CO-TDMA: A TDMA Protocol for Collecting Data and OAP at the Same Time

Wireless reprogramming of wireless sensor networks (WSNs) usually requires switching to dedicated over-the-air programming (OAP) protocols, and often needs to stop current work of data collection. This paper presents CO-TDMA, a low power consumption TDMA protocol using adaptive beacons, which provides a capability to both collect data and transmit OAP codes at the same time. A CO-TDMA frame consists of several data slots, an access slot and several beacon slots. The data slots are used to transmit collecting data, the access slot is used to update network topology or other changes, and the beacon slots are used to transmit data ACK beacon and optional OAP data. The major contribution is the design of the adaptive beacon transmitted in beacon slots: in data collection state, the beacon only carries the ACK information of collecting data for every node in the network (Beacon-piggyback mechanism); when the OAP transmissions are needed, the OAP codes will attach behind the ACK bytes in the payload of a packet. The OAP information is encoded with rateless digital fountain codes to close to 100% reliability if enough packets are received. By multiplex use of beacon slots, we can transmit the OAP codes with very little extra energy consumptions (0.113% RDC), without impacting the normal data collection.