A Redundant Data Transmission Protocol for a Wireless Sensor Network

In a wireless sensor-actuator network (WSAN), sensor nodes deliver messages with sensed values to only nearby nodes due to weak radio. Messages are forwarded by sensor nodes to an actuator node by a routing protocol like a flooding protocol. In the redundant data transmission (RT) protocol, a sensor node sends a message with not only its sensed value but also sensed values received from other sensor nodes. Each message carries so many number of sensed values that the message loss ratio is not increased. Even if a message with a sensed value v is lost, an actuator node can receive the value v from a message sent by another sensor node. Thus, each sensed value is redundantly carried in multiple messages. The redundancy of a sensed value is in nature increased by broadcasting the value. In order to reduce the redundancy, we take a strategy that the farther sensor nodes from an actuator node forward the fewer number of sensed values. We evaluate the RT protocol in terms of loss ratio, redundancy, and delay time of sensed values. We show that about 80% of sensed values can be delivered to an actuator node even if 95% of messages are lost due to noise and collision.