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Mobile Ad hoc Networks COE 549

Power ControlTarek Sheltami

KFUPMCCSECOE

http://faculty.kfupm.edu.sa/coe/tarek/coe549.htm

Outline

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Basic Mechanisms Distributed Algorithm Estimating the Minimum Transmit Power Topology Description of a Cluster-Based

Procotol Gateways Comparison Between Different Schemes

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Basic Mechanisms Considered for Indoor and Outdoor Applications:

1. Reflection and transmission: that occurs when the signal intrude on impediments larger than its wavelength.

2. Diffraction: a second source created by signal incidence on the verge of obstructions.

3. Scattering: signals scatters after hitting rough surfaces automobiles, etc., forming spherical waves, which reduces power levels.

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Power Control for Voice Traffic

Nodes interfere with each other. Each node has a target S/N

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A Toy Problem

Nodes 1,2 transmit with powers Pi (0,1] W Nodes hampered by thermal noise Target Signal to Interference and Noise Ratio is :

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The Power Feasibility Region

The point P = (P*1 , P*

2 ) is optimal, because it minimizes energy consumption.

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A Distributed Algorithm We need a distributed solution:

Each node uses only information it has locally: measured S/N and its own transmitter power.

Only distributed solutions scale with the number of nodes (very important in wireless ad hoc networks).

One solution: We slot time (and index slots by k). Transmitter powers constant for the duration of a slot k: Pi(k).

Motivation: Each node tries to achieve S/N target in next slot, pretending the other node will keep their powers constant.

Very intuitive, but there is no reason why it should converge as k∞

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Does it work?

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Topology Description of Cluster-Based Protocol

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Estimating the Minimum Transmit PowerAssumptions All nodes use the full transmit power in the hello message. In ad hoc networks, the

typical maximum transmit power is 1 Watt. All power calculation is based on the received signal strength (RSS) in the hello

message. The path loss gradient, α, equals 2. For BER=10-6, (Differential Quadrature-Phase-Shift Keying) DQPSK modulation: (Bit

Energy-to-Noise Density), Eb/N0 =11.1dB [7]. Check Eb/N0 Condition:

X=S/N*BW/RATE. If X< Eb/N0, then reject it, else accept packet.

Path Loss ( Lp ) = Lo +10 α log(dmax) where: dmax = maximum possible distance between transceivers,

d > (c/(a(1-21-α)))1/α for Cooperative transmission and d < (c/(a(1-21-α)))1/α for direct transmission

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Pt, min = Pr, perv + Lp + Fade Mragin (1) (2)

Find Pt, min, i for d, Pr, prev, i using (1) and (2) (3) Pt, min, i is the minimum required transmit power by node nj

to node ni Pr, prev, i is the pervious received power by node nj from node

ni Before an intermediate node nj, on the route forwards its

packets to the next node, it enters Pr, prev, i calculated in (3) Node ni uses Pr, prev, j entered by nj to calculate its Pt, min, j

Estimating the Minimum Transmit Power..

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Gateways

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Gateways Selection Schemes

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Highest Energy Level This method balances the energy consumption among the

gateways, it keeps them alive as much as possible. On the other side, the gateways with HEL might have large number of neighbors, which they will be affect by its transmission. The energy consumption in this case is in the order of O(n2),which will greatly affect the energy consumed on the network as a whole

Least Number Of Neighbors Schemes Chooses the gateway with the least number of neighbors Hybrid Method of Both Random Selection

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Comparison Between Different Schemes

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Comparison Between Different Schemes..

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Comparison Between Different Schemes..

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Comparison Between Different Schemes..

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Comparison Between Different Schemes..

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Comparison Between Different Schemes..

References

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1] G. J. Foschini and Z. Miljanic, “A simple distributed autonomous power control algorithm and itsconvergence,” IEEE Trans. Veh. Tech., vol. 42, no. 4, pp. 641–646, Apr. 1993.[2] J. Zander, “Distributed cochannel interference control in cellular radio systems,” IEEE Trans. Veh.Technol, vol. 41, no. 3, pp. 305–311, Aug. 1992.[3] N. Bambos, S. C. Chen, and G. J. Pottie, “Channel access algorithms with active link protection forwireless communication networks with power control,” IEEE/ACM Trans. Networking, vol. 46, no. 2,pp. 388–404, Mar. 2000.[4] N. Bambos, “Toward power-sensitive network architectures in wireless communications: Concepts, issues, and design aspects,” IEEE Personal Commun. Mag., vol. 5, no. 3, pp. 50–59, June 1998.[5] N. Bambos and S. Kandukuri, “Power-controlled multiple access schemes for next-generation wirelesspacket networks,” IEEE Wireless Commun., vol. 9, no. 3, pp. 58–63, June 2002.[6] S. Gitzenis, “Network control architectures and wireless communication and mobile computing: Power control and quality of service issues,” Ph.D. dissertation, Stanford University, July 2005.[7] F. Sasamori, H. Umeda, S. Handa, F. Maehara, F. Takahata and S. Ohshita, “Approximate Equation of Bit Error Ratein DQPSK/OFDM Systems over Fading Channels,” Proc. Of European Wireless 2002, Vol. 1, pp.602-607.[8] Tarek Sheltami, “Gateway Selection Review in Ad hoc Networks,” The Journal of Computers, VOL. 1, No.2, May 2006, pp. 8-14.[9] T. R. Sheltami, and H. T. Mouftah, “Performance Comparison of COMPOW and Minimum Energy Routing Protocols for Sensor Networks,” the 22nd  Biennial Symposium on Communications, June 1–3, 2004 Queen’s University, Kingston, ON, Canada, pp 232-235.