Poll-before-data multiple access

Abstract

We introduce a new medium access control (MAC) protocol named PDMA (poll-before-data multiple access). Most prior MAC protocols aimed at avoiding collisions of data packets in networks with hidden terminals are sender-initiated, in that the sender transmits a short request to send (RTS) asking the receiver for permission to transmit. In contrast in PDMA, when a data packet arrives at the receiver, the receiver sends a ready-to-receive-and-transmit (RT2) packet stating the identifiers of a specific sender and receiver. A node receiving an RT2 packet addressed to it as a sender is enabled to send a data packet if it has one; otherwise, if the sender specified in the RT2 is quiet, the receiver specified in the RT2 sends a clear-to-send (CTS) packet, enabling the sender of the RT2 to send its own data packet free of collisions. PDMA is shown to avoid the collision of data packets with any type of packet. An analytical model is used to show that PDMA achieves higher throughput than prior collision-avoidance protocols for wireless networks, namely MACA-BI, FAMA NCS, and MACA. Average delays in PMA are also shown to be shorter than those in CSMA.