10,521 research outputs found
A Relay Can Increase Degrees of Freedom in Bursty Interference Networks
We investigate the benefits of relays in multi-user wireless networks with
bursty user traffic, where intermittent data traffic restricts the users to
bursty transmissions. To this end, we study a two-user bursty MIMO Gaussian
interference channel with a relay, where two Bernoulli random states govern the
bursty user traffic. We show that an in-band relay can provide a degrees of
freedom (DoF) gain in this bursty channel. This beneficial role of in-band
relays in the bursty channel is in direct contrast to their role in the
non-bursty channel which is not as significant to provide a DoF gain. More
importantly, we demonstrate that for certain antenna configurations, an in-band
relay can help achieve interference-free performances with increased DoF. We
find the benefits particularly substantial with low data traffic, as the DoF
gain can grow linearly with the number of antennas at the relay. In this work,
we first derive an outer bound from which we obtain a necessary condition for
interference-free DoF performances. Then, we develop a novel scheme that
exploits information of the bursty traffic states to achieve them.Comment: submitted to the IEEE Transactions on Information Theor
Distributed Beamforming in Wireless Multiuser Relay-Interference Networks with Quantized Feedback
We study quantized beamforming in wireless amplify-and-forward
relay-interference networks with any number of transmitters, relays, and
receivers. We design the quantizer of the channel state information to minimize
the probability that at least one receiver incorrectly decodes its desired
symbol(s). Correspondingly, we introduce a generalized diversity measure that
encapsulates the conventional one as the first-order diversity. Additionally,
it incorporates the second-order diversity, which is concerned with the
transmitter power dependent logarithmic terms that appear in the error rate
expression. First, we show that, regardless of the quantizer and the amount of
feedback that is used, the relay-interference network suffers a second-order
diversity loss compared to interference-free networks. Then, two different
quantization schemes are studied: First, using a global quantizer, we show that
a simple relay selection scheme can achieve maximal diversity. Then, using the
localization method, we construct both fixed-length and variable-length local
(distributed) quantizers (fLQs and vLQs). Our fLQs achieve maximal first-order
diversity, whereas our vLQs achieve maximal diversity. Moreover, we show that
all the promised diversity and array gains can be obtained with arbitrarily low
feedback rates when the transmitter powers are sufficiently large. Finally, we
confirm our analytical findings through simulations.Comment: 41 pages, 14 figures, submitted to IEEE Transactions on Information
Theory, July 2010. This work was presented in part at IEEE Global
Communications Conference (GLOBECOM), Nov. 200
Capacity Theorems for the Fading Interference Channel with a Relay and Feedback Links
Handling interference is one of the main challenges in the design of wireless
networks. One of the key approaches to interference management is node
cooperation, which can be classified into two main types: relaying and
feedback. In this work we consider simultaneous application of both cooperation
types in the presence of interference. We obtain exact characterization of the
capacity regions for Rayleigh fading and phase fading interference channels
with a relay and with feedback links, in the strong and very strong
interference regimes. Four feedback configurations are considered: (1) feedback
from both receivers to the relay, (2) feedback from each receiver to the relay
and to one of the transmitters (either corresponding or opposite), (3) feedback
from one of the receivers to the relay, (4) feedback from one of the receivers
to the relay and to one of the transmitters. Our results show that there is a
strong motivation for incorporating relaying and feedback into wireless
networks.Comment: Accepted to the IEEE Transactions on Information Theor
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Beacon-Assisted Spectrum Access with Cooperative Cognitive Transmitter and Receiver
Spectrum access is an important function of cognitive radios for detecting
and utilizing spectrum holes without interfering with the legacy systems. In
this paper we propose novel cooperative communication models and show how
deploying such cooperations between a pair of secondary transmitter and
receiver assists them in identifying spectrum opportunities more reliably.
These cooperations are facilitated by dynamically and opportunistically
assigning one of the secondary users as a relay to assist the other one which
results in more efficient spectrum hole detection. Also, we investigate the
impact of erroneous detection of spectrum holes and thereof missing
communication opportunities on the capacity of the secondary channel. The
capacity of the secondary users with interference-avoiding spectrum access is
affected by 1) how effectively the availability of vacant spectrum is sensed by
the secondary transmitter-receiver pair, and 2) how correlated are the
perceptions of the secondary transmitter-receiver pair about network spectral
activity. We show that both factors are improved by using the proposed
cooperative protocols. One of the proposed protocols requires explicit
information exchange in the network. Such information exchange in practice is
prone to wireless channel errors (i.e., is imperfect) and costs bandwidth loss.
We analyze the effects of such imperfect information exchange on the capacity
as well as the effect of bandwidth cost on the achievable throughput. The
protocols are also extended to multiuser secondary networks.Comment: 36 pages, 6 figures, To appear in IEEE Transaction on Mobile
Computin
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