A survey on control separation techniques in multi-radio multi-channel MAC protocols <s> D. Common Control Channel for Signalling <s> The ALOHA and Carrier Sense Multiple Access (CSMA) protocols have been proposed for packet radio networks (PRN). However, CSMA/CD which gives superior performance and has been successful applied in local area networks cannot be readily applied in PRN since the locally generated signals will overwhelm a remote transmission, rendering it impossible to tell whether a collision has occurred or not. In addition, CSMA and CSMA/CD suffer from the “hidden node” problem in a multihop PRN. In this paper, we develop the Receiver-Initiated Busy-Tone Multiple Access Protocol to resolve these difficulties. Both fully connected and multihop networks are studied. The busy tone serves as an acknowledgement and prevents conflicting transmissions from other nodes, including “hidden nodes”. <s> BIB001 </s> A survey on control separation techniques in multi-radio multi-channel MAC protocols <s> D. Common Control Channel for Signalling <s> In ad hoc networks, the hidden- and the exposed-terminal problems can severely reduce the network capacity on the MAC layer. To address these problems, the ready-to-send and clear-to-send (RTS/CTS) dialogue has been proposed in the literature. However, MAC schemes using only the RTS/CTS dialogue cannot completely solve the hidden and the exposed terminal problems, as pure "packet sensing" MAC schemes are not safe even in fully connected networks. We propose a new MAC protocol, termed the dual busy tone multiple access (DBTMA) scheme. The operation of the DBTMA protocol is based on the RTS packet and two narrow-bandwidth, out-of-band busy tones. With the use of the RTS packet and the receive busy tone, which is set up by the receiver, our scheme completely solves the hidden- and the exposed-terminal problems. The busy tone, which is set up by the transmitter, provides protection for the RTS packets, increasing the probability of successful RTS reception and, consequently, increasing the throughput. This paper outlines the operation rules of the DBTMA scheme and analyzes its performance. Simulation results are also provided to support the analytical results. It is concluded that the DBTMA protocol is superior to other schemes that rely on the RTS/CTS dialogue on a single channel or to those that rely on a single busy tone. As a point of reference, the DBTMA scheme out-performs FAMA-NCS by 20-40% in our simulations using the network topologies borrowed from the FAMA-NCS paper. In an ad hoc network with a large coverage area, DBTMA achieves performance gain of 140% over FAMA-NCS and performance gain of 20% over RI-BTMA. <s> BIB002
The third control separation approach -the common control channel for signalling is often referred as a tone-based approach. In this scheme, one or more separate narrow bandwidth radios are used to empower mobile hosts to send busy tone to emulate the collision detection function as that in wired network. The basic operation of tone-based approach is depicted in Figure 1c , instead of providing conventional RTS-CTS-DATA-ACK handshake, the busy tone serves two purposes one is collision avoidance and the other one is acknowledgement. The busy tone is a small pulse that occupies the control channel for duration of each data transmission. This, in effect, provides continuous physical carrier sensing to inform nearby nodes about the ongoing transmission on data channel. The nodes are not permitted to transmit any data if the busy tone is sensed. Upon the completion of data transmission, the busy tone will be terminated in order to inform the availability of data channel. The use of busy tone to combat the hidden-terminal problems of CSMA has been appeared in a very early study of Busy Tone Multiple Access (BTMA) protocol proposed by Tobagi and Kleinrock  . BTMA is an infrastructure-based protocol which divides the channel into a message channel and the busy-tone channel. BTMA proposes that whenever a centralized base station senses a busy data channel, it transmits a busy tone over the busy tone channel to prevent nearby nodes from transmitting. Since, the base station is a centralized entity and is in line of sight of all terminals, each terminal can sense the busy-tone channel and determine the current state of data channel. Wu and Li BIB001 proposed a receiver initiated busy-tone multiple access (RI-BTMA) protocol for packet-radio network. In this scheme, the sender transmits a preamble packet (eg. RTS) to the receiver prior to the data transmission. When the receiver successfully obtains the preamble and the data channel is available. The receiver will initiate a busy tone in a separate channel to inform nearby node that they should backoff. So the correct source can always be notified that it can proceed with transmission of data packet. In the subsequent work of tone-based approach, Haas and Deng BIB002 designed a Dual Busy Tone Multiple Access (DBTMA) for ad hoc network which uses RTS requests and two out-of-band busy tones. This scheme features two busy tone signals, namely "Transmit-Busy-Tone" (BT t ) and "Receive-Busy-Tone" (BT r ). BT t prevents the exposed node becoming new receiver, so RTS can be promptly delivered to all nearby nodes. On the other hand, BT r is used to prevent the hidden terminals from becoming new transmitter, and avoid collision between control and data packets. In addition, the BT r can only be initiated upon successful reception of RTS packet, thus, BT r can replace CTS and serve as an acknowledgement to the RTS packets.