409 research outputs found
A novel cooperative opportunistic routing scheme for underwater sensor networks
Increasing attention has recently been devoted to underwater sensor networks (UWSNs) because of their capabilities in the ocean monitoring and resource discovery. UWSNs are faced with different challenges, the most notable of which is perhaps how to efficiently deliver packets taking into account all of the constraints of the available acoustic communication channel. The opportunistic routing provides a reliable solution with the aid of intermediate nodes’ collaboration to relay a packet toward the destination. In this paper, we propose a new routing protocol, called opportunistic void avoidance routing (OVAR), to address the void problem and also the energy-reliability trade-off in the forwarding set selection. OVAR takes advantage of distributed beaconing, constructs the adjacency graph at each hop and selects a forwarding set that holds the best trade-off between reliability and energy efficiency. The unique features of OVAR in selecting the candidate nodes in the vicinity of each other leads to the resolution of the hidden node problem. OVAR is also able to select the forwarding set in any direction from the sender, which increases its flexibility to bypass any kind of void area with the minimum deviation from the optimal path. The results of our extensive simulation study show that OVAR outperforms other protocols in terms of the packet delivery ratio, energy consumption, end-to-end delay, hop count and traversed distance
A Tutorial on Clique Problems in Communications and Signal Processing
Since its first use by Euler on the problem of the seven bridges of
K\"onigsberg, graph theory has shown excellent abilities in solving and
unveiling the properties of multiple discrete optimization problems. The study
of the structure of some integer programs reveals equivalence with graph theory
problems making a large body of the literature readily available for solving
and characterizing the complexity of these problems. This tutorial presents a
framework for utilizing a particular graph theory problem, known as the clique
problem, for solving communications and signal processing problems. In
particular, the paper aims to illustrate the structural properties of integer
programs that can be formulated as clique problems through multiple examples in
communications and signal processing. To that end, the first part of the
tutorial provides various optimal and heuristic solutions for the maximum
clique, maximum weight clique, and -clique problems. The tutorial, further,
illustrates the use of the clique formulation through numerous contemporary
examples in communications and signal processing, mainly in maximum access for
non-orthogonal multiple access networks, throughput maximization using index
and instantly decodable network coding, collision-free radio frequency
identification networks, and resource allocation in cloud-radio access
networks. Finally, the tutorial sheds light on the recent advances of such
applications, and provides technical insights on ways of dealing with mixed
discrete-continuous optimization problems
Local Multicoloring Algorithms: Computing a Nearly-Optimal TDMA Schedule in Constant Time
The described multicoloring problem has direct applications in the context of
wireless ad hoc and sensor networks. In order to coordinate the access to the
shared wireless medium, the nodes of such a network need to employ some medium
access control (MAC) protocol. Typical MAC protocols control the access to the
shared channel by time (TDMA), frequency (FDMA), or code division multiple
access (CDMA) schemes. Many channel access schemes assign a fixed set of time
slots, frequencies, or (orthogonal) codes to the nodes of a network such that
nodes that interfere with each other receive disjoint sets of time slots,
frequencies, or code sets. Finding a valid assignment of time slots,
frequencies, or codes hence directly corresponds to computing a multicoloring
of a graph . The scarcity of bandwidth, energy, and computing resources in
ad hoc and sensor networks, as well as the often highly dynamic nature of these
networks require that the multicoloring can be computed based on as little and
as local information as possible
Centralized and Cooperative Transmission of Secure Multiple Unicasts using Network Coding
We introduce a method for securely delivering a set of messages to a group of
clients over a broadcast erasure channel where each client is interested in a
distinct message. Each client is able to obtain its own message but not the
others'. In the proposed method the messages are combined together using a
special variant of random linear network coding. Each client is provided with a
private set of decoding coefficients to decode its own message. Our method
provides security for the transmission sessions against computational
brute-force attacks and also weakly security in information theoretic sense. As
the broadcast channel is assumed to be erroneous, the missing coded packets
should be recovered in some way. We consider two different scenarios. In the
first scenario the missing packets are retransmitted by the base station
(centralized). In the second scenario the clients cooperate with each other by
exchanging packets (decentralized). In both scenarios, network coding
techniques are exploited to increase the total throughput. For the case of
centralized retransmissions we provide an analytical approximation for the
throughput performance of instantly decodable network coded (IDNC)
retransmissions as well as numerical experiments. For the decentralized
scenario, we propose a new IDNC based retransmission method where its
performance is evaluated via simulations and analytical approximation.
Application of this method is not limited to our special problem and can be
generalized to a new class of problems introduced in this paper as the
cooperative index coding problem
Community-based asynchronous wakeup protocol for wireless peer-to-peer file sharing networks
Ubiquitous Peer-to-Peer (P2P) networking is widely expected to be manifested in a wireless environment in the near future. However, to realize such an interesting mobile computing platform, energy efficiency is one of the most critical resources management issues yet to be tackled. Unfortunately, energy efficient wireless P2P networking is still a relatively less explored topic as it is quite challenging to tackle the energy management problem without centralized control. In this paper, we meet this research challenge by proposing a new distributed protocol, called Community-Based Asynchronous Wakeup Protocol, CAWP, for energy conservation in wireless P2P file sharing networks. Simulation results show that our proposed CAWP is found to be highly effective in that it can remarkably increase the energy efficiency of the participants in a wireless P2P system. © 2005 IEEE.published_or_final_versio
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