We investigate the use of multiple transmitting and/or receiving antennas for single user communications over the additive Gaussian channel with and without fading. We derive formulas for the capacities and error exponents of such channels, and describe computational procedures to evaluate such formulas. We show that the potential gains of such multi-antenna systems over single-antenna systems is rather large under independenceassumptions for the fades and noises at different receiving antennas.

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Capacity of Multi‐antenna Gaussian Channels

Cognitive radio is viewed as a novel approach for improving the utilization of a precious natural resource: the radio electromagnetic spectrum. The cognitive radio, built on a software-defined radio, is defined as an intelligent wireless communication system that is aware of its environment and uses the methodology of understanding-by-building to learn from the environment and adapt to statistical variations in the input stimuli, with two primary objectives in mind: /spl middot/ highly reliable communication whenever and wherever needed; /spl middot/ efficient utilization of the radio spectrum. Following the discussion of interference temperature as a new metric for the quantification and management of interference, the paper addresses three fundamental cognitive tasks. 1) Radio-scene analysis. 2) Channel-state estimation and predictive modeling. 3) Transmit-power control and dynamic spectrum management. This work also discusses the emergent behavior of cognitive radio.

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Cognitive radio: brain-empowered wireless communications

Wireless Communications

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

The global bandwidth shortage facing wireless carriers has motivated the exploration of the underutilized millimeter wave (mm-wave) frequency spectrum for future broadband cellular communication networks. There is, however, little knowledge about cellular mm-wave propagation in densely populated indoor and outdoor environments. Obtaining this information is vital for the design and operation of future fifth generation cellular networks that use the mm-wave spectrum. In this paper, we present the motivation for new mm-wave cellular systems, methodology, and hardware for measurements and offer a variety of measurement results that show 28 and 38 GHz frequencies can be used when employing steerable directional antennas at base stations and mobile devices.

Millimeter Wave Mobile Communications for 5G Cellular: It Will Work!

A signal-space approach is presented to study the Nyquist sampling and number of degrees of freedom of an electromagnetic field under arbitrary propagation conditions. Conventional signal processing tools such as the multidimensional sampling theorem and Fourier theory are used to build a linear system theoretic interpretation of electromagnetic wave propagations and revisit classical electromagnetic theory results, e.g., bandlimited property of an electromagnetic field, from a signal processing perspective. Scalar electromagnetic fields are considered for simplicity, which physically correspond to acoustic propagation in general or electromagnetic propagation under certain conditions. The developed approach is extended to study ensembles of a stationary random electromagnetic field that is representative of different propagation conditions.

Nyquist-Sampling and Degrees of Freedom of Electromagnetic Fields.

Holographic MIMO is a spatially-constrained MIMO system with a massive number of antennas, possibly thought of, in its ultimate form, as a spatially-continuous electromagnetic aperture. Accurate and tractable channel modeling is critical to understanding the full potential of this technology. This paper considers arbitrary spatially-stationary scattering and provides a 4D plane-wave representation in Cartesian coordinates, which captures the essence of electromagnetic propagation and allows to evaluate the capacity of Holographic MIMO systems with rectangular volumetric arrays. The developed framework generalizes the virtual channel representation, which was originally developed for uniform linear arrays.

Holographic MIMO Communications Under Spatially-Stationary Scattering

Embodiments are described to mitigate network interference issues and to enable a significant increase in the throughput of wireless systems. In one method, pilot transmissions of a first and second group of wireless units are synchronized. Each wireless unit of the first group and each wireless unit of the second group use a different orthogonal pilot (than others in their group) from the same group of orthogonal pilots. Also, the pilot transmissions of the second group of wireless units are synchronized so as to be shifted in time from the pilot transmissions of the first group. In another method, data from neighboring cells and pilots from wireless units are received at a cell. Channel vectors for the wireless units are then estimated using the received data from neighboring cells, the received pilots from the wireless units and previously estimated channel vectors between the cell and the neighboring cells.

Interference reduction for wireless networks

Prior treatments of space-time communications in Rayleigh flat fading generally assume that channel coding covers either one fading interval-in which case there is a nonzero "outage capacity"-or multiple fading intervals-in which case there is a nonzero Shannon capacity. However, we establish conditions under which channel codes span only one fading interval and yet are arbitrarily reliable. In short, space-time signals are their own channel codes. We call this phenomenon space-time autocoding, and the accompanying capacity the space-time autocapacity.

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Space-time autocoding: arbitrarily reliable communication in a single fading interval

A method and apparatus for communication between a wireless base station and a population of one or more terminals are provided, involving, in each of a plurality of iterations, transmitting a block of forward-link data from an array of multiple base station antennas to the terminal population. In each iteration, a forward-link power level is updated for each said terminal using a distributed algorithm and purely local information. Meanwhile, a set of beamforming coefficients based on channel state information (CSI) obtained from reverse-link pilot signals is periodically updated, and each data block is precoded with the most recently updated beamforming coefficients. Each data block is transmitted at the most recently updated forward-link power levels.

Thomas L. Marzetta

Papers

Nyquist-Sampling and Degrees of Freedom of Electromagnetic Fields.

Holographic MIMO Communications Under Spatially-Stationary Scattering

Interference reduction for wireless networks

Space-time autocoding: arbitrarily reliable communication in a single fading interval

Method and apparatus for power optimization in wireless systems with large antenna arrays