1,075 research outputs found
Modeling and Analyzing Millimeter Wave Cellular Systems
We provide a comprehensive overview of mathematical models and analytical
techniques for millimeter wave (mmWave) cellular systems. The two fundamental
physical differences from conventional Sub-6GHz cellular systems are (i)
vulnerability to blocking, and (ii) the need for significant directionality at
the transmitter and/or receiver, which is achieved through the use of large
antenna arrays of small individual elements. We overview and compare models for
both of these factors, and present a baseline analytical approach based on
stochastic geometry that allows the computation of the statistical
distributions of the downlink signal-to-interference-plus-noise ratio (SINR)
and also the per link data rate, which depends on the SINR as well as the
average load. There are many implications of the models and analysis: (a)
mmWave systems are significantly more noise-limited than at Sub-6GHz for most
parameter configurations; (b) initial access is much more difficult in mmWave;
(c) self-backhauling is more viable than in Sub-6GHz systems which makes
ultra-dense deployments more viable, but this leads to increasingly
interference-limited behavior; and (d) in sharp contrast to Sub-6GHz systems
cellular operators can mutually benefit by sharing their spectrum licenses
despite the uncontrolled interference that results from doing so. We conclude
by outlining several important extensions of the baseline model, many of which
are promising avenues for future research.Comment: 50 pages, 10 figures, submitted to IEEE Trans. Communications,
invited pape
5G Cellular User Equipment: From Theory to Practical Hardware Design
Research and development on the next generation wireless systems, namely 5G,
has experienced explosive growth in recent years. In the physical layer (PHY),
the massive multiple-input-multiple-output (MIMO) technique and the use of high
GHz frequency bands are two promising trends for adoption. Millimeter-wave
(mmWave) bands such as 28 GHz, 38 GHz, 64 GHz, and 71 GHz, which were
previously considered not suitable for commercial cellular networks, will play
an important role in 5G. Currently, most 5G research deals with the algorithms
and implementations of modulation and coding schemes, new spatial signal
processing technologies, new spectrum opportunities, channel modeling, 5G proof
of concept (PoC) systems, and other system-level enabling technologies. In this
paper, we first investigate the contemporary wireless user equipment (UE)
hardware design, and unveil the critical 5G UE hardware design constraints on
circuits and systems. On top of the said investigation and design trade-off
analysis, a new, highly reconfigurable system architecture for 5G cellular user
equipment, namely distributed phased arrays based MIMO (DPA-MIMO) is proposed.
Finally, the link budget calculation and data throughput numerical results are
presented for the evaluation of the proposed architecture.Comment: Submitted to IEEE ACCESS. It has 18 pages, 17 figures, and 5 table
Millimeter Wave MIMO with Lens Antenna Array: A New Path Division Multiplexing Paradigm
Millimeter wave (mmWave) communication is a promising technology for 5G
cellular systems. To compensate for the severe path loss in mmWave systems,
large antenna arrays are generally used to achieve significant beamforming
gains. However, due to the high hardware and power consumption cost associated
with radio frequency (RF) chains, it is desirable to achieve the large-antenna
gains, but with only limited number of RF chains for mmWave communications. To
this end, we study in this paper a new lens antenna array enabled mmWave MIMO
communication system. We first show that the array response of the proposed
lens antenna array at the receiver/transmitter follows a "sinc" function, where
the antenna with the peak response is determined by the angle of arrival
(AoA)/departure (AoD) of the received/transmitted signal. By exploiting this
unique property of lens antenna arrays along with the multi-path sparsity of
mmWave channels, we propose a novel low-cost and capacity-achieving MIMO
transmission scheme, termed \emph{orthogonal path division multiplexing
(OPDM)}. For channels with insufficiently separated AoAs and/or AoDs, we also
propose a simple \emph{path grouping} technique with group-based small-scale
MIMO processing to mitigate the inter-path interference. Numerical results are
provided to compare the performance of the proposed lens antenna arrays for
mmWave MIMO system against that of conventional arrays, under different
practical setups. It is shown that the proposed system achieves significant
throughput gain as well as complexity and hardware cost reduction, both making
it an appealing new paradigm for mmWave MIMO communications.Comment: submitted for possible journal publicatio
Millimeter Wave Cellular Wireless Networks: Potentials and Challenges
Millimeter wave (mmW) frequencies between 30 and 300 GHz are a new frontier
for cellular communication that offers the promise of orders of magnitude
greater bandwidths combined with further gains via beamforming and spatial
multiplexing from multi-element antenna arrays. This paper surveys measurements
and capacity studies to assess this technology with a focus on small cell
deployments in urban environments. The conclusions are extremely encouraging;
measurements in New York City at 28 and 73 GHz demonstrate that, even in an
urban canyon environment, significant non-line-of-sight (NLOS) outdoor,
street-level coverage is possible up to approximately 200 m from a potential
low power micro- or picocell base station. In addition, based on statistical
channel models from these measurements, it is shown that mmW systems can offer
more than an order of magnitude increase in capacity over current
state-of-the-art 4G cellular networks at current cell densities. Cellular
systems, however, will need to be significantly redesigned to fully achieve
these gains. Specifically, the requirement of highly directional and adaptive
transmissions, directional isolation between links and significant
possibilities of outage have strong implications on multiple access, channel
structure, synchronization and receiver design. To address these challenges,
the paper discusses how various technologies including adaptive beamforming,
multihop relaying, heterogeneous network architectures and carrier aggregation
can be leveraged in the mmW context.Comment: 17 pages, 15 figures. arXiv admin note: text overlap with
arXiv:1312.492
A Survey of Millimeter Wave (mmWave) Communications for 5G: Opportunities and Challenges
With the explosive growth of mobile data demand, the fifth generation (5G)
mobile network would exploit the enormous amount of spectrum in the millimeter
wave (mmWave) bands to greatly increase communication capacity. There are
fundamental differences between mmWave communications and existing other
communication systems, in terms of high propagation loss, directivity, and
sensitivity to blockage. These characteristics of mmWave communications pose
several challenges to fully exploit the potential of mmWave communications,
including integrated circuits and system design, interference management,
spatial reuse, anti-blockage, and dynamics control. To address these
challenges, we carry out a survey of existing solutions and standards, and
propose design guidelines in architectures and protocols for mmWave
communications. We also discuss the potential applications of mmWave
communications in the 5G network, including the small cell access, the cellular
access, and the wireless backhaul. Finally, we discuss relevant open research
issues including the new physical layer technology, software-defined network
architecture, measurements of network state information, efficient control
mechanisms, and heterogeneous networking, which should be further investigated
to facilitate the deployment of mmWave communication systems in the future 5G
networks.Comment: 17 pages, 8 figures, 7 tables, Journal pape
Joint Spatial Division and Multiplexing for mm-Wave Channels
Massive MIMO systems are well-suited for mm-Wave communications, as large
arrays can be built with reasonable form factors, and the high array gains
enable reasonable coverage even for outdoor communications. One of the main
obstacles for using such systems in frequency-division duplex mode, namely the
high overhead for the feedback of channel state information (CSI) to the
transmitter, can be mitigated by the recently proposed JSDM (Joint Spatial
Division and Multiplexing) algorithm. In this paper we analyze the performance
of this algorithm in some realistic propagation channels that take into account
the partial overlap of the angular spectra from different users, as well as the
sparsity of mm-Wave channels. We formulate the problem of user grouping for two
different objectives, namely maximizing spatial multiplexing, and maximizing
total received power, in a graph-theoretic framework. As the resulting problems
are numerically difficult, we proposed (sub optimum) greedy algorithms as
efficient solution methods. Numerical examples show that the different
algorithms may be superior in different settings.We furthermore develop a new,
"degenerate" version of JSDM that only requires average CSI at the transmitter,
and thus greatly reduces the computational burden. Evaluations in propagation
channels obtained from ray tracing results, as well as in measured outdoor
channels show that this low-complexity version performs surprisingly well in
mm-Wave channels.Comment: Accepted for publication in "JSAC Special Issue in 5G Communication
Systems
An Overview of Signal Processing Techniques for Millimeter Wave MIMO Systems
Communication at millimeter wave (mmWave) frequencies is defining a new era
of wireless communication. The mmWave band offers higher bandwidth
communication channels versus those presently used in commercial wireless
systems. The applications of mmWave are immense: wireless local and personal
area networks in the unlicensed band, 5G cellular systems, not to mention
vehicular area networks, ad hoc networks, and wearables. Signal processing is
critical for enabling the next generation of mmWave communication. Due to the
use of large antenna arrays at the transmitter and receiver, combined with
radio frequency and mixed signal power constraints, new multiple-input
multiple-output (MIMO) communication signal processing techniques are needed.
Because of the wide bandwidths, low complexity transceiver algorithms become
important. There are opportunities to exploit techniques like compressed
sensing for channel estimation and beamforming. This article provides an
overview of signal processing challenges in mmWave wireless systems, with an
emphasis on those faced by using MIMO communication at higher carrier
frequencies.Comment: Submitted to IEEE Journal of Selected Topics in Signal Processin
Comparative Analysis of Initial Access Techniques in 5G mmWave Cellular Networks
The millimeter wave frequencies (roughly above 10 GHz) offer the availability
of massive bandwidth to greatly increase the capacity of fifth generation (5G)
cellular wireless systems. However, to overcome the high isotropic pathloss at
these frequencies, highly directional transmissions will be required at both
the base station (BS) and the mobile user equipment (UE) to establish
sufficient link budget in wide area networks. This reliance on directionality
has important implications for control layer procedures. Initial access in
particular can be significantly delayed due to the need for the BS and the UE
to find the initial directions of transmission. This paper provides a survey of
several recently proposed techniques. Detection probability and delay analysis
is performed to compare various techniques including exhaustive and iterative
search. We show that the optimal strategy depends on the target SNR regime.Comment: Accepted at 50th Annual Conference on Information Sciences and
Systems (CISS), 201
Near-Optimal Hybrid Analog and Digital Precoding for Downlink mmWave Massive MIMO Systems
Millimeter wave (mmWave) massive MIMO can achieve orders of magnitude
increase in spectral and energy efficiency, and it usually exploits the hybrid
analog and digital precoding to overcome the serious signal attenuation induced
by mmWave frequencies. However, most of hybrid precoding schemes focus on the
full-array structure, which involves a high complexity. In this paper, we
propose a near-optimal iterative hybrid precoding scheme based on the more
realistic subarray structure with low complexity. We first decompose the
complicated capacity optimization problem into a series of ones easier to be
handled by considering each antenna array one by one. Then we optimize the
achievable capacity of each antenna array from the first one to the last one by
utilizing the idea of successive interference cancelation (SIC), which is
realized in an iterative procedure that is easy to be parallelized. It is shown
that the proposed hybrid precoding scheme can achieve better performance than
other recently proposed hybrid precoding schemes, while it also enjoys an
acceptable computational complexity
Eliminating Interference in LOS Massive Multi-User MIMO with a Few Transceivers
Wireless cellular communication networks are bandwidth and interference
limited. An important means to overcome these resource limitations is the use
of multiple antennas. Base stations equipped with a very large (massive) number
of antennas have been the focus of recent research. A bottleneck in such
systems is the limited number of transmit/receive chains. In this work, a
line-of-sight (LOS) channel model is considered. It is shown that for a given
number of interferers, it suffices that the number of transmit/receive chains
exceeds the number of desired users by one, assuming a sufficiently large
antenna array. From a theoretical point of view, this is the first result
proving the near-optimal performance of antenna selection, even when the total
number of signals (desired and interfering) is larger than the number of
receive chains. Specifically, a single additional chain suffices to reduce the
interference to any desired level. We prove that using the proposed selection,
a simple linear receiver/transmitter for the uplink/downlink provides
near-optimal rates. In particular, in the downlink direction, there is no need
for complicated dirty paper coding; each user can use an optimal code for a
single user interference-free channel. In the uplink direction, there is almost
no gain in implementing joint decoding. The proposed approach is also a
significant improvement both from system and computational perspectives.
Simulation results demonstrating the performance of the proposed method are
provided
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