1 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

2 Reliable broadcast problem Transmissions collide at the common neighbor SOLUTION: Common neighbor should arbitrate between its neighbors

3 Channel Reservation to overcome hidden terminal problem Common neighbor warns other neighbors when it is receiving transmission from any neighbor Busy Elimination Multiple Access ( BEMA )– Channel reservation with a busy timeslot (TDMA) Busy Tone Multiple Access ( BTMA ) – Channel reservation with distinct frequency busy signal (FDMA) C B A E D A BC busy signal (Double power transmission) busy signal data transmission

4 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

5 DATA i j k 1.i and k compete 2.i wins and transmits data for 2 rounds 3.j and k transmit busy signal for entire busy timeslot in the meantime 4.k competes again BEMA in action

6 BEMA: Protocol Actions {idle, candidate, waiting, leader, locked} DATA PHASE ACTIONS – 3,4,5 CONTROL PHASE ACTIONS – 1,2,6

7 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

8 Number of Collisions Collisions in BEMA and BMMM` remain largely constant with increase in traffic load

9 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.