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Busy Elimination Multiple Access. Dramatically reduces collisions in data broadcasting due to the hidden terminal problem Geared to support prioritization of data transmissions Geared for use in mobile ad-hoc networks Has little overall control overhead and provides impressive good-put.
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Busy Elimination Multiple Access • Dramatically reduces collisions in data broadcasting due to the hidden terminal problem • Geared to support prioritization of data transmissions • Geared for use in mobile ad-hoc networks • Has little overall control overhead and provides impressive good-put
Reliable broadcast problem • Transmissions collide at the common neighbor • SOLUTION: Common neighbor should arbitrate between its neighbors
C B A E D A B C data transmission busy signal (Double power transmission) busy signal Channel Reservation to overcome hidden terminal problem • Common neighbor warns other neighbors when it is receiving transmission from any neighbor • Busy Tone Multiple Access(BTMA) – Channel reservation with distinct frequency busy signal (FDMA) • Busy Elimination Multiple Access (BEMA)– Channel reservation with a busy timeslot (TDMA)
BEMA protocol • Rounds consist of BUSY/CONTROL phase and DATA phase • Each potential sender transmits for random/priority-based period of time bounded by Δ - β • Contender listens for a busy signal or collision AFTER it completes its busy signal transmission • Transmitter of longest duration signal wins
DATA DATA BEMA in action 2 1 3 4 i j k • i and k compete • i wins and transmits data for 2 rounds • j and k transmit busy signal for entire busy timeslot in the meantime • k competes again
BEMA: Protocol Actions {idle, candidate, waiting, leader, locked} DATA PHASE ACTIONS – 3,4,5 CONTROL PHASE ACTIONS – 1,2,6
Logical Proof Lemma 1: If no leader in the beginning of a round at most one leader in one-hop neighborhood of any node k Lemma 2: If j is a neighbor of k and j is a leader k must be ‘locked’ to j Lemma 3: If j is a neighbor of k and j is a leader in the beginning of a round no other node can transmit in the DATA phase of the round Lemma 4: Starting from the initial state at most one leader in one-hop neighborhood of any node k Hence hidden terminal problem does not arise
Number of Collisions • Collisions in BEMA and BMMM` remain largely constant with increase in traffic load
Good-put (True Data throughput) • BMMM` suffers heavily due to high control overhead • BSMA’s good-put decrease almost linearly as the number of collisions increase. • CSMA’s good-put is high and constant because the data loss due to collisions is made up with the increase in transmitters transmitting with NO overhead.