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Mobile Ad hoc Networks COE 549

Power ControlTarek Sheltami

KFUPMCCSECOE

www.ccse.kfupm.edu.sa/~tarek

Outline

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Why power control? Basic power control Power control Dual Channels Power control with busy tone

channel Adaptive power control Class correlative power control

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Targets of power control Improve network throughput* Reduce overall energy consumption* Improve fairness Reduce packet latency Partial Combination of above targets

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Why power control helps to improve throughput?

Reduce data retransmission probability With a good assignment of transmission power,

each transmitter guarantees its transmission in a low number of attempts and reduces its interference on other nodes.

Increase spatial reuse ratio Transmission range is proportional to

transmission power Number of simultaneous transmission is

inversely proportional to average transmission range

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Energy consumption in Ad Hoc network

SensingReceiving

Transmitting

Idling

Similar energy consumption

Little energy consumption

How to reduce energy consumption?

• Reducing transmission power

• Reducing retransmission count

• Reducing number of nodes in sensing mode

Depends on transmission power

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Necessary and sufficient condition to receive packet successfully

Pr ≥ Rxthreshold

Pr: received power level Rxthreshold : minimal necessary power level

Pr ≥ SIRthreshold * Pnoise

Pnoise: noise power level at receiver side SIRthreshold : signal to interference ratio (SIR)

threshold

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Classification of power control Algorithms Deterministic power control algorithms

Transmission power is determined by a some equation base on several parameters (such as busy tone signal strength, received packet power level, node degree, …)

Adaptive power control algorithms Each node adaptively changes its

transmission power based on the network performance (packets loss rate, average access time,…)

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Some deterministic power control algorithms

BASIC power control algorithm [1] Power control algorithm with multiple

channels [2] Power control algorithm with busy

tone channel [3] [4]

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BASIC Power Control algorithm [1]

RTS/CTS are sent at max power DATA/ ACK are sent at minimal required power

Pt=Fpath* Rxthreshold* c

Pt : minimal required transmission power Pmax: maximal power level Fpath:path loss factor (Fpath=Pt/Pr) Rxthreshold : minimal necessary power level to

decode packets c: constant

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Multiple channels: RTS/CTS channel DATA channel ACK channel

RTS, CTS, ACK are transmitted at Pmax

DATA from node s to node t are transmitted at

C(t) *SIRthreshold*Pnoise(t)*Fpath(s,t)

Fpath(s,t): path loss factor between s and t C(t): a safety factor determined by node t Pnoise(t) : noise power level at node t

Power Control Dual channels (PCDC) [2]

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Power control with busy tone channel [3] [4]

Busy tone channel Narrow band Only signal strength rather than content is

known Does not collide with data channel

Each node broadcasts its data-channel noise level information by busy tone Busy tone signal strength inversely

proportional to data-channel noise power, or Busy tone transmitted at maximum power

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Power control with busy tone channel [3] [4]..

Transmission power requirement for RTS: set to avoid collision at other

receivers. Inferred from received busy tones.

CTS: In [3] maximal power In [4] computed by

max{Fpath*RXthreshold,SIRthreshold*Pnoise*Fpath}

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Power control with busy tone channel [3] [4]

DATA: both [3] and [4] use

max{Fpath*RXthreshold, SIRthreshold*Pnoise*Fpath}

ACK: maximal power

Pnoise is known from the busy tone signal

Fpath is calculated by Fpath= Psend/received

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Possible drawback for deterministic power control algorithms

May need extra hardware support (busy tone, multiple channels)

The noise power level estimation may not be accurate enough noise power level when receiver receives RTS

and when receives DATA may be different (RTS and CTS affects the noise on the receiver side)

noise power level changes with time The safety factor c(t) is heuristic and may not

work for certain scenarios

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Adaptive power control algorithm

Adaptively changes transmission power on a packet by packet basis

Increase/decrease transmission power when Too many packets lost /Very few packets lost [5]

Average access time is very large/ small [6]

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Possible drawback for adaptive power control algorithms

Increase/decrease transmission power too frequently /too rarely

How to determine the initial transmission power? Falsely increases transmission power when it is not

necessary When a RTS times out,

the receiver channel is busy (receiving data, or NAV set) there is no need to increase power

the transmission power of RTS is not large enough Ignore the relationship between the transmission power of

sequential packets. (RTS<->CTS<->DATA<->ACK)

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Correlative power control (CPC) algorithms

Intuition Noise level depends on how many

transmitters generate interference The number of transmitters around the

receiver depends on the transmission range of the last control packet sent by the receiver

There exists a relationship between the necessary transmission power for RTS, CTS, DATA, ACK.

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Correlative power control algorithm

Basic definition PRTS,B = PRTS,A/d4

PCTS,A = PCTS,B/d4

R4RTS,A = PRTS,A/Rxthreshold

R4CTS,B = PCTS,B/Rxthreshold

R4avg = Pavg / Rxthreshold

gain(A,B) = PRTS,B/PRTS,A gain(B,A) = PCTS,A/PCTS,B

Given the Tx power of RTS from A to B, what is the appropriate Tx power for a CTS from B to A to be received correctly

Px,t : power of packet x at location t

Rx,t : transmission range of packet x from transmitter t

RTS

CTS

DATA

ACK

RCTS,B

A B

RRTS,A

d

A BA

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Correlative power control algorithm

Requirement (1) RRTS,A ≥ d RCTS,B ≥ d

• Requirement (2)

• PCTS,A≥Pnoise,A*SIRthreshold

• And…

RTS

CTS

DATA

ACK

RCTS,B

A B

RRTS,A

d

A B

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Requirement to receive CTS successfully PRTS,A ≥ Rxthreshold / gain(A,B) PCTS,B ≥ Rxthreshold / gain(B,A) PCTS,B *(PRTS,A/Pavg)1/2 ≥ Rxthreshold*SIRthresohld*π/gain(A,B)

RCTS,B

A B

RRTS,A

d

Correlative power control algorithm

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Requirement for successful RTS-CTS-DATA-ACK handshaking

We can derive similar correlative requirement between

PCTS,B and PDATA,A

PDATA,A and PACK,B

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Requirement for successful RTS-CTS-DATA-ACK handshaking

We finally obtain Four Path loss constraints (1)-(4)

PRTS,A ≥ Rxthreshold / gain(A,B) PCTS,B ≥ Rxthreshold / gain(B,A) PDATA,A ≥ Rxthreshold / gain(A,B) PACK,B ≥ Rxthreshold / gain(B,A)

and …

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Requirement for successful RTS-CTS-DATA-ACK handshaking

Three correlative constraints (5)-(7)

- PCTS,B *(PRTS,A/Pavg)1/2 ≥ Rxthreshold*SIRthresohld*π/gain(A,B)

- PDATA,A *(PCTS,B/Pavg)1/2 ≥ Rxthreshold*SIRthresohld*π/gain(B,A)

- PACK,B *(PDATA,A/Pavg)1/2 ≥ Rxthreshold*SIRthresohld*π/gain(A,B)

If Pavg and PRTS are known PCTS, PDATA and PACK can be calculated

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Deterministic correlative power control (CPC) algorithm

Let U = Py,s* Px,r

(1/2)

Pavg equal to Pmax

(x,y) in {(RTS,CTS),(CTS,DATA),(DATA,ACK)} s is the sender of packet x r is the sender of packet y

Assign the transmission power of RTS to be Pmax

Calculate U from the correlative constraints (5)-(7); assign appropriate transmission power for RTS, CTS, DATA, ACK

Ensure that power assignment fulfills path loss constraints (1)-(4)

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Asymmetric Adaptive CPC algorithm(Implementation ongoing)

Let U = Py,s* Px,r

(1/2)

V=Pavg (may be initialized to Pmax) (x,y) in {(RTS,CTS),(CTS,DATA),(DATA,ACK)} s is the sender of packet x r is the sender of packet y

Assign the transmission power of RTS to be Pmax

Calculate U from the correlative constraints (5)-(7); assign appropriate transmission power for RTS, CTS, DATA, ACK

Ensure that power assignment fulfills path loss constraints (1)-(4) Change V adaptively

Increase/decrease V when packet loss too frequent/too rare

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Reference

[1] A Power Control MAC Protocol for Ad Hoc Networks (MobiCom2002) Eun-Sun Jung, Nitin H. Vaidya

[2] Power Controlled Dual Channel (PCDC) Medium Access Protocol for Wireless Ad Hoc Networks (INFOCOM 2003) Alaa Muquattash and Marwan Krunz

[3] A Power Controlled Multiple Access Protocol for Wireless Packet Networks (INFOCOM 2001) Jeffrey P. Monks, Vaduvur Bharghavan and Wen-mei W. Hwu

[4] Intelligent Medium Access for Mobile Ad Hoc Networks with Busy Tones and Power Control (IEEE Journal on Selected Area in Communications 2000) Shu-Lin Wu, Yu-Chee Tseng, and Jang-Ping Sheu

[5] Distributed Power Control in Ad-hoc Wireless Networks (PIMRC 2001)Sharad Agarwal Srikanth et. Al.

[6] Load Sensitive Transmission Power Control in Wireless Ad-hoc Networks (GLOBECOM 2002) Seung-Jong Park and Raghupathy Sivakumar