Ultra Low-Energy 
Wireless Sensor Nodes

Research:

The goal of the PicoRadio project is to build a wireless sensor network that is versatile, self-organizing, dynamically reconfigurable, and multi-functional. The primary constraint in building the nodes is the extremely low energy budget. This imposes tight constraints on the entire design, and instead of the traditional layered protocol design, we are tightly integrating the protocol stack vertically for maximum energy optimization. The network layer of the Piconode protocol stack has two primary functions: routing and addressing of nodes.

Addressing of nodes is based on the geographical positions of nodes. Queries in sensor networks are typically not concerned with a particular node, rather they are directed to any nodes which satisfy particular criteria of position, type, etc. This leads to our concept of class-based addressing, which is a triplet consisting of location, node type, node sub-type. This eliminates the overhead of assigning and maintaining fixed addresses across the network as well as the problem of distributing them dynamically.

For the routing of packets across the network, we have developed an energy efficient protocol we call "energy aware routing." This scheme takes the view that trying to optimize every route to consume the least amount of energy is not in the best interest of the network, instead we try to optimize the power of the entire network and in the process maximize the lifetime. Thus, we find a set of routes on demand and choose between them in a probabilistic fashion. The choice is based on a metric which combines both transmit/receive power and residual energy at a node. This means that all nodes across the network participate more actively in routing, and a few nodes do not die out just because they are in a good position to forward packets. Simulations verify this behavior and the network lifetime also increases substantially. Further work is needed to show its efficacy for more mobile networks and also in the presence of barriers in the network. Simulations are carried out in Opnet which provides an easy way to define protocols and obtain simulation results for different scenarios.

We have also developed an algorithm which performs data aggregation while routing called "data funneling". This further improves the efficiency in low-energy networks. Again Opnet has been used extensively for simulating and evaluating the protocol for different simulation scenarios.

Authored Papers:

1. Rahul C. Shah and Jan M. Rabaey, "Energy aware routing for low energy ad hoc sensor networks", IEEE WCNC 2002.

2. Dragan Petrovic, Rahul C. Shah, Jan M. Rabaey and Kannan Ramchandran, "Data funneling: routing with aggregation and compression for wireless sensor networks", submitted to IEEE SNPA 2003.