and channel access mechanism but only the cooperative packet transmission procedure. It is important to be clear that the adoption of the well-known and understood binary exponential backoff algorithm allows one node to obtain access to the channel at a specific time instant and transmit an RTS/CTS. Therefore, it is impossible for two nodes to successfully complete the RTS/CTS exchange. Since the two nodes that are about to be involved in a communication are identified with the method above, the problem that remains to be addressed is to identify which node can be the optimal relay and if there are any additional nodes that can transmit concurrently.

Basic Protocol and Busy Tones
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The $tx\_data()$ subroutine in the pseudo-algorithm of Fig. \[fig:canc-mac\] depicts the actions executed at a sender when it desires to transmit a data packet. Let us assume that an RTS/CTS message exchange has finished (line 5 in the previous subroutine) and several relays have updated the $\mathbf{rate\_estimates}$ as we explained in the previous section. Then the potential relays indicate their ability to relay a transmission by using busy tones that are transmitted after a time duration equal to $T_{SIFS}$ after the end of the CTS transmission[^4]. Note 