Jérôme Rousselot

Low power medium access control (MAC) protocols have received a lot of attention in the last few years because of their impact on the lifetime of wireless sensor networks. Due to the cost of implementation on real hardware, and sometimes to a lack of detail in the description of these protocols, it is difficult to evaluate them. This paper describes the latest advances in the field and introduces an ideal protocol as a benchmark. It presents detailed analytical models of the power consumption of the best and latest low power MAC protocols. These models are then used to evaluate how the performance of these protocols evolves when modifying traffic rate and network density. It is shown that the most recent scheduled protocols cannot go below the maximal acceptable mean power consumption for battery operated sensor networks. The synchronous random access protocols S-MAC and SCP-MAC scale better, but are outperformed by asynchronous random access protocols based on preamble sensing such as WiseMAC, CSMA-MPS, X-MAC and SyncWUF. These last protocols offer the lowest power consumption for all considered data rates and for all considered network densities.

Ultra Wideband Impulse Radio (UWB-IR) technology has received a lot of attention from the radio engineering community during the past few years. It features a number of attractive characteristics for wireless sensor networks, among which an ultra low power consumption, a strong robustness to interference and a high accuracy ranging capability.

Unfortunately, its time-based nature makes it difficult to model in a network simulator. Although some mathematical models have been proposed, all of them are limited to a particular modulation type, a specific receiver architecture and often to a channel model. This situation has slowed down the development of communication protocols specifically designed for these radios.

This paper presents a novel symbol-level simulator for UWB-IR which can accurately model pathloss, large-scale fading, small-scale fading and collisions. This physical layer is used to implement a model of an IEEE 802.15.4A UWB-IR radio transceiver based on energy detection.

To the knowledge of the authors, this is the first network simulation model of IEEE 802.15.4A UWB-IR radios, the first model of an energy-detection receiver and more generally the first network simulation model of symbol-level UWB-IR. It offers several channel models of various complexity, so that exploratory simulations can be run quickly and high precision results can be generated when desired. This simulation model allows to evaluate precisely the bit error rate and in particular the impact of collisions, a major cause of energy waste at the medium access control level.

Continuous multiparameter health monitoring has applications in telemedicine, rehabilitation, home care, sport, firefighting and other life-threatening situations. Current implementations rely on wires for data collection, energy distribution and management, and measure synchronization. These wires make the products more difficult to use, uncomfortable and less reliable. Although energy distribution and management can be dealt with at the sensor level, a wireless link must still address numerous challenges: reliability, low power consumption, low latency, robustness to interference, coexistence... Some of these problems have been addressed by research in communication protocols for wireless sensor networks. At the physical layer, Ultra Wideband technologies such as Impulse Radio, Chirp UWB and FM-UWB are promising in terms of power consumption and are considered by the IEEE 802.15.6 Body Area Network standardization task group. This paper evaluates the replacement of wires in a prototype medical body area network by wireless data links. Two solutions are compared in terms of reliability, power consumption and latency. The first is based on FM-UWB and the other one on a narrow band radio. Both rely on WiseMAC, an ultra low power medium access control protocol for wireless sensor networks. It is shown that FM-UWB offers a lower power consumption when compared to a narrow band radio transceiver. WiseMAC is shown to maintain high packet success rates and low power consumption even when handling traffic rates higher than what it had been designed for. The combination of FM-UWB and WiseMAC is thus a good choice for medical body area networks that require ultra low power consumption and high robustness to interference.

This paper introduces WideMac, a novel low power medium access control protocol designed specifically for Ultra Wide Band Impulse Radio transceivers. The UWB-IR channel offers ultra low power transmissions and unmatchable robustness to multiple access interference. WideMac takes advantage of these two key properties by using asynchronous periodic beacon transmissions from each network node, thereby avoiding the need for network-wide clock synchronization and at the same time allowing fast and power efficient neighbour discovery. WideMac power consumption is compared analytically to the state of the art, and it is shown to be on par with the best and close to the optimum on a broad range of traffic rates and network densities. Additionally, WideMac UWB-IR beaconing mechanism offers unique low power neighbour discovery and ranging. Since the operation of distributed routing protocols often heavily depends on such features, it is argued that the performance of a complete UWB-IR communications stack can be greatly improved by choosing WideMac.

The use of wireless sensor networks is rapidly growing in various types of applications that benefit from spatially distributed data collection. Some of these applications, such as industrial automation, fire detection or health monitoring, have strong timeliness constraints. Since field deployments are difficult to monitor and debug, the development of real-time communication protocols for wireless sensor networks necessitates accurate simulation models. This paper presents open source Omnet++ simulation models based on the IEEE 802.15.4 standard. Four evaluation scenarios are used to compare simulation timeliness and packet error rate results with experimental measurements. The small scale of the scenarios allows to isolate the effect of each system component. The comparison validates the models for timeliness estimates in sensor networks and pinpoints the variability of software implementations in embedded systems as a major cause of differences between simulated and measured results.

This paper provides an overview of CSEMs FM-UWB PHY-MAC proposal to IEEE802.15.6, Task Group 6, Body Area Networks. The proposed solution provides for an ultra low power, yet robust and reliable solution for low data rate medical BAN. The paper examines the key features and performance aspects of the proposal.

This poster presents an innovative dual-mode medium access control scheme that combines the ultra low power MAC protocol WiseMAC with the wireless sensor networking standard IEEE 802.15.4. Each network device can independently and autonomously switch between the two modes depending on its residual energy resources and the current application traffic. We observe that this approach can reduce the power consumption and the average latency by almost two orders of magnitude.

New technologies can help to develop preventive healthcare, thereby leading to significant life quality improvements. Medical Body Area Networks are expected to become a key element in tomorrow's medical IT infrastructure by enabling the long term collection and analysis of health parameters. For this vision to become a reality, several challenges must be addressed. This work focuses on the technological aspects of ultra low power consumption, low latency and packet error rate. We consider and evaluate state of the art technologies currently under evaluation by the IEEE Standard Association 802.15.6 task group on body area networks, using detailed network simulation models, which have been calibrated with hardware measurements whenever possible and with MATLAB communication link simulations otherwise. We observe that the expected power consumption levels are similar for all considered platforms, and that they are determined mainly by the medium access control protocol. Trade-offs between communications latency, throughput and power consumption are identified. The performance of the Ultra Wideband Impulse Radio system is clearly impacted by its lack of carrier sensing capability. We conclude that the existing technologies are mature enough and that the remaing obstacles to widespread adoption are organizational and societal.

This paper presents a novel modeling technique of Ultra-Wideband Impulse Radio for the simulation of wireless sensor networks, to evaluate this technology from a systems point of view that includes the effect of communication protocols. The adopted approach, named Maximum Pulse Amplitude Estimation, considers the characteristics of the propagation channel, the transmitter and receiver architectures, the modulation type, the robustness to multiple access interference and the impact of error correction coding. It differs from the state of the art by working at the symbol level instead of developing an analytical model. While this technique increases the processing time, it offers more flexibility in terms of modulations, channel models and receiver architecture. Our approach enabled us to implement the first network simulation model of the UWB PHY specified in the IEEE 802.15.4A standard. It is also the first UWB-IR network simulation model to consider an energy detection receiver. Several channel models have been implemented, offering trade-offs between simulation speed and accuracy. The performance of this energy detection transceiver is compared with MATLAB models. The packet error rate is evaluated as a function of distance with several channel models, and in the presence of interferers. It is shown that our approach leads to results in line with MATLAB models, that the choice of channel model greatly impacts the simulation speed and that the IEEE 802.15.4A UWB PHY allows some limited degree of protection against multiple access interference even when using a low performance energy detection receiver architecture.

This thesis evaluates the potential of Ultra Wideband Impulse Radio for wireless sensor network applications.

Wireless sensor networks are collections of small electronic devices composed of one or more sensors to acquire information on their environment, an energy source (typically a battery), a microcontroller to control the measurements, process the information and communicate with its peers, and a radio transceiver to enable these communications. They are used to regularly collect information within their deployment area, often for very long periods of time (up to several years). The large number of devices often considered, as well as the long deployment durations, makes any manual intervention complex and costly. Therefore, these networks must self-configure, and automatically adapt to changes in their electromagnetic environment (channel variations, interferers) and network topology modifications: some nodes may run out of energy, or suffer from a hardware failure.

Ultra Wideband Impulse Radio is a novel wireless technology that, thanks to its extremely large bandwidth, is more robust to frequency dependent propagation effects. Its impulsional nature makes it robust to multipath fading, as the short duration of the pulses leads most multipath components to arrive isolated. This technology should also enable high precision ranging through time of flight measurements, and operate at ultra low power levels.

The main challenge is to design a system that reaches the same or higher degree of energy savings as existing narrowband systems considering all the protocol layers.

As these radios are not yet widely available, the first part of this thesis presents Maximum Pulse Amplitude Estimation, a novel approach to symbol-level modeling of UWB-IR systems that enabled us to implement the first network simulator of devices compatible with the UWB physical layer of the IEEE 802.15.4A standard for wireless sensor networks.

In the second part of this thesis, WideMac, a novel ultra low power MAC protocol specifically designed for UWB-IR devices is presented. It uses asynchronous duty cycling of the radio transceiver to minimize the power consumption, combined with periodic beacon emissions so that devices can learn each other's wake-up patterns and exchange packets. After an analytical study of the protocol, the network simulation tool presented in the first part of the thesis is used to evaluate the performance of WideMac in a medical body area network application. It is compared to two narrowband and an FM-UWB solutions. The protocol stack parameters are optimized for each solution, and it is observed that WideMac combined to UWB-IR is a credible technology for such applications. Similar simulations, considering this time a static multi-hop network are performed. It is found that WideMac and UWB-IR perform as well as a mature and highly optimized narrowband solution (based on the WiseMAC ULP MAC protocol), despite the lack of clear channel assessment functionality on the UWB radio.

The last part of this thesis studies analytically a dual mode MAC protocol named WideMac-High Availability. It combines the Ultra Low PowerWideMac with the higher performance Aloha protocol, so that ultra low power consumption and hence long deployment times can be combined with high performance low latency communications when required by the application. The potential of this scheme is quantified, and it is proposed to adapt it to narrowband radio transceivers by combining WiseMAC and CSMA under the name WiseMAC-HA.