Busy Elimination Multiple Access

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 Tone Multiple Access (BTMA) Channel
  reservation with distinct frequency busy signal
  (FDMA)

• Busy Elimination Multiple Access (BEMA)
  Channel reservation with a busy timeslot
  (TDMA)

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
  ? - ß
• Contender listens for a busy signal or collision
  AFTER it completes its busy signal transmission
• Transmitter of longest duration signal wins

5
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

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
• BSMAs good-put decrease almost linearly as the
  number of collisions increase.
• CSMAs 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.