power control and cross-layer design in ad-hoc and sensor networks

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Power Control and Cross-Layer Design in Ad-Hoc and Sensor Networks

Di Wang 11/07/2005

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Outline

Overview Design Principles for Power Control Power Control Protocols Unintended Consequences Control-Theory Based Approach Conclusion Reference

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Overview

Why is Power Control Important? Limited resources of energy Aiming to bring better performances: Throughput,

Delay,…

Why is Power Control a Cross-Layer Design Problem?

Affect the physical layer: quality of the signal Affect the network layer: range of transmission Affect the transport later: magnitude of the

interference

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Overview

Multi-dimensional Effect Mac Layer Performance: contention for the medium Topology Control Problem: Connectivity of the

network Effect on several important metrics:

Energy Consumption Throughput Capacity End-to-End Delay

Impact on protocols in existence Create unidirectional links Affect MAC/routing protocols:

Distributed Bellman Ford, RTS/CTS handshake in IEEE 802.11

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Design Principles For Power Control

To increase network capacity it is optimal to reduce the transmit power level

For transmit range r: The area of interference is proportional to r2

The relaying burden is proportional to 1/r, Then

The area consumed by a packet is proportional to r

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Reducing the transmit power level reduces the average contention at the MAC layer

For any given point in the domain: An average of cr2

transmitters within range; Traffic flowing through each node is proportional to 1/r,

then

The net radio traffic in contention range is proportional to r

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The impact of power control on total energy consumption depends on the energy consumption pattern of the hardwareTerms: PRxelec: the power consumed in the receiver

electronics for processing PTxelec: the power consumed in the transmitter

electronics for processing PTxRad(p): Power consumed by the power amplifier to

transmit a packet at the power level p PIdle , PSleep

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The impact of power control on total energy consumption

If the energy consumed for transmission, PTxRad(p), Dominates:

Using low power level is broadly commensurate with energy efficient routing for commonly used inverse αth

law path loss models, with α≥2

Energy efficient routing seeks to minimize : Can get the graph consisting of edges lying along some

power optimal route between any pair of nodes

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Connections only with nearby nodes, and no intercections

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For α=2, can find an angle j < 90:

2ji2

jl2

li xxxxxx

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When PSleep is much less than PIdle: turning the radio off whenever possible becomes an

important energy saving strategy

Estimates show that usually PIdle > 20PSleep

Power management protocols seeking to put nodes to sleep while maintaining the network connectivity

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When a common power level is used throughout the network:

There exists a critical transmission range rcrit, below which transmissions are sub-optimal with regards to energy consumption

Given two nodes with distance d, the energy consumed for transmitting one packet:

Which can be minimized at:

crPPr

dTxelecRxelec

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The impact of power control on end-to-end delay

Power level and Traffic load jointly determine the end-to-end delay

Under high load a lower power gives lower delay Under low load a higher power gives lower delay

A packet experiences: Propagation delay: neglectable Processing delay: time taken in receiving, decoding

and retransmitting, inversely proportional to range r; Queuing delay: can be shown it increases super-

linearly with the power level p

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The impact of power control on end-to-end delay

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Power control can be regarded as a network layer problem

In fact it impacts multiple layers Numerous approaches attempt to solve it at MAC

Layer Adjust the transmit power level to make the SINR just

enough for receiver to decode the packet Only a local optimization

Network layer power control is capable of a global optimization

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Power Control Protocols

COMPOW Protocol Design Strategies

Choose a common power level; Set this power level to the lowest value which keeps

the network connected; Keeps the energy consumption close to minimum, while

restricting the lowest admissible power level to rcrit.

Implementation Running multiple proactive routing protocols at each

power level, and find out the routing table with lowest p.

Appealing feature: Provides bidirectional links

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CLUSTERPOW Protocol COMPOW is not energy-efficient when there are

outlying node Design Strategies:

Select n different power levels to form a n-level hierarchical structure

Implementation Building routing table for each power level Transmitting packet at the smallest power level p such

that the destination can be found on the p-routing table.

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CLUSTERPOW Protocol

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CLUSTERPOW Protocol

CLUSTERPOW is loop free Still can be further improved

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Recursive Lookup Schemes

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Recursive Lookup Schemes

may not be loop-free

Solution: Tunnelled CLUSTERPOW

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Tunnelled CLUSTERPOW Protocol When doing recursive lookup for an intermediate

node, encapsulates the packet with the address of the node.

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MINPOW Protocol Design Objective: Provide a globally optimal solution with

respect to total power consumption Implementation:

Proactively sends “hello” at multiple transmit power levels Only the “hello” packets at the Pmax contain routing updates For each link, computes the power consumption per packet

PTxtotal = PTxelec + PTxrad(p) at all power level and take the minimum as the link cost in the distance vector algorithm

Feature: a globally optimal solution for power consumption, but may not be the optimal solution for network capacity

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Simulation Results

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Simulation Results

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Simulation Results

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Unintended Consequences

Power Control can be addressed as

Multi-dimensional OptimizationUsually one objective is achieved at the expense of one

another

Cross-Layer OptimizationShould not ignore the interactions between different

layers

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Unintended Consequences

Example: the MINPOW Power Control ProtocolCompared with MHRP/802.11 solution (Min-Hop

Routing) MHRP/802.11:

A->B and E->D can happenconcurrently

MINPOW: A has to resort to C to sendpackets to B Then E->D cannot happen

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Control-Theory Based Approach

Channel Model

It is simple to use the inverse αth

law path loss model

It will be rather complicated when taking into account the time-variance of the channel gain

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Feedback-based Power Control

Can Derive the closed loop system:

Time delay can be compensated for using the Smith predictor

Predict the power gain to improve the reactions so as to decrease the disturbulance

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Ts=0.015(solid) Ts=0.05(dashed)

With Smith Predictor (dark) Without Predictor (light)

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Conclusion

Power Control can be addressed as a cross-layer design problem, which involves a multi-dimensional optimization;

Introduced the impact of power control on a variety of parameters and phenomenon, and then presented fundamental design principles;

Introduced power control protocols achieving successful power saving, but sometimes at the expense of a reduction in the sense of other metrics;

Put power control algorithms into a control theory context

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Reference

Kawadia, V.; Kumar, P.R.; Principles and protocols for power control in wireless ad hoc networks, Selected Areas in Communications, IEEE Journal on Volume 23, Issue 1, Jan. 2005 Page(s):76 – 88

Krunz, M.; Muqattash, A.; Sung-Ju Lee; Transmission power control in wireless ad hoc networks: challenges, solutions and open issuesNetwork, IEEE Volume 18, Issue 5, Sept.-Oct. 2004 Page(s):8 - 14

Fredrik Gunnarsson, Fredrik Gustafsson, Power control in Wireless Communications Networks – From a Control Theory Perspective

Cautionary Aspects of Cross Layer Design: Context, Architecture and Interactions, http://www.eas.asu.edu/~junshan/ICC/KumarICC.pdf

power control and cross-layer design in ad-hoc and sensor networks

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