17,587 research outputs found
The Practical Challenges of Interference Alignment
Interference alignment (IA) is a revolutionary wireless transmission strategy
that reduces the impact of interference. The idea of interference alignment is
to coordinate multiple transmitters so that their mutual interference aligns at
the receivers, facilitating simple interference cancellation techniques. Since
IA's inception, researchers have investigated its performance and proposed
improvements, verifying IA's ability to achieve the maximum degrees of freedom
(an approximation of sum capacity) in a variety of settings, developing
algorithms for determining alignment solutions, and generalizing transmission
strategies that relax the need for perfect alignment but yield better
performance. This article provides an overview of the concept of interference
alignment as well as an assessment of practical issues including performance in
realistic propagation environments, the role of channel state information at
the transmitter, and the practicality of interference alignment in large
networks.Comment: submitted to IEEE Wireless Communications Magazin
Overhead-Aware Distributed CSI Selection in the MIMO Interference Channel
We consider a MIMO interference channel in which the transmitters and
receivers operate in frequency-division duplex mode. In this setting,
interference management through coordinated transceiver design necessitates
channel state information at the transmitters (CSI-T). The acquisition of CSI-T
is done through feedback from the receivers, which entitles a loss in degrees
of freedom, due to training and feedback. This loss increases with the amount
of CSI-T. In this work, after formulating an overhead model for CSI acquisition
at the transmitters, we propose a distributed mechanism to find for each
transmitter a subset of the complete CSI, which is used to perform interference
management. The mechanism is based on many-to-many stable matching. We prove
the existence of a stable matching and exploit an algorithm to reach it.
Simulation results show performance improvement compared to full and minimal
CSI-T.Comment: 5 pages, 2 figures. to appear at EUSIPCO 2015, Special Session on
Algorithms for Distributed Coordination and Learnin
Interference Alignment-Aided Base Station Clustering using Coalition Formation
Base station clustering is necessary in large interference networks, where
the channel state information (CSI) acquisition overhead otherwise would be
overwhelming. In this paper, we propose a novel long-term throughput model for
the clustered users which addresses the balance between interference mitigation
capability and CSI acquisition overhead. The model only depends on statistical
CSI, thus enabling long-term clustering. Based on notions from coalitional game
theory, we propose a low-complexity distributed clustering method. The
algorithm converges in a couple of iterations, and only requires limited
communication between base stations. Numerical simulations show the viability
of the proposed approach.Comment: 2nd Prize, Student Paper Contest. Copyright 2015 SS&C. Published in
the Proceedings of the 49th Asilomar Conference on Signals, Systems and
Computers, Nov 8-11, 2015, Pacific Grove, CA, US
Degrees of Freedom of Certain Interference Alignment Schemes with Distributed CSIT
In this work, we consider the use of interference alignment (IA) in a MIMO
interference channel (IC) under the assumption that each transmitter (TX) has
access to channel state information (CSI) that generally differs from that
available to other TXs. This setting is referred to as distributed CSIT. In a
setting where CSI accuracy is controlled by a set of power exponents, we show
that in the static 3-user MIMO square IC, the number of degrees-of-freedom
(DoF) that can be achieved with distributed CSIT is at least equal to the DoF
achieved with the worst accuracy taken across the TXs and across the
interfering links. We conjecture further that this represents exactly the DoF
achieved. This result is in strong contrast with the centralized CSIT
configuration usually studied (where all the TXs share the same, possibly
imperfect, channel estimate) for which it was shown that the DoF achieved at
receiver (RX) i is solely limited by the quality of its own feedback. This
shows the critical impact of CSI discrepancies between the TXs, and highlights
the price paid by distributed precoding.Comment: This is an extended version of a conference submission which will be
presented at the IEEE conference SPAWC, Darmstadt, June 201
Degrees of Freedom of Time Correlated MISO Broadcast Channel with Delayed CSIT
We consider the time correlated multiple-input single-output (MISO) broadcast
channel where the transmitter has imperfect knowledge on the current channel
state, in addition to delayed channel state information. By representing the
quality of the current channel state information as P^-{\alpha} for the
signal-to-noise ratio P and some constant {\alpha} \geq 0, we characterize the
optimal degree of freedom region for this more general two-user MISO broadcast
correlated channel. The essential ingredients of the proposed scheme lie in the
quantization and multicasting of the overheard interferences, while
broadcasting new private messages. Our proposed scheme smoothly bridges between
the scheme recently proposed by Maddah-Ali and Tse with no current state
information and a simple zero-forcing beamforming with perfect current state
information.Comment: revised and final version, to appear in IEEE transactions on
Information Theor
Millimeter Wave Cellular Networks: A MAC Layer Perspective
The millimeter wave (mmWave) frequency band is seen as a key enabler of
multi-gigabit wireless access in future cellular networks. In order to overcome
the propagation challenges, mmWave systems use a large number of antenna
elements both at the base station and at the user equipment, which lead to high
directivity gains, fully-directional communications, and possible noise-limited
operations. The fundamental differences between mmWave networks and traditional
ones challenge the classical design constraints, objectives, and available
degrees of freedom. This paper addresses the implications that highly
directional communication has on the design of an efficient medium access
control (MAC) layer. The paper discusses key MAC layer issues, such as
synchronization, random access, handover, channelization, interference
management, scheduling, and association. The paper provides an integrated view
on MAC layer issues for cellular networks, identifies new challenges and
tradeoffs, and provides novel insights and solution approaches.Comment: 21 pages, 9 figures, 2 tables, to appear in IEEE Transactions on
Communication
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