Multichannel MAC Protocols for Wireless Networks

1
Multichannel MAC Protocols for Wireless Networks

• Ritesh Maheshwari
• Himanshu Gupta
• Samir R. Das

SECON 2006
2
Outline

• Introduction
• Background and related work
• Receiver directed transmission and performance
  issues
• xRDT Extended Receiver Directed Transmission
  scheme
• Local Coordination-based Multichannel (LCM) MAC
• Simulation-based performance evaluation
• Conclusions

3
Introduction

• The research community has been addressing the
  multichannel question using two very different
  approaches.
• The first is a static approach based on topology
  control
• The other approach is more dynamic

4
Introduction (cont.)

• 2 MAC protocol
• Extended receiver directed transmission (xRDT)
• uses one packet interface and one busy tone
  interface
• local coordination-based multichannel (LCM) MAC
• uses a single packet interface only

5
Background and related work

• Dynamic approach
• SSCH
• Switche channels at slot-boundaries in a
  pseudo-random sequence
• MMAC
• Beacon intervalATIM window Data window
• RDT
• Quiescent channel
• DCA
• 1 ctrl channel, others data channel

6
Receiver Directed Transmission and performance
issues

• Every node is assumed to be have a single
  interface and also selects a well-known
  quiescent channel for itself

1?2
2?1
2
2
A
A
B
B
(1)
(1)
(2)
(2)
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Multichannel hidden terminal problem
(2)
(2)
(1)
(1)
C
B
A
D
RTS (2)
CTS (2)
CTS (2)
Data (2)
Collision
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Deafness problem
(3)
(2)
(1)
B
C
A
2?3
1?2
DATA (3)
Backoff Retry ...
3?2
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xRDT Extended Receiver Directed Transmission
scheme

• Addressing multichannel hidden terminal
• Channel memory helps propagate the channel state
  to a potential transmitter at all times--busy
  tone
• A receiver when receiving a data packet on
  channel c turns on the tone in corresponding busy
  tone channel bc.
• Use of the busy tone prevents any collision of
  data packets.

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xRDT (cont.)

• Addressing deafness
• The deaf nodes broadcast a Data Transmission
  Complete (DTC) notification message in its own
  quiescent channel
• Ensure that all potential transmitters (who may
  be in backoff) come to know of the receivers
  availability
• DTC does not prevent deafness

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xRDT (cont.)
Switch to q and sense
Switch to p
DATA(q)
RTS(q)
DTC(p)
A (p)
B (q)
ACK packet duration
off
on
on
bq
Interframe spacing
DTC(bp)
bp
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xRDT (cont.)

• Selection of quiescent channel
• Optimized assignment of quiescent channels is
  akin to the problem of coloring vertices of a
  graph with available channels
• Find maximum weighted k-cut in the G2 graph
• G is the original communication graph and G2 has
  edges between node pairs (i j) such that
  distance between i and j in G is at most 2

i
j
1
2
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Local Coordination-based Multichannel (LCM) MAC

• Use only one interface
• Ctrl window data window
• All control packets are transmitted in the same
  channel during the control window. All nodes in a
  neighborhood are tuned to this same channel at
  this time.
• Avoid multichannel hidden terminal and deafness
• All data packets are transmitted concurrently in
  different channels during the data window.
• Data packet transmit parallelly on different
  channels

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LCM MAC (cont.)
Master node
nTneg or (k1)Tneg
DATAACKinterframe spacings
RTS ctrl window duration, data window duration,
a list of free channels CTS a channel id,
schedual information RES a channel id, schedual
information
Set NAV
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LCM MAC (cont.)
inflexible bit0 in RTS B can send a CTS with a
changed schedule to match its own
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Simulation-based performance evaluation

• Ns2 simulator
• Transmission range 250m
• Carrier sense range 500m
• Nominal bit rate of each channel 1 Mbps
• 100 nodes at random locations (50 CBR)
• Data packet sizes 1000 bytes
• Shortest path routing

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Simulation-based performance evaluation (cont.)
2 interface protocol
1 interface protocol
6 channel
13 channel
Throughput vs. load in ns2 simulations with 1Mbps
channels, 100 nodes in a 500m X 500m area.
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Simulation-based performance evaluation (cont.)
6 channel
13 channel
Throughput vs. load in ns2 simulations with 1Mbps
channels, 100 nodes in a 1000m X1000m area.
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Simulation-based performance evaluation (cont.)
A chart comparing saturation throughput of xRDT
and LCM MAC with varying number of channels in a
500m X 500m area. The chart also includes single
channel 802.11 for baseline comparison
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Conclusions

• This paper developed two multichannel MAC
  protocols
• xRDT with a packet and a busy tone interface
• LCM MAC, with just one interface