  This paper presents a TDMA based energy efficient cognitive radio
multichannel medium access control (MAC) protocol called ECR-MAC for wireless
Ad Hoc Networks. ECR-MAC requires only a single half-duplex radio transceiver
on each node that integrates the spectrum sensing at physical (PHY) layer and
the packet scheduling at MAC layer. In addition to explicit frequency
negotiation which is adopted by conventional multichannel MAC protocols,
ECR-MAC introduces lightweight explicit time negotiation. This two-dimensional
negotiation enables ECR-MAC to exploit the advantage of both multiple channels
and TDMA, and achieve aggressive power savings by allowing nodes that are not
involved in communication to go into doze mode. The IEEE 802.11 standard allows
for the use of multiple channels available at the PHY layer, but its MAC
protocol is designed only for a single channel. A single channel MAC protocol
does not work well in a multichannel environment, because of the multichannel
hidden terminal problem. The proposed energy efficient ECR-MAC protocol allows
SUs to identify and use the unused frequency spectrum in a way that constrains
the level of interference to the primary users (PUs). Extensive simulation
results show that our proposed ECR-MAC protocol successfully exploits multiple
channels and significantly improves network performance by using the licensed
spectrum band opportunistically and protects QoS provisioning over cognitive
radio ad hoc networks.
