools from stochastic geometry, we derive an analytical expression for the achievable average secrecy rate. The obtained results show that both approaches of densifying the SCs and/or increasing the number of antennas per cell enhance the secrecy level of communication. Interestingly, we show that reducing the density of SCs can be compensated by increasing the number of antennas per cell in terms of the achievable secrecy rate.

Coexistence of Human-Type Communications (HTCs) and Machine-Type Communications (MTCs) is inevitable. Ultra-Dense Networks (UDNs) will be efficacious in supporting both types of communications. In a UDN, a massive number of low-power and low-cost Small Cells (SCs) are deployed with density higher than that of the HTC users. In such a scenario, the backhaul capacities constitute an intrinsic bottleneck for the system. Hence, we propose a multiple association scheme where each HTC user associates to and activates multiple SCs to overcome the backhaul capacity constraints mainly encountered in the downlink. In addition, having more active cells allows for more MTC devices to be supported by the network. Using tools from stochastic geometry, we formulate a novel mathematical framework investigating the performance of HTC in both downlink and uplink as well as the uplink MTC. Stretched Exponential Path Loss (SEPL) model is considered to practically reflect the UDN environment. Extensive simulations were conducted to verify the accuracy of the mathematical analysis under different system parameters. Results show the existence of an optimum number of SCs to which an HTC user may connect under backhaul capacity constraints. Besides, the proposed multiple-association scheme improves the performance of MTC in terms of both ASE and density of supported devices.

Non-Orthogonal Multiple-Access (NOMA) where multiple users share the same resources simultaneously, is one promising candidate for beyond 5G. Besides, an Ultra-Dense Network (UDN) with massive numbers of deployed Small Cells (SCs) can significantly boost the performance of the network. In this paper, we propose a hybrid NOMA/OMA scenario deployed within a UDN environment to support a massive number of devices under the umbrella of the massive MachineType Communication (mMTC) use case. NOMA is performed through pairing devices from two disjoint groups with different normalized Signal-to-Interference Ratio (SIR). Using tools from stochastic geometry, we derive an analytical expression for the Area Spectral Efficiency (ASE) gain when deploying our proposed hybrid NOMA/OMA scheme and compare it to a scenario of pure Orthogonal Multiple-Access (OMA). Moreover, in order to reflect the characteristics of the UDN environment, we model the large scale fading using the Stretched Exponential Path Loss (SEPL) model. We show through both simulations and analyses that the gain obtained from the hybrid NOMA/OMA scheme can be optimized based on the different system parameters. We also investigate the impact of densifying the network on the significance of NOMA deployment.