SenProbe: Path Capacity Estimation in Wireless Sensor Networks

Tony Sun, Ling-Jyh Chen, Guang Yang Tony Sun, Ling-Jyh Chen, Guang Yang M. Y. Sanadidi, Mario GerlaM. Y. Sanadidi, Mario Gerla

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OutlineOutline

Motivation Background

Design Consideration What do we want to measure? Effective Capacity Previous Method

Proposed Approach: SenProbe Simulation Results Conclusion

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MotivationMotivation

Mobile computing platforms may interact with ambient sensor environment establishing “Opportunistic wireless networks”

Evaluation and measurement of wireless path capacity in sensor network is of realistic interest (i.e. Capacity planning, protocol design, performance

analysis, system deployment, assess applicability of deployment)

Need a tool that can monitor and measure opportunistic path capacity in wireless sensor networks

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OutlineOutline

Motivation BackgroundBackground

Design ConsiderationDesign Consideration What does SenProbe actually measure?What does SenProbe actually measure? Effective CapacityEffective Capacity Previous MethodPrevious Method

Proposed Approach: SenProbe Simulation Results Conclusion

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Design ConsiderationDesign Consideration

CSMA-CA and variant schemes still popularly used in sensor network for its simplicity (IEEE 802.15.4 beaconless mode, Berkeley motes,

etc)

Basic CSMA-CA doesn’t incorporate RTS/CTS mechanisms Send packet when an idle channel is detected Smaller packet overhead if idle channel can be

detected quickly Suffers from hidden terminal problem

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What do we want to What do we want to measure? (1)measure? (1) The effective end-to-end rate is defined as

the maximum achievable data rate in the absence of any cross traffic connection.

It is smaller than the raw data rate at the physical layer due to Packet Overhead Interference between multiple packets in the

pipeline

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What do we want to What do we want to measure? (2)measure? (2) In fact, path capacity in wireless net also

varies with: MAC protocol and link scheduling Link interference S/N ratio; Tx power Encoding/modulation scheme Number of antennas (eg MIMO) Antenna directionality etc

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Neighborhood ExampleNeighborhood Example

If Dr=Di=250m , nodes {3,4,5} are within the same n-hood, C’=C/3 If Dr=250m, Di=500m, nodes {2,3,4,5,6} are in n-hood, C’=C/4

Dr= effective receive range from node 4 (solid-line circle)

Di = interference range caused by node 4 (dotted-line circle)

Distance between nodes: 200m

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Effective Capacity of CSMA-Effective Capacity of CSMA-CA Enabled Wireless ChannelCA Enabled Wireless Channel

The effective capacity of a one-hop link can be calculated as

For the CSMA environment in our study (if ACKs are used)

POverheadACKPacket

Packet CTTT

TC

P

PacketPacket C

ST

P

ACKACK C

ST

MbpsMbpsmsmsms

msC 89.12

188.0156.06

6

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Previous Work (Morris et Previous Work (Morris et al)al) Dr=250m, Di=500m Use UDP flows to probe the maximum achievable throughput

(brute force method)

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OutlineOutline

Motivation Background

Design Consideration What does SenProbe actually measure? Effective Capacity Previous Method

Proposed Approach: SenProbeProposed Approach: SenProbe Simulation Results Conclusion

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CapProbe Concept CapProbe Concept

Key insight: a packet pair that gets through with zero queueing delay yields the exact estimate

CapacityCapacity

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Issues: Compression and Issues: Compression and ExpansionExpansion

• Queueing delay on the first packet => compression

• Queueing delay on the second packet => expansion

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SenProbeSenProbe

Path capacity estimation tool specially designed for the multi-hop CSMA based wireless networks. One-way estimation technique, based on CapProbe concepts Aimed to simplify the path capacity estimation process

A back-to-back packet train technique designed to overcome the hidden terminal effects in CSMA environment

SenProbe measures end-to-end effective capacity in wireless ad hoc networks.

SenProbe is simple, fast and less intrusive to comparative techniques.

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SenProbe Algorithm(1)SenProbe Algorithm(1)

Instead of using back-to-back packet pairs, SenProbe relies on back-to-back packet train to overcome the effect of hidden terminal in CSMA-CA

The length of this back-to-back packet train depends on the interference range and the transmission range of the

specific radio technology under question

2

nRangeTranmissio

ceRangeInterferenNTRAIN

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SenProbe Algorithm(2)SenProbe Algorithm(2)

The receiver measures the OWD of every packet in kth packet train received as the difference between time received and time sent

the minimum OWDSUM is kept for the kth packet train. The “good” dispersion sample r (i.e. samples encountering no cross traffic) is the sample with the minimum OWD sum

Dispersion of the good sample calculated, and used to estimation capacity

TRAINsendrcv NiikTikTikOWD 1],,[],[],[

],[],[min][1

jkOWDikOWDkOWDSUMTRAINNji

][minarg kOWDSUMrk

],[],[ urOWDvrOWDT

T

PC

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SenProbe-VisualizationSenProbe-Visualization

1

1

1

1

4 23

4 3

4

2

3

4

1)

2)

3)

4)

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OutlineOutline

Motivation Background

Design Consideration What does SenProbe actually measure? Effective Capacity Previous Method

Proposed Approach: SenProbe Simulation ResultsSimulation Results Conclusion

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Simulation Results (1)Simulation Results (1)

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Number of hops

En

d-t

o-E

nd

Ca

pa

city

(M

bp

s)Packet-pair techniqueFTP

Path Capacity measured via FTP connection and Packet-Pair technique (one way CapProbe)

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Simulation Results (2)Simulation Results (2)

Path capacity of adhoc multi-hop forwarding chain in CSMA-CA wireless environment

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Number of hops

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(M

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Simulation Results (3)Simulation Results (3)

End-to-end capacity estimation of multi-hop connections within the same collision domain

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Number of hops

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Simulation Results (4)Simulation Results (4)

Capacity estimates along a multi-hop forwarding chain for CSMA-CA with ACK enabled wireless sensor network

0

0.5

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1 2 3 4 5 6 7 8Number of hops

End

-to-

End

Cap

acity

(M

bps)

Theoretical

SensorProbe

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ConclusionConclusion

SenProbe uses back-to-back packet trains, and relies on packet dispersion between the packet trains to measure the path capacities in a one-way fashion.

SenProbe estimates e2e path capacity in CSMA enabled wireless sensor networks.

SenProbe is a simple and non-intrusive technique that can accurately reflects the effective path capacity

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ThanksThanks!!