Ad Hoc Wireless Media Access Protocols Mikko Raatikainen, TiTe 5

MAC Protocols protocol to use shared medium sender node sends to shared medium receiver node receives current transmission concerned with per-link connections (not end-to- end) synchronous MAC protocols asynchronous MAC protocols Ad Hoc Wireless Media Access Protocols

Problems in channel access Two nodes transmit concurrently data to the same receiver -> collision prevent by using control messages (handshake protocol) RTS-CTS approach (request-to-send/clear- to-send) problem: control message collision Hidden Terminal Problem

Problems in channel access overhearing data transmission from neighboring nodes -> unable to transmit solution: separate control and data channels or directional antennas Exposed node problem

MAC Initiation receiver informs sender that it is ready to receive data no way of knowing for sure that sender has data to send for example MACA-BI Receiver-Initiated MAC protocols

MAC Initiation sender informs receiver it has data to send receiver confirms it is ready to receive 2 control messages: RTS-CTS for example MACA, MACAW Sender-Initiated MAC protocols

Ad Hoc MAC Protocols three-way handshake: RTS-CTS-Data power control features: geographic reuse of channels no carrier sensing: control message collisions on control message collision resend at ramdom delay MACA (Multiple Access with Collision Avoidance)

Ad Hoc MAC Protocols Receiver initiative two-way handshake: RTR-Data (request-to receive) Less control messages -> less collisons, reduced turn around time Does sender have data to send? Timeliness of invitation? add info on transmitters backlog to each packet MACA features preserved MACA-BI (By Invitation)

Ad Hoc MAC Protocols Based on MACA with separate signaling channel for RTS-CTS –dialogue When receiving transfer, node sends busy signal to signaling channel Power-off nodes when not receiving nor transmitting When to power-up? Duration of power-off affects on delay and performance PAMAS (Power-Aware Multi-Access with Signalling)

Ad Hoc MAC Protocols RTS-CTS approach Separate signaling and data channels When transmiting data, sends transmit busy signal via signaling channel to neighbours When receiving data, sends receive busy signal via signaling channel to neighbours Busy signal separated by in frequency DBTMA (Dual Busy Tone Multiple Access)

Ad Hoc MAC Protocols Reduced RTS-CTS handshake Improves throughput by reducing control overhead Knowledge of data packet arrivals at neighboring nodes by overhearing CTS packets RTS-CTS handshake is reduced to CTS-only after the first hop (receiver initiative) Access to tables that maintain information on routes the node participates in (no routing though) High performance MARCH (Media Access with Reduced Handshake)