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A New Multi-Channel MAC Protocol with On-
Demand Channel Assignment for Mobile Ad Hoc
Networks
S.-L. Wu, C.-Y. Lin, Y.-C. Tseng, and J.-P. Sheu
Int'l Symposium on Parallel Architectures, Algorithms and
Networks (I-SPAN), 2000
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Abstract
̈ considers the access of multiple
channels in a MANET
̈ Features
̈ “on-demand” style to assign channels
̈ Degree-independent
̈ It adapts to exchange few control
messages to achieve channel assignment
̈ No form of clock synchronization

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Outline
̈ Introduction
̈ Concerns with Using Multiple Channels
̈ Our Multi-Channel MAC Protocol
̈ Analysis and Simulation Results
̈ Conclusions
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Introduction(1)
̈ Single-channel MAC protocols
̈ A common channel is shared by all mobile
hosts
̈ The standard of IEEE 802.11 has been
widely accepted
̈ The performance will degrade quickly as
the number of mobile hosts increases

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Introduction(2)
̈ Multi-channel MAC protocol
̈ Several advantages
̈ Higher throughput
̈ Less normalized propagation delay per channel
̈ It is easier to support QoS
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Introduction(3)
̈ how to access the channel is
technology-dependent
̈ The categorization of mobile host
̈ Single-transceiver
̈ A mobile host can only access one channel at a
time
̈ Multi-transceiver
̈ A mobile host can access multiple channels
simultaneously

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Introduction(4)
̈ Related work
̈ Channel assignment in a traditional packet radio
network
̈ Two IEEE 802.11-like protocols separate control
traffic and data traffic into two distinct channels
̈ A scheme based on Latin square assumes a
TDMA-over-FDMA technology
̈ Channel assignment is static
̈ A clock synchronization is necessary
̈ A number of transceivers is equal to the number of
frequency bands
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Introduction(5)
̈ Related work(cont.)
̈ The protocol [12] for Reconfigurable
wireless network assigns channels statically
and has a polling transceiver and a sending
transceiver
̈ The protocol [10] assigns channels
dynamically and mandates tow-hop
information

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Introduction(6)
̈ Related work(cont.)
̈ The protocol [24] is degree-independent
and each host has one transmitter and n
receivers concurrently listening on all n
channels
̈ A hop-reservation MAC protocol is also
degree-independent and requires clock
synchronization
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Introduction(7)
̈ Our new MAC protocol
̈ Applies to FDMA and CDMA
̈ Requires two simplex transceivers per host
̈ Based on RTS/CTS-like reservation
mechanism and degree-independent
̈ The clock synchronization is un-necessary
̈ Dynamic assigns channels and in an “on-
demand” fashion

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Introduction(8)
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Concerns with Using Multiple Channels(1)
̈ SM:A Simple Multi-channel Protocol
̈ Static channel assignment
̈ The transmission follows IEEE 802.11
̈ The basic idea
̈ When a host X needs to send to a host Y,
X should tune to Y’s channel
̈ Two states
̈ RECEIVE
̈ SEND

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Concerns with Using Multiple Channels(2)
̈ Some Observations
̈ The traditional problem in a single-channel
system
̈ Hidden-terminal:(a)
̈ Exposed-terminal:(b)
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Concerns with Using Multiple Channels(3)
̈ In SM protocol
̈ The hidden-terminal problem will become
more serious
̈ the exposed-terminal problem will become
less serious
̈ Some new problems may appear
̈ False Connectivity Detection
̈ Channel Deadlock Problem

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Concerns with Using Multiple Channels(4)
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Concerns with Using Multiple Channels(5)

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Concerns with Using Multiple Channels(6)
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Concerns with Using Multiple Channels(7)

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Our Multi-Channel MAC
Protocol(1)
̈ DCA(dynamic channel assignment)
̈ Our channel model
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Our Multi-Channel MAC
Protocol(2)
̈ Each mobile host is equipped with tow
half-duplex transceivers
̈ Control transceiver
̈ Operates on the control channel to exchange
control packets with other mobile hosts
̈ Data transceiver
̈ Dynamically switches to one of the data
channels to transmit the data packet and ACK

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Our Multi-Channel MAC
Protocol(3)
̈ Each mobile host,say X,maintains the
following data structure
̈ CUL[]:channel usage list
̈ CUL[i] has three fields
̈ CUL[i].host
̈ CUL[i].ch
̈ CUL[i].rel_time
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Our Multi-Channel MAC
Protocol(4)
̈ FCL:free channel list
̈ It is dynamically computed from CUL
̈ The complete protocol
̈ A wants to send to B,it first checks whether
the following two conditions are true:
̈ B is not equal to any CUL[i].host such that
CUL[i].rel_time>Tcurr+(TDIFS+ TRTS+TSIFS+TC
TS)

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Our Multi-Channel MAC
Protocol(5)
̈ There is at least a channel Dj such that for all i:
(CUL[i].ch=Dj) (CUL[i].rel_time≦
Tcurr+(TDIFS+TRTS+TSIFS+TCTS))
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Our Multi-Channel MAC
Protocol(6)

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Our Multi-Channel MAC
Protocol(7)
̈ Then A can send RTS(FCL,Ld) to B only if there is
no carrier on the control channel
̈ On a host B receiving the RTS(FCL,Ld) from A, it
has to check whether there is any
data channel Dj FCL such that for all i:
(CUL[i].ch=Dj) (CUL[i].rel_time≦Tcurr + (TSIFS +
TCTS))
̈ If so,then B replies a CTS(Dj,NAVCTS) to A, where
NAVCTS = Ld/Bd+TACK+2τ
̈ Otherwise,B replies a CTS(Test) to A
̈ Test=min{ ,CUL[i].rel_time} - Tcurr - TSIFS- TCTS
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Our Multi-Channel MAC
Protocol(8)
̈ On an irrelevant host C≠B receiving
A's RTS(FCL,Ld), it has to inhibit itself
from using the control channel for a
period
NAVRTS = 2TSIFS+TCTS+TRES+2τ
̈ Host A, after sending its RTS, will wait
for B's CTS with a timeout period of
TSIFS+TCTS+2τ

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Our Multi-Channel MAC
Protocol(9)
̈ On host A receiving B's
CTS(Dj,NAVCTS) , it performs the
following steps:
̈ Append an entry CUL[k] to its CUL such
that
̈ CUL[k].host = B
̈ CUL[k].ch = Dj
̈ CUL[k].rel_time = Tcurr +NAVCTS
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Our Multi-Channel MAC
Protocol(10)
̈ Broadcast RES(Dj,NAVRES) on the control
channel, where
̈ NAVRES=NAVCTS-TSIFS-TRES
̈ Send its DATA packet to B on the data
channel Dj. Note that this steps happens
in concurrent with step b)
̈ On an irrelevant host C≠A receiving
B's CTS(Dj,NAVCTS), C updates its CUL.

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Our Multi-Channel MAC
Protocol(11)
̈ On a host C receiving RES(Dj,NAVRES),
it appends an entry CUL[k] to its CUL
such that:
̈ CUL[k].host = A
̈ CUL[k].ch = Dj
̈ CUL[k].re_time = Tcurr +NAVRES
̈ On B completely receiving A's data
packet, B replies an ACK on Dj
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Our Multi-Channel MAC
Protocol(12)
̈ To summarize our protocol
̈ Relies on the control channel to assign
data channels
̈ the deadlock problem can be avoided
̈ the missing RTS/CTS and the hidden-terminal
problems will be less serious.

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Analysis and Simulation
Results(1)
̈ Arrangement of Control and Data
Channels
̈ For simplicity, let's assume that the lengths
of all control packets(RTS, CTS, and RES)
are Lc,and those of all data packets Ld=9Lc.
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Analysis and Simulation
Results(2)
̈ In this paper,we consider two bandwidth
models
̈ Fixed-channel-bandwidth:
̈ Each channel has a fixed bandwidth.
̈ Fixed-total-bandwidth:
̈ The total bandwidth offered to the network is
fixed.

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Analysis and Simulation
Results(3)
̈ Fixed-channel-bandwidth
̈ the maximum number of data channels
̈ n ≦Ld/3* Lc (1)
̈ the utilization U of the total given
bandwidth.
̈ U≦n/(n+1) (2)
̈ From (1) and (2),we derive that
̈ U≦ Ld/3* Lc +Ld (3)
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Analysis and Simulation
Results(4)
̈ Fixed-total-bandwidth
̈ The problems are:
̈ (i) how to assign the bandwidth to the control
and data channels
̈ (ii) how many data channels (n) are needed, to
achieve the best utilization.
̈ the maximum number of data channels
̈ n ≦(Ld/Bd) / (3* Lc/Bc) (4)

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Analysis and Simulation
Results(5)
̈ the utilization U of the total given
bandwidth.
̈ U≦(n* Bd) / (n* Bd+Bc) (5)
̈ From (4) and (5),we derive that
̈ U≦ Ld/3* Lc +Ld (6)
̈ Ld/(3* Lc +Ld)=(n* Bd) / (n* Bd+Bc)
Bc/(n* Bd)=3* Lc /Ld (7)
̈ Thus,the best ratio is
̈ 3* Lc /Ld
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Analysis and Simulation
Results(6)
̈ Experimental Results
̈ Tow performance metrics
̈ Throughput =(Packet_Length*No_Successful_
Packets)/Total_Time
̈ Utilization =(Packet_Length*No_Successful_
Packets)/Total_Time*No_Channels
̈ Present results from 4 aspects
̈ Effect of the Number of Channels

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Analysis and Simulation
Results(7)
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Analysis and Simulation
Results(8)

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Analysis and Simulation
Results(9)
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Analysis and Simulation
Results(10)
̈ Effect of Data Packet Length
̈ Fig11(a)(b)(c)(d) and Fig(12)
̈ Effect of the Bandwidth of the Control
Channel
̈ Fig(13)
̈ Effect of Host Density
̈ Fig(14)

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Analysis and Simulation
Results(11)
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Analysis and Simulation
Results(12)

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Analysis and Simulation
Results(13)
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Analysis and Simulation
Results(14)

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Analysis and Simulation
Results(15)
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Analysis and Simulation
Results(16)

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Analysis and Simulation
Results(17)
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Conclusion
̈ The result for the fixed-channel-
bandwidth model is particularly
interesting for the currently favorable
CDMA technology
̈ We are currently working on extending
our access mechanism to a reservation
one