UC Santa Cruz

A new approach for collision avoidance and collision detection in ad-hoc networks of nodes with half-duplex radios is introduced. Rather than using a single busy tone indicating that a receiver is busy, three types of carrier tones sent by receivers or passive listeners indicate that an intended receiver is busy receiving or acknowledging a data packet, or a passive listener has detected a collision. All carrier tones are sent over a single control channel, and the data channel is used only for data and request-to-send (RTS) packets. The Carrier-Tone Multiple Access with Collision Avoidance and Detection (CTMA/CAD) is described and its performance is compared with the performance of DBTMA in a hidden-terminal scenario. The results of the analysis show that CTMA/CAD is a more efficient channel-access method for networks with hidden terminals.