1,620 research outputs found
Full-Duplex Non-Orthogonal Multiple Access for Modern Wireless Networks
Non-orthogonal multiple access (NOMA) is an interesting concept to provide
higher capacity for future wireless communications. In this article, we
consider the feasibility and benefits of combining full-duplex operation with
NOMA for modern communication systems. Specifically, we provide a comprehensive
overview on application of full-duplex NOMA in cellular networks, cooperative
and cognitive radio networks, and characterize gains possible due to
full-duplex operation. Accordingly, we discuss challenges, particularly the
self-interference and inter-user interference and provide potential solutions
to interference mitigation and quality-of-service provision based on
beamforming, power control, and link scheduling. We further discuss future
research challenges and interesting directions to pursue to bring full-duplex
NOMA into maturity and use in practice.Comment: Revised, IEEE Wireless Communication Magazin
Relaying Strategies for Uplink in Wireless Cellular Networks
In this paper, we analyze the impact of relays on the uplink performance of
FDMA cellular networks. We focus our analysis on Decode and Forward techniques,
with the aim of measuring the improvements which can be achieved in terms of
throughput and energy saving. We apply a stochastic geometry based approach to
a scenario with inter-cell interference and reuse factor equal to 1. The first
goal of this work is to observe what is the impact of various relay features,
such as transmission power, location and antenna pattern, when a half-duplex
constraint is imposed. The second goal is to determine how much relaying can be
beneficial also for users who are not at the cell edge, and who can therefore
use a direct link towards the base station. We show that if more refined
decoding techniques, such as Successive Interference Cancellation and
Superposition Coding, are properly used, considerable gains can be obtained for
these mobiles as well.Comment: 30 pages, 10 figure
Full-Duplex Cloud Radio Access Networks: An Information-Theoretic Viewpoint
The conventional design of cellular systems prescribes the separation of
uplink and downlink transmissions via time-division or frequency-division
duplex. Recent advances in analog and digital domain self-interference
interference cancellation challenge the need for this arrangement and open up
the possibility to operate base stations, especially low-power ones, in a
full-duplex mode. As a means to cope with the resulting downlink-to-uplink
interference among base stations, this letter investigates the impact of the
Cloud Radio Access Network (C-RAN) architecture. The analysis follows an
information theoretic approach based on the classical Wyner model. The
analytical results herein confirm the significant potential advantages of the
C-RAN architecture in the presence of full-duplex base stations, as long as
sufficient fronthaul capacity is available and appropriate mobile station
scheduling, or successive interference cancellation at the mobile stations, is
implemented.Comment: To appear in IEEE Wireless Communications Letter
Anywhere Decoding: Low-Overhead Uplink Interference Management for Wireless Networks
Inter-cell interference (ICI) is one of the major performance-limiting
factors in the context of modern cellular systems. To tackle ICI, coordinated
multi-point (CoMP) schemes have been proposed as a key technology for
next-generation mobile communication systems. Although CoMP schemes offer
promising theoretical gains, their performance could degrade significantly
because of practical issues such as limited backhaul. To address this issue, we
explore a novel uplink interference management scheme called anywhere decoding,
which requires exchanging just a few bits of information per coding interval
among the base stations (BSs). In spite of the low overhead of anywhere
decoding, we observe considerable gains in the outage probability performance
of cell-edge users, compared to no cooperation between BSs. Additionally,
asymptotic results of the outage probability for high-SNR regimes demonstrate
that anywhere decoding schemes achieve full spatial diversity through multiple
decoding opportunities, and they are within 1.5 dB of full cooperation
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
Joint Bi-Directional Training of Nonlinear Precoders and Receivers in Cellular Networks
Joint optimization of nonlinear precoders and receive filters is studied for
both the uplink and downlink in a cellular system. For the uplink, the base
transceiver station (BTS) receiver implements successive interference
cancellation, and for the downlink, the BTS station pre-compensates for the
interference with Tomlinson-Harashima precoding (THP). Convergence of
alternating optimization of receivers and transmitters in a single cell is
established when filters are updated according to a minimum mean squared error
(MMSE) criterion, subject to appropriate power constraints. Adaptive algorithms
are then introduced for updating the precoders and receivers in the absence of
channel state information, assuming time-division duplex transmissions with
channel reciprocity. Instead of estimating the channels, the filters are
directly estimated according to a least squares criterion via bi-directional
training: Uplink pilots are used to update the feedforward and feedback
filters, which are then used as interference pre-compensation filters for
downlink training of the mobile receivers. Numerical results show that
nonlinear filters can provide substantial gains relative to linear filters with
limited forward-backward iterations.Comment: 12 pages, 9 figures, submitted to IEEE Trans. Signal Process., Aug.
201
Cell Associations that Maximize the Average Uplink-Downlink Degrees of Freedom
We study the problem of associating mobile terminals to base stations in a
linear interference network, with the goal of maximizing the average rate
achieved over both the uplink and downlink sessions. The cell association
decision is made at a centralized cloud level, with access to global network
topology information. More specifically, given the constraint that each mobile
terminal can be associated to a maximum of N base stations at once, we
characterize the maximum achievable pre-log factor (degrees of freedom) and the
corresponding cell association pattern. Interestingly, the result indicates
that for the case where N > 1, the optimal cell association guarantees the
achievability of the maximum uplink rate even when optimizing for the uplink
alone, and for the case where N=1, the optimal cell association is that of the
downlink. Hence, this work draws attention to the question of characterizing
network topologies for which the problem can be simplified by optimizing only
for the uplink or only for the downlink.Comment: 5 pages, In proceedings of ISIT 201
Uplink Cooperative NOMA for Cellular-Connected UAV
Aerial-ground interference mitigation is a challenging issue in the
cellular-connected unmanned aerial vehicle (UAV) communications. Due to the
strong line-of-sight (LoS) air-to-ground (A2G) channels, the UAV may
impose/suffer more severe uplink/downlink interference to/from the cellular
base stations (BSs) than the ground users. To tackle this challenge, we propose
to apply the non-orthogonal multiple access (NOMA) technique to the uplink
communication from a UAV to cellular BSs, under spectrum sharing with the
existing ground users. However, for our considered system, traditional NOMA
with local interference cancellation (IC), termed non-cooperative NOMA, may
provide very limited gain compared to the OMA. This is because there are many
co-channel BSs due to the LoS A2G channels and thus the UAV's rate performance
is severely limited by the BS with the worst channel condition with the UAV. To
improve the UAV's achievable rate, a new cooperative NOMA scheme is proposed by
exploiting the backhaul links among BSs. Specifically, some BSs with better
channel conditions are selected to decode the UAV's signals first, and then
forward the decoded signals to their backhaul-connected BSs for IC. To
investigate the optimal design of cooperative NOMA, we maximize the weighted
sum-rate of the UAV and ground users by jointly optimizing the UAV's rate and
power allocations over multiple resource blocks. However, this problem is hard
to be solved optimally. To obtain useful insights, we first consider two
special cases with egoistic and altruistic transmission strategies of the UAV,
respectively, and solve their corresponding problems optimally. Next, we
consider the general case and propose an efficient suboptimal solution via the
alternating optimization. Numerical results show that the proposed cooperative
NOMA yields significant throughput gains than the OMA and the non-cooperative
NOMA benchmark.Comment: 13 pages, 6 figures. Accepted for publication in IEEE JSTSP. arXiv
admin note: text overlap with arXiv:1807.0821
Large-Scale NOMA: Promises for Massive Machine-Type Communication
We investigate on large-scale deployment of non-orthogonal multiple access
(NOMA) for improved spectral and power efficiency in cellular networks to
provide massive wireless connectivity (e.g. for machine-type communication
[mMTC]). First, we describe the basics of single-antenna NOMA technology and
its extension to co-located multiple-antenna NOMA as well as coordinated
multipoint transmission (CoMP)-enabled NOMA technologies. Then we discuss some
of the practical challenges of large-scale deployment of NOMA such as the
inter-NOMA-interference (INI), inter-cell interference, and hardware
implementation complexity. To this end, we present one key enabling technique
to overcome the challenges of large-scale deployment of NOMA. Generally
speaking, for a feasible large-scale NOMA implementation, sophisticated
diversity enhancing techniques can be used to compensate for the degradation in
coding gain and to decrease the complexity resulting from excessive INI and
increased level of required successive interference cancellation (SIC).
Furthermore, to massively extend NOMA over the network coverage area, NOMA
transmitters have to cooperate in a generalized manner to serve all nearby
users simultaneously
Capacity and outage analysis of a dual-hop decode-and-forward relay-aided NOMA scheme
Non-orthogonal multiple access (NOMA) is regarded as a candidate radio access
technique for the next generation wireless networks because of its manifold
spectral gains. A two-phase cooperative relaying strategy (CRS) is proposed in
this paper by exploiting the concept of both downlink and uplink NOMA (termed
as DU-CNOMA). In the proposed protocol, a transmitter considered as a source
transmits a NOMA composite signal consisting of two symbols to the destination
and relay during the first phase, following the principle of downlink NOMA. In
the second phase, the relay forwards the symbol decoded by successive
interference cancellation to the destination, whereas the source transmits a
new symbol to the destination in parallel with the relay, following the
principle of uplink NOMA. The ergodic sum capacity, outage probability, and
outage sum capacity are investigated comprehensively along with analytical
derivations, under both perfect and imperfect successive interference
cancellation. The performance improvement of the proposed DU-CNOMA over the
conventional CRS using NOMA, is proved through analysis and computer
simulation. Furthermore, the correctness of the author's analysis is proved
through a strong agreement between simulation and analytical results.Comment: Accepted for possible publication in Digital Signal Processing,
Elsevier. 22 pages, 11 figure
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