Over the last five years, CHESS is actively developing Wireless Sensor Network technology and intellectual property, but with a nice twist. There is obviously an enormous amount of off-the-shelf WSN technology readily available such as Wi-Fi, Bluetooth, Z-wave and ZigBee. They all have their advantages in specific areas of application, but they suffer from a common set of problems: constructing a robust network that is both energy efficient, self-organizing, and scalable. In our opinion, neither of these technologies satisfy all these criteria. In practice, the cable wiring problem is replaced by network configuration and routing problems.

CHESS has worked on a novel approach to overcome this solution, which is inspired on nature. Our solution uses an epidemic communication style based on standard RF broadcasting. This approach is called GOSSIP, which actually reflects the way humans interact. Messages are sent periodically which are received by adjoining neighbors. If this message is new to the receiving node (meaning the data was not received in previous communication rounds), the neighbor will also transmit this message to its own neighbors. If the message is old (meaning the data was already received before, i.e. through another neighbor) than the message is discarded. Basically each message is repeated and duplicated towards all nodes that span the network, it spreads like a virus (hence the term epidemic communication). Although this seems very inefficient at first glance, it turns out to be the opposite in practice, mainly for two reasons. First of all, the nodes do not need to know who is in their neighborhood at the time of sending a message, there is no notion of an a-priori planned transmission route required, data is just shared instantaneously.

Second of all, the network is implicitly reliable since messages may follow different communication routes in parallel. So the loss of a message between two nodes does not mean that the data is lost. As a bonus, having contact with any one of the wireless sensor nodes, allows communication with all other nodes in the same network. Nodes can be added, removed or may be physically moving without the need to reconfigure the network. The GOSSIP protocol is a truly self-configuring network solution. The network may even be heterogeneous, where several types of nodes communicate different pieces of information with each other at the same time. This is possible due to the fact that no interpretation of the message content is required in order to be able to forward it other nodes. Message communication is fully transparent, providing a seamless communication platform, where new functionality can be added later, without the need to change the installed base. Furthermore, we have also developed technology to update the wireless sensor nodes software by means of “over the air” programming of a deployed network.

The GOSSIP protocol is basically an event-driven communication mechanism that has a certain (configurable) heartbeat. A node may offer its information to its neighbors and then waits for incoming messages from the other nodes. The list of exchanged message are processed and this process then repeats itself. We have developed a media access control layer (MAC) which allows the use of broadcast RF communication using Time Division Multiple Access (TDMA) scheduling. The MAC protocol ensures that adjoining nodes all send at specific points in time, one by one, while all other nodes listen. By putting these communication slots close together, we can communicate at a very low duty cycle, reducing power usage for both transmission and reception significantly. The crux of the GOSSIP MAC protocol, or GMAC as we call it, is the way nodes automatically synchronize to the network heartbeat and dynamically select a slot for communication. This area is well researched and established over the last few years leading to two filed patents (i.e. PCT/IB2009/006027) and several proof of concept demonstrations with deployments of 1000+ nodes.

Best regards,
Chess

Chess is member of RFID Platform Nederland
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