that busy tones are also transmitted in the same channel while there is no separate control channel. The conditions for transmitting busy tones are the following: A busy tone is transmitted from a relay candidate in the first slot after $T_{SIFS}$, if the relay desires to indicate that the ANC-OL mode is efficient for improving the rate of the system by combining the indicated transmission with another transmission. This is indicated in line 5 of the $relay\_overhear()$ subroutine in Fig. \[fig:canc-mac\]. When no busy tone is transmitted after $T_{SIFS}$ plus $T_s$, this means that this transmission cannot use the ANC-OL mode jointly with another transmission based on the latest estimate by the relay(s). On the other hand, the first slot after CTS plus $T_{SIFS}$ remains idle, and a busy tone is transmitted by a relay in the second slot, when the rate can be improved by enabling the COOP mode (again depicted in the $relay\_overhear()$ subroutine in Fig. \[fig:canc-mac\]). Similarly with before, several potential relays can transmit a busy tone. The optimal one has again to be selected in a similar way as in the case of ANC-OL.

Finally, if no busy tone is transmitted in any of the first 