Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Spectral Properties of tg4a Signals] Date Submitted: [30-Sep-2005] Source: [Laurent Ouvry, Samuel Dubouloz, Mathieu Sambuq] Company [CEA-Leti] Address [17 rue des Martyrs 38054 Grenoble]

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Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

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Project ieee p802 15 working group for wireless personal area networks wpans

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: [Spectral Properties of tg4a Signals]

Date Submitted: [30-Sep-2005]

Source: [Laurent Ouvry, Samuel Dubouloz, Mathieu Sambuq]

Company [CEA-Leti]

Address [17 rue des Martyrs 38054 Grenoble]

Voice:[+33-4-38-38-93-88 ], FAX: [+ 33-4-38-38-51-59 ],

E−Mail: [[email protected]; [email protected]; [email protected]]

Re: [802.15.4a.]

Abstract:[Spectral Properties of tg4a Signals]

Purpose:[To promote discussion in 802.15.4a.]

Notice:This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

Release:The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Objective

Objective

  • Determine impact of :

    • Peak PRF

    • Burst length

    • Scrambling (polarity and time)

    • Symbol duration (& mean PRF)

      on signal average power (with FCC definitions)

  • Study of the signals peak power

    • Polarity and time Scrambling influence

    • Peak PRF (PRFmax)

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Introduction

Scrambling polarity code word

1 chip ~ (1/PRFmax) ns

+ - - + - + + -

N chips

Ts

Introduction

  • Average Power Measurements

    • Measure in a 1MHz RBW Bandwidth

    • Averaging time lower or equal to 1ms (video integration time)

    • Use of matlab functions given in doc #354r1-UWB-Power-Measurements

  • Peak Power Measurements

    • Measurement in a 3MHz RBW

    • 5MHz of Video Bandwidth (VBW)

    • Use of matlab functions given in doc #354r1-UWB-Power-Measurements

  • Signal Models

    • Burst composed by N pulses repeated at peak “PRFmax”

    • Symbol time is noted Ts

    • Mean PRF is therefore N/Ts

    • Scrambling is used

      • Pulse polarity codes

      • Burst position scrambling

        • PPM Modulation

        • Fine time scrambling on the whole symbol time

FCC Compliant

Measurements

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Average measurements

Average Measurements

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Worst case no polarity code no time scrambling

Worst Case : No polarity code, no time scrambling

  • Signal can be expressed as:

  • According to doc # 354r1:

Burst of N impulsions p(t)

Burst repeated every Ts

Pulse Spectrum composed by spectral lines

spaced by PRF and convolved by a sinc function of

N/PRF width

TF

Pulse PSD, which max is -41.3 dBm/MHz

RBW < 1/Ts

Spectral lines amplitudes, not depending on PRF

RBW ≥ 1/Ts

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Example no polarity code no time scrambling

Example (No polarity code, no time scrambling)

Measurement

Calculation

-32.7362

PRF = 247 MHz

Amplitude = -41.3 + 10*log10(RBW * N) – 60 = -32.26

Difference is due to sinc

Function sidelobes

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


No modulation no time scrambling

Burst Size (N)

No Modulation – No Time Scrambling

+ 3 dB

Y-scale is what is above –41.3dBm/MHz (in previous simple example, would be 8.6dB)

identical

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Modulation effects

Modulation Effects

  • PPM Modulation

It is worst with PPM modulation only

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Modulation effects 2

Modulation Effects (2)

  • PPM + Polarity

PPM + Polarity is better than PPM only

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Time scrambling effects

Time Scrambling Effects

Fine time scrambling on the whole symbol time

 No Difference between simple modulation (2-PPM, 4-PPM) and fine time scrambling

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Polarity codes effect

Polarity Codes Effect

Each pulse has a random polarity

Standard deviation is about 0.25dB

Polarity Codes are required for spectrum smoothing

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Conclusions

Conclusions

  • Peak PRF has no influence on the average transmitted power (w.r.t. FCC)

  • Time scrambling has a minor effect on spectrum smoothing and is not better than PPM Modulation in this respect

  • Random Polarity codes are required as soon as bursts of pulses are used

  • Burst size and symbol time do not influence the spectrum anymore with random polarity codes

  • A power backoff (margin) of about 1.5dB is required  compliant with doc # 605r1

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Peak measurements

Peak Measurements

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Peak power measurements

Peak Power Measurements

Ts = 1µs

  • Generation of short signals (~10µs) and statistics (1000 realizations) on the peak power measurement, with random polarity scrambling sequences (length 8) and with/without time scrambling

  • The CDF of the difference between the measurementand the FCC Limit is plotted (if abscissa < 0, the measurement was below the limit and if > 0, the measurement was above the limit)

  • Measurement performed in a 3MHz RBW, so FCC limit is 20log10(3/50) = -24.44 dBm

BelowFCC Limit

Above FCC Limit

No significant effect of the peak PRF

 No significant effect of the time scrambling (performed randomly on whole Ts)

 As for the average power, the biggest effect is given by the polarity scrambling (variation between -3 and +5 dB around the FCC peak Limit).

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Peak power effect of polarity scrambling

(decimal)

Peak Power: Effect of polarity scrambling

Generation of signal (~10µs) and peak power measurement, for all polarity scrambling sequences (with length 8  256 sequences, and symbol time = 1µs).

  • Some sequences enable a significant peak power reduction

  • Symmetry for

    • flip left  right

    • Complementary values -1  1

  • Example: code word 22 (0 -1 and left msb) is polarity scrambling sequence

    -1 -1 -1 1 -1 1 1 -1

Difference between the measurement and the FCC limit for all polarity sequences of length 8

Above FCC Limit

BelowFCC Limit

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Peak power best polarity scrambling sequences

Peak Power Best Polarity Scrambling Sequences

CDF for the previous curves

  • Best sequences depend on PRFmax

    • About 35% of polarity sequences provide a peak power lower than the FCC limit for a 494MHz PRFmax

    • About 50% for 247MHz

New statistics with the best sequences only

BelowFCC Limit

Above FCC Limit

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Peak power best polarity scrambling sequences1

Peak Power Best Polarity Scrambling Sequences

Statistics on Peak Measurement (1000 realizations) but with only the polarity scrambling code words involvinga peak measurement lower than the FCC limit

  • If there is no time scrambling, the peak measurement is always lower than the FCC limit (due to sequence choice)

  • If time scrambling, some occurrences are above the FCC limit

  • Difference between PRFmax 247MHz and 494 MHz is not significant

BelowFCC Limit

Above FCC Limit

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


Conclusions peak power

Conclusions (Peak Power)

  • Very slight differences between 494MHz and 247MHz peak PRF

  • The choice of the polarity scrambling sequences has an important effect on the radiated peak power(but hardly compatible with simple scrambler…)

  • This choice does not affect the average power measurement

L. Ouvry, S. Dubouloz, M. Sambuq — CEA-Leti


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