6.1 Existing Candidate Coordination Schemes

In this section, we review five state-of-the-art candidate coordination schemes: GeRaF collision avoidance MAC, ExOR batch-based MAC, contention-based forwarding (CBF), slotted acknowledgement and compressed slotted acknowledgement.

6.1.1 GeRaF Collision Avoidance MAC

The GeRaF collision-avoidance MAC-coordination scheme is proposed in (Zorzi and Rao 2003). This scheme applies to a sensor network scenario, where nodes wake up and go to sleep periodically. It is basically a geographic opportunistic routing, where each transmitter knows its own location information and that of its neighbors, and the destination. The transmitter node's location information as well as the destination node's location information are embedded in the ready-to-send (RTS) frame. It assumes that sensor nodes are equipped with two radios (Schurgers et al. 2002). Therefore, the data traffic and the wakeup signaling can be operated on two different channels simultaneously. That is, all messages exchange on the first “data” frequency while the busy tone is sent on the second frequency. We present this protocol from transmitter and receiver point of view as described in Zorzi and Rao (2003). Transmitter Behavior

When a sleeping node has a packet to send, it wakes up and enters the active state and monitors both data and busy tone frequencies for τ seconds. If either frequency is busy, the node reschedules an attempt at a later time. If both frequencies are sensed ...

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