What will 5G be? What it will not be is an incremental advance on 4G. The previous four generations of cellular technology have each been a major paradigm shift that has broken backward compatibility. Indeed, 5G will need to be a paradigm shift that includes very high carrier frequencies with massive bandwidths, extreme base station and device densities, and unprecedented numbers of antennas. However, unlike the previous four generations, it will also be highly integrative: tying any new 5G air interface and spectrum together with LTE and WiFi to provide universal high-rate coverage and a seamless user experience. To support this, the core network will also have to reach unprecedented levels of flexibility and intelligence, spectrum regulation will need to be rethought and improved, and energy and cost efficiencies will become even more critical considerations. This paper discusses all of these topics, identifying key challenges for future research and preliminary 5G standardization activities, while providing a comprehensive overview of the current literature, and in particular of the papers appearing in this special issue.

What Will 5G Be

In the near future, i.e., beyond 4G, some of the prime objectives or demands that need to be addressed are increased capacity, improved data rate, decreased latency, and better quality of service. To meet these demands, drastic improvements need to be made in cellular network architecture. This paper presents the results of a detailed survey on the fifth generation (5G) cellular network architecture and some of the key emerging technologies that are helpful in improving the architecture and meeting the demands of users. In this detailed survey, the prime focus is on the 5G cellular network architecture, massive multiple input multiple output technology, and device-to-device communication (D2D). Along with this, some of the emerging technologies that are addressed in this paper include interference management, spectrum sharing with cognitive radio, ultra-dense networks, multi-radio access technology association, full duplex radios, millimeter wave solutions for 5G cellular networks, and cloud technologies for 5G radio access networks and software defined networks. In this paper, a general probable 5G cellular network architecture is proposed, which shows that D2D, small cell access points, network cloud, and the Internet of Things can be a part of 5G cellular network architecture. A detailed survey is included regarding current research projects being conducted in different countries by research groups and institutions that are working on 5G technologies.

A Survey of 5G Network: Architecture and Emerging Technologies

A key challenge of future mobile communication research is to strike an attractive compromise between wireless network's area spectral efficiency and energy efficiency. This necessitates a clean-slate approach to wireless system design, embracing the rich body of existing knowledge, especially on multiple-input-multiple-ouput (MIMO) technologies. This motivates the proposal of an emerging wireless communications concept conceived for single-radio-frequency (RF) large-scale MIMO communications, which is termed as SM. The concept of SM has established itself as a beneficial transmission paradigm, subsuming numerous members of the MIMO system family. The research of SM has reached sufficient maturity to motivate its comparison to state-of-the-art MIMO communications, as well as to inspire its application to other emerging wireless systems such as relay-aided, cooperative, small-cell, optical wireless, and power-efficient communications. Furthermore, it has received sufficient research attention to be implemented in testbeds, and it holds the promise of stimulating further vigorous interdisciplinary research in the years to come. This tutorial paper is intended to offer a comprehensive state-of-the-art survey on SM-MIMO research, to provide a critical appraisal of its potential advantages, and to promote the discussion of its beneficial application areas and their research challenges leading to the analysis of the technological issues associated with the implementation of SM-MIMO. The paper is concluded with the description of the world's first experimental activities in this vibrant research field.

https://hal-supelec.archives-ouvertes.fr/hal-00840278/document

Spatial Modulation for Generalized MIMO: Challenges, Opportunities, and Implementation

Imagine a world with more base stations than cell phones: this is where cellular technology is headed in 10-20 years. This mega-trend requires many fundamental differences in visualizing, modeling, analyzing, simulating, and designing cellular networks vs. the current textbook approach. In this article, the most important shifts are distilled down to seven key factors, with the implications described and new models and techniques proposed for some, while others are ripe areas for future exploration.

Seven ways that HetNets are a cellular paradigm shift

We provide a comprehensive overview of mathematical models and analytical techniques for millimeter wave (mmWave) cellular systems. The two fundamental physical differences from conventional sub-6-GHz cellular systems are: 1) vulnerability to blocking and 2) the need for significant directionality at the transmitter and/or receiver, which is achieved through the use of large antenna arrays of small individual elements. We overview and compare models for both of these factors, and present a baseline analytical approach based on stochastic geometry that allows the computation of the statistical distributions of the downlink signal-to-interference-plus-noise ratio (SINR) and also the per link data rate, which depends on the SINR as well as the average load. There are many implications of the models and analysis: 1) mmWave systems are significantly more noise-limited than at sub-6 GHz for most parameter configurations; 2) initial access is much more difficult in mmWave; 3) self-backhauling is more viable than in sub-6-GHz systems, which makes ultra-dense deployments more viable, but this leads to increasingly interference-limited behavior; and 4) in sharp contrast to sub-6-GHz systems cellular operators can mutually benefit by sharing their spectrum licenses despite the uncontrolled interference that results from doing so. We conclude by outlining several important extensions of the baseline model, many of which are promising avenues for future research.

Modeling and Analyzing Millimeter Wave Cellular Systems

We study the impact of user cooperation in wireless networks on improving the stable throughput and delay performance. Specifically, we consider a multiaccess system in which a set of source users generate packets to deliver to a common destination. A cooperation strategy is proposed at the protocol level, where users with a better channel to the destination have the option to relay packets from users that are farther afield. For the case of erasure channels with single-packet reception, we derive the stable throughput regions under different multiple access policies based on such cooperation strategy. Then we prove that the stable throughput region of the cooperative system strictly contains the stable throughput region achieved without cooperation. We also assess the delay performance, and show that cooperation significantly reduces the delay of all users. Finally, we characterize the effect of inter-user channel quality on performance, and show that the gain in performance through cooperation increases as the channel quality improves. Our work offers an innovative perspective by implementing cooperation at the network protocol level, while taking into consideration of fading and attenuation at the physical layer as well as the nature of traffic burstiness in a network.

Protocol-level cooperation in wireless networks: Stable throughput and delay analysis

We investigate how a heterogeneous cellular network should self-organize by proposing a load-aware user association scheme. This is an important consideration, in order to move traffic off congested cells and onto more lightly loaded cells. Although the network-wide optimal association problem is NP hard, a closely related utility maximization problem can be made convex by applying relaxations on the association metric. We then address a low-complexity distributed algorithm that converges to a near-optimal solution with theoretical guarantee on its performance, requiring limited information and no coordination. This is directly related to range extension and small-cell biasing, which is how cell associations are likely to work in practice. Our load-aware association scheme provides theoretical guidance on the best “biasing factor” for different tiers of base stations. Numerical results show a 3.5x throughput gain for cell-edge users and a 2x gain for median users relative to the standard max-SINR association where a mobile connects to the strongest base station.

Towards an optimal user association in heterogeneous cellular networks

Power control in a digital handset is practically implemented in a discrete fashion, and usually, such a discrete power control (DPC) scheme is suboptimal. In this paper, we first show that in a Poison-distributed ad hoc network, if DPC is properly designed with a certain condition satisfied, it can strictly work better than no power control (i.e., users use the same constant power) in terms of average signal-to-interference ratio, outage probability, and spatial reuse. This motivates us to propose an $N$ -layer DPC scheme in a wireless clustered ad hoc network, where transmitters and their intended receivers in circular clusters are characterized by a Poisson cluster process on the plane $\BBR^{2}$ . The cluster of each transmitter is tessellated into $N$ -layer annuli with transmit power $P_{i}$ adopted if the intended receiver is located at the $i$ th layer. Two performance metrics of transmission capacity (TC) and outage-free spatial reuse factor are redefined based on the $N$ -layer DPC. The outage probability of each layer in a cluster is characterized and used to derive the optimal power scaling law $P_{i}\in\Theta(\eta_{i}^{-(\alpha/2)})$ , with $\eta_{i}$ as the probability of selecting power $P_{i}$ and $\alpha$ as the path loss exponent. Moreover, the specific design approaches to optimize $P_{i}$ and $N$ based on $\eta_{i}$ are also discussed. Simulation results indicate that the proposed optimal $N$ -layer DPC significantly outperforms other existing power control schemes in terms of TC and spatial reuse.

Optimal Discrete Power Control in Poisson-Clustered Ad Hoc Networks

Power control in a digital handset is practically implemented in a discrete fashion and usually such a discrete power control (DPC) scheme is suboptimal. In this paper, we first show that in a Poison-distributed ad hoc network, if DPC is properly designed with a certain condition satisfied, it can strictly work better than constant power control (i.e. no power control) in terms of average signal-to-interference ratio, outage probability and spatial reuse. This motivates us to propose an $N$-layer DPC scheme in a wireless clustered ad hoc network, where transmitters and their intended receivers in circular clusters are characterized by a Poisson cluster process (PCP) on the plane $\mathbb{R}^2$. The cluster of each transmitter is tessellated into $N$-layer annuli with transmit power $P_i$ adopted if the intended receiver is located at the $i$-th layer. Two performance metrics of transmission capacity (TC) and outage-free spatial reuse factor are redefined based on the $N$-layer DPC. The outage probability of each layer in a cluster is characterized and used to derive the optimal power scaling law $P_i=\Theta\left(\eta_i^{-\frac{\alpha}{2}}\right)$, with $\eta_i$ the probability of selecting power $P_i$ and $\alpha$ the path loss exponent. Moreover, the specific design approaches to optimize $P_i$ and $N$ based on $\eta_i$ are also discussed. Simulation results indicate that the proposed optimal $N$-layer DPC significantly outperforms other existing power control schemes in terms of TC and spatial reuse.

We investigate the composite effects of multipacket reception (MPR) and relaying capability in affecting the stability region of a wireless network With a general MPR channel, a trade-off arises as to whether to activate the relay simultaneously with the source so that both transmissions might be successful, or to let the relay remain silent to overhear the source's transmission and then activate the cooperation As such, we consider a two-user multiple-access system where the user with a better user-destination channel may act as the relay for the other An opportunistic cooperation scheme through scheduling the relay's transmission is proposed Then the optimal scheduling probability for maximizing the stability region is characterized, and the corresponding stability region is derived We show that the stability region of the opportunistic scheme may be convex under certain channel conditions, and may strictly outer-bound the stability region of the conventional cooperation scheme

Beiyu Rong

Papers

Protocol-level cooperation in wireless networks: Stable throughput and delay analysis

Towards an optimal user association in heterogeneous cellular networks

Optimal Discrete Power Control in Poisson-Clustered Ad Hoc Networks

Optimal Discrete Power Control in Poisson-Clustered Ad Hoc Networks

On Opportunistic Cooperation for Improving the Stability Region with Multipacket Reception