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

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 backwards compatibility. And 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. But 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.

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

Massive multiple-input multiple-output MIMO is one of themost promising technologies for the next generation of wirelesscommunication networks because it has the potential to providegame-changing improvements in spectral efficiency SE and energyefficiency EE. This monograph summarizes many years ofresearch insights in a clear and self-contained way and providesthe reader with the necessary knowledge and mathematical toolsto carry out independent research in this area. Starting froma rigorous definition of Massive MIMO, the monograph coversthe important aspects of channel estimation, SE, EE, hardwareefficiency HE, and various practical deployment considerations.From the beginning, a very general, yet tractable, canonical systemmodel with spatial channel correlation is introduced. This modelis used to realistically assess the SE and EE, and is later extendedto also include the impact of hardware impairments. Owing tothis rigorous modeling approach, a lot of classic "wisdom" aboutMassive MIMO, based on too simplistic system models, is shownto be questionable.

https://www.nowpublishers.com/article/DownloadSummary/SIG-093

Massive MIMO Networks: Spectral, Energy, and Hardware Efficiency

Cooperation is viewed as a key ingredient for interference management in wireless networks. This paper shows that cooperation has fundamental limitations. First, it is established that in systems that rely on pilot-assisted channel estimation, the spectral efficiency is upper-bounded by a quantity that does not depend on the transmit powers; in this framework, cooperation is possible only within clusters of limited size, which are subject to out-of-cluster interference whose power scales with that of the in-cluster signals. Second, an upper bound is also shown to exist if the cooperation extends to an entire (large) system operating as a single cluster; here, pilot-assisted transmission is necessarily transcended. Altogether, it is concluded that cooperation cannot in general change an interference-limited network to a noise-limited one. Consequently, the existing literature that routinely assumes that the high-power spectral efficiency scales with the log-scale transmit power provides only a partial characterization. The complete characterization proposed in this paper subdivides the high-power regime into a degree-of-freedom regime, where the scaling with the log-scale transmit power holds approximately, and a saturation regime, where the spectral efficiency hits a ceiling that is independent of the power. Using a cellular system as an example, it is demonstrated that the spectral efficiency saturates at power levels of operational relevance.

/pdf/fundamental-limits-of-cooperation-68uqkxtw2g.pdf

Fundamental Limits of Cooperation

This paper is concerned with the capacity of multiple-input multiple-output (MIMO) cellular systems. We assume an equal rate constraint for all users and adopt a realistic channel model that incorporates path loss, lognormal fading and Rayleigh fading. Several bounds are derived for the minimum transmission power of such rate-constrained MIMO cellular systems with various base station (BS) cooperation strategies. In particular, the upper power bound is based on the maximum eigenmode beamforming (MEB) scheme. These power bounds are then used to obtain the corresponding cellular capacity bounds when partial BS cooperation strategies are adopted. Our results show that, allowing more users to transmit simultaneously, introducing cooperation among BSs and increasing the number of antennas (especially at each BS) are efficient ways to improve system performance.

On the Capacity of MIMO Cellular Systems with Base Station Cooperation

This letter is concerned with multi-user multiple-input multiple-output (MIMO) systems with rate constraints. We show that antenna correlation at mobile units (MUs) is actually beneficial from the capacity point of view. This finding is useful in practice as minimizing the physical size of MUs is highly desirable, but it may result in antenna correlation.

On the impact of antenna correlation in multi-user MIMO systems with rate constraints

This paper is concerned with cellular systems with rate constraints in fading environments. We consider a simple but asymptotically optimal matched filtering/successive interference cancellation (MF-SIC) scheme. We derive several concise and closed-form bounds for the power and spectral efficiencies of various base station cooperation strategies, which provide some useful insights into cellular systems.

On Cellular Capacity with Base Station Cooperation

In this paper, we consider multi-user multiple-input multiple-output (MIMO) systems over either multiple access channels (MACs) or broadcast channels (BCs). Contrary to common views, we show that antenna correlation at the mobile unit (MU), the base station (BS) or both sides can be potentially beneficial for such systems. Both asymptotic analysis and numerical results indicate that antenna correlation can provide a significant capacity gain in multi-user environments.

On the capacity gain from antenna correlation in multi-user MIMO systems

In this paper, we study the impact of antenna correlation at mobile units (MUs) on the capacity of multi-user multiple-input multiple-output (MIMO) systems with rate constraints. Both numerical results and asymptotic analyses show that antenna correlation can actually be regarded as a beneficial factor for such systems. It is also shown that the maximum eigenmode beamforming (MEB) based interleave-division multiple-access (IDMA) system is an effective platform to exploit the potential gain provided by antenna correlation at MUs.

How Does Correlation Affect the Capacity of MIMO Systems with Rate Constraints

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