299 research outputs found
A Localized Slot Allocation Algorithm for Wireless Sensor Networks
While energy efficiency is typically considered the
major concern in wireless sensor networks (WSNs), many
real-life applications also require reliability, timeliness, and
scalability. In such scenarios, Time Division Multiple Access
(TDMA) is typically used for data communication, as it avoids
collisions and provides predictable latency and minimum
energy consumption. TDMA requires a slot scheduling
algorithm to allocate transmission slots to sensor nodes. In
this paper, we propose a decentralized slot allocation
algorithm which is localized and self adaptive, i.e., each node
selects its slot(s) and adapts its behavior only basing on
locally-available information. We derive analytically the time
taken by the algorithm and the average energy consumed by
the network to achieve a complete schedule. We also show
that our solution performs significantly better than another
previous similar algorithm
Throughput Fairness Enhancement Using Differentiated Channel Access in Heterogeneous Sensor Networks
Nowadays, with wireless sensor networks (WSNs) being widely applied to diverse applications, heterogeneous sensor networks (HSNs), which can simultaneously support multiple sensing tasks in a common sensor field, are being considered as the general form of WSN system deployment. In HSNs, each application generates data packets with a different size, thereby resulting in fairness issues in terms of the network performance. In this paper, we present the design and performance evaluation of a differentiated channel access scheme (abbreviated to DiffCA) to resolve the fairness problem in HSNs. DiffCA achieves fair performance among the application groups by providing each node with an additional backoff counter, whose value varies according to the size of the packets. A mathematical model based on the discrete time Markov chain is presented and is analyzed to measure the performance of DiffCA. The numerical results show that the performance degradation of disadvantaged application groups can be effectively compensated for by DiffCA. Simulation results are given to verify the accuracy of the numerical model
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
Strategies for Optimal MAC Parameter Setting in IEEE 802.15.4 Wireless Sensor Networks: a Performance Comparison
Recent studies have shown that the IEEE 802.15.4
MAC protocol may suffer from severe limitations in terms of
reliability and energy efficiency if a non appropriate
parameter setting is used. Hence, a number of solutions have
been proposed to select the optimal parameter setting to
provide reliability with minimum energy consumption. In this
paper we compare, by simulation, three different algorithms
that take different approaches to the problem, namely offline
computation, model-based adaptation, and measurement-based
adaptation. We show that adaptive algorithms perform well,
however the model-based adaptive approach has some
limitations that make it unsuitable in practical scenarios,
where operating conditions may vary over time and
transmission errors cannot be neglected. Instead, the
measurement-based adaptive approach is flexible and
effectiv
Performance Analysis of Distributed MAC Protocols for Wireless Networks
How to improve the radio resource utilization and provide better
quality-of-service (QoS) is an everlasting challenge to the
designers of wireless networks. As an indispensable element of
the solution to the above task, medium access control (MAC)
protocols coordinate the stations and resolve the channel access
contentions so that the scarce radio resources are shared fairly
and efficiently among the participating users. With a given
physical layer, a properly designed MAC protocol is the key to
desired system performance, and directly affects the perceived QoS
of end users.
Distributed random access protocols are widely used MAC protocols
in both infrastructure-based and infrastructureless wireless
networks. To understand the characteristics of these protocols,
there have been enormous efforts on their performance study by
means of analytical modeling in the literature. However, the
existing approaches are inflexible to adapt to different protocol
variants and traffic situations, due to either many unrealistic
assumptions or high complexity.
In this thesis, we propose a simple and scalable generic
performance analysis framework for a family of carrier sense
multiple access with collision avoidance (CSMA/CA) based
distributed MAC protocols, regardless of the detailed backoff and
channel access policies, with more realistic and fewer
assumptions. It provides a systematic approach to the performance
study and comparison of diverse MAC protocols in various
situations. Developed from the viewpoint of a tagged station, the
proposed framework focuses on modeling the backoff and channel
access behavior of an individual station. A set of fixed point
equations is obtained based on a novel three-level renewal process
concept, which leads to the fundamental MAC performance metric,
average frame service time. With this result, the important
network saturation throughput is then obtained straightforwardly.
The above distinctive approach makes the proposed analytical
framework unified for both saturated and unsaturated stations.
The proposed framework is successfully applied to study and
compare the performance of three representative distributed MAC
protocols: the legacy p-persistent CSMA/CA protocol, the IEEE
802.15.4 contention access period MAC protocol, and the IEEE
802.11 distributed coordination function, in a network with
homogeneous service. It is also extended naturally to study the
effects of three prevalent mechanisms for prioritized channel
access in a network with service differentiation. In particular,
the novel concepts of ``virtual backoff event'' and ``pre-backoff
waiting periods'' greatly simplify the analysis of the arbitration
interframe space mechanism, which is the most challenging one
among the three, as shown in the previous works reported in the
literature. The comparison with comprehensive simulations shows
that the proposed analytical framework provides accurate
performance predictions in a broad range of stations. The results
obtained provide many helpful insights into how to improve the
performance of current protocols and design better new ones
Survey of Spectrum Sharing for Inter-Technology Coexistence
Increasing capacity demands in emerging wireless technologies are expected to
be met by network densification and spectrum bands open to multiple
technologies. These will, in turn, increase the level of interference and also
result in more complex inter-technology interactions, which will need to be
managed through spectrum sharing mechanisms. Consequently, novel spectrum
sharing mechanisms should be designed to allow spectrum access for multiple
technologies, while efficiently utilizing the spectrum resources overall.
Importantly, it is not trivial to design such efficient mechanisms, not only
due to technical aspects, but also due to regulatory and business model
constraints. In this survey we address spectrum sharing mechanisms for wireless
inter-technology coexistence by means of a technology circle that incorporates
in a unified, system-level view the technical and non-technical aspects. We
thus systematically explore the spectrum sharing design space consisting of
parameters at different layers. Using this framework, we present a literature
review on inter-technology coexistence with a focus on wireless technologies
with equal spectrum access rights, i.e. (i) primary/primary, (ii)
secondary/secondary, and (iii) technologies operating in a spectrum commons.
Moreover, we reflect on our literature review to identify possible spectrum
sharing design solutions and performance evaluation approaches useful for
future coexistence cases. Finally, we discuss spectrum sharing design
challenges and suggest future research directions
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