Massive multiple-input multiple-output (MIMO) wireless communications refers to the idea equipping cellular base stations (BSs) with a very large number of antennas, and has been shown to potentially allow for orders of magnitude improvement in spectral and energy efficiency using relatively simple (linear) processing. In this paper, we present a comprehensive overview of state-of-the-art research on the topic, which has recently attracted considerable attention. We begin with an information theoretic analysis to illustrate the conjectured advantages of massive MIMO, and then we address implementation issues related to channel estimation, detection and precoding schemes. We particularly focus on the potential impact of pilot contamination caused by the use of non-orthogonal pilot sequences by users in adjacent cells. We also analyze the energy efficiency achieved by massive MIMO systems, and demonstrate how the degrees of freedom provided by massive MIMO systems enable efficient single-carrier transmission. Finally, the challenges and opportunities associated with implementing massive MIMO in future wireless communications systems are discussed.

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An Overview of Massive MIMO: Benefits and Challenges

Intelligent reflecting surface (IRS) is an enabling technology to engineer the radio signal propagation in wireless networks. By smartly tuning the signal reflection via a large number of low-cost passive reflecting elements, IRS is capable of dynamically altering wireless channels to enhance the communication performance. It is thus expected that the new IRS-aided hybrid wireless network comprising both active and passive components will be highly promising to achieve a sustainable capacity growth cost-effectively in the future. Despite its great potential, IRS faces new challenges to be efficiently integrated into wireless networks, such as reflection optimization, channel estimation, and deployment from communication design perspectives. In this paper, we provide a tutorial overview of IRS-aided wireless communications to address the above issues, and elaborate its reflection and channel models, hardware architecture and practical constraints, as well as various appealing applications in wireless networks. Moreover, we highlight important directions worthy of further investigation in future work.

Intelligent Reflecting Surface-Aided Wireless Communications: A Tutorial

Advances in wireless communication technologies, such as wearable and implantable biosensors, along with recent developments in the embedded computing area are enabling the design, development, and implementation of body area networks. This class of networks is paving the way for the deployment of innovative healthcare monitoring applications. In the past few years, much of the research in the area of body area networks has focused on issues related to wireless sensor designs, sensor miniaturization, low-power sensor circuitry, signal processing, and communications protocols. In this paper, we present an overview of body area networks, and a discussion of BAN communications types and their related issues. We provide a detailed investigation of sensor devices, physical layer, data link layer, and radio technology aspects of BAN research. We also present a taxonomy of BAN projects that have been introduced/proposed to date. Finally, we highlight some of the design challenges and open issues that still need to be addressed to make BANs truly ubiquitous for a wide range of applications.

Body Area Networks: A Survey

This paper presents an overview of ultrawideband (UWB) propagation channels. It first demonstrates how the frequency selectivity of propagation processes causes fundamental differences between UWB channels and "conventional" (narrowband) channels. The concept of pathloss has to be modified, and the well-known WSSUS model is not applicable anymore. The paper also describes deterministic and stochastic models for UWB channels, identifies the key parameters for the description of delay dispersion, attenuation, and directional characterization, and surveys the typical parameter values that have been measured. Measurement techniques and methods for extracting model parameters are also different in UWB channels; for example, the concepts of narrowband channel parameter estimation (e.g., maximum-likelihood estimation) have to be modified. Finally, channel models also have an important impact on the performance evaluation of various UWB systems.

Ultrawideband propagation channels-theory, measurement, and modeling

Antenna Theory And Design

In this paper, on-body propagation modelling has been investigated applying various numerical computational techniques. Propagation measurements with body-worn antennas have been carried out at 2.4 GHz inside and outside an anechoic chamber respectively for narrowband communication channel characterisation. Both simulation and measurement results have been also obtained at the UWB (ultra wide-band) band.

Antennas And Propagation for Body-Centric Wireless Communications

A wideband neutralization line is proposed to reduce the mutual coupling of a compact ultrawideband (UWB) multiple-input-multiple-output (MIMO) antenna. With the introduced decoupling method, the designed UWB MIMO antenna covers the band of 3.1-5 GHz with an isolation of higher than 22 dB. The proposed wideband neutralization line is not necessarily placed in the clearance area between two MIMO elements and can be put above the copper ground. A small clearance (antenna area) of 35 ×16 mm
 2
 is achieved. The designed UWB MIMO antenna is fabricated. Sparameters, radiation patterns, total efficiency, and realized gain of the prototype are measured and compared to the simulations.

Mutual Coupling Reduction for UWB MIMO Antennas with a Wideband Neutralization Line

COST 231 - Digital Mobile Radio Towards Future generation Systems

This letter proposes a new design of millimeter-wave (mm-Wave) array antenna package with beam steering characteristic for the fifth-generation (5G) mobile applications. In order to achieve a broad three-dimensional scanning coverage of the space with high-gain beams, three identical subarrays of patch antennas have been compactly arranged along the edge region of the mobile phone printed circuit board (PCB) to form the antenna package. By switching the feeding to one of the subarrays, the desired direction of coverage can be achieved. The proposed design has >10-dB gain in the upper spherical space, good directivity, and efficiency, which is suitable for 5G mobile communications. In addition, the impact of the user's hand on the antenna performance has been investigated.

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A Switchable 3-D-Coverage-Phased Array Antenna Package for 5G Mobile Terminals

This paper presents a novel small-size directional antenna design for ultrawide-band wireless body area networks/wireless personal area networks applications. The design is based on a typical slot antenna structure with an added reflector in order to achieve directionality. The effects of different antenna parameters and human body proximity on the radiation characteristics are analyzed. Antenna measurements with an optic RF setup were performed in order to characterize the small-size antenna far field radiation pattern. The different structural antenna parameters were optimized via extensive numerical simulations. Results show that for frequencies above 3.5 GHz, where the power front-to-back ratio of the directional antenna is greater than 10 dB, its impedance is nearly the same as in the free space. It is not the case neither for the omnidirectional slot antenna nor the monopole antenna next to the body. Between 3 and 6 GHz performance of the novel directional antenna, in terms of radiation efficiency and SAR values, is significantly improved compared to omnidirectional antenna designs.

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Gert Frølund Pedersen

Papers

Antennas And Propagation for Body-Centric Wireless Communications

Mutual Coupling Reduction for UWB MIMO Antennas with a Wideband Neutralization Line

COST 231 - Digital Mobile Radio Towards Future generation Systems

A Switchable 3-D-Coverage-Phased Array Antenna Package for 5G Mobile Terminals

Novel small-size directional antenna for UWB WBAN/WPAN applications