## 2 Literature Review
The asynchronous multi-channel MAC (AMMAC) differs from the above two protocols due to the reuse of the control channel for data transmission. Contending nodes in the control channel send RTS-CTS control frames, such as other protocols, and also send an additional announce-to-send (ATS) frame to inform the neighbors of both the sender and receiver of the intended data transmission. Nodes switch to the data channel that has been agreed upon during the contention in the control channel. When there is no data channel available, the nodes that win the contention are allowed to send one frame in the control channel. Spectrum utilization is increased due to the use of the control channel for data transmission. Due to this behavior, one mandatory waiting frame time is added to nodes coming back to the control channel for contention. Although an overhead, this ensures nodes returning to the control channel do not collide with ongoing transmission. Therefore, the issue of the multi-channel hidden terminal is solved due to this asynchronous mode of operation. However, the disadvantage of this scheme is that nodes returning to the control channel need to wait a mandatory period before transmitting frames. The authors of [46] propose a hybrid and adaptive H-MMAC protocol, which improves the AMMAC protocol in utilizing the control channel for data transmissions as well as extending data transmissions in data channels. Further, H-MMAC utilizes an ad hoc traffic indication message (ATIM) of the IEEE 802.11 power saving mode (PSM) for power management. Using the ATIM window, nodes negotiate data transmission sessions and exchange data/ACK packets while the other nodes go into sleep mode. H-MMAC defines data transmissions in two modes: normal and extended modes. Normal transmissions occur within the data window and extended transmissions extend to the ATIM window based on the network traffic load. The extended mode can continue to the next data window if other nodes do not use the specific data channel. For control channel reuse, the control channel cycles between two intervals (contention and data intervals). In contention intervals, nodes negotiate with RTS-CTS packets, and in data intervals, nodes that successfully negotiate data transmission slots exchange data and ACK packets. The spectrally efficient asynchronous multi-channel MAC (SA-MMAC) [47] enhances the spectrum utilization by reusing the control channel for data transmission, such as AMMAC. If no free data channels are found, the node can transmit one frame in the control channel. Moreover, it follows the bidirectional data transmission mechanism explained in BiMMAC. SA-MMAC uses one common channel and the rest as data channels out of all orthogonal channels. The contention mechanism in the control channel is similar to IEEE 802.11 MAC protocol. The control frames used during contention are RTS-CTS-ATS and solve the issue of multi-channel hidden terminal problems. Once the nodes negotiate which data channel to use, they switch to it and start the data transmission. The receiver can send its frame without contention, backoff, or RTS-CTS handshakes. After data transmission,the nodes return to the control channel where they wait for a mandatory one frame of time to avoid collision with ongoing transmission in the control channel. SA-MMAC reduces the signaling overhead and increases the utilization of the spectrum. Moreover, it solves the deafness and multi-channel hidden terminal problem. Delay incurred by the other nodes in obtaining the channel would be high due to two frames in the data channel. Moreover, nodes need to wait an additional frame of time before they contend due to data transmission in the control channel.