24,399 research outputs found
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
DMT Optimal Cooperative Protocols with Destination-Based Selection of the Best Relay
We design a cooperative protocol in the context of wireless mesh networks in order to increase the reliability of wireless links. Destination terminals ask for cooperation when they fail in decoding data frames transmitted by source terminals. In that case, each destination terminal D calls a specific relay terminal B with a signaling frame to help its transmission with source terminal S. To select appropriate relays, destination terminals maintain tables of relay terminals, one for each possible source address. These tables are constituted by passively overhearing ongoing transmissions. Hence, when cooperation is needed between S and D, and when a relay B is found by terminal D in the relay table associated with terminal S, the destination terminal sends a negative acknowledgment frame that contains the address of B. When the best relay B has successfully decoded the source message, it sends a copy of the data frame to D using a selective decode-andforward transmission scheme. The on-demand approach allows maximization of the spatial multiplexing gain and the cooperation of the best relay allows maximization of the spatial diversity order. Hence, the proposed protocol achieves optimal diversitymultiplexing trade-off performance. Moreover, this performance is achieved through a collision-free selection process
Markov Decision Processes with Applications in Wireless Sensor Networks: A Survey
Wireless sensor networks (WSNs) consist of autonomous and resource-limited
devices. The devices cooperate to monitor one or more physical phenomena within
an area of interest. WSNs operate as stochastic systems because of randomness
in the monitored environments. For long service time and low maintenance cost,
WSNs require adaptive and robust methods to address data exchange, topology
formulation, resource and power optimization, sensing coverage and object
detection, and security challenges. In these problems, sensor nodes are to make
optimized decisions from a set of accessible strategies to achieve design
goals. This survey reviews numerous applications of the Markov decision process
(MDP) framework, a powerful decision-making tool to develop adaptive algorithms
and protocols for WSNs. Furthermore, various solution methods are discussed and
compared to serve as a guide for using MDPs in WSNs
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,
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