Now showing 1 - 9 of 9
  • Publication
    Engineering ambient visual sensors
    Visual sensors are an indispensable prerequisite for those AmI environments that require a surveillance component. One practical issue concerns maximizing the operational longevity of such sensors as the operational lifetime of an AmI environment itself is dependent on that of its constituent components. In this paper, the intelligent agent paradigm is considered as a basis for managing a camera collective such that the conflicting demands of power usage optimization and system performance are reconciled.
  • Publication
    On the RFID Wake-up Impulse for Multi-hop Sensor Networks
    Communication protocols for wireless sensor networks reduce the energy consumption by duty cycling the node activity and adopting a periodic sleeping scheduling. This approach often results in idle listening and therefore energy dissipated for listening to a channel free from packet transmitted. Duty cycling trades-off energy consumption due to idle listening and high end-to-end delay. Proposed solutions mitigate this issue for example through extra low-power radio components (wake-up radio) that listen to the radio and wake-up the node if some channel activity is sensed. These extra components also consume some energy to listen to the channel. In contrast, we propose an on-demand wake-up capability, namely RFIDimpulse, which is achieved through using an off-the-shelf batteryless RFID tag attached to each sensor node that is also provided with RFID reader capability. Because modern RFID techniques can trigger all the neighbouring tags at once or pinpoint a particular tag, RFIDimpluse provides both unicast and multicast capability. RFIDimpulse allows eventdriven communication and eliminates node idle listening.
  • Publication
    Dynamic reassignment of aggregation point for network load balancing
    Some wireless sensor network applications forward data to a central aggregation point (AP) that is responsible for processing, aggregating, and relaying information to the base station. For example one node in a body sensor network is responsible for aggregating data and then forwarding only useful information to an external ambient network. This procedure leads to asymmetry in the AP node energy consumption due to (1) higher forwarding activity for nodes in the vicinity of the AP and (2) higher AP activity relative to nodes. Existing approaches of load and energy consumption balancing employ either suboptimal periodical route changes or random AP rotations. In contrast, we propose a novel technique1 to enable a dynamic reassignment of the sensor AP according to a novel cost function that is based on relevant node energy metrics. We show that the technique lead to a network lifetime extension up to 50% for applications, such as medical, that require power-intensive tasks at the AP and for high traffic applications.
  • Publication
    MERLIN : cross-layer integration of MAC and routing for low duty-cycle sensor networks
    Sensor network MAC protocols typically sacrifice packet latency to achieve energy efficiency. Such delays may well increase due to routing protocol operation. For this reason it is imperative that we attempt to quantify the end-to-end delay and energy consumption when jointly using low duty cycle MAC and routing protocols. In this paper, we present a comprehensive evaluation of MERLIN (MAC and efficient routing integrated with support for localization), a cross-layer protocol that integrates both MAC and routing features. In contrast to many sensor network protocols, it employs a multicast upstream and multicast downstream approach to relaying packets to and from the gateway. Simultaneous reception and transmission errors are notified by asynchronous burst ACK and negative burst ACK messages. A division of the network into timezones, together with an appropriate scheduling policy, enables the routing of packets to the closest gateway. An evaluation of MERLIN has been conducted through simulation, against both the SMAC and the ESR routing protocols (an improved version of the DSR algorithm). The results illustrate that the joint usage of both SMAC and ESR, in low duty cycle scenarios, causes extremely high end-to-end delays and prevents acceptable data delivery rate. MERLIN, as an integrated approach, notably reduces latency, resulting in nodes that can deliver data in a very low duty cycle, yielding a significant extension to network lifetime.
      1178Scopus© Citations 42
  • Publication
    Multi-hop RFID wake-up radio : design, evaluation and energy tradeoffs
    Energy efficiency is a central challenge in battery operated sensor networks. Current energy-efficient mechanisms employ either duty cycling, which reduces idle listening but does not eliminate it, or low power wake-up radio, which adds complexity and cost to the sensor platform. In this paper, we propose a novel mechanism called RFIDImpulse that uses RFID technology as an out-of-band wake-up channel for sensor networks. RFIDImpulse is an on-demand mechanism that enables nodes to sleep until they have to send or receive packets. It relies on IEEE 802.15.4 radio to emulate an RFID reader at a sender node, and on an off-the-shelf RFID tag attached to the external interrupt pin of each sensor node. The sender can simply activate the receiver’s tag before sending it data packets. This setup enables both radio and microcontroller to go into deep sleep mode until they need to be active. We develop an analytical model to evaluate the energy tradeoffs of RFIDImpulse, and then evaluate the mechanism against BMAC and IEEE 802.15.4 in high and low traffic scenarios. The results confirm that RFIDImpulse reduces the energy consumption relative to both protocols for low and medium traffic scenarios, and they reveal the thresholds for adaptive activation of RFIDImpulse based on traffic load.
      1032Scopus© Citations 31
  • Publication
    Advantages of Dual Channel MAC for Wireless Sensor Networks
    Traditional low cost radios for wireless sensor networks operate with one frequency channel at any given time. However, recent advances in radio hardware for WSNs made available transceivers that can support two simultaneous channels. In this work, we investigate the benefits of using two parallel independent frequency channels at the MAC layer. In particular, the paper introduces a technique of Dual Channel Multiple Access with Adaptive Preamble (DCMA/AP). The protocol uses two separate frequencies for data and control packets to avoid the use of handshake mechanisms (e.g. RTS/CTS) in order to reduce energy consumption and packet delay. To address the hidden and exposed terminal problems, DCMA/AP enables a receiver to send a busy tone signal on the control channel to notify neighbors that an ongoing reception is in progress. As a result, packet collisions are nullified with an increase of node throughput. Furthermore, an adaptive preamble mechanism in DCMA/AP avoids secondary processes of node synchronization together with a reduction of idle listening of receiving nodes that are considered to be one of the major sources of energy consumption in wireless sensor networks. Finally, DCMA/AP introduces a mechanism of opportunistic crossover speeds up the process of packet forwarding by pre-announcing the successive candidate node intended to receive the packet.
  • Publication
    Managing mobile-based participatory sensing communities
    Participation of mobile phone users in sensorial data collection both from the individual and from the surrounding environment presents a wide range of opportunities for truly pervasive applications. This paper highlights relevant issues related to mobile-phone participatory sensing and describes an architecture framework to flexibly create new communities of data interest, to manage and interact with those communities and to finally provide useful information to the users.
  • Publication
    Radio Sleep Mode Optimization in Wireless Sensor Networks
    Energy efficiency is a central challenge in sensor networks, and the radio is a major contributor to overall energy node consumption. Current energy-efficient MAC protocols for sensor networks use a fixed low-power radio mode for putting the radio to sleep. Fixed low-power modes involve an inherent trade-off: deep sleep modes have low current draw and high energy cost and latency for switching the radio to active mode, while light sleep modes have quick and inexpensive switching to active mode with a higher current draw. This paper proposes adaptive radio low-power sleep modes based on current traffic conditions in the network. It first introduces a comprehensive node energy model, which includes energy components for radio switching, transmission, reception, listening, and sleeping, as well as the often disregarded microcontroller energy component for determining the optimal sleep mode and MAC protocol to use for given traffic scenarios. The model is then used for evaluating the energy-related performance of our recently proposed RFIDImpulse protocol enhanced with adaptive low-power modes, and comparing it against BMAC and IEEE 802.15.4, for both MicaZ and TelosB platforms under varying data rates. The comparative analysis confirms that RFIDImpulse with adaptive low-power modes provides up to 20 times lower energy consumption than IEEE 802.15.4 in low traffic scenario. The evaluation also yields the optimal settings of low-power modes on the basis of data rates for each node platform, and provides guidelines and a simple algorithm for the selection of appropriate MAC protocol, low-power mode, and node platform for a given set of traffic requirements of a sensor network application.
      1084Scopus© Citations 121