The exponential growth and availability of data in all forms is the main booster to the continuing evolution in the communications industry. The popularization of traffic-intensive applications including high definition video, 3-D visualization, augmented reality, wearable devices, and cloud computing defines a new era of mobile communications. The immense amount of traffic generated by today’s customers requires a paradigm shift in all aspects of mobile networks. Ultradense network (UDN) is one of the leading ideas in this racetrack. In UDNs, the access nodes and/or the number of communication links per unit area are densified. In this paper, we provide a survey-style introduction to dense small cell networks. Moreover, we summarize and compare some of the recent achievements and research findings. We discuss the modeling techniques and the performance metrics widely used to model problems in UDN. Also, we present the enabling technologies for network densification in order to understand the state-of-the-art. We consider many research directions in this survey, namely, user association, interference management, energy efficiency, spectrum sharing, resource management, scheduling, backhauling, propagation modeling, and the economics of UDN deployment. Finally, we discuss the challenges and open problems to the researchers in the field or newcomers who aim to conduct research in this interesting and active area of research.

Ultra-Dense Networks: A Survey

In studying the performance of coded communications over memoryless channels (with or without fading), the results are given as upper bounds on the average bit error probability (BEP). In principle, there are three different approaches to arriving at these bounds, all of which employ obtaining the so-called pairwise error probability , or the probability of choosing one symbol sequence over another for a given pair of possible transmitted symbol sequences, followed by a weighted summation over all pairwise events. In this chapter, we will focus on the results obtained from the third approach since these provide the tightest upper bounds on the true performance. The first emphasis will be placed on evaluating the pairwise error probability with and without CSI, following which we shall discuss how the results of these evaluations can be used via the transfer bound approach to evaluate average BEP of coded modulation transmitted over the fading channel.

Coded Communication over Fading Channels

This paper presents a literature review on recent applications and design aspects of the intelligent reflecting surface (IRS) in the future wireless networks. Conventionally, the network optimization has been limited to transmission control at two endpoints, i.e., end users and network controller. The fading wireless channel is uncontrollable and becomes one of the main limiting factors for performance improvement. The IRS is composed of a large array of scattering elements, which can be individually configured to generate additional phase shifts to the signal reflections. Hence, it can actively control the signal propagation properties in favor of signal reception, and thus realize the notion of a smart radio environment. As such, the IRS’s phase control, combined with the conventional transmission control, can potentially bring performance gain compared to wireless networks without IRS. In this survey, we first introduce basic concepts of the IRS and the realizations of its reconfigurability. Then, we focus on applications of the IRS in wireless communications. We overview different performance metrics and analytical approaches to characterize the performance improvement of IRS-assisted wireless networks. To exploit the performance gain, we discuss the joint optimization of the IRS’s phase control and the transceivers’ transmission control in different network design problems, e.g., rate maximization and power minimization problems. Furthermore, we extend the discussion of IRS-assisted wireless networks to some emerging use cases. Finally, we highlight important practical challenges and future research directions for realizing IRS-assisted wireless networks in beyond 5G communications.

Toward Smart Wireless Communications via Intelligent Reflecting Surfaces: A Contemporary Survey

Massive MIMO is a reality—What is next?: Five promising research directions for antenna arrays

While celebrating the 21st year since the very first IEEE 802.11 “legacy” 2 Mbit/s wireless local area network standard, the latest Wi-Fi newborn is today reaching the finish line, topping the remarkable speed of 10 Gbit/s. IEEE 802.11ax was launched in May 2014 with the goal of enhancing throughput-per-area in high-density scenarios. The first 802.11ax draft versions, namely, D1.0 and D2.0, were released at the end of 2016 and 2017. Focusing on a more mature version D3.0, in this tutorial paper, we help the reader to smoothly enter into the several major 802.11ax breakthroughs, including a brand new orthogonal frequency-division multiple access-based random access approach as well as novel spatial frequency reuse techniques. In addition, this tutorial will highlight selected significant improvements (including physical layer enhancements, multi-user multiple input multiple output extensions, power saving advances, and so on) which make this standard a very significant step forward with respect to its predecessor 802.11ac.

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A Tutorial on IEEE 802.11ax High Efficiency WLANs

The successful virtualization of wireless access networks is strongly affected by the way in which radio resources are managed. The Infrastructure Provider (InP) is required to deploy efficient and flexible scheduling techniques to dynamically allocate the resources for the users associated with different Service Providers (SPs). Service contracts with different SPs and fairness among their users are crucial to the success of the virtualization scheme deployed by the InP. In this paper we develop an efficient resource allocation scheme to allocate the radio resource blocks in LTE networks. The scheme keeps track of the service contracts with the SPs and also the fairness requirements between cell-center users and cell-edge users. Also the scheme allows the flexible definition of fairness requirements for different SPs. The performance of the proposed schemes is evaluated and the results show that the proposed low-complexity scheme is very efficient in terms of computation time and its performance in terms of sum rate is close to the results due to the relaxed solution and coordinate search algorithm.

LTE Wireless Network Virtualization: Dynamic Slicing via Flexible Scheduling

Enhanced Inter-Cell Interference Coordination (eICIC) is a proposed framework by the 3GPP to handle Inter-Cell Interference (ICI) in heterogeneous network (HetNet) environments. Almost-blank subframe (ABSF) is one of the time-domain techniques proposed in the eICIC framework as a candidate for deployment in LTE release 10 (LTE-Advanced). In this paper, a comprehensive ABSF framework is proposed to mitigate the interference in HetNet environments comprised of macro-cells and femto-cells. The ABSF framework proposes a tracking procedure to mark and unmark the macro-cell victim users. Also, new control message to coordinate between macro-cells and femto-cells is proposed, a novel approach to trigger the ABSF mode at aggressor Home eNBs (HeNBs), and enhancements to the macro-cell scheduling process. Finally, a novel approach for the estimation of victim users' signal-to-interference-plus-noise ratio (SINR) level during ABSF is proposed based on the well-known discrete Kalman filter. The performance evaluation results show that the proposed ABSF framework significantly improves the throughput of the macro-cell victim users with a slight degradation in the throughput of the femto-cells.

Performance evaluation of a coordinated time-domain eICIC framework based on ABSF in heterogeneous LTE-Advanced networks

The inevitable next era of smart living requires unprecedented advances in enabling technologies. The building blocks of this era are devices such as sensors, actuators, and Internet of Things (IoT) devices. Machine-Type Communication (MTC), also known as Machine-to-Machine (M2M) communication, constitutes the main enabling technology to support communications among such devices. The massive number of these devices and the immense amount of traffic generated by them require a paramount shift in cellular and non-cellular wireless technologies to achieve the required connectivity. Ultra-Dense Network (UDN) is intuitively one of the most convenient approaches to tackle such requirements of massive connectivity and high throughput found in MTC. In UDNs, small cells are deployed in large densities compared to Human-Type Communication Users (HTCUs) like smartphones and tablets. In a different scope, multiple access techniques also require a paradigm shift to cope with the increasing density of required connections while confined by limited resources. Recently, Non-Orthogonal Multiple Access (NOMA) has received a great attention as an efficacious candidate to enhance the network’s performance compared to traditional Orthogonal Multiple Access (OMA) techniques. For this sake, in this paper, we provide a comprehensive survey and illustrative simulation results on the application of NOMA to support MTC in a UDN environment. First, we give a brief discussion on MTC and its different applications and supporting technologies. Then, we focus our effort on investigating the main challenges facing MTC along with the existing opportunities found in both NOMA and UDN, respectively. Finally, we show via simulations the possible gains of both technologies and conclude by discussing the open problems for future research directions.

NOMA-Assisted Machine-Type Communications in UDN: State-of-the-Art and Challenges

In this paper, we propose a general mathematical framework to compute the average downlink rate in a multiple connectivity context considering ultra-dense network (UDN) environment. UDN is a dense small cells network featured by the high density of small cells that may exceed the density of active users. In multiple association, a user connects to $M$ base stations (BSs) that provide the maximum average received power forming a multicell . This provides the user with a “data-shower,” where the user’s traffic is split into multiple paths, which helps overcoming the capacity limitations imposed by the backhaul links. The developed framework significantly simplifies the computation of the average downlink rate of the individual connections to the cells of a multicell . Moreover, the accuracy of the mathematical framework is confirmed by extensive simulations. The simulation results show a perfect match with the numerical results computed from the mathematical framework in different combinations of the system parameters including multicell size, small cells density, active users density, pathloss exponent, and fading channel distribution of the signal link.

Mahmoud Kamel

Papers

Ultra-Dense Networks: A Survey

LTE Wireless Network Virtualization: Dynamic Slicing via Flexible Scheduling

Performance evaluation of a coordinated time-domain eICIC framework based on ABSF in heterogeneous LTE-Advanced networks

NOMA-Assisted Machine-Type Communications in UDN: State-of-the-Art and Challenges

Performance Analysis of Multiple Association in Ultra-Dense Networks