283 research outputs found
Upper Bounds to the Performance of Cooperative Traffic Relaying in Wireless Linear Networks
Wireless networks with linear topology, where nodes generate their own traffic and relay other nodes' traffic, have attracted increasing attention. Indeed, they well represent sensor networks monitoring paths or streets, as well as multihop networks for videosurveillance of roads or vehicular traffic. We study the performance limits of such network systems when (i) the nodes' transmissions can reach receivers farther than one-hop distance from the sender, (ii) the transmitters cooperate in the data delivery, and (iii) interference due to concurrent transmissions is taken into account. By adopting an information-theoretic approach, we derive analytical bounds to the achievable data rate in both the cases where the nodes have full-duplex and half-duplex radios. The expressions we provide are mathematically tractable and allow the analysis of multihop networks with a large number of nodes. Our analysis highlights that increasing the number of coop- erating transmitters beyond two leads to a very limited gain in the achievable data rate. Also, for half-duplex radios, it indicates the existence of dominant network states, which have a major influence on the bound. It follows that efficient, yet simple, communication strategies can be designed by considering at most two cooperating transmitters and by letting half-duplex nodes operate according to the aforementioned dominant state
On Buffer-Aided Multiple-Access Relay Channel
The paper treats uplink scenario where M user equipments (UEs) send to a Base
Station (BS), possibly via a common Relay Station (RS) that is equipped with a
buffer. This is a multiple-access relay channel (MARC) aided by a buffer. We
devise a protocol in which the transmission mode is selected adaptively, using
the buffer at the RS in order to maximize the average system throughput. We
consider the general case in which the RS and the BS can have limits on the
maximal number of transmitters that can be received over the multiple access
channel. In each slot there are three type possible actions: (A1) multiple UEs
transmit at rates that enable BS to decode them (A2) multiple UEs transmit, the
BS can only decode the messages partially, while the RS completely; (A3) RS
forwards the side information to BS about the partially decoded messages, which
are going to be combined and decoded entirely at the BS, while simultaneously a
number of UEs sends new messages to the BS. The results show that the adaptive
selection of direct and buffer-aided relay transmissions leads to significant
average throughput gains.Comment: 13 pages, 3 figures, accepted to IEEE Communications letter
A Survey of Physical Layer Security Techniques for 5G Wireless Networks and Challenges Ahead
Physical layer security which safeguards data confidentiality based on the
information-theoretic approaches has received significant research interest
recently. The key idea behind physical layer security is to utilize the
intrinsic randomness of the transmission channel to guarantee the security in
physical layer. The evolution towards 5G wireless communications poses new
challenges for physical layer security research. This paper provides a latest
survey of the physical layer security research on various promising 5G
technologies, including physical layer security coding, massive multiple-input
multiple-output, millimeter wave communications, heterogeneous networks,
non-orthogonal multiple access, full duplex technology, etc. Technical
challenges which remain unresolved at the time of writing are summarized and
the future trends of physical layer security in 5G and beyond are discussed.Comment: To appear in IEEE Journal on Selected Areas in Communication
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
Cooperative Jamming for Secure Communications in MIMO Relay Networks
Secure communications can be impeded by eavesdroppers in conventional relay
systems. This paper proposes cooperative jamming strategies for two-hop relay
networks where the eavesdropper can wiretap the relay channels in both hops. In
these approaches, the normally inactive nodes in the relay network can be used
as cooperative jamming sources to confuse the eavesdropper. Linear precoding
schemes are investigated for two scenarios where single or multiple data
streams are transmitted via a decode-and-forward (DF) relay, under the
assumption that global channel state information (CSI) is available. For the
case of single data stream transmission, we derive closed-form jamming
beamformers and the corresponding optimal power allocation. Generalized
singular value decomposition (GSVD)-based secure relaying schemes are proposed
for the transmission of multiple data streams. The optimal power allocation is
found for the GSVD relaying scheme via geometric programming. Based on this
result, a GSVD-based cooperative jamming scheme is proposed that shows
significant improvement in terms of secrecy rate compared to the approach
without jamming. Furthermore, the case involving an eavesdropper with unknown
CSI is also investigated in this paper. Simulation results show that the
secrecy rate is dramatically increased when inactive nodes in the relay network
participate in cooperative jamming.Comment: 30 pages, 7 figures, to appear in IEEE Transactions on Signal
Processin
Interference Alignment for Cognitive Radio Communications and Networks: A Survey
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Interference alignment (IA) is an innovative wireless transmission strategy that has shown to be a promising technique for achieving optimal capacity scaling of a multiuser interference channel at asymptotically high-signal-to-noise ratio (SNR). Transmitters exploit the availability of multiple signaling dimensions in order to align their mutual interference at the receivers. Most of the research has focused on developing algorithms for determining alignment solutions as well as proving interference alignment’s theoretical ability to achieve the maximum degrees of freedom in a wireless network. Cognitive radio, on the other hand, is a technique used to improve the utilization of the radio spectrum by opportunistically sensing and accessing unused licensed frequency spectrum, without causing harmful interference to the licensed users. With the increased deployment of wireless services, the possibility of detecting unused frequency spectrum becomes diminished. Thus, the concept of introducing interference alignment in cognitive radio has become a very attractive proposition. This paper provides a survey of the implementation of IA in cognitive radio under the main research paradigms, along with a summary and analysis of results under each system model.Peer reviewe
Wireless D&F relay channels: time allocation strategies for cooperation and optimum operation
Transmission over the wireless medium is a challenge compared to its wired counterpart.
Scarcity of spectrum, rapid degradation of signal power over distance, interference
from neighboring nodes and random behavior of the channel are some of the difficulties
with which a wireless system designer has to deal. Moreover, emerging wireless networks
assume mobile users with limited or no infrastructure. Since its early application,
relaying offered a practical solution to some of these challenges. Recently, interest on
the relay channel is revived by the work on user-cooperative communications. Latest
studies aim to re-employ the channel to serve modern wireless networks.
In this work, the decode-and-forward (D&F) relay channel with half-duplex constraint
on the relay is studied. Focus is on producing analytical results for the half-duplex
D&F relay channel with more attention given to time allocation. First, an
expression for the mutual information for the channel with arbitrary time allocation
is developed. Introduction of the concept of conversion point explains some of the
channel behavior and help in classifying the channel into suppressed and unsuppressed
types. In the case of Rayleigh fading, cumulative distribution function (cdf) and probability
density function (pdf) are evaluated for the mutual information. Consequently,
expressions for average mutual information and outage probability are obtained.
Optimal operation of the channel is investigated. Optimal time allocation for maximum
mutual information and optimal time allocation for minimum total transmission
time are worked out for the case of channel state information at transmitter (CSIT).
Results revealed important duality between optimization problems.
Results obtained are extended from a two-hop channel to any number of hops.
Only sequential transmission is considered.
A cooperative scheme is also developed based on the three-node relay channel.
A two-user network is used as a prototype for a multi-user cooperative system. Based
on the model assumed, an algorithm for partner selection is developed. Simulation
results showed advantages of cooperation for individual users as well as the overall
performance of the network
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