©2012 Aclara Technologies LLC

David W. Rieken, Zhixi Li, and Chris Fleck

Advanced Systems Research & DevelopmentAclara Technologies, LLC

St. Louis, MO, USA

VLF-band Power Line Channel

Sounding

©2012 Aclara Technologies LLC

Summary

VLF band (1-9 KHz)– Not regulated by the FCC

– Legacy AMI systems (e.g. TWACS, Turtle)

– Good signal propagation properties?

– Signal frequency is higher than mains, but still low enough to permit long distance comms

– Presents unique challenges to PLC because of low data rate and significant mains interference

Overview– VLF-band channel sounding

– Experimental setup

– Survey results

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Channel sounding algorithm: signal model

3

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Channel sounding algorithm: transmitted signal

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Channel sounding algorithm: sounding procedure

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Channel sounding algorithm: periodic noise cancelation

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Experiment setup

7

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Experiment setup: transmission point

8

Laptop PC

DAQ

Filtered & unfilteredTx signals

Filtered Tx signal

Amplified Tx signal

LV line at premise

ZOH Tx signal

Anti-AliasingFilter

Power-lineCoupler

Tx Signal

PowerAmplifier

Anti-AliasingFilter

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Experiment setup: receive point

9

Laptop PC DAQ

Filtered Rx signal

Anti-AliasingFilter

Power-lineCoupler

Rx signal

LV line at subst ation

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Analysis: convolution with sounding signal

Spreading signal so that it is orthogonal to mains makes detection in low SNR channels easy.

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Survey results: Illinois site

11

0 1 2 3 4 5 6 7 8 9 10-80

-70

-60

-50

-40

-30

-20

f (kHz)

|H(f

)|2 (dB

)

1.3 mi1.8 mi3.3 mi5.4 mi7.2 mi9.7 mi

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Survey results: Missouri site

12

0 1 2 3 4 5 6 7 8 9 10-80

-70

-60

-50

-40

-30

-20

f (kHz)

|H(f

)|2 (dB

)

1.1 mi3.4 mi25.2 mi

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SNR Analysis

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SNR analysis: Illinois site (7.2 mi link)

14

0 2 4 6 8 10 6 7 8 9 10-120

-100

-80

-60

-40

-20

0

f (kHz)

dB

total SNR= 18.48 dB

TXNoise PSDChannel TransferRX

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SNR analysis: Illinois site (7.2 mi link)

Transmitter Power Max Data Rate

1 W 35.3 bps

5 W 176.5 bps

100 W 3.53 kbps

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SNR analysis: Missouri site (25.2 mi link)

16

0 2 4 6 8 10 6,000 7,000 8,000 9,000 10,000-160

-140

-120

-100

-80

-60

-40

-20

0

f (kHz)

dB

total SNR= 29.52 dB

TXNoise PSDChannel TransferRX

©2012 Aclara Technologies LLC17

SNR analysis: Missouri site (25.2 mi link)

Transmitter Power Max Data Rate

1 W 448.7 bps

5 W 2.24 kbps

100 W 44.87 kbps

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Survey results: SNR by band

-20 -10 0 10 20 30 400

1

2

3

4

5

6

7

8

9

10

dB

Num

ber

of S

ites

1.5 - 2.5 kHz2.5 - 5 kHz5 - 10 kHz

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Conclusions

19

Any VLF-band PLC system must– Accommodate a wide range of link strengths

– Leverage higher concentrator data rates than endpoint data rates

– Maximize system throughput, rather than instantaneous data rate

Analysis shortcomings– Sampling rate offset

– Time-varying channel IPR