MACA-P : A MAC for Concurrent Transmissions in Multi-Hop Wireless Networks

This paper presents the design and performance of MACA-P, a RTS/CTS based MAC protocol, that enables simultaneous transmissions in multi-hop ad-hoc wireless networks. The IEEE 802.11 DCF MAC enforces that no parallel transmission is possible in either neighborhood of a sender or a receiver (of an ongoing transmission). MACA-P is a set of enhancements to the 802.11 MAC that allows parallel transmissions in many situations when two neighboring nodes are either both receivers or transmitters, but a receiver and a transmitter are not neighbors. Like 802.11, MACA-P contains a contention-based reservation phase prior to data transmission. Unlike 802.11, the data transmission is delayed by a control phase interval which allows multiple sender-receiver pairs to synchronize their data transfers thereby avoiding collisions. To enable MACA-P in realizing its gains, we sketch the improvements needed at the modem and physical layer designs of wLAN interface cards. The performance of MACA-P in terms of system throughput is obtained through a simulation of the protocol using ns and is compared with the performance of 802.11 RTS/CTS MAC.