William J. Phillips

Assignment of dynamic transmission range based on estimation of vehicle density

Vehicular Ad Hoc Networks (VANET) have several characteristics that distinguish them from other ad hoc networks. Among those is the rapid change in topology due to traffic jams, which also disturbs the homogenous distribution of vehicles on the road. For this reason, a dynamic transmission range is more effective in maintaining connectivity while minimizing the adverse effects of a high transmission power.We provide a relationship that allows vehicles to estimate the local density and distinguish between two phases of traffic, free-flow and congested traffic. The density estimate is used to develop an algorithm that sets a vehicle transmission range dynamically according to local traffic conditions.Simulations of various road configurations show that the algorithm is successful in maintaining connectivity in highly dynamic networks.

A multi-criterion optimization technique for energy efficient cluster formation in wireless sensor networks

Clustering techniques have emerged as a popular choice for achieving energy efficiency and scalable performance in large scale sensor networks. Cluster formation is a process whereby sensor nodes decide which cluster head they should associate with among multiple choices. Typically this cluster head selection decision involves a metric based on parameters including residual energy and distance to the cluster head. This decision is a critical embarkation point as a poor choice can lead to increased energy consumption, thus compromising network lifetime. In this paper we present a novel energy efficient cluster formation algorithm based on a multi-criterion optimization technique. Our technique is capable of using multiple individual metrics in the cluster head selection process as input while simultaneously optimizing on the energy efficiency of the individual sensor nodes as well as the overall system. The proposed technique is implemented as a distributed protocol in which each node makes its decision based on local information only. The feasibility of the proposed technique is demonstrated with simulation results. It is shown that the proposed technique outperforms all other well known protocols including LEACH, EECS and HEED resulting in a significant increase in network life.

Connectivity in inter-vehicle ad hoc networks

A two-stage simulation model is developed to investigate the effects of free flow traffic on connectivity in inter-vehicle ad hoc networks. A traffic microsimulator generates vehicle movement in a multi-lane, unidirectional highway, and a simple network model maintains connectivity graphs between the moving vehicles. The free flow conditions allow vehicles to travel at their maximum velocities, virtually unobstructed by other vehicles because of low vehicle density. We examine some factors that determine the networks ability to maintain an active communication session between a pair of vehicles. Vehicle density, relative velocity, and number of lanes are found to have a key influence on connectivity. The effect of distance, however, depends on the communication range. We also find that the probability distribution of connection lifetime resembles a power law function.

Online stabilization of block-diagonal recurrent neural networks

This paper deals with a discrete-time recurrent neural network (DTRNN) with a block-diagonal feedback weight matrix, called the block-diagonal recurrent neural network (BDRNN), that allows a simplified approach to online training and to address network and training stability issues. The structure of the BDRNN is exploited to modify the conventional backpropagation through time (BPTT) algorithm. to reduce its storage requirement by a numerically stable method of recomputing the network state variables. The network and training stability is addressed by exploiting the BDRNN structure to directly monitor and maintain stability during weight updates by developing a functional measure of system stability that augments the cost function being minimized. Simulation results are presented to demonstrate the performance of the BDRNN architecture, its training algorithm, and the stabilization method.

Connectivity with static transmission range in vehicular ad hoc networks

Connectivity in mobile wireless ad-hoc networks is maintained by setting the transmission range so that a node can establish a link to any other node in the network either directly or over multiple hops. Many analytical and experimental studies have focused on determining the minimum transmission range (MTR) that provides connectivity while minimizing transceiver power for various levels of node densities. In this paper, we determine, using simulations, the MTR in vehicular ad hoc networks (VANET) of various road configurations. We show that in 1-lane, 2-lane, and 2-way roads, MTR values confirm the analytical relations developed in the literature for 1-dimensional networks until density increases beyond a critical vehicle density. Moreover, where traffic jams are forming at intersections, MTR values are not affected by the change in vehicle density. Therefore, a large static transmission range must be chosen in order to keep the network connected in all traffic scenarios.

An Energy Efficient Fuzzy Logic Cluster Formation Protocol in Wireless Sensor Networks

Despite significant advancements in wireless sensor networks (WSNs), energy conservation remains one of the most important research challenges. Researchers have investigated architectures and topologies that allow energy efficient operation of WSNs. One of the popular techniques in this regard is clustering. While many researchers have investigated cluster head selection, this paper investigates the cluster formation. In particular, we propose a novel scheme, the Fuzzy Logic Cluster Formation Protocol (FLCFP), which uses Fuzzy Logic Inference System (FIS) in the cluster formation process. We demonstrate that using multiple parameters in cluster formation reduces energy consumption. We compare our technique with the well known LEACH protocol to show that using a multi parameter FIS enhances the network lifetime significantly.

A QoS-aware Routing Protocol for Reliability Sensitive Data in Hospital Body Area Networks

Abstract The reliability, energy efficiency, and real-time display of patients data are important factors for Body Area Network (BAN) communication in indoor hospital environments. In this paper we propose a novel routing protocol by considering the QoS requirements of BAN data with strict reliability requirements. Our proposed algorithm increases the reliable delivery of critical BAN data at the destination We have performed extensive simulations in the OMNeT++ based simulator Castalia to demonstrate the better performance of the proposed QoS based routing protocol for reliability sensitive data in terms of successful transmission rate, lower network routing traffic (hello packets) overhead, and lower end-to-end delay (latency) in both stationary and movable patient scenarios.

Energy Conserving Architectures and Algorithms for Wireless Sensor Networks

This paper derives an algorithm for minimizing energy spent by a hierarchical wireless sensor network in transmitting data to a sink, referred to as a base station. The network model considered is a single-hop multi-level clustered network. We draw on results from stochastic geometry to analytically determine the optimum number of clusters at each level. We show, both analytically and by simulation results, that a multi-level approach can significantly reduce the required network energy.

Comparing audio compression using wavelets with other audio compression schemes

Speech compression is the technology of converting human speech into an efficient encoded representation that can be decoded to produce a close approximation of the original signal. In this paper, we propose a new algorithm which compresses speech signals using a wavelet compression technique. The performance of this method is compared against the following representative coding and compression schemes: adaptive differential pulse code modulation (ADPCM) which reduces the transmitted data by a factor of two; linear predictive coding (LPC) with compression ratio of more than twelve to one; linear predictive coding algorithm using the United States Department of Defense Standard 1015 with compression ratio of 26:1; Global System Mobile (GSM) algorithm which reduces the transmitted data by a factor of five. The following parameters are compared: (i) quality of the reconstructed signal after decoding; (ii) compression ratios. (iii) signal to noise ratio (SNR); (iv) peak signal to noise ratio (PSNR); (v) normalized root mean square error (NRMSE).

QPRD: QoS-aware Peering Routing Protocol for Delay Sensitive Data in Hospital Body Area Network Communication

The consistent performance, energy efficiency, and reliability are important factors for real-time monitoring of a patients data, especially in a hospital environment. In this paper a routing protocol is proposed by considering the Quality of Service requirements of the body area network data packets. A mechanism for handling delay-sensitive packets is provided by this protocol. Extensive simulations using OMNeT++ based simulator Castalia illustrate that the proposed algorithm provides better performance than other QoS-aware routing protocols in terms of higher successful transmission rates, lower overall network traffic load, and fewer number of packet timeouts in both the mobile and static patient scenarios.