Olivier Alphand

GreenNet: An Energy-Harvesting IP-Enabled Wireless Sensor Network

This paper presents GreenNet, an energy efficient and fully operational protocol stack for IP-enabled wireless sensor networks based on the IEEE 802.15.4 beacon-enabled mode. The stack runs on a hardware platform with photovoltaic cell energy harvesting developed by STMicroelectronics (STM) that can operate autonomously for long periods of time. GreenNet integrates several standard mechanisms and enhances existing protocols, which results in an operational platform with the performance beyond the current state of the art. In particular, it includes the IEEE 802.15.4 beacon-enabled medium access control (MAC) integrated with lightweight IP routing for achieving very low duty cycles. It offers an advanced discovery scheme that accelerates the process of joining the network and proposes an adaptation scheme for adjusting the duty cycle of harvested nodes to the available energy for increased performance. Finally, it supports security at two levels: a basic standard secure operation at the link layer and advanced scalable data payload security. This paper describes all techniques and mechanisms for saving energy and operating at very low duty cycles. It also provides an evaluation of the performance and energy consumption of GreenNet.

Link quality metrics in large scale indoor wireless sensor networks

We report results of measurements on SensLAB, an indoor wireless sensor network testbed with a large number of nodes equipped with a CC1101 radio chip. We analyze RSSI and LQI to find the best way to discriminate good links from weak ones and in particular, to derive a metric that estimates the Packet Reception Ratio (PRR) the best. To obtain an estimator of PRR, we have fitted a Fermi-Dirac function to the scatter diagram of the average and standard variation of LQI. The function enables us to find PRR for a given level of LQI. We evaluate the estimator by computing PRR over a varying size window of transmissions and comparing with the estimator.

A multimedia architecture for 802.11b networks

Wireless networks have become increasingly popular for the past few years, especially IEEE 802.11 as the most widespread wireless technology. This article proposes a new architecture for broadband 802.11 networks to support distributed multimedia applications. After discussing the differences between multimedia and traditional applications, we show how the 802.11b mechanism ensuring enhanced robustness connectivity for low signal to noise ratio (SNR) areas, penalizes multimedia stream transmissions. A new multimedia architecture disabling the dynamic rate shifting mechanism and using a performance enhancing proxy is then proposed.

Fast and energy-efficient topology construction in multi-hop multi-channel 802.15.4 networks

In multi-hop IEEE 802.15.4 networks with nodes operating in the beacon-enabled mode, the time and energy spent in the cluster-tree construction may be long and highly variable especially if there are no a priori restrictions on duty-cycle durations or on the channels used in the network. In this paper, we propose a Multi-Channel Beacon Train (MCBT) protocol in which coordinator nodes send trains of beacons on all channels at random instants during the inactive part of a superframe, so that nodes entering the network can quickly acquire the network parameters or routing metrics and join the network. The scheme drastically shortens the delay for topology construction and lowers the consumed energy.

Energy consumption and performance of IEEE 802.15.4e TSCH and DSME

The recent IEEE 802.15.4e standard has introduced two interesting modes of operation: Time Slotted Channel Hopping (TSCH) and Deterministic and Synchronous Multi-channel Extension (DSME). Both provide a mix of time and frequency division to improve the performance of the previously available synchronized MAC mode (beacon-enabled 802.15.4). In this paper, we compare the performance of DSME and TSCH with respect to the energy consumption, throughput, and delay through an analysis of their respective ways of operation. We use an energy consumption model coming from our previous experience on the design of recent energy harvesting motes for the GreenNet platform. Our results show that DSME performs slightly better in terms of the energy consumption spent in data transfers. Both protocols exhibit similar delays for a given duty cycle, nevertheless, TSCH obtains shorter delay and higher throughput for low duty cycles. For higher duty cycles, TSCH results in lower throughput - for applications that send little data, the fixed slot configuration of TSCH results in wasted bandwidth. DSME can allocate shorter slots, which is beneficial for applications that transmit short packets.

An architecture for seamless mobility in spontaneous wireless mesh networks

In this paper, we consider spontaneous wireless mesh networks that can provide wide coverage connectivity to mobile nodes. Our mobility scheme builds upon separation between a persistent node identifier and its current address. When joining the mesh, a mobile node associates with a mesh router that updates a location service managed in the mesh as a distributed hash table. Mobility implies changing addresses while a node moves in the mesh. To keep the rate of location updates and correspondent node notifications low, the address of the new mesh router with which the mobile node is associated needs to be topologically close to the previous one. Thus, such a mobility scheme requires an addressing space with specific properties. We achieve this by defining an algorithm for constructing a pseudo-geographical addressing space: a few nodes know their exact locations and others estimate their relative positions to form a topologically consistent addressing space. Such an addressing space also enables scalable and low overhead routing in the wireless mesh---we propose a trajectory based long distance ballistic geographical routing.

DINAS: A distributed naming service for all-IP wireless sensor networks

The Internet of Things requires a naming service that can also be beneficial for searching for services and applications. To avoid the traditional DNS approach in which a DNS server provides mapping of names to IP addresses in its domain, we propose a novel network service called DINAS (DIstributed NAming Service). It is based on three pillars: 1) Bloom filters for creating compact names from node descriptions, 2) distributed caches for storing names within the network, and 3) overlay routing strategies to publish and discover information - not only names - within the network. In this work, we assume ContikiMAC at Layer 2, 6LoWPAN at Layer 2.5, IPv6 and RPL (routing protocol) at Layer 3, and we present a particular UDP-based overlay routing strategy. We evaluate the proposal by Cooja simulations and compare its performance with a centralized naming service at the sink. The results show that DINAS outperforms the centralized solution.

Topology construction in RPL networks over beacon-enabled 802.15.4

In this paper, we propose a new scheme that allows coupling beacon-enabled IEEE 802.15.4 with the RPL routing protocol while keeping full compliance with both standards. We provide a means for RPL to pass the routing information to Layer 2 before the 802.15.4 topology is created by encapsulating RPL DIO messages in beacon frames. The scheme takes advantage of 802.15.4 command frames to solicit RPL DIO messages. The effect of the command frames is to reset the Trickle timer that governs sending DIO messages. We provide a detailed analysis of the overhead incurred by the proposed scheme to understand topology construction costs. We have evaluated the scheme using Contiki and the instruction-level Cooja simulator and compared our results against the most common scheme used for dissemination of the upper-layer information in beacon-enabled PANs. The results show energy savings during the topology construction phase and in the steady state.

SatiPSec : An Optimized Solution for Securing Multicast and Unicast Satellite Transmissions

In satellite networks, the security of data exchanged on the satellite segment is threatened by many types of attacks such as eavesdropping, intrusion of unauthorized satellite terminals, satellite terminal cloning... The integration of security mechanisms is therefore considered today as an essential requirement. Some existing solutions may be recommended, however they do not offer all the necessary security services. For instance, the optional security mechanisms defined in the DVB-RCS standard provide insufficient security support, especially in satellite networks with natural broadcast/multicast capability over large areas. The use of well-known upper layers security protocols such as SSL (Secure Socket Layer) or IPSec/IKE can be considered too, but they are dedicated to unicast communications. The SatIPSec solution has been designed to provide an optimized and adapted security solution for satellite networks. It offers a new way of transparently and efficiently securing unicast and multicast satellite transmissions, with a strong access control, data confidentiality, data integrity, and data authentication as security services. SatIPSec has recently been implemented in a demonstrator developed in the context of the SATIP6 IST project. In this implementation, which allows to manage centrally secure multicast groups and Virtual Private Networks, key distribution is achieved according to the “Flat Multicast Key Exchange” protocol of SatIPSec, and data are encrypted and authenticated according to the IPSec protocol adapted to multicast. This paper introduces the principles of the security mechanisms involved in SatIPSec, and presents the features of the implementation and its results.

Sustainable Traffic Aware Duty-Cycle Adaptation in Harvested Multi-Hop Wireless Sensor Networks

Sustainable power management techniques in energy harvesting wireless sensors currently adapt the consumption of sensors to their harvesting rate within the limits of their battery residual energy, but regardless of the traffic profile. To provide a fairer distribution of the energy according to application needs, we propose a new sustainable traffic aware duty-cycle adaptation scheme (STADA) that takes into account the traffic load in addition to previous factors. We evaluate our protocol in the specific context of multi-hop IEEE 802.15.4 beacon-enabled wireless sensor networks powered by solar energy. Simulations show that our solution outperforms traffic-unaware adaptation schemes while minimizing the variance of the quality of service provided to applications.