May 2008
  
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How to improve the Performance of a Mesh Wireless Sensor Network?

This white paper presents Diversity Path Mesh, a technology designed to maximize the most important performance factors of wireless mesh networks, as well as their trade-off envelope.

  Virtual Extension Ltd

Email: info@virtual-extension.com

Technology White Paper

Overview - Wireless Sensor Networks and their Performance
The main goal of a wireless sensor network is to enable the reception of data from the sensor field without the need for physical connection or access. An additional possible goal is the remote control of the sensors by the sensor application.

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In a classic example of an electrical metering application, wireless sensor networks can be used to build an Advanced Metering Infrastructure (AMI) which can continuously monitor the power consumption, and control the functionality of the meters, as well as limit the end-user consumption or report about tampering with the meters in real-time.

Such capabilities are important for enabling the electric utilities to reduce operational expenses, implement flexible management systems based on real-time energy consumption monitoring, increase the system’s reliability and ultimately help to reduce cost and save energy.

Mesh topology has proved to offer the best choice for a large range of wireless sensor network applications. Furthermore, often mesh is the only feasible topology for modern projects. The critical factors influencing the performance of a wireless mesh network vary from application to application, and applications usually require most of the following capabilities:

Reliability and data throughput are always important performance factors.

Despite the fact that mesh topology is often the best option for numerous applications, the vast majority of wireless network technologies today are configurable to all the relevant topologies, thus addressing their lowest common denominator. Such strategy can be justified only if the application requires several topologies to be applied concomitantly or at least in the same project.

However, when it is clear that the only topology is mesh, it only makes sense to use a technology targeted specifically to the mesh topology.

"Everything should be made as simple as possible, but not simpler"1
This white paper presents Diversity Path Mesh, a technology designed to maximize the most important performance factors of wireless mesh networks, as well as their trade-off envelope. Diversity Path Mesh™ is a multi-hop, bi-directional communication technology, developed for wireless sensor networks using mesh topology and operating in the unlicensed frequency ranges. The basic technique employed in Diversity Path Mesh is known as flooding, where a node transmits the very same message to all the nodes in the network cell, in a flat hierarchy. The theoretical concept of flooding in networks as an alternative to routing is well known.

CUBE In a flooding-based network, all units receive the message data, thus eliminating the need to rout messages in the network - a most demanding network management task. Eliminating the routing also decreases the amount of data carried in the network, since messages contain only pure data, with no waste on routing information. In addition, flooding adds to the network a dimension of multiple propagation paths which improves the robustness tremendously. Furthermore, there is no set-up time and any number of nodes can be inserted or removed, and as long as the added or remaining nodes are within the reception range, the network simply continues to operate. There is no realigning time and no down-time of the network.

However, the use of flooding in standard mesh network architectures has been avoided for several reasons, the main one being the “broadcast storm problem”, where nodes within reception range retransmit the message approximately at the same time, with the resulting collisions increasing the energy consumption to unreasonable levels.

To channel the flooding technique into a practical and useful solution, Diversity Path Mesh complements it with a technique known as simulcast. Messages of each node are relayed by the surrounding nodes at controlled timing, thus forming multiple transmission paths on the way to the destination. The retransmission of the messages through the network is synchronised to sub-bit level, with TDMA as the master construction framework. The multiple identical transmissions received by the node receivers are summed in the de-modulator, increasing the strength of the signal.

The results are increased reliability, as there is no single point (node) of failure; and increased propagation robustness, due to the inherent spatial diversity of the propagation through the various diverse channels of the multiple relay paths. This propagation robustness translates to greater range and also practically eliminates dead spots in all conditions - in steady state, when multipath occurs, when there is RF interference and when changes in the propagation conditions occur.

In other words, there is a significant reduction in the probability of a message to fail reaching its destination. As the propagation over many paths occurs simultaneously, the propagation time that would have been required if they would have been transmitted one after the other is reduced to a minimum. Relaying the messages also enables Diversity Path Mesh networks to extend as far as needed, with the cell overall range and robustness rising with the increase of the number of the nodes. The maximum number of nodes exceeds any practical requirement of such applications.

In a nutshell, the behaviour of a Diversity Path Mesh network based on these techniques is as following:

Conclusion
Control Solutions, Inc Designing and developing from scratch a wireless sensor network specifically for mesh topology, while learning from the drawbacks of the existing technologies, seems like the most suitable approach for achieving the highest set of performance. Flooding is arguably the most appropriate technique to be considered for this purpose, as it addresses the most critical performance factors of wireless mesh networks, as well as the overall factors’ envelope. However, the flooding technique carries several grave drawbacks, which have until now precluded its use in this type of networks.

Diversity Path Mesh is probably the first mesh wireless network to use the flooding technique instead of routing, as it has managed to overcome any disadvantages of flooding by using the simulcast technique, which combines relaying and synchronization at sub-bit level, resulting in a surprisingly and revolutionary set of performances. At the same time, it encompasses all the benefits of the flooding technique.

Products based on this technology and deployed by its originator, Virtual Extension, have proven the Diversity Path Mesh capability, as they have been successfully deployed in numerous projects, where products based on other technologies either have failed or would have failed. These applications include Utility Automation – Electricity and Water, Building Automation, Industrial Automation, Vending Machines, Agriculture and Security.

Copyright © 2008 Virtual Extension Ltd. All rights reserved worldwide.


Virtual Extension and Diversity Path Mesh are trademarks of Virtual Extension Ltd. Other trademarks and trade names mentioned maybe marks and names of their owners as indicated. All trademarks are the property of their respective owners and are used here in an editorial context without intent of infringement. Specifications are subject to change without notice.

Virtual Extension HQ, 2 Halamed-He Street, Givatayim 53402 Israel +972-3-7321207
Virtual Extension US, 108 Ringtail Run, Kennett Square, PA 19348 (610) 388 9897


1 Albert Einstein (1879 - 1955)

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