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Mobile Ad hoc Networks COE 549 Power Control

Mobile Ad hoc Networks COE 549 Power Control. Tarek Sheltami KFUPM CCSE COE www.ccse.kfupm.edu.sa/~tarek. Outline. 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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Mobile Ad hoc Networks COE 549 Power Control

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  1. Mobile Ad hoc Networks COE 549Power Control Tarek Sheltami KFUPM CCSE COE www.ccse.kfupm.edu.sa/~tarek

  2. Outline • Why power control? • Basic power control • Power control Dual Channels • Power control with busy tone channel • Adaptive power control • Class correlative power control

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

  4. 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

  5. How to reduce energy consumption? Energy consumption in Ad Hoc network • Sensing • Receiving • Transmitting • Idling Similar energy consumption Depends on transmission power Little energy consumption • Reducing transmission power • Reducing retransmission count • Reducing number of nodes in sensing mode

  6. 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

  7. 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,…)

  8. 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]

  9. 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

  10. Power Control Dual channels (PCDC) [2] • 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

  11. 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

  12. 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}

  13. 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

  14. 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

  15. 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]

  16. 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)

  17. 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.

  18. A B d RCTS,B RRTS,A Correlative power control algorithm 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 • 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 Px,t : power of packet x at location t Rx,t : transmission range of packet x from transmitter t A B A RTS CTS DATA ACK

  19. A B d RCTS,B RRTS,A Correlative power control algorithm • Requirement (1) • RRTS,A ≥ d • RCTS,B ≥ d • Requirement (2) • PCTS,A≥Pnoise,A*SIRthreshold • And… A B RTS CTS DATA ACK

  20. 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) A B d RCTS,B RRTS,A Correlative power control algorithm

  21. 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

  22. 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 …

  23. 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

  24. 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)

  25. 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

  26. 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) AlaaMuquattash 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

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