Millimeter wave (mmWave) holds promise as a carrier frequency for fifth generation cellular networks. Because mmWave signals are sensitive to blockage, prior models for cellular networks operated in the ultra high frequency (UHF) band do not apply to analyze mmWave cellular networks directly. Leveraging concepts from stochastic geometry, this paper proposes a general framework to evaluate the coverage and rate performance in mmWave cellular networks. Using a distance-dependent line-of-site (LOS) probability function, the locations of the LOS and non-LOS base stations are modeled as two independent non-homogeneous Poisson point processes, to which different path loss laws are applied. Based on the proposed framework, expressions for the signal-to-noise-and-interference ratio (SINR) and rate coverage probability are derived. The mmWave coverage and rate performance are examined as a function of the antenna geometry and base station density. The case of dense networks is further analyzed by applying a simplified system model, in which the LOS region of a user is approximated as a fixed LOS ball. The results show that dense mmWave networks can achieve comparable coverage and much higher data rates than conventional UHF cellular systems, despite the presence of blockages. The results suggest that the cell size to achieve the optimal SINR scales with the average size of the area that is LOS to a user.

Coverage and Rate Analysis for Millimeter-Wave Cellular Networks

Femtocells, despite their name, pose a potentially large disruption to the carefully planned cellular networks that now connect a majority of the planet's citizens to the Internet and with each other. Femtocells - which by the end of 2010 already outnumbered traditional base stations and at the time of publication are being deployed at a rate of about five million a year - both enhance and interfere with this network in ways that are not yet well understood. Will femtocells be crucial for offloading data and video from the creaking traditional network? Or will femtocells prove more trouble than they are worth, undermining decades of careful base station deployment with unpredictable interference while delivering only limited gains? Or possibly neither: are femtocells just a "flash in the pan"; an exciting but short-lived stage of network evolution that will be rendered obsolete by improved WiFi offloading, new backhaul regulations and/or pricing, or other unforeseen technological developments? This tutorial article overviews the history of femtocells, demystifies their key aspects, and provides a preview of the next few years, which the authors believe will see a rapid acceleration towards small cell technology. In the course of the article, we also position and introduce the articles that headline this special issue.

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Femtocells: Past, Present, and Future

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

With the explosive growth of mobile data demand, the fifth generation (5G) mobile network would exploit the enormous amount of spectrum in the millimeter wave (mmWave) bands to greatly increase communication capacity. There are fundamental differences between mmWave communications and existing other communication systems, in terms of high propagation loss, directivity, and sensitivity to blockage. These characteristics of mmWave communications pose several challenges to fully exploit the potential of mmWave communications, including integrated circuits and system design, interference management, spatial reuse, anti-blockage, and dynamics control. To address these challenges, we carry out a survey of existing solutions and standards, and propose design guidelines in architectures and protocols for mmWave communications. We also discuss the potential applications of mmWave communications in the 5G network, including the small cell access, the cellular access, and the wireless backhaul. Finally, we discuss relevant open research issues including the new physical layer technology, software-defined network architecture, measurements of network state information, efficient control mechanisms, and heterogeneous networking, which should be further investigated to facilitate the deployment of mmWave communication systems in the future 5G networks.

A survey of millimeter wave communications (mmWave) for 5G: opportunities and challenges

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

National Telecommunications and Information Administration (NTIA) has proposed vast exclusions zones between radar and Worldwide Interoperability for Microwave Access (WiMAX) systems which are also being considered as geographic separations between radars and 3.5 GHz Long Term Evolution (LTE) systems without investigating any changes induced by the distinct nature of LTE as opposed to WiMAX. This paper performs a detailed system-level analysis of the interference effects from shipborne radar systems into LTE systems. Even though the results reveal impacts of radar interference on LTE systems performance, they provide clear indications of conspicuously narrower exclusion zones for LTE vis-a-vis those of WiMAX and pave the way toward deploying LTE at 3.5 GHz within the coastline populous areas.

Radar in-band interference effects on macrocell LTE uplink deployments in the U.S. 3.5 GHz band

Coordinated Multi-Point (CoMP) transmission has been recognized as a primary method of further enhancing the downlink spectral efficiency of LTE Rel-10. A series of air interface enhancements have been made in LTE Rel-11 to support CoMP with Ideal Backhaul (IB), but the support of CoMP using Non-Ideal Backhaul (NIB) was not considered in Rel-11. Recently, 3GPP evaluated CoMP performance gains with non- ideal backhaul and currently considering the necessary signaling to support inter-eNB CoMP. In this study, two types of network architecture are considered, namely i) the current distributed architecture and ii) the centralized architecture with a new node/entity to enable a centralized scheduler. In this paper, a dynamic coordinated muting scheme is proposed using LTE Rel-11 framework for both Macro and HetNet scenarios. Next, the performance of CoMP using non-ideal backhaul is evaluated under various traffic models with distributed and centralized architectures separately. It is shown that dynamic coordinated muting scheme with NIB can achieve a cell edge gain of approximately 40% over a system without coordination for Macro only and ~10% over FeICIC based HetNet scenario. The simulation results also indicate that a centralized architecture is more sensitive to backhaul latency comparing with distributed approach. Finally, it is concluded that the current LTE distributed architecture is well suited to support coordinated scheduling with non-ideal backhaul.

Coordinated scheduling and network architecture for LTE Macro and small cell deployments

A user equipment UE takes measurements of at least a first and a second transmission point. The UE applies a bias value in favor of the second transmission point to at least one of the measurements, and thereafter utilizes the measurements after the bias value is applied to select a set of transmission points to recommend for cooperative multipoint CoMP transmissions. In more specific examples: the first and second transmission points are respective macro and micro/pico cells, and the UE further measures channel state information CSI from each transmission point of the selected CoMP set and reports that without applying the bias value to any of them. The examples show this approach works even if the cells share a common physical cell ID PCID.

Cell range extension for cooperative multipoint

Precoding for coordinated multi-point joint transmission

The large bandwidths available at the millimeter wave (mmWave) carrier frequencies (e.g., 30–100 GHz) have sparked significant interest in developing cellular systems in those bands to meet the ever-increasing demand for high data rates. Large-scale antenna arrays with tens or hundreds of antennas are envisioned to be a prerequisite for operating in the mmWave bands due to the poor path loss conditions in those bands. Previous studies for 72GHz carrier frequencies have shown how extremely high data rates can be achieved in ultra-dense small cell deployments through simple single-user MIMO techniques mainly by virtue of the high system bandwidth (on the order of 1–2GHz). In this paper, we extend the prior work on single-user MIMO (SU-MIMO) for mmWave bands and examine the question of whether Multi-User MIMO (MU-MIMO) is a useful approach for mmWave bands. We show that there are definite cases where MU-MIMO can provide significant system capacity gains over SU-MIMO in the mmWave bands, which is in contrast to the expectation that the poor path loss conditions necessitate simple high gain beamforming techniques. We show that in many cases, a large-scale array provides sufficient SINR gain that can enable further gains from multi-user spatial multiplexing. We show how those gains depend on a variety of factors such as the user density and the transmission strategy.

Eugene Visotsky

Papers

Radar in-band interference effects on macrocell LTE uplink deployments in the U.S. 3.5 GHz band

Coordinated scheduling and network architecture for LTE Macro and small cell deployments

Cell range extension for cooperative multipoint

Precoding for coordinated multi-point joint transmission

Massive MIMO for mmWave systems