INFOCOM 2014

What is MMAC?▣ Multi-Channel MAC

Channel negotiation and assignment (sender – destination pair) Destination discovery (same channel) and load balancing (exploit all channels)

▣ Multi-Channel Hidden Terminal Problem If node C is a neighbor of A and B, C defers from transmission for MTU + ACK.

What is MMAC? (cont.)▣ Multi-Channel Exposed Terminal Problem

What If switching to a busy channel in the middle of data transmission?

(Suppose B is transimitting data to A and C is transmitting to D)

Previous MMAC protocols▣ Split-phase MMAC ( SP-MMAC )

Time is devided to alternating control and data phases. During the control phase, all nodes converge to a default channel to negotiate

the channel assignment using RTS/CTS. During the data phase, nodes exchange data on the assigned channels. Hidden Terminal and extra message overhead avoided. However, low spectural

efficiency with high contention conditions due to control phase.

▣ Dedicated Control Channel MMAC ( DCC-MMAC ) Nodes are equipped with 2 radios. One radio is always tuned to a control channel

and the other radio switches between the remaining channels for transmissions. Hidden Terminal avoided. However, higher device cost and low spectural effi-

ciency due to dedicated control channel. (DCC can also be a bottle neck in high-contention scenarios.)

▣ Randezvous MMAC ( MMAC ) Nodes hop between channels using predefined hopping sequences. Initial discovery is incurred until sender’s and dest’s hop sequences overlap. No solution for Hidden Terminal Problem.

FD-MMAC

▣ Full-Duplex MMAC

First to exploit FD communication(single radio). Nodes independently switch to idle channels by tracking the

state of each channel. (w/o exchange of control messages) Common synchronized time-slotted system. (GPS) Physical Layer Technique (SIS, EVM, RSS, Signal correlation)

Full-Duplex in a channel▣ Cross correlation technique (SIGCOMM’08)

Nodes can apply signal correlation techniques for detecting transmission of known bit patterns. Common in frame de-tection even in the presence of collisions.

Review

▣ Multi-channel Transmission The delay and throughput performance of wireless networks

can be significantly improved by accommodating parallel transmissions over orthogonal frequency channels.

A BHT ET

F E

Review (cont.)▣ Problems - MMAC

Channel negotiation & destination discovery Load balancing Multi-channel HT, ET.

Full-Duplex in a channel▣ Cross correlation technique (SIGCOMM’08)

Nodes can apply signal correlation techniques for detecting transmission of known bit patterns. Common in frame de-tection even in the presence of collisions.

A BF E

State Classification

RSS – Received Signal Strength

Hidden & Exposed

A B C

Destination & Sender State machine

Sample Scenarios

Experimental Result

▣ Elimination of channel negotiation and VCS + single-channel ET.