Chiara Petrioli

Controlled sink mobility for prolonging wireless sensor networks lifetime

This paper demonstrates the advantages of using controlled mobility in wireless sensor networks (WSNs) for increasing their lifetime, i.e., the period of time the network is able to provide its intended functionalities. More specifically, for WSNs that comprise a large number of statically placed sensor nodes transmitting data to a collection point (the sink), we show that by controlling the sink movements we can obtain remarkable lifetime improvements. In order to determine sink movements, we first define a Mixed Integer Linear Programming (MILP) analytical model whose solution determines those sink routes that maximize network lifetime. Our contribution expands further by defining the first heuristics for controlled sink movements that are fully distributed and localized. Our Greedy Maximum Residual Energy (GMRE) heuristic moves the sink from its current location to a new site as if drawn toward the area where nodes have the highest residual energy. We also introduce a simple distributed mobility scheme (Random Movement or RM) according to which the sink moves uncontrolled and randomly throughout the network. The different mobility schemes are compared through extensive ns2-based simulations in networks with different nodes deployment, data routing protocols, and constraints on the sink movements. In all considered scenarios, we observe that moving the sink always increases network lifetime. In particular, our experiments show that controlling the mobility of the sink leads to remarkable improvements, which are as high as sixfold compared to having the sink statically (and optimally) placed, and as high as twofold compared to uncontrolled mobility.

Throughput analysis of end-to-end measurement-based admission control in IP

This paper introduces approximate analytical models to evaluate the performance of end-to-end measurement based connection admission control (EMBAC) mechanisms, devised for the setup of real time flows over the Internet. These mechanisms rely on users probing the current congestion status of their required network path using a succession of probing packets. If the probing rate measured at the end receivers is greater than a certain threshold, users are allowed to switch to a phase of data exchange; otherwise they abort the call setup attempts. In conformance with the differentiated services framework, routers are oblivious to individual flows, and only need to give higher priority to data packets than to probing traffic. Despite the approximations introduced to make the analysis tractable, our model appears to be extremely accurate for a scenario of constant rate connections. Much less accurate, but useful as a possible starting point for future work, is the extension of the model to a scenario of variable rate connections. Simulation results are also presented in the paper to gain additional quantitative insights on the effectiveness of EMBAC to provide support for tight QoS requirements.

Anticollision Protocols for Single-Reader RFID Systems: Temporal Analysis and Optimization

One of the major challenges in the use of Radio Frequency-based Identification (RFID) on a large scale is the ability to read a large number of tags quickly. Central to solving this problem is resolving collisions that occur when multiple tags reply to the query of a reader. To this purpose, several MAC protocols for passive RFID systems have been proposed. These typically build on traditional MAC schemes, such as aloha and tree-based protocols. In this paper, we propose a new performance metric by which to judge these anticollision protocols: time system efficiency. This metric provides a direct measure of the time taken to read a group of tags. We then evaluate a set of well-known RFID MAC protocols in light of this metric. Based on the insights gained, we propose a new anticollision protocol, and show that it significantly outperforms previously proposed mechanisms.

Energy-conserving access protocols for identification networks

A myriad of applications are emerging, in which energy conservation is a critical system parameter for communications. Radio frequency identification device (RFID) networks, smart cards, and even mobile computing devices, in general, need to conserve energy. In RFID systems, nodes are small battery-operated inexpensive devices with radio receiving/transmitting and processing capabilities, integrated into the size of an ID card or smaller. These identification devices are designed for extremely low-cost large-scale applications, such that the replacement of batteries is not feasible. This imposes a critical energy constraint on the communications (access) protocols used in these systems, so that the total time a node needs to be active for transmitting or receiving information should be minimized. Among existing protocols, classical random access protocols are not energy conserving, while deterministic protocols lead to unacceptable delays. This paper deals with designing communications protocols with energy constraint, in which the number of time slots in which tags need to be in the active state is minimized, while the access delay meets the applications constraints. We propose three classes of protocols which combine the fairness of random access protocols with low energy requirements.

Degree-constrained multihop scatternet formation for Bluetooth networks

We describe BlueMesh, a new protocol for the establishment of scatternets, i.e., multihop ad hoc networks of Bluetooth devices. BlueMesh defines rules for device discovery, piconet formation and piconet interconnection in order to achieve the following desirable properties: a) BlueMesh generates connected scatternets without requiring the Bluetooth devices all to be in each others transmission range; b) the BlueMesh scatternet topology is a mesh with multiple paths between any pair of nodes; c) BlueMesh piconets are made up of no more than 7 slaves. Simulation results in networks with 200 nodes show that BlueMesh is effective in quickly generating a connected scatternet in which each node, on average, does not assume more than 2.3 roles. Moreover, the length of routes between any two nodes in the network, is comparable to that of the shortest paths between the nodes.

Pro-Energy: A novel energy prediction model for solar and wind energy-harvesting wireless sensor networks

Energy harvesting is one of the most promising technologies towards the goal of perpetual operation of wireless sensor networks (WSNs). Environmentally-powered systems, however, have to deal with the variable behavior of ambient energy sources, which results in different amounts and rates of energy available over time. To alleviate the problem of the harvested power being neither constant nor continuous, energy prediction methods can be employed. Such models forecast the source availability and estimate the expected energy intake, allowing the system to take critical decisions about the utilization of the available energy. In this work, we present a novel energy prediction model, named Pro-Energy (PROfile energy prediction model), for multi-source energy harvesting WSNs, which is able to leverage past energy observations to provide accurate estimations of future energy availability. To assess the performance of our proposed solution, we use real-life solar and wind traces that we collected by interfacing TelosB nodes with solar cells and wind micro-turbines, as well as public available traces of solar and wind obtained from weather monitoring stations in the US. A comparative performance evaluation between Pro-Energy and energy predictors previously proposed in the literature, such as EWMA and WCMA, has shown that our solution significantly outperforms existing algorithms for both short and medium term prediction horizons, improving the prediction accuracy up to 60%.

BlueMesh: degree-constrained multi-hop scatternet formation for Bluetooth networks

In this paper we describe BlueMesh, a new protocol for the establishment of scatternets, i.e., multi-hop wireless networks of Bluetooth devices. BlueMesh defines rules for device discovery, piconet formation and piconet interconnection so to generate connected scatternets with the following desirable properties. BlueMesh forms scatternets without requiring the Bluetooth devices to be all in each other transmission range. BlueMesh scatternet topologies are meshes with multiple paths between any pair of nodes. BlueMesh piconets are made up of no more than 7 slaves. Simulation results in networks with over 200 nodes show that BlueMesh is effective in quickly generating a connected scatternet in which each node, on average, does not assume more than 2.4 roles. Moreover, the route length between any two nodes in the network is comparable to that of the shortest paths between the nodes.

A performance comparison of protocols for clustering and backbone formation in large scale ad hoc networks

This work concerns the comparative performance evaluation of protocols for clustering and backbone formation in ad hoc networks characterized by a large number of resource-constrained nodes. A typical example of these networks are wireless sensor networks. The DCA protocol represents those protocols whose backbone construction method is based on selecting nodes as clusterheads and then joining them to form a connected backbone. The algorithm proposed by Wu and Li has been chosen to exemplify those algorithms that build a connected backbone and then prune away redundant nodes. Finally, the algorithm by Wan et al. has been considered here for its more theoretical properties of producing a backbone with a constant approximation factor, linear time complexity and optimal message complexity. In order to obtain a backbone reasonably small at reasonable cost we propose an enhancement of the DCA algorithm, termed DCA-S, which enriches the DCA backbone construction with a recently proposed and resource effective sparsification rule. DCA-S leads to a robust backbone close in size to that generated by the Wan et al. protocol without significantly degrading the performance in terms of all the other relevant metrics.

Comparative performance evaluation of scatternet formation protocols for networks of bluetooth devices

This paper describes the results of the first ns2-based comparative performance evaluation among four major solutions presented in the literature for forming multi-hop networks of Bluetooth devices (scatternet formation). The four protocols considered in this paper are BlueTrees [1], BlueStars [2], BlueNet [3] and the protocol presented in [4] which proposes geometric techniques for topology reduction combined with cluster-based scatternet formation. We implemented the operations of the four protocols from device discovery to scatternet formation. By means of a thorough performance evaluation we have identified protocol parameters and Bluetooth technology features that affect the duration of the formation process and the properties of the produced scatternet. We have investigated how possible modifications of the BT technology (e.g., backoff duration, possibility for a BT inquirer to identify itself) make device discovery more efficient for scatternet formation in multi-hop networks. We have then discussed implementation concerns for each of the selected protocols. Finally, we have analyzed the protocols overhead as well as the effect of the different protocols operations on key metrics of the generated scatternets, which includes the time needed for forming a scatternet, the number of its piconets, the number of slaves per piconet, the number of roles assumed by each node and the scatternet route lengths.

Beyond duty cycling: Wake-up radio with selective awakenings for long-lived wireless sensing systems

Emerging wake-up radio technologies have the potential to bring the performance of sensing systems and of the Internet of Things to the levels of low latency and very low energy consumption required to enable critical new applications. This paper provides a step towards this goal with a twofold contribution. We first describe the design and prototyping of a wake-up receiver (WRx) and its integration to a wireless sensor node. Our WRx features very low power consumption (<; 1.3μW), high sensitivity (up to -55dBm), fast reactivity (wake-up time of 130μs), and selective addressing, a key enabler of new high performance protocols. We then present ALBA-WUR, a cross-layer solution for data gathering in sensing systems that redesigns a previous leading protocol, ALBA-R, extending it to exploit the features of our WRx. We evaluate the performance of ALBA-WUR via simulations, showing that the use of the WRx produces remarkable energy savings (up to five orders of magnitude), and achieves lifetimes that are decades longer than those obtained by ALBA-R in sensing systems with duty cycling, while keeping latencies at bay.