Portability in MAC protocol and transceiver software implementations for LR-WPAN platforms

In a variety of emerging networked computing system domains over the years, there have been bursts of activity on new medium access control (MAC) protocols, as new communication transceiver technologies with greater data-movement performance or lower power dissipation have been introduced. To enable implementations flexible to evolving standards and improving application-domain insight, such MAC protocols are typically initially implemented in software, and interface between applications or system software, typically executing on an embedded processor or microcontroller, and the evolving radio transceiver hardware. Many challenges exist in implementing MAC protocols across evolving or competing transceiver hardware implementations and processor architectures. Some of these challenges are peculiar to the requirements of MAC protocols, and others are a result of the plethora of system and processor architectures in the embedded systems domain. This article studies the challenges facing software implementations of MAC protocols running on embedded microcontrollers, and interfacing with radio transceiver hardware. Experience with an implementation of the IEEE 802.15.4 MAC across three hardware platforms with different processor, system, and systems software architectures is presented, focusing on implementation approach and interfaces. Pitfalls are pointed out, and guidelines are provided for ensuring that new MAC implementations are easily portable across processor architectures and transceiver hardware.Science Foundation Irelandau ti ke st en SB. 14/10/1

Portability in MAC protocol and transceiver software implementations for LR-WPAN platforms

In a variety of emerging networked computing system domains over the years, there have been bursts of activity on new medium access control (MAC) protocols, as new communication transceiver technologies with greater data-movement performance or lower power dissipation have been introduced. To enable implementations flexible to evolving standards and improving application-domain insight, such MAC protocols are typically initially implemented in software, and interface between applications or system software, typically executing on an embedded processor or microcontroller, and the evolving radio transceiver hardware. Many challenges exist in implementing MAC protocols across evolving or competing transceiver hardware implementations and processor architectures. Some of these challenges are peculiar to the requirements of MAC protocols, and others are a result of the plethora of system and processor architectures in the embedded systems domain. This article studies the challenges facing software implementations of MAC protocols running on embedded microcontrollers, and interfacing with radio transceiver hardware. Experience with an implementation of the IEEE 802.15.4 MAC across three hardware platforms with different processor, system, and systems software architectures is presented, focusing on implementation approach and interfaces. Pitfalls are pointed out, and guidelines are provided for ensuring that new MAC implementations are easily portable across processor architectures and transceiver hardware. © 2010 John Wiley & Sons, Ltd

On a Joint Physical Layer and Medium Access Control Sublayer Design for Efficient Wireless Sensor Networks and Applications

Wireless sensor networks (WSNs) are distributed networks comprising small sensing devices equipped with a processor, memory, power source, and often with the capability for short range wireless communication. These networks are used in various applications, and have created interest in WSN research and commercial uses, including industrial, scientific, household, military, medical and environmental domains. These initiatives have also been stimulated by the finalisation of the IEEE 802.15.4 standard, which defines the medium access control (MAC) and physical layer (PHY) for low-rate wireless personal area networks (LR-WPAN). Future applications may require large WSNs consisting of huge numbers of inexpensive wireless sensor nodes with limited resources (energy, bandwidth), operating in harsh environmental conditions. WSNs must perform reliably despite novel resource constraints including limited bandwidth, channel errors, and nodes that have limited operating energy. Improving resource utilisation and quality-of-service (QoS), in terms of reliable connectivity and energy efficiency, are major challenges in WSNs. Hence, the development of new WSN applications with severe resource constraints will require innovative solutions to overcome the above issues as well as improving the robustness of network components, and developing sustainable and cost effective implementation models. The main purpose of this research is to investigate methods for improving the performance of WSNs to maintain reliable network connectivity, scalability and energy efficiency. The study focuses on the IEEE 802.15.4 MAC/PHY layers and the carrier sense multiple access with collision avoidance (CSMA/CA) based networks. First, transmission power control (TPC) is investigated in multi and single-hop WSNs using typical hardware platform parameters via simulation and numerical analysis. A novel approach to testing TPC at the physical layer is developed, and results show that contrary to what has been reported from previous studies, in multi-hop networks TPC does not save energy. Next, the network initialization/self-configuration phase is addressed through investigation of the 802.15.4 MAC beacon interval setting and the number of associating nodes, in terms of association delay with the coordinator. The results raise doubt whether that the association energy consumption will outweigh the benefit of duty cycle power management for larger beacon intervals as the number of associating nodes increases. The third main contribution of this thesis is a new cross layer (PHY-MAC) design to improve network energy efficiency, reliability and scalability by minimising packet collisions due to hidden nodes. This is undertaken in response to findings in this thesis on the IEEE 802.15.4 MAC performance in the presence of hidden nodes. Specifically, simulation results show that it is the random backoff exponent that is of paramount importance for resolving collisions and not the number of times the channel is sensed before transmitting. However, the random backoff is ineffective in the presence of hidden nodes. The proposed design uses a new algorithm to increase the sensing coverage area, and therefore greatly reduces the chance of packet collisions due to hidden nodes. Moreover, the design uses a new dynamic transmission power control (TPC) to further reduce energy consumption and interference. The above proposed changes can smoothly coexist with the legacy 802.15.4 CSMA/CA. Finally, an improved two dimensional discrete time Markov chain model is proposed to capture the performance of the slotted 802.15.4 CSMA/CA. This model rectifies minor issues apparent in previous studies. The relationship derived for the successful transmission probability, throughput and average energy consumption, will provide better performance predictions. It will also offer greater insight into the strengths and weaknesses of the MAC operation, and possible enhancement opportunities. Overall, the work presented in this thesis provides several significant insights into WSN performance improvements with both existing protocols and newly designed protocols. Finally, some of the numerous challenges for future research are described