Kris Steenhaut

Low-overhead dynamic multi-channel MAC for wireless sensor networks

Most of the existing popular MAC protocols for Wireless Sensor Networks (WSN) only use a single channel for relaying data. Most popular platforms however are equipped with a radio chip capable of switching its channel, and are therefor not restricted to a single-channel operation. Operating on multiple channels can increase bandwidth and can provide robustness against external interference. We argue that this feature is not only useful for dense, high-throughput WSNs but also for sparser networks with low average data rates but with occasional traffic bursts. We present MuChMAC, a low-overhead Multi-Channel MAC protocol which uses a combination of TDMA and asynchronous MAC techniques to exploit multi-channel operation without the need for coordination or tight synchronization between nodes. We describe an interface to scale MuChMAC’s duty cycle to adapt to varying traffic conditions or energy constraints. We demonstrate MuChMAC’s usefulness on a testbed consisting out Sentilla JCreate motes running it as the MAC layer for Contiki-based applications.

REST Enabled Wireless Sensor Networks for Seamless Integration with Web Applications

The use of Internet Protocol (IP) technology in Wireless Sensor Network (WSN) is a key prerequisite for the realization of the Internet of Things (IoT) vision. The IPv6 over Low power Wireless Personal Area Networks (6LoWPAN) standard enables the use of IPv6 in networks of constrained devices. 6LowPAN enables the use of Service Oriented Architectures (SOAs) in WSN. The Internet Engineering Task Force (IETF) has defined the Constrained Application Protocol (CoAP), a web transfer protocol which provides several Hypertext Transfer Protocol (HTTP) functionalities, re-designed for constrained embedded devices. CoAP allows WSN applications to be built on top of Representational State Transfer (REST) architectures. This considerably eases the IoT application development and facilitates the integration of constrained devices with the Web. This work describes the prototype design and development of a Web platform which integrates a REST/CoAP WSN with a REST/HTTP Web application and allows a user to visualize WSN measurements in the Web browser. Since the WSN Web integration relies on a non-transparent gateway/server, we also show how to provide transparent cross-protocol resource access by means of an HTTP-CoAP proxy. The paper describes the major building blocks, functionalities and the implementation approach.

Evaluation of constrained application protocol for wireless sensor networks

IPv6 over Low power Wireless Personal Area Networks (6LoWPAN) and IPv6 Routing Protocol for Low-power and Lossy networks (RPL) have accelerated the integration of Wireless Sensor Networks (WSNs) and smart objects with the Internet. At the same time, the development of the Constrained Application Protocol (CoAP) has made it possible to provide resource constrained devices with web service functionalities. CoAP is an HTTP like web transfer protocol able to extend the REpresentational State Transfer (REST) architecture to LoWPANs. The major difference between CoAP and HTTP is the different transport layer protocol (UDP instead of TCP) and the header compression which makes the packet size significantly smaller. This work provides an evaluation of CoAP compared to HTTP. The performance is evaluated in terms of motes energy consumption and response time. The aim of the paper is to demonstrate, with a quantitative and qualitative analysis, that CoAP is more suited to REST based WSNs compared to HTTP. The results have been obtained by means of simulation as well as tests on real sensor motes.

Comparison of two lightweight protocols for smartphone-based sensing

Smartphones are equipped with numerous sensors and have become sophisticated sensing platforms. However, several sensing applications running on a smartphone can degrade the device performance. This can be overcome by using lightweight application protocols which improve the smartphone performance in terms of bandwidth consumption, battery lifetime and communication latency. This work focuses on two emerging application protocols: the Message Queuing Telemetry Transport (MQTT) and the Constrained Application Protocol (CoAP). Although both protocols have been designed for highly constrained environments such as sensors, they are also appropriate to be adopted in smartphone applications. We provide a qualitative and quantitative comparison between MQTT and CoAP when used as smartphone application protocols and we give preliminary indications on the application scenarios in which either protocol should be adopted. While MQTT has already been adopted in smartphone applications, CoAP is relatively new and has up to now mainly been considered for sensors and actuators. Our comparison shows that CoAP can be a valid alternative to MQTT for certain application scenarios.

Schedule-based multi-channel communication in wireless sensor networks

Recently, wireless sensor networks (WSNs), enabling the connection between the physical world and the digital world, have become an important component of the Internet of Things (IoT). Several applications in the IoT require the efficient and timely collection of larger amounts of data. Due to the interference and contention over the wireless medium, the limited bandwidth of the radios, the limited resources of the battery-operated sensor nodes, this requirement becomes a challenging task. In this research, we exploit the multi-channel operation capability of the radios to provide the higher network throughput and propose an efficient scheduling algorithm to eliminate collision, idle-listening or over-hearing, which are consequences of non-coordinated transmissions. Our work focuses on scheduling the regular traffic that is periodically transmitted and on adapting the schedule to the additional traffic that can be requested at some point in time. To deploy the schedule-based multi-channel protocol on real applications, we design the complete communication procedure that is necessary for sensor nodes to communicate among them to form a network and to propagate the sensed data to the collection point. We also propose a low-overhead time synchronization scheme that is critical for a schedule-based protocol. The results of extensive simulation experiments show that the proposed scheduling algorithm can achieve collision-free parallel transmissions over different channels to provide high throughput and high delivery ratio while meeting the crucial energy efficiency requirements. Finally, we demonstrate the feasibility of the protocol and the time synchronization scheme on a laboratory-scaled test-bed of real motes.

High-density wireless sensor networks: a new clustering approach for prediction-based monitoring

We propose a new cluster-based approach that simplifies prediction-based monitoring for homogeneous, high-density wireless sensor networks composed of a large number of small, power-restricted nodes. Prediction-based monitoring can increase the autonomous lifetime of the network by reducing communication. In our clustering approach, the cluster-heads spatio-temporally correlate and predict the measurements of the cluster-members by executing their prediction model. Routing is only done by the gateway nodes at the circumference of the clusters while the nongateway nodes, which are positioned between the cluster-heads and their gateway nodes, are allowed to turn off their radio communication as long as their measurements satisfy the predictions of their cluster-head. Turning off radio communication results in high energy savings and can greatly improve system lifetime. Our main contribution is the description of this clustering approach while the prediction models are beyond the scope of this paper.

Using sound-taste correspondences to enhance the subjective value of tasting experiences

The soundscapes of those places where we eat and drink can influence our perception of taste. Here, we investigated whether contextual sound would enhance the subjective value of a tasting experience. The customers in a chocolate shop were invited to take part in an experiment in which they had to evaluate a chocolate’s taste while listening to an auditory stimulus. Four different conditions were presented in a between-participants design. Envisioning a more ecological approach, a pre-recorded piece of popular music and the shop’s own soundscape were used as the sonic stimuli. The results revealed that not only did the customers report having a significantly better tasting experience when the sounds were presented as part of the food’s identity, but they were also willing to pay significantly more for the experience. The method outlined here paves a new approach to dealing with the design of multisensory tasting experiences, and gastronomic situations.

QoS-aware cross-layer mechanism for multiple instances RPL

In Low power and Lossy Networks (LNNs), routing has been considered as a main design and development challenge. This has led to the open design of the IPv6 routing protocol for LLNs called RPL. The protocol allows creating groups (instances) of multiple loop-free routing topologies over a physical network. The purpose of forming an optimized tree routing topology is to drive packets from the nodes to the collection point or sink which is the root of the tree. In this paper, we take advantage of extracted routing information to support high performance transmission of priority packets by proposing a QoS-aware cross-layer mechanism. The mechanism is explained and its performance is evaluated through simulation experiments. Simulation results show that the proposed mechanism provides high Packet Reception Ratio with low Packet Delivery Latency for priority traffic.

Adaptive Learning Based Scheduling in Multichannel Protocol for Energy-Efficient Data-Gathering Wireless Sensor Networks

Multichannel communication protocols have been developed to alleviate the effects of interference and consequently improve the network performance in wireless sensor networks requiring high bandwidth. In this paper, we propose a contention-free multichannel protocol to maximize network throughput while ensuring energy-efficient operation. Arguing that routing decisions influence to a large extent the network throughput, we formulate route selection and transmission scheduling as a joint problem and propose a Reinforcement Learning based scheduling algorithm to solve it in a distributed manner. The results of extensive simulation experiments show that the proposed solution not only provides a collision-free transmission schedule but also minimizes energy waste, which makes it appropriate for energy-constrained wireless sensor networks.

Performance evaluation of multiple RPL routing tree instances for Internet of Things applications

To meet the development of Internet of Things (IoT), IETF has proposed IPv6 standards working under low-power and low-cost constraints. In this paper, we provide insights on RPL (routing protocol for low power and lossy networks) under the condition of multiple RPL instances. For the study, we use the Contiki operating system, together with the COOJA simulator. Our work investigates the use of two distinctive objective functions under multiple RPL instances for differentiating QoS at network layer in WSNs. The metrics evaluated include routing tree convergence, latency and packet delivery ratio. The study can also serves as a basis for future enhancement of the use of multiple RPL instances for a plethora of IoT applications.