1,164 research outputs found
KPI/KQI-Driven Coordinated Multi-Point in 5G: Measurements, Field Trials, and Technical Solutions
The fifth generation (5G) systems are expected to be able to support massive
number of wireless devices and intense demands for high data rates while
maintaining low latency. Coordinated multipoint (CoMP) is advocated by recent
advances and is envisioned to continue its adoption in 5G to meet these
requirements by alleviating inter-cell interference and improving spectral
efficiency. The higher requirements in 5G have raised the stakes on developing
a new CoMP architecture. To understand the merits and limitations of CoMP in
5G, this article systematically investigates evaluation criteria including key
performance indicators (KPIs) and key quality indicators (KQIs) in 5G, conducts
empirical measurements and field tests, and then proposes a KPI/KQI-driven CoMP
architecture that fulfills KPI requirements and provides KQI guarantee for each
user
Large System Analysis of Cooperative Multi-cell Downlink Transmission via Regularized Channel Inversion with Imperfect CSIT
In this paper, we analyze the ergodic sum-rate of a multi-cell downlink
system with base station (BS) cooperation using regularized zero-forcing (RZF)
precoding. Our model assumes that the channels between BSs and users have
independent spatial correlations and imperfect channel state information at the
transmitter (CSIT) is available. Our derivations are based on large dimensional
random matrix theory (RMT) under the assumption that the numbers of antennas at
the BS and users approach to infinity with some fixed ratios. In particular, a
deterministic equivalent expression of the ergodic sum-rate is obtained and is
instrumental in getting insight about the joint operations of BSs, which leads
to an efficient method to find the asymptotic-optimal regularization parameter
for the RZF. In another application, we use the deterministic channel rate to
study the optimal feedback bit allocation among the BSs for maximizing the
ergodic sum-rate, subject to a total number of feedback bits constraint. By
inspecting the properties of the allocation, we further propose a scheme to
greatly reduce the search space for optimization. Simulation results
demonstrate that the ergodic sum-rates achievable by a subspace search provides
comparable results to those by an exhaustive search under various typical
settings.Comment: 13 pages, 9 figures, IEEE Transactions on Wireless Communication
Non-Orthogonal Multiple Access: Common Myths and Critical Questions
Non-orthogonal multiple access (NOMA) has received tremendous attention for
the design of radio access techniques for fifth generation (5G) wireless
networks and beyond. The basic concept behind NOMA is to serve more than one
user in the same resource block, e.g., a time slot, subcarrier, spreading code,
or space. With this, NOMA promotes massive connectivity, lowers latency,
improves user fairness and spectral efficiency, and increases reliability
compared to orthogonal multiple access (OMA) techniques. While NOMA has gained
significant attention from the communications community, it has also been
subject to several widespread misunderstandings, such as The above statements are actually false, and this paper aims at
identifying such common myths about NOMA and clarifying why they are not true.
We also pose critical questions that are important for the effective adoption
of NOMA in 5G and beyond and identify promising research directions for NOMA,
which will require intense investigation in the future.Comment: To appear in the IEEE Wireless Communication
Downlink Performance of Uplink Fractional Power Control in 5G Massive MIMO Systems
Uplink power control is an efficient scheme to mitigate pilot contamination
in massive multiple-input multiple-output (MIMO) systems. In this work, we
provide a comprehensive study on the effects of fractional power control (FPC)
on the downlink performance of the most relevant fifth generation (5G) massive
MIMO deployments. Specifically, we perform thorough system simulations based on
the most recent three dimensional spatial channel model released by the 3rd
Generation Partnership Project to evaluate the impact of different
deployment-related parameters such as pilot reuse factor, beamforming
criterion, and base station array size. Our results indicate the most suitable
tuning of the FPC parameters and show that optimized FPC provides huge gains in
the cell border throughput when compared to a baseline scheme with all the
users transmitting at maximum power. Moreover, our simulations also demonstrate
that the effectiveness of FPC grows in scenarios with severe pilot
contamination, confirming that implementing this feature is essential in
realistic deployments.Comment: Accepted at the IEEE GLOBECOM Workshop on Emerging Technologies for
5G and Beyond Wireless and Mobile Networks, Abu Dhabi (UAE), Dec. 201
Overview of Full-Dimension MIMO in LTE-Advanced Pro
Multiple-input multiple-output (MIMO) systems with a large number of
basestation antennas, often called massive MIMO, have received much attention
in academia and industry as a means to improve the spectral efficiency, energy
efficiency, and processing complexity of next generation cellular system.
Mobile communication industry has initiated a feasibility study of massive MIMO
systems to meet the increasing demand of future wireless systems. Field trials
of the proof-of-concept systems have demonstrated the potential gain of the
Full-Dimension MIMO (FD-MIMO), an official name for the MIMO enhancement in 3rd
generation partnership project (3GPP). 3GPP initiated standardization activity
for the seamless integration of this technology into current 4G LTE systems. In
this article, we provide an overview of the FD-MIMO system, with emphasis on
the discussion and debate conducted on the standardization process of Release
13. We present key features for FD-MIMO systems, a summary of the major issues
for the standardization and practical system design, and performance
evaluations for typical FD-MIMO scenarios
Recent Advances in Cloud Radio Access Networks: System Architectures, Key Techniques, and Open Issues
As a promising paradigm to reduce both capital and operating expenditures,
the cloud radio access network (C-RAN) has been shown to provide high spectral
efficiency and energy efficiency. Motivated by its significant theoretical
performance gains and potential advantages, C-RANs have been advocated by both
the industry and research community. This paper comprehensively surveys the
recent advances of C-RANs, including system architectures, key techniques, and
open issues. The system architectures with different functional splits and the
corresponding characteristics are comprehensively summarized and discussed. The
state-of-the-art key techniques in C-RANs are classified as: the fronthaul
compression, large-scale collaborative processing, and channel estimation in
the physical layer; and the radio resource allocation and optimization in the
upper layer. Additionally, given the extensiveness of the research area, open
issues and challenges are presented to spur future investigations, in which the
involvement of edge cache, big data mining, social-aware device-to-device,
cognitive radio, software defined network, and physical layer security for
C-RANs are discussed, and the progress of testbed development and trial test
are introduced as well.Comment: 27 pages, 11 figure
Spatial Intercell Interference Cancellation with CSI Training and Feedback
We investigate intercell interference cancellation (ICIC) with a practical
downlink training and uplink channel state information (CSI) feedback model.
The average downlink throughput for such a 2-cell network is derived. The user
location has a strong effect on the signal-to-interference ratio (SIR) and the
channel estimation error. This motivates adaptively switching between
traditional (single-cell) beamforming and ICIC at low signal-to-noise ratio
(SNR) where ICIC is preferred only with low SIR and accurate channel
estimation, and the use of ICIC with optimized training and feedback at high
SNR. For a given channel coherence time and fixed training and feedback
overheads, we develop optimal data vs. pilot power allocation for CSI training
as well as optimal feedback resource allocation to feed back CSI of different
channels. Both analog and finite-rate digital feedback are considered. With
analog feedback, the training power optimization provides a more significant
performance gain than feedback optimization; while conversely for digital
feedback, performance is more sensitive to the feedback bit allocation than the
training power optimization. We show that even with low-rate feedback and
standard training, ICIC can transform an interference-limited cellular network
into a noise-limited one.Comment: 24 pages, 10 figures, submitted to IEEE Trans. Wireless Commun., May,
201
Pushing the Limits of LTE: A Survey on Research Enhancing the Standard
Cellular networks are an essential part of todays communication
infrastructure. The ever-increasing demand for higher data-rates calls for a
close cooperation between researchers and industry/standardization experts
which hardly exists in practice. In this article we give an overview about our
efforts in trying to bridge this gap. Our research group provides a
standard-compliant open-source simulation platform for 3GPP LTE that enables
reproducible research in a well-defined environment. We demonstrate that much
innovative research under the confined framework of a real-world standard is
still possible, sometimes even encouraged. With examplary samples of our
research work we investigate on the potential of several important research
areas under typical practical conditions.Comment: The final version of the manuscript is available at:
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6514821&isnumber=633654
Massive MIMO for Drone Communications: Case Studies and Future Directions
Unmanned aerial vehicles (UAVs), also known as drones, are proliferating.
Applications, such as surveillance, disaster management, and drone racing,
place high requirements on the communication with the drones in terms of
throughput, reliability, and latency. The existing wireless technologies,
notably Wi-Fi, that are currently used for drone connectivity are limited to
short ranges and low-mobility situations. New, scalable technology is needed to
meet future demands on long connectivity ranges, support for fast-moving
drones, and the possibility to simultaneously communicate with entire swarms of
drones. Massive multiple-input and multiple-output (MIMO), the main technology
component of emerging 5G standards, has the potential to meet these
requirements.Comment: To appear in IEEE Acces
Cloud Radio Access Network: Virtualizing Wireless Access for Dense Heterogeneous Systems
Cloud Radio Access Network (C-RAN) refers to the virtualization of base
station functionalities by means of cloud computing. This results in a novel
cellular architecture in which low-cost wireless access points, known as radio
units (RUs) or remote radio heads (RRHs), are centrally managed by a
reconfigurable centralized "cloud", or central, unit (CU). C-RAN allows
operators to reduce the capital and operating expenses needed to deploy and
maintain dense heterogeneous networks. This critical advantage, along with
spectral efficiency, statistical multiplexing and load balancing gains, make
C-RAN well positioned to be one of the key technologies in the development of
5G systems. In this paper, a succinct overview is presented regarding the state
of the art on the research on C-RAN with emphasis on fronthaul compression,
baseband processing, medium access control, resource allocation, system-level
considerations and standardization efforts.Comment: To appear on JC
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