1,146 research outputs found
mmWave Massive MIMO with Simple RF and Appropriate DSP
There is considerable interest in the combined use of millimeter-wave
(mmwave) frequencies and arrays of massive numbers of antennas (massive MIMO)
for next-generation wireless communications systems. A symbiotic relationship
exists between these two factors: mmwave frequencies allow for densely packed
antenna arrays, and hence massive MIMO can be achieved with a small form
factor; low per-antenna SNR and shadowing can be overcome with a large array
gain; steering narrow beams or nulls with a large array is a good match for the
line-of-sight (LOS) or near-LOS mmwave propagation environments, etc.. However,
the cost and power consumption for standard implementations of massive MIMO
arrays at mmwave frequencies is a significant drawback to rapid adoption and
deployment. In this paper, we examine a number of possible approaches to reduce
cost and power at both the basestation and user terminal, making up for it with
signal processing and additional (cheap) antennas. These approaches include
lowresolution Analog-to-Digital Converters (ADCs), wireless local oscillator
distribution networks, spatial multiplexing and multistreaming instead of
higher-order modulation etc.. We will examine the potential of these approaches
in making mmwave massive MIMO a reality and discuss the requirements in terms
of digital signal processing (DSP).Comment: published in Asilomar 201
Impact of polarization diversity in massive MIMO for industry 4.0
The massive polarimetric radio channel is evaluated in an indoor industrial scenario at 3.5 GHz using a 10×10 uniform rectangular array (URA). The analysis is based on (1) propagation characteristics like the average received gain and the power to interference ratio from the Gram matrix and (2) system-oriented metrics such as sum-rate capacity with maximum-ratio transmitter (MRT). The results clearly show the impact of polarization diversity in an industrial scenario and how it can considerably improve different aspects of the system design. Results for sum-rate capacity are promising and show that the extra degree of freedom, provided by polarization diversity, can optimize the performance of a very simple precoder, the MRT
Spectral Efficiency Optimization in Flexi-Grid Long-Haul Optical Systems
Flexible grid optical networks allow a better exploitation of fiber capacity,
by enabling a denser frequency allocation. A tighter channel spacing, however,
requires narrower filters, which increase linear intersymbol interference
(ISI), and may dramatically reduce system reach. Commercial coherent receivers
are based on symbol by symbol detectors, which are quite sensitive to ISI. In
this context, Nyquist spacing is considered as the ultimate limit to
wavelength-division multiplexing (WDM) packing.
In this paper, we show that by introducing a limited-complexity trellis
processing at the receiver, either the reach of Nyquist WDM flexi-grid networks
can be significantly extended, or a denser-than-Nyquist channel packing (i.e.,
a higher spectral efficiency (SE)) is possible at equal reach. By adopting
well-known information-theoretic techniques, we design a limited-complexity
trellis processing and quantify its SE gain in flexi-grid architectures where
wavelength selective switches over a frequency grid of 12.5GHz are employed.Comment: 7 pages, 9 figure
A Survey of Physical Layer Security Techniques for 5G Wireless Networks and Challenges Ahead
Physical layer security which safeguards data confidentiality based on the
information-theoretic approaches has received significant research interest
recently. The key idea behind physical layer security is to utilize the
intrinsic randomness of the transmission channel to guarantee the security in
physical layer. The evolution towards 5G wireless communications poses new
challenges for physical layer security research. This paper provides a latest
survey of the physical layer security research on various promising 5G
technologies, including physical layer security coding, massive multiple-input
multiple-output, millimeter wave communications, heterogeneous networks,
non-orthogonal multiple access, full duplex technology, etc. Technical
challenges which remain unresolved at the time of writing are summarized and
the future trends of physical layer security in 5G and beyond are discussed.Comment: To appear in IEEE Journal on Selected Areas in Communication
Achieving Large Multiplexing Gain in Distributed Antenna Systems via Cooperation with pCell Technology
In this paper we present pCellTM technology, the first commercial-grade
wireless system that employs cooperation between distributed transceiver
stations to create concurrent data links to multiple users in the same
spectrum. First we analyze the per-user signal-to-interference-plus-noise ratio
(SINR) employing a geometrical spatial channel model to define volumes in space
of coherent signal around user antennas (or personal cells, i.e., pCells). Then
we describe the system architecture consisting of a general-purpose-processor
(GPP) based software-defined radio (SDR) wireless platform implementing a
real-time LTE protocol stack to communicate with off-the-shelf LTE devices.
Finally we present experimental results demonstrating up to 16 concurrent
spatial channels for an aggregate average spectral efficiency of 59.3 bps/Hz in
the downlink and 27.5 bps/Hz in the uplink, providing data rates of 200 Mbps
downlink and 25 Mbps uplink in 5 MHz of TDD spectrum.Comment: IEEE Asilomar Conference on Signals, Systems, and Computers, Nov.
8-11th 2015, Pacific Grove, CA, US
Reconfigurable Intelligent Surfaces for Wireless Communications: Principles, Challenges, and Opportunities
Recently there has been a flurry of research on the use of reconfigurable
intelligent surfaces (RIS) in wireless networks to create smart radio
environments. In a smart radio environment, surfaces are capable of
manipulating the propagation of incident electromagnetic waves in a
programmable manner to actively alter the channel realization, which turns the
wireless channel into a controllable system block that can be optimized to
improve overall system performance. In this article, we provide a tutorial
overview of reconfigurable intelligent surfaces (RIS) for wireless
communications. We describe the working principles of reconfigurable
intelligent surfaces (RIS) and elaborate on different candidate implementations
using metasurfaces and reflectarrays. We discuss the channel models suitable
for both implementations and examine the feasibility of obtaining accurate
channel estimates. Furthermore, we discuss the aspects that differentiate RIS
optimization from precoding for traditional MIMO arrays highlighting both the
arising challenges and the potential opportunities associated with this
emerging technology. Finally, we present numerical results to illustrate the
power of an RIS in shaping the key properties of a MIMO channel.Comment: to appear in the IEEE Transactions on Cognitive Communications and
Networking (TCCN
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