Sleepy Nodes And Sleepy Meshes - Ultra-Low-Power Mesh Routing

By Synapse Wireless Inc.

Physical nodes in a SNAP based network communicate wirelessly using a full mesh topology. Nodes that are in direct radio range of each other will communicate directly. When nodes are not in direct radio range, intermediate nodes will automatically forward any messages to their intended destinations. This is known as "mesh routing".

All SNAP based nodes have mesh routing capability "out-of-the-box". Such a network is self-forming, which means that when a new node is powered-up, it is automatically integrated into the network. The network is also selfhealing, which means that if a node catastrophically fails for any reason, other nodes will automatically route signals around the failed node.

In some wireless network deployments, it is possible for all of the physical nodes to be externally powered ("plugged into a wall socket"). In this case, power consumption is not a problem and all of the nodes can be active – "talking"/transmitting and/or "listening"/receiving – all of the time.

In many environments, however, it is necessary for the nodes to be powered by batteries, in which case power consumption can be a significant problem. Even in the case of a low-power Synapse RF Engine module running SNAP, an active module will consume an average of 50 milli-amps (mA). When powered by AA batteries capable of supplying say 2,500 milli-amp-hours (mAh), this means that a node can stay active for 2,500 / 50 = 50 hours, which is a little over two days.

This is simply not acceptable in terms of resource requirements (someone changing the batteries) and expense (batteries aren't cheap) for the vast majority of installations, especially in the case of networks involving hundreds or thousands of wireless nodes. The solution is for the nodes to alternate between being "awake" for a short amount of time and then entering a "sleep" mode in which they consume dramatically less power.

Unfortunately, traditional mesh networks find it difficult to fully-implement a network-wide sleep scenario. By comparison, SNAP based network can be configured to implement a "sleepy mesh" that can extend each node's battery life to more than a year.