9 research outputs found
Distributed Time-Frequency Division Multiple Access Protocol For Wireless Sensor Networks
It is well known that biology-inspired self-maintaining algorithms in
wireless sensor nodes achieve near optimum time division multiple access (TDMA)
characteristics in a decentralized manner and with very low complexity. We
extend such distributed TDMA approaches to multiple channels (frequencies).
This is achieved by extending the concept of collaborative reactive listening
in order to balance the number of nodes in all available channels. We prove the
stability of the new protocol and estimate the delay until the balanced system
state is reached. Our approach is benchmarked against single-channel
distributed TDMA and channel hopping approaches using TinyOS imote2 wireless
sensors.Comment: 4 pages, IEEE Wireless Communications Letters, to appear in 201
Convergence of Desynchronization Primitives in Wireless Sensor Networks: A Stochastic Modeling Approach
Desynchronization approaches in wireless sensor networks converge to
time-division multiple access (TDMA) of the shared medium without requiring
clock synchronization amongst the wireless sensors, or indeed the presence of a
central (coordinator) node. All such methods are based on the principle of
reactive listening of periodic "fire" or "pulse" broadcasts: each node updates
the time of its fire message broadcasts based on received fire messages from
some of the remaining nodes sharing the given spectrum. In this paper, we
present a novel framework to estimate the required iterations for convergence
to fair TDMA scheduling. Our estimates are fundamentally different from
previous conjectures or bounds found in the literature as, for the first time,
convergence to TDMA is defined in a stochastic sense. Our analytic results
apply to the Desync algorithm and to pulse-coupled oscillator algorithms with
inhibitory coupling. The experimental evaluation via iMote2 TinyOS nodes (based
on the IEEE 802.15.4 standard) as well as via computer simulations demonstrates
that, for the vast majority of settings, our stochastic model is within one
standard deviation from the experimentally-observed convergence iterations. The
proposed estimates are thus shown to characterize the desynchronization
convergence iterations significantly better than existing conjectures or
bounds. Therefore, they contribute towards the analytic understanding of how a
desynchronization-based system is expected to evolve from random initial
conditions to the desynchronized steady state.Comment: to appear, IEEE Transactions on Signal Processing, 201
Energy Consumption Of Visual Sensor Networks: Impact Of Spatio-Temporal Coverage
Wireless visual sensor networks (VSNs) are expected to play a major role in
future IEEE 802.15.4 personal area networks (PAN) under recently-established
collision-free medium access control (MAC) protocols, such as the IEEE
802.15.4e-2012 MAC. In such environments, the VSN energy consumption is
affected by the number of camera sensors deployed (spatial coverage), as well
as the number of captured video frames out of which each node processes and
transmits data (temporal coverage). In this paper, we explore this aspect for
uniformly-formed VSNs, i.e., networks comprising identical wireless visual
sensor nodes connected to a collection node via a balanced cluster-tree
topology, with each node producing independent identically-distributed
bitstream sizes after processing the video frames captured within each network
activation interval. We derive analytic results for the energy-optimal
spatio-temporal coverage parameters of such VSNs under a-priori known bounds
for the number of frames to process per sensor and the number of nodes to
deploy within each tier of the VSN. Our results are parametric to the
probability density function characterizing the bitstream size produced by each
node and the energy consumption rates of the system of interest. Experimental
results reveal that our analytic results are always within 7% of the energy
consumption measurements for a wide range of settings. In addition, results
obtained via a multimedia subsystem show that the optimal spatio-temporal
settings derived by the proposed framework allow for substantial reduction of
energy consumption in comparison to ad-hoc settings. As such, our analytic
modeling is useful for early-stage studies of possible VSN deployments under
collision-free MAC protocols prior to costly and time-consuming experiments in
the field.Comment: to appear in IEEE Transactions on Circuits and Systems for Video
Technology, 201
Implementation and evaluation of a 2.4 GHz multi-hop WSN: LoS, NLoS, different floors, and outdoor-to-indoor communications
In this paper, the communication reliability of a 2.4 GHz multi-hop wireless sensor network (WSN) in various test scenarios is evaluated through experiments. First, we implement an autonomous communication procedure for a multi-hop WSN on Tmote sky sensor nodes; 2.4 GHz, an IEEE 802.15.4 standard. Here, all nodes including a transmitter node (Tx), forwarder nodes (Fw), and a base station node (BS) can automatically work for transmitting and receiving data. The experiments have been tested in different scenarios including: i) in a room, ii) line-of-sight (LoS) communications on the 2nd floor of a building, iii) LoS and non-line-of-sight (NLoS) communications on the 1st floor to the 2nd floor, iv) LoS and NLoS communications from outdoor to the 1st and the 2nd floors of the building. The experimental results demonstrate that the communication reliability indicated by the packet delivery ratio (PDR) can vary from 99.89% in the case of i) to 14.40% in the case of iv), respectively. Here, the experiments reveal that multi-hop wireless commutations for outdoor to indoor with different floors and NLoS largely affect the PDR results, where the PDR more decreases from the best case (i.e., the case of a)) by 85.49%. Our research methodology and findings can be useful for users and researchers to carefully consider and deploy an efficient 2.4 GHz multi-hop WSN in their works, since different WSN applications require different communication reliability level
Cross-Layer Optimization Scheme Using Cooperative Diversity for Reliable Data Transfer in Wireless Sensor Networks
Cooperative diversity has been shown to provide significant performance gains in wireless networks where communication is impeded by channel fading. In resource constraint networks, the advantages of cooperation can be further exploited by optimally allocating the energy and bandwidth resources among users in a cross-layer way. In this paper, we investigate the problem of transmission power minimization and network lifetime maximization using cooperative diversity for wireless sensor networks, under the constraint of a target end-to-end transmission reliability and a given transmission rate. By utilizing a cross-layer optimization scheme, distributive algorithms which jointly consider routing, relay selection, and power allocation strategies are proposed for the reliability constraint wireless sensor networks. We demonstrate through simulations that the proposed cross-layer cooperative strategies achieve significant energy savings and prolong the network lifetime considerably
IEEE TRANS. ON WIRELESS COMMUNICATIONS, PAPER-TW-OCT-12-1649.R2 1 Analytic Conditions For Energy Neutrality In Uniformly-formed Wireless Sensor Networks
Abstract—Future deployments of wireless sensor network (WSN) infrastructures for environmental or event monitoring are expected to be equipped with energy harvesters (e.g. piezoelectric, thermal, photovoltaic) in order to substantially increase their autonomy. In this paper we derive conditions for energy neutrality, i.e. perpetual energy autonomy per sensor node, by balancing the node’s expected energy consumption with its expected energy harvesting capability. Our analysis assumes a uniformly-formed WSN, i.e. a network comprising identical transmitter sensor nodes and identical receiver/relay sensor nodes with a balanced cluster-tree topology. The proposed framework is parametric to: (i) the duty cycle for the network activation; (ii) the number of nodes in the same tier of the cluster-tree topology; (iii) the consumption rate of the receiver node(s) that collect (and possibly relay) data along with their own; (iv) the marginal probability density function (PDF) characterizing the data transmission rate per node; (v) the expected amount of energy harvested by each node. Based on our analysis, we obtain the number of nodes leading to the minimum energy harvesting requirement for each tier of the WSN cluster-tree topology. We also derive closed-form expressions for the difference in the minimum energy harvesting requirements between four transmission rate PDFs in function of the WSN parameters. Our analytic results are validated via experiments using TelosB sensor nodes and an energy measurement testbed. Our framework is useful for feasibility studies on energy harvesting technologies in WSNs and for optimizing the operational settings of hierarchical WSN-based monitoring infrastructures prior to time-consuming testing and deployment within the application environment. Keywords—wireless sensor networks, energy harvesting, energy neutrality, analytic modeling I