6,436 research outputs found
Advanced Interference Management Technique: Potentials and Limitations
Interference management has the potential to improve spectrum efficiency in
current and next generation wireless systems (e.g. 3GPP LTE and IEEE 802.11).
Recently, new paradigms for interference management have emerged to tackle
interference in a general class of wireless networks: interference shaping and
interference exploitation. Both approaches offer better performance in
interference-limited communication regimes than traditionally thought possible.
This article provides a high-level overview of several different interference
shaping and exploitation techniques for single-hop, multi-hop, and multi-way
network architectures. Graphical illustrations that explain the intuition
behind each strategy are provided. The article concludes with a discussion of
practical challenges associated with adopting sophisticated interference
management strategies in the future.Comment: To appear in IEEE Wireless Communications Magazin
Partial Zero-Forcing for Multi-Way Relay Networks
The ever increasing demands for mobile network access have resulted in a
significant increase in bandwidth usage. By improving the system spectral
efficiency, multi-way relay networks (MWRNs) provide promising approaches to
address this challenge. In this paper, we propose a novel linear beamforming
design, namely partial zero-forcing (PZF), for MWRNs with a
multiple-input-multiple-output (MIMO) relay. Compared to zero-forcing (ZF), PZF
relaxes the constraints on the relay beamforming matrix such that only partial
user-interference, instead of all, is canceled at the relay. The users
eliminate the remaining interferences through self-interference and successive
interference cancellation. A sum-rate maximization problem is formulated and
solved to exploit the extra degrees-of-freedom resulted from PZF. Simulation
results show that the proposed PZF relay beamforming design achieves
significantly higher network sum-rates than the existing linear beamforming
designs
Dynamic Interference Steering in Heterogeneous Cellular Networks
With the development of diverse wireless communication technologies,
interference has become a key impediment in network performance, thus making
effective interference management (IM) essential to accommodate a rapidly
increasing number of subscribers with diverse services. Although there have
been numerous IM schemes proposed thus far, none of them are free of some form
of cost. It is, therefore, important to balance the benefit brought by and cost
of each adopted IM scheme by adapting its operating parameters to various
network deployments and dynamic channel conditions.
We propose a novel IM scheme, called dynamic interference steering (DIS), by
recognizing the fact that interference can be not only suppressed or mitigated
but also steered in a particular direction. Specifically, DIS exploits both
channel state information (CSI) and the data contained in the interfering
signal to generate a signal that modifies the spatial feature of the original
interference to partially or fully cancel the interference appearing at the
victim receiver. By intelligently determining the strength of the steering
signal, DIS can steer the interference in an optimal direction to balance the
transmitter's power used for IS and the desired signal's transmission. DIS is
shown via simulation to be able to make better use of the transmit power, hence
enhancing users' spectral efficiency (SE) effectively
Multi-user Cognitive Interference Channels: A Survey and New Capacity Results
This paper provides a survey of the state-of-the-art information theoretic
analysis for overlay multi-user (more than two pairs) cognitive networks and
reports new capacity results. In an overlay scenario, cognitive / secondary
users share the same frequency band with licensed / primary users to
efficiently exploit the spectrum. They do so without degrading the performance
of the incumbent users, and may possibly even aid in transmitting their
messages as cognitive users are assumed to possess the message(s) of primary
user(s) and possibly other cognitive user(s). The survey begins with a short
overview of the two-user overlay cognitive interference channel. The evolution
from two-user to three-user overlay cognitive interference channels is
described next, followed by generalizations to multi-user (arbitrary number of
users) cognitive networks. The rest of the paper considers K-user cognitive
interference channels with different message knowledge structures at the
transmitters. Novel capacity inner and outer bounds are proposed. Channel
conditions under which the bounds meet, thus characterizing the information
theoretic capacity of the channel, for both Linear Deterministic and Gaussian
channel models, are derived. The results show that for certain channel
conditions distributed cognition, or having a cumulative message knowledge
structure at the nodes, may not be worth the overhead as (approximately) the
same capacity can be achieved by having only one global cognitive user whose
role is to manage all the interference in the network. The paper concludes with
future research directions.Comment: 7 figures, 16 pages, 1 tabl
Degrees-of-Freedom of the MIMO Three-Way Channel with Node-Intermittency
The characterization of fundamental performance bounds of many-to-many
communication systems in which participating nodes are active in an
intermittent way is one of the major challenges in communication theory. In
order to address this issue, we introduce the multiple-input multiple-output
(MIMO) three-way channel (3WC) with an intermittent node and study its
degrees-of-freedom (DoF) region and sum-DoF. We devise a non-adaptive encoding
scheme based on zero-forcing, interference alignment and erasure coding, and
show its DoF region (and thus sum-DoF) optimality for non-intermittent 3WCs and
its sum-DoF optimality for (node-)intermittent 3WCs. However, we show by
example that in general some DoF tuples in the intermittent 3WC can only be
achieved by adaptive schemes, such as decode-forward relaying. This shows that
non-adaptive encoding is sufficient for the non-intermittent 3WC and for the
sum-DoF of intermittent 3WCs, but adaptive encoding is necessary for the DoF
region of intermittent 3WCs. Our work contributes to a better understanding of
the fundamental limits of multi-way communication systems with intermittency
and the impact of adaptation therein
Sum-Rate Analysis and Optimization of Self-Backhauling Based Full-Duplex Radio Access System
In this article, a radio access system with a self-backhauling full-duplex
access node serving legacy half-duplex mobile devices is studied and analyzed.
In particular, it is assumed that the access node is using the same center
frequency for all the transmissions, meaning that also the backhauling is done
using the same frequency resources as the uplink and downlink transmissions. It
is further assumed that the access node has a massive array to facilitate
efficient beamforming and self-interference nulling in its own receiver. As a
starting point, the signal model for the considered access node is first
derived, including all the transmitted and received signals within the cell.
This is then used as a basis for obtaining the sum-rate expressions, which
depict the overall rates experienced by the mobile users that are served by the
access node. In addition, the data rate for the bi-directional backhaul link is
also derived, since the access node must be able to backhaul itself wirelessly.
The maximum achievable sum-rate is then determined by numerically solving an
optimization problem constructed from the data rate expressions. The
full-duplex scheme is also compared to two alternative transmission schemes,
which perform all or some of the transmissions in half-duplex mode. The results
show that the full-duplex capability of the access node is beneficial for
maximizing the sum-rate, meaning that a simple half-duplex transmission scheme
is typically not optimal. In particular, the highest sum-rate is usually
provided by a relay type solution, where the access node acts as a full-duplex
relay between the mobiles and the backhaul node.Comment: 30 pages, submitted for revie
On-off Switched Interference Alignment for Diversity Multiplexing Tradeoff Improvement in the 2-User X-Network with Two Antennas
To improve diversity gain in an interference channel and hence to maximize
diversity multiplexing tradeoff (DMT), we propose on-off switched interference
alignment (IA) where IA is intermittently utilized by switching IA on/off. For
on-off switching, either IA with symbol extension or IA with Alamouti coding is
adopted in this paper. Deriving and analyzing DMT of the proposed schemes, we
reveal that the intermittent utilization of IA with simultaneous non-unique
decoding can improve DMT in the 2-user X-channel with two antennas. Both the
proposed schemes are shown to achieve diversity gain of 4 and DoF per user of
. In particular, the on-off switched IA with Alamouti coding, to
the best of our knowledge, surpasses any other existing schemes for the 2-user
X-channel with two antennas and nearly approaches the ideal DMT.Comment: 13 pages, 13 figures, to appear in IEEE Transactions on Wireless
Communication
Wireless Physical Layer Security with Imperfect Channel State Information: A Survey
Physical layer security is an emerging technique to improve the wireless
communication security, which is widely regarded as a complement to
cryptographic technologies. To design physical layer security techniques under
practical scenarios, the uncertainty and imperfections in the channel knowledge
need to be taken into consideration. This paper provides a survey of recent
research and development in physical layer security considering the imperfect
channel state information (CSI) at communication nodes. We first present an
overview of the main information-theoretic measures of the secrecy performance
with imperfect CSI. Then, we describe several signal processing enhancements in
secure transmission designs, such as secure on-off transmission, beamforming
with artificial noise, and secure communication assisted by relay nodes or in
cognitive radio systems. The recent studies of physical layer security in
large-scale decentralized wireless networks are also summarized. Finally, the
open problems for the on-going and future research are discussed
Wireless Backhaul Networks: Capacity Bound, Scalability Analysis and Design Guidelines
This paper studies the scalability of a wireless backhaul network modeled as
a random extended network with multi-antenna base stations (BSs), where the
number of antennas per BS is allowed to scale as a function of the network
size. The antenna scaling is justified by the current trend towards the use of
higher carrier frequencies, which allows to pack large number of antennas in
small form factors. The main goal is to study the per-BS antenna requirement
that ensures scalability of this network, i.e., its ability to deliver
non-vanishing rate to each source-destination pair. We first derive an
information theoretic upper bound on the capacity of this network under a
general propagation model, which provides a lower bound on the per-BS antenna
requirement. Then, we characterize the scalability requirements for two
competing strategies of interest: (i) long hop: each source-destination pair
minimizes the number of hops by sacrificing multiplexing gain while achieving
full beamforming (power) gain over each hop, and (ii) short hop: each
source-destination pair communicates through a series of short hops, each
achieving full multiplexing gain. While long hop may seem more intuitive in the
context of massive multiple-input multiple-output (MIMO) transmission, we show
that the short hop strategy is significantly more efficient in terms of per-BS
antenna requirement for throughput scalability. As a part of the proof, we
construct a scalable short hop strategy and show that it does not violate any
fundamental limits on the spatial degrees of freedom (DoFs)
Harvest the potential of massive MIMO with multi-layer techniques
Massive MIMO is envisioned as a promising technology for 5G wireless networks
due to its high potential to improve both spectral and energy efficiency.
Although the massive MIMO system is based on innovations in the physical layer,
the upper layer techniques also play important roles in harvesting the
performance gains of massive MIMO. In this article, we begin with an analysis
of the benefits and challenges of massive MIMO systems. We then investigate the
multi-layer techniques for incorporating massive MIMO in several important
network deployment scenarios. We conclude this article with a discussion of
open and potential problems for future research.Comment: IEEE Networ
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