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.

/pdf/capacity-of-multi-antenna-gaussian-channels-3axdfdd5ns.pdf

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.

/pdf/cognitive-radio-brain-empowered-wireless-communications-9m6gu0vz1z.pdf

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!

Wireless power transfer between an array of antennas and a single-antenna terminal is governed by matrix circuit theory. A complex-valued, non-conjugate symmetric impedance matrix constitutes a complete quantitative description of the system. The real-part of the impedance matrix is non-negative definite. The efficiency with which power can be transferred-either down-link (from the antenna array to the single-antenna terminal) or up-link (from the terminal to the array) is equal to the ratio of received power to transmitted power. The maximization of power transfer efficiency with respect to the joint transmit/receive activities yields the fact that the optimized up-link efficiency is equal to the optimized down-link efficiency. The typical operation of antenna arrays seeks to minimize mutual coupling among the constituent antennas by spacing the antennas at least half of a wave-length apart, which yields an array gain proportional to the number of antennas. By utilizing closer spacing, and deliberately creating strong mutual coupling, in principle it is possible to realize considerably higher array gains for the same number of antennas, a phenomenon called super-directivity. Practical super-directivity would benefit not only wireless communications, but also wireless power transfer.

Super-Directive Antenna Arrays: Fundamentals and New Perspectives

Methods are provided for mitigating interference due to pilot contamination in a cellular network in which there is reuse of pilot signals. In embodiments, forward-link signals are precoded, using knowledge of slow-fading coefficients, to mitigate the interference. In embodiments, interference in reverse-link signals destined for a given base station is mitigated by linearly combining reverse-link signals destined for the given base station and for other base stations of the network, using knowledge of slow-fading coefficients.

Large-scale antenna method and apparatus of wireless communication with suppression of intercell interference

Differential unitary space-time modulation (DUSTM) and its earlier nondifferential counterpart, USTM, permit high-throughput multiple-input multiple-output (MIMO) communication entirely without the possession of channel state information by either the transmitter or the receiver. For an isotropically random unitary input we obtain the exact closed-form expression for the probability density of the DUSTM received signal, permitting the straightforward Monte Carlo evaluation of its mutual information. We compare the performance of DUSTM and USTM through both numerical computations of mutual information and through the analysis of low- and high-signal-to-noise ratio (SNR) asymptotic expressions. In our comparisons the symbol durations of the equivalent unitary space-time signals are equal to T. For DUSTM the number of transmit antennas is constrained by the scheme to be M=T/2, while USTM has no such constraint. If DUSTM and USTM utilize the same number of transmit antennas at high SNRs the normalized mutual information of the two schemes expressed in bits/s/Hz are asymptotically equal, with the differential scheme performing somewhat better. At low SNRs the normalized mutual information of DUSTM is asymptotically twice the normalized mutual information of USTM. If, instead, USTM utilizes the optimum number of transmit antennas then USTM can outperform DUSTM at sufficiently low SNRs

Capacity of Differential Versus Nondifferential Unitary Space&#8211;Time Modulation for MIMO Channels

We study the joint unicast and multi-group multicast transmission in massive multiple-input-multiple-output (MIMO) systems We consider a system model that accounts for channel estimation and pilot contamination, and derive achievable spectral efficiencies (SEs) for unicast and multicast user terminals (UTs), under maximum ratio transmission and zero-forcing precoding For unicast transmission, our objective is to maximize the weighted sum SE of the unicast UTs, and for the multicast transmission, our objective is to maximize the minimum SE of the multicast UTs These two objectives are coupled in a conflicting manner, due to their shared power resource Therefore, we formulate a multiobjective optimization problem (MOOP) for the two conflicting objectives We derive the Pareto boundary of the MOOP analytically As each Pareto optimal point describes a particular efficient trade-off between the two objectives of the system, we determine the values of the system parameters (uplink training powers, downlink transmission powers, etc) to achieve any desired Pareto optimal point Moreover, we prove that the Pareto region is convex, hence the system should serve the unicast and multicast UTs at the same time-frequency resource Finally, we validate our results using numerical simulations

Joint Unicast and Multi-group Multicast Transmission in Massive MIMO Systems.

[Guest Editors introduction to: Special issue on space-time transmission, reception, coding and signal processing] 

Every episode of the classic 1966–1969 television series Star Trek begins with Captain Kirk’s (played by William Shatner) famous words : “Space: The final frontier….” While space may not be the final frontier for the information and communication theory community, it is proving to be an important and fruitful one. 

In the information theory community, the notion of space can be broadly defined as the simultaneous use of multiple, possibly coupled, channels. The notions of space–time and multiple-input multiple-output (MIMO) channels are therefore often used interchangeably. The connection between space and MIMO is most transparent when we view the multiple channels as created by two or more spatially separated antennas at a wireless transmitter or receiver. 

A large component of the current interest in space–time methods can be attributed to discoveries in the late 1980s and early 1990s that a rich wireless scattering environment can be beneficial when multiple antennas are used on a point-to-point link. We now know that adding antennas in a rich environment provides proportional increases in point-to-point data rates, without extra transmitted power or bandwidth.

/pdf/the-academic-and-industrial-embrace-of-space-time-methods-13lur237mv.pdf

Thomas L. Marzetta

Papers

Super-Directive Antenna Arrays: Fundamentals and New Perspectives

Large-scale antenna method and apparatus of wireless communication with suppression of intercell interference

Capacity of Differential Versus Nondifferential Unitary Space–Time Modulation for MIMO Channels

Joint Unicast and Multi-group Multicast Transmission in Massive MIMO Systems.

The academic and industrial embrace of space-time methods

Thomas L. Marzetta

Papers

Super-Directive Antenna Arrays: Fundamentals and New Perspectives

Large-scale antenna method and apparatus of wireless communication with suppression of intercell interference

Capacity of Differential Versus Nondifferential Unitary Space&#8211;Time Modulation for MIMO Channels

Joint Unicast and Multi-group Multicast Transmission in Massive MIMO Systems.

The academic and industrial embrace of space-time methods

Capacity of Differential Versus Nondifferential Unitary Space–Time Modulation for MIMO Channels