Experimental study of the effects of Transmission Power Control and

Blacklisting in Wireless Sensor Networks

Dongjin Son, Bhaskar Krishnamachari and John Heidemann

Presented by Anandha Gopalan

Nov. 3, 2004

Outline

IntroductionExperiments Transmission Power Control (TPC) with

blacklistingConclusion and Future work

Introduction

Zikes !!! Yet another paper on power-management

This one has a slightly different take about it Thank goodness for that

So, what’s different ??? Simulations usually assume idealized link conditions

Experimentally evaluate the effect of transmission power on link conditions

Sometimes, increasing TP may help Aha !!! that’s a bit different

Experiments

Effects of unreliable wireless linksEffects of TPCExperimental study of varying TP on a

single wireless link One receiver and multiple transmitters One transmitter and multiple receivers Wireless link distance Node location (Multi-Path and Interference) Time (Environment change)

Experiments

Testbed PC104 testbed with mica2 motes Directed diffusion routing S-MAC MAC protocol

Weak link Packet Reception Rate (PRR) < Threshold

Asymmetric link PRR > Threshold in only one direction

Experiments

Effect of unreliable wireless links Having unreliable links is worse than having any

links at all They tend to be utilized

Convert unreliable links to good links or prevent them from being used

Experiments

Effects of TPC Increased TP leads to more good links

Unreliable links can be converted to good links New communication links can be discovered

and used for packet delivery Problem: May lead to new unreliable links

Taken care of by blacklisting Problem: May use up more network capacity

Experiments

New definitions: Weak link

Packet Reception Rate (PRR) < Threshold, even after TPC

Asymmetric link PRR > Threshold in only one direction, even after

TPC

Experiments

One receiver and multiple transmitters Difference is not obvious at close distances Difference b/w node 27 and nodes (30,20)

noticed after a distance of 17m Difference b/w nodes 30 and 20 noticed after a

distance of 23m

Experiments

One transmitter and multiple receivers In the TP range b/w -3 and 6 dBm, the link

quality is different at the same TP level, while different TP is required for each link to reach the same PRR level

Range of TP that generates this kind of variation is called unreliable transmission power range (UTPR)

UTPR can be avoided in two ways: Assign a TP high enough for every link to be outside

UTPR Assign a distinct TP for each link

Experiments

Effect of wireless link distance Clear line of sight b/w transmitter and receiver Distance b/w transmitter and receiver is varied Experiments show that new reliable,

communication links that are not available at default TP can be generated with TPC

Experiments

Effect of node location No clear line of sight b/w the sender and

receiver Receiver is placed in six different locations in

the same indoor environment Results:

Multi-path interference effect are severe indoors, where signal is weak

Severe link quality variation can be expected with small movement of sensor nodes

Experiments

Effect of surrounding environment change Variation in link quality is observed at different

times of the day and night Results:

Variation in link quality observed during the day due to change in surrounding environment

The difference in link quality is only b/w the TP of -7 to 2 dBm

TPC with blacklisting (PCBL) - Characteristics

TPC for link quality control Convert unreliable links to reliable links

Packet-based TPC TP is assigned to each packet based on its

destination and type of packet, considering link quality requirement

Metric-based link quality estimation Link quality is measured based on PRR

PCBL - Characteristics

Blacklisting at adjusted TP level Not all links can be converted to a good link

with TPC New weak or asymmetric links can be

generated at adjusted TP level Blacklisting is used with TPC to remove

remaining unreliable links after TPC

PCBL - Algorithm

1. Collect link statistics in PRR metric2. Select a unicast power for each link3. Blacklist unreliable links4. Select a broadcast power for each node

PCBL - Algorithm

1. Collect link statistics PRRs at pre-selected transmission power levels

are collected

2. Select a unicast power for each link Select a link quality control threshold (THLQ) Unicast power for each link is assigned such

as: Ui->j = P where PRRpi > THLQ and P = min pi, otherwise Ui->j is set to maximum TP (Pmax)

PCBL - Algorithm

3. Blacklist unreliable links Links that cannot be converted to good links

based on the blacklist threshold (THBL) are blacklisted and not used for any packet transmission or reception

4. Select a broadcast power for each node Broadcast transmission power of node i (Bi) is

selected to be max (Ui->j ) Ensures that broadcast packets reach every node

with a good wireless link

PCBL Algorithm – On-demand optimization for Long-lived Routing

1. Collect link statistics only at the maximum transmission power level

2. Blacklist unreliable links before using a routing protocol

3. Find a delivery path with a routing protocol

4. Identify unicast transmission powers to use only for links in the delivery path

PCBL – Analysis for Single Data Flows

Packet Delivery Rates PCBL is better than TPP-P0, TPP-P5 and TPP-

P10, but worse than M-BL

Energy Consumption PCBL consumes more than TPP-P0

Energy consumption per packet PCBL consumes less than TPP-P0

PCBL – Analysis for Multiple Data Flows

Packet Delivery Rates PCBL is better than M-BL for flows 1&2, but is

slightly worse for flow 3 Improvement in flows 1&2 due to the saturation

of the wireless link around node 11 for M-BL

Conclusion and Future work

Presented an experimental study of the effects of TPC on wireless link quality

A TPC scheme with blacklisting for link quality control was proposed

Analysis of the proposed scheme was carried out using experiments

Optimizations for the proposed algorithm is to be studied for future work

Issues with the paper

Overhead of collecting link statistics ???How are the statistics collected ???Comparing PCBL with TPP-P0, TPP-P5

and TPP-P10 for multiple flowsHow do you get the threshold values ???Mistakes in the paper

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