The performance of two-phase collaborative communication protocols is studied for wireless networks. All the communication nodes in the cluster are assumed to share the same channel and transmit or receive collaboratively in a quasi-static Rayleigh flat-fading environment. In addition to small-scale fading, the effect of large-scale path loss is also considered. Based on a decode-and-forward approach, we consider various variable-rate two-phase protocols that can achieve full diversity order and analyze the effect of node geometry on their performance in terms of the outage probability of mutual information. For the single-relay node case, it is shown that if the collaborator node is close to the source node, a protocol based on space-time coding (STC) can achieve good diversity gain. Otherwise, a protocol based on receiver diversity performs better. These protocols are also compared with one based on fixed-rate repetition coding and their performance tradeoffs with node geometry are studied. The second part deals with multiple relays. It is known that with N relays an asymptotic diversity order of N+1 is achievable with STC-based protocols in the two-phase framework. However, in the framework of collaborative STC, those relay nodes which fail to decode remain silent (this event is referred to as a node erasure). We show that this node erasure has the potential to considerably reduce the diversity order and point out the importance of designing the STC to be robust against such node erasure

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Variable-Rate Two-Phase Collaborative Communication Protocols for Wireless Networks

The sensor nodes deployed in wireless sensor networks are extremely power constrained, so maximizing the lifetime of the entire networks is mainly considered in the design. An energy efficient clustering algorithm with optimum parameters is designed for reducing the energy consumption and prolonging the system lifetime. An analytical clustering model with one-hop distance and clustering angle is given. The optimum one-hop distance and clustering angle are formulated by minimizing the energy consumption between inter-cluster and intra-cluster. Furthermore, the continuous working mechanism of each cluster head which acts as the local control center and will not be replaced by the candidate cluster head until its continuous working times reach the optimum values is given, and the optimum continuous working times of each cluster head can be obtained through the optimum one-hop distance and the clustering angle. With the mechanism, the frequency of updating cluster head and the energy consumption for establishing new cluster head can be reduced. The simulation results demonstrate that the clustering algorithm can effectively reduce the energy consumption and increase the system lifetime.

Energy efficient clustering algorithm for maximizing lifetime of wireless sensor networks

Deployment guidelines for achieving maximum lifetime and avoiding energy holes in sensor network

This paper provides an analytical model for the study of energy consumption in multihop wireless embedded and sensor networks where nodes are extremely power constrained. Low-power optimization techniques developed for conventional ad hoc networks are not sufficient as they do not properly address particular features of embedded and sensor networks. It is not enough to reduce overall energy consumption, it is also important to maximize the lifetime of the entire network, that is, maintain full network connectivity for as long as possible. This paper considers different multihop scenarios to compute the energy per bit, efficiency and energy consumed by individual nodes and the network as a whole. The analysis uses a detailed model for the energy consumed by the radio at each node. Multihop topologies with equidistant and optimal node spacing are studied. Numerical computations illustrate the effects of packet routing, and explore the effects of coding and medium access control. These results show that always using a simple multihop message relay strategy is not always the best procedure.

Energy Optimization in Multihop Wireless Embedded and Sensor Networks

In the paper, we consider a network of energy- constrained sensors deployed over a region. Each sensor node in such a network is systematically gathering and transmission sensed data to a base station (via clusterhead) for further processing. A key challenge in data gathering is to maximize the system lifetime, given the energy constraints. We focus on reducing the power consumption of wireless sensor networks. The dominate component in energy consumption is almost always due to communication. Therefore, we heavily modify an exist- ing communication protocol, Low-Energy Adaptive Clustering Hierarchy (LEACH). We extend LEACH's stochastic cluster- head selection algorithm by a deterministic component to reduce energy consumption. Simulation results show that our modified scheme can extend the network life around 50% for First Node Dies (FND) and 62% for Last Nodes Dies (LND). Index Terms-Wireless sensor networks, energy efficiency, cluster- head selection, LEACH I. INTRODUCTION Wireless sensor network consists of hundreds to several thousands of small sensor nodes scattered throughout an area of interest. Sensor nodes may spontaneously create impromptu network, assemble the network themselves, dynamically adapt to device failure and degradation, manage movement of sensor nodes, and react to changes in task and network requirements. Each individual sensor contains both processing and communi- cation elements and is designed to monitor the environment for events specified by the deployer of the network. Information

An energy-efficient protocol for wireless sensor networks

In ad hoc networks, devices are required to self-organize themselves into a network without previously established infrastructure. The kind of ad hoc network we consider is made up of a multitude of relatively low mobility, short range, wireless devices, pervasively deployed throughout the environment. One of the most important design criteria for this type of network is energy efficiency. This paper looks at the energy efficiency aspect of the system design. Specifically, this paper looks at the optimum one-hop transmission distance that will minimize the total system energy. The analysis assumes that the individual devices do not have power control, but that the transmission range of all the devices as a group can be varied in the design stage. The results show that the optimum one-hop transmission distance is independent of the physical network topology, the number of transmission sources, and the total transmission distance. It only depends on the propagation environment and the device parameters. With this result, some system design trade offs can be made to minimize the total system energy. We discuss what these parameters are, how they interact with each other, and how they can be used to obtain an energy efficient wireless system. We also discuss the implications this result has for future developments of low bit rate, short range, and highly dense wireless devices for ad hoc networks.

Energy efficient system design with optimum transmission range for wireless ad hoc networks

NeuRFon/spl trade/ Netform is a sensor network made up of very low cost, low power, wireless devices (neuRFon/spl trade/ devices) that are relatively static, and are pervasively deployed throughout the environment. In this paper, we are interested in finding the relationship between the optimum one-hop transmission distance and the transceiver device parameters that will minimize the total system energy. Our analysis assumes that the individual neuRFon/spl trade/ devices do not have power control and therefore will transmit at a common range. Our results show that the optimum one-hop transmission distance is independent of the physical network topology, the number of transmission sources, and the total transmission distance. It only depends on the propagation environment and the device parameters. The implications and usefulness of this result on present day transceiver devices are also discussed.

P. Chen

Papers

Energy efficient system design with optimum transmission range for wireless ad hoc networks

Using optimum transmission range to design energy efficient systems for the neuRFon/spl trade/ Netform