ESENSE
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25 July 2007

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D3.2.1 - Protocol Elements


Description of the deliverable content and purpose

The goal of WP3 Task 2 (T3.2) is to identify the solutions, at different layers of the protocol stack and mainly for the connectivity subsystem of deliverable D2.1.1, which will be used as the building blocks for the overall integrated and cross-layer optimised protocol stack to be developed in T3.3. For developing such solutions T3.2 exploits measurements and information provided from T3.1 (nodes relative position, relative mobility, channel quality, etc), the knowledge of application spaces provided by D1.2.1, and the e-SENSE architecture presented in D2.1.1.

While the aim of the interim report version of the deliverable D3.2.1 “Efficient Protocol Elements” (IR3.2.1) was to provide a very good though concise state-of-the-art of protocol techniques at each OSI layer for wireless sensor network (WSN) applications, this deliverable, D3.2.1, presents the research work done and results achieved on selected protocols and algorithms based on the state-of-the-art provided by IR3.2.1. The selected protocols and algorithms on which research has been done are compatible with the e-SENSE themes presented in D1.1.2 and application spaces of D1.2.1 and all with the exception of transport techniques in 3.5 belong to the connectivity subsystem of the e-SENSE early reference model D2.1.1. With this deliverable, e-SENSE shall be equipped with the most important, required elements to build the “e-Stack” protocol stack.

More specifically, this deliverable describes the e-Stack building blocks on self-organisation and topology control that relate to the formation of a network on initialisation as well as the maintenance of connectivity with the varying topology changes in the network. Furthermore, Section 3. , named Sensor Connectivity, deals with scalability, medium access control, relaying, and routing; protocols and algorithms all of which are essential in forming the Connectivity subsystem of the e-SENSE reference model. Some components for the Middleware subsystem of D2.1.1, namely transport techniques are also described in Section 3.5 since the part is relevant for the e-Stack. While not directly related to the connectivity subsystem, Section 4 provides an important subject related to both topology control and routing: mobility. It also provides an investigation on coexistence and internetworking, a highly relevant topic in e-SENSE because it is expected that several application spaces and therefore, networks will occupy the same spatial location and can have a significant effect on the performance of the networks.

In detail, the deliverable describes in Section 1.1 how the WP2 and WP4 affects the research reported in this document. Section 2.1 describes a clustering approach on self-organisation that is compatible with a number of e-SENSE scenarios and how the approach reacts to topology changes. Further, Section 2.2 (Topology Control) provides an energy consumption evaluation between the clustering approach and that of a flat topology. It is shown that the clustering approach can have a considerable gain in performance over the flat topology, a value over 50%.

Sensor connectivity is the dominating topic of this deliverable and Section 2 focuses on scalability issues in WSNs, namely connectivity to Internet gateways and different methods of achieving it. Section 3.2 concentrates on energy-efficient medium access control. First, recommendations for usage of MAC protocols in e-SENSE application spaces are given followed by an in depth analysis of the IEEE Std 802.15.4 and the IEEE 802.15.4a draft MAC protocols with possible improvements and recommendations for usage. Note that these MAC protocols were the starting point of MAC protocol research in e-SENSE and therefore the analysis is essential. Because the 15.4a draft utilises IR-UWB physical layer the effect of IRUWB on MAC protocol performance is modelled and based on the analysis a new MAC protocol, suitable with the super-frame structure of IEEE 802.15.4 is proposed. The 15.4 is modelled both analytically and by simulations and a proposal for improvement, still compatible with the standard, is presented. Lastly in the section a novel energy-efficient MAC protocol with a synchronisation scheme is presented.

Section 3.3 concentrates on cooperative relaying. The relaying model is presented along with the possible forwarding choices and its gains are analytically demonstrated. In addition three scenarios: ideal, cooperative relaying and cooperative relaying with leapfrogging are presented.
Routing is the theme of Section 3.4 beginning with recommendations for usage of routing protocols in e-SENSE application spaces. Thereafter, three routing or route-assisting methods are presented, all especially relevant to resource and energy constrained sensor networks. The first method deals with statistical assisted routing and, by using rigorous mathematics, derives Pareto-optimal schemes and statistical assisted techniques. These are then compared and it is shown that statistical assisted schemes produce performance close to the optimal ones. The second method concentrates on using the simple method of RSSI as a reliable link quality indicator. Generally RSSI is fairly unreliable, but a method of high reliability is presented and will find usage in wireless sensor networks. The third method describes flooding with pruning to rapidly but energy-efficiently spread packets throughout the network.
This deliverable is quite limited in describing transport techniques of Section 3.5. There are three reasons; the first one is that the deliverable concentrates on the Connectivity subsystem and transport protocols reside in the Middleware subsystem of the e-SENSE architecture (D2.1.1 and D2.2.1). The second reason is that publish ? subscribe procedure (presented in IR2.2.1) is expected to be dominant and the third reason is the promising IEEE 6LoWPAN miniaturisations [2]. Nevertheless, Section 3.5 describes a transport protocol for continuous datagram flows and by simulations evaluates it to function well in wireless environment.
Section 4.1 addresses the topic of coexistence and internetworking and performs an extensive analysis on the IR-UWB physical layer. Multiple networks are expected to spatially overlap in e-SENSE environment because several application spaces can be used in the same location. Therefore, the effect of the networks on each other should be evaluated.
Section 4.2 on the other hand deals with mobility, and especially exploiting mobility to prolong network lifetime. This is done by sink mobility, and it is proven to consume energy in a large network in a more equal fashion. An online person tracking system is presented in Section 4.2.2 and lastly, mobility exploitation is discussed and an analysis in link stability is given.

 

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