Rodolfo De Paz Alberola

AvroraZ: extending Avrora with an IEEE 802.15.4 compliant radio chip model

This paper presents AvroraZ, an extension of the Avrora emulator -- The AVR Simulation and Analysis Framework -- which allows the emulation of the Atmel AVR microcontroller based sensor node platforms with IEEE 802.15.4 compliant radio chips thus allowing emulation of sensor nodes such as Crossbows MicaZ. AvroraZ is based on design, implementation and verification of several extensions to Avrora: the address recognition algorithm, an indoor radio model, the clear channel assessment (CCA) and link quality indicator (LQI) of the IEEE 802.15.4 standard. We have AvroraZ and demonstrated its correctness in emulating MicaZ code.

Duty cycle learning algorithm (DCLA) for IEEE 802.15.4 beacon-enabled wireless sensor networks

The current specification of the IEEE 802.15.4 standard for beacon-enabled wireless sensor networks does not define how the fraction of the time that wireless nodes are active, known as the duty cycle, needs to be configured in order to achieve the optimal network performance in all traffic conditions. The work presented here proposes a duty cycle learning algorithm (DCLA) that adapts the duty cycle during run time without the need of human intervention in order to minimise power consumption while balancing probability of successful data delivery and delay constraints of the application. Running on coordinator devices, DCLA collects network statistics during each active duration to estimate the incoming traffic. Then, at each beacon interval uses the reinforcement learning (RL) framework as the method for learning the best duty cycle. Our approach eliminates the necessity for manually (re-)configuring the nodes duty cycle for the specific requirements of each network deployment. This presents the advantage of greatly reducing the time and cost of the wireless sensor network deployment, operation and management phases. DCLA has low memory and processing requirements making it suitable for typical wireless sensor platforms. Simulations show that DCLA achieves the best overall performance for either constant and event-based traffic when compared with existing IEEE 802.15.4 duty cycle adaptation schemes.

Service Discovery Protocols for Constrained Machine-to-Machine Communications

An emerging trend in many applications is to use resource-constrained wireless devices for machine-to-machine (M2M) communications. The observed proliferation of wireless embedded systems is expected to have a significant impact on future M2M applications if the services provided can be automatically discovered and accessed at runtime. In order to realize the decoupling of M2M applications and services, energy efficient service discovery mechanisms must be designed so as to minimize human intervention during configuration and management phases. However, many traditional service discovery protocols cannot be applied to wireless constrained devices because they introduce too much overhead, fail in a duty-cycled environment or require significant memory resources. To address this, either new protocols are being proposed or existing ones are adapted to meet the requirements of constrained networks. In this article, we provide a comprehensive overview of service discovery protocols that have been recently proposed for constrained M2M communications by the Internet Engineering Task Force (IETF). Advantages, disadvantages, performance and challenges of the existing solutions for different M2M scenarios are also analyzed.

Constrained Application Protocol for Low Power Embedded Networks: A Survey

IPv6 will make it possible to provide Internet connectivity to any object embedding a communication device. In the same line, Web technologies will make managing, communicating and visualizing any information provided by these devices attractive to the end users and application developers. Most of the new devices connected to this Web of Things (WoT) will be embedded and wirelessly connected. However, current Web technologies have been developed with powerful devices in mind not being suited for this kind of constrained environment. In order to make the WoT a reality for low power embedded networks, specialised protocols that consider the energy, memory and processing constraints of wireless embedded devices must be designed. The IETF recently created the CoRE group whose first goal has been developing a Restful application layer protocol for communications within embedded wireless networks referred to as Constrained Application Protocol (CoAP). The year 2011 has seen a big push in the research community towards evaluating the performance and features of CoAP protocol, indicating a growing interest in the community towards Restful interactions in low power wireless embedded networks. This paper analyses those recent advances to provide a clear picture on what has been achieved so far in the evaluation and development of the Constrained Application Protocol.

Experimental Evaluation of Beacon Scheduling Mechanisms for Multihop IEEE 802.15.4 Wireless Sensor Networks

Recently, several scheduling techniques to enable multihop communications in the beacon enabled mode of the IEEE 802.15.4 standard have been proposed. Using the beacon enabled mode allows node synchronization and hence energy savings which is an important concern in wireless sensor networks (WSNs). However, and to the best of our knowledge, current available scheduling techniques have not been formally compared. This makes it difficult to decide which technique gives a better performance with regard to different WSN scenarios or applications. In this paper, we compare the two most popular methods for beacon enabled multihop IEEE 802.15.4 WSNs for different scenarios and performance parameters. Based on our findings, we propose recommendations for the use of each scheduling technique.

Commissioning of low power embedded devices with IPv6/CoAP

The commissioning of sensors and actuators within a building is often carried out by an operator who manually gathers and later inserts configuration data into the building management system. Data sets collected can easily reach hundreds which makes this manual process a slow complex operation which in turn is prone to errors. In this paper, we present a client-server architecture for a simple web based commissioning application, based on the Constrained Application Protocol (CoAP), that allows an operator to easily discover and browse through newly installed devices in order to perform commissioning configurations onsite.