Download - Spread Spectrum MAC Protocol with Dynamic Rate and Collision Avoidance for Mobile Ad Hoc Network
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Spread Spectrum MAC Spread Spectrum MAC Protocol with Dynamic Protocol with Dynamic Rate and Collision Rate and Collision Avoidance for Mobile Ad Avoidance for Mobile Ad Hoc NetworkHoc Network
Zaihan Jian, and Mengchu Zhou
Department of Electrical and Computer EngineeringNew Jersey Institute of Technology
IEEE Transaction on Vehicular Technology,Vol. 56, No. 5, September 2007
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Outline Outline
IntroductionIntroduction DRCA protocolDRCA protocol Throughput analysisThroughput analysis Evaluation resultsEvaluation results ConclusionConclusion
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IntroductionIntroduction
Spread spectrum (SS) has been Spread spectrum (SS) has been used as one of the basic wireless used as one of the basic wireless access technologies access technologies – 2G, IS-95, CDMA2000, and WCDMA2G, IS-95, CDMA2000, and WCDMA
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Introduction Introduction
Advantage of SSAdvantage of SS– Concurrent transmission in one Concurrent transmission in one
channel without using TDMA/FDMAchannel without using TDMA/FDMA– SS can provide at most 1.5 times SS can provide at most 1.5 times
capacity compared with TDMA and capacity compared with TDMA and 4.6 times compared with FDMA in 4.6 times compared with FDMA in cellular systemcellular system
– Is feasible to switch from signal to Is feasible to switch from signal to signal for a transmitter or receiversignal for a transmitter or receiver
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IntroductionIntroduction
MANETs become extremely useful in MANETs become extremely useful in scenarios where fixed infrastructure iscenarios where fixed infrastructure is infeasible or expensive to builds infeasible or expensive to build
Most proposed MAC protocols for MAMost proposed MAC protocols for MANETs are not SS basedNETs are not SS based– IEEE 802.11 use only one spread codeIEEE 802.11 use only one spread code
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Research issues of Research issues of code assignmentcode assignment To assign transmission codes to To assign transmission codes to
network terminals to avoid packet network terminals to avoid packet collision as much as possiblecollision as much as possible
4 kinds of code assignment 4 kinds of code assignment protocolsprotocols– Common-codeCommon-code– Receiver-basedReceiver-based– Transmitter-basedTransmitter-based– HybridHybrid
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Collision avoidance in Collision avoidance in SSSS
Collision can be classified into two Collision can be classified into two categoriescategories– Primary collisionPrimary collision: signals with the same : signals with the same
spread code being received at the same spread code being received at the same receiverreceiver
– Secondary collision: collision between two or Secondary collision: collision between two or more transmission that use different codemore transmission that use different code
The paper only focuses on primary The paper only focuses on primary collisioncollision
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Bandwidth waste in Bandwidth waste in static code allocation static code allocation casecase
Usable bandwidth = real bandwidth / spreading factor
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Spreading factorSpreading factor
Under the white Gaussian noise channelUnder the white Gaussian noise channel
Under the Rayleight fading channel Under the Rayleight fading channel
# of pairs# of pairs 11 22 33 44 55 66 77 88 99 1010
Spreading Spreading factorfactor
11 1212 2323 3434 4545 5757 6868 7979 8989 101011
# of pairs# of pairs 11 22 33 44 55 66 77 88 99 1010
Spreading Spreading factorfactor
11 795795 15815899
23823833
31731788
39739722
47647666
55655611
63563555
71471499
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Drawbacks of static Drawbacks of static code assignmentcode assignment
High peak rate for a terminal can be High peak rate for a terminal can be achieved in such contention-based achieved in such contention-based MAC protocolsMAC protocols
In static code assignment SS MAC In static code assignment SS MAC protocol, it is hard to predict which protocol, it is hard to predict which terminal need more bandwidthterminal need more bandwidth– Hard to dynamically assign codeHard to dynamically assign code
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Control message Control message formatformat
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Operation of DRCAOperation of DRCA
CR: code for RTS and Short Message (SM)CC: code for CTS and ACKCi: code for data transmission
Random backoff,
no carrier sensing
Code for RTS
Code for CTS
Broadcast the selective code,
for avoiding collision
Broadcast the selective code, for code reuse
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Throughput analysisThroughput analysis
NN terminals in the system terminals in the system Terminals are directly connected Terminals are directly connected
with each otherwith each other No mobilityNo mobility Slot time t is chosen to Slot time t is chosen to
accomplish RTS-CTSaccomplish RTS-CTS An idle terminal sends out an RTS An idle terminal sends out an RTS
with probability with probability pp
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Throughput analysisThroughput analysis
A terminal generates a packet with sA terminal generates a packet with spreading factor preading factor KKe e ,,KKminmin ≦ ≦ KKe e ≦ ≦ KKmaxmax
Channel transmission bit rate: Channel transmission bit rate: m m //KKee
Packet transmission time: Packet transmission time: LL**KKe e //mm Slots of a packet: Slots of a packet: L’L’= = L *KL *Ke e / (/ (mm**tt))
– Packet length is geometrically distributPacket length is geometrically distributed with probability ed with probability qq
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ParameterParameter
Transmission probability from state Transmission probability from state aa t to state o state b b ::PPabab
– a/b: a/b transmission pairs is busya/b: a/b transmission pairs is busy– a and b range from 0 to N/2a and b range from 0 to N/2
ii: number of pairs become idle from bus: number of pairs become idle from busy at the beginning of slot fy at the beginning of slot f
N’N’ = = NN - 2 - 2aa + 2 + 2ii– Number of terminals that are available to cNumber of terminals that are available to c
ommunicateommunicate
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Parameter Parameter
d: number of successful RTS-CST d: number of successful RTS-CST dialogs in a slotdialogs in a slot– 0 and 10 and 1
d + a – i = bd + a – i = b c: number of RTS transmission at c: number of RTS transmission at
the beginning of a slotthe beginning of a slot d’ = c – dd’ = c – d
– Number of failed RTS transmissionNumber of failed RTS transmission
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State transition in State transition in Markov chainMarkov chain
H: event of a transition from state a to H: event of a transition from state a to state bstate b
A: event of exactly one transmission A: event of exactly one transmission occurs and is addressed to an idle terminaloccurs and is addressed to an idle terminal
B: event of one transmission occurs and is B: event of one transmission occurs and is addressed to a busy terminaladdressed to a busy terminal
C: event of zero or more than one C: event of zero or more than one transmission occurtransmission occur
BBii: event that i pairs become idle from : event that i pairs become idle from busybusy
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State transition in State transition in Markov chainMarkov chain
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State transition in State transition in Markov chainMarkov chain Simplified formSimplified form
Steady state distribution SSteady state distribution Sa a is is given bygiven by
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Throughput of DRCA Throughput of DRCA and static allocationand static allocation
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Example value of Example value of SSrr
Sr: steady probability of r communication pairs
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Simulation parameters in Simulation parameters in multihop environmentmultihop environment
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Throughput: 24 pairsThroughput: 24 pairs
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Throughput: 9 pairsThroughput: 9 pairs
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Throughput differenceThroughput difference
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ConclusionConclusion
The paper proposes an SS MAC The paper proposes an SS MAC protocol with dynamic rate and protocol with dynamic rate and collision avoidance call DRCAcollision avoidance call DRCA
Both theoretical and simulation Both theoretical and simulation results show that DRCA outperforms results show that DRCA outperforms static code allocation mechanismsstatic code allocation mechanisms
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Thank you!!Thank you!!