Spectrum Shaping for UltraWideband Signals

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Spectrum Shaping for Ultra-Wideband Signals

• Ou Yang
• 4/24/2007

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Outline

• Introduction to UWB
• Motivation
• Methodology
• Summary

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Introduction to UWB
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Definition

• Time domain - extremely short pulses - very low
  duty cycle
• Frequency domain - ultra wide spectrum - low
  power spectral density - acceptable interference
  with other users
• FCC definition - - total bandwidth gt 500MHz

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Time-Hopping UWB (TH-UWB)

• TH-UWB- Ns frames per symbol- Nc time hopping
  chips per frame- 1 pulse/frame/user
• TH sequence determines pulse location

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Direct Spread UWB (DS-UWB)

• DS-UWB- Nc direct spread chips per symbol- 1
  pulse/chip
• DS sequence determines pulse polarity

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Motivation
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FCC Regulations
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Interference Mitigation

• Avoid existing narrowband interference- notch
  the signal spectrum

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Methodology
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Methodology

• Spectrum Analysis
• Fit FCC Regulation
• Interference Mitigation

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Spectrum Analysis

• PSD of UWB signals
• Continuous PSD determined by pulse
• Spectral lines may violate FCC mask

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Fit FCC Regulation

• Pulse design
• Modulation
• Randomization

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Pulse Design

• Derivative of Gaussian pulses 3
• Higher order, narrower band, fit FCC mask

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Modulation

• Modulation Schemes- PPM - BPSK- BOK -
  PAM

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Modulation

• Target- coefficient of discrete PSD component0
• Coefficient depends on- signal amplitude- pulse
  position
• Conclusion- using BOK (BPSK2-PPM) in TH-UWB

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Randomization

• Polarity randomization in TH-UWB- known at tx
  and rx- symbol-based or pulse-based- eliminate
  spectral lines

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Randomization

• Scrambling in DS-UWB- DS-UWB has severe spectral
  lines- scrambling code has whitening effect

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Interference Mitigation

• Pulse Design- Doublet- Notch Spectrum

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Doublet

• Doublet- a pair of Gaussian shaped pulses-
  separation between pulses- separation between
  doublet
• Pulse spectrum- spectrum nulls exist- nulls
  controlled by the pulse separation

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Doublet
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Notch Spectrum

• Solution- eigenfunction decomposition of the
  desired frequency mask H(f)- higher eigenvalue,
  better fits the mask

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Summary
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Thank YouQ A
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References

• 1 Lic.Tech. Matti Hämäläinen, Introduction to
  existing ultra wideband (UWB) technologies,
  UWB_070406.ppt.
• 2 Fred Bhesania, Brad Hosler, UWB A
  High-Speed Wireless PAN Technology,
  TWMO05003_WinHEC05.ppt.
• 3 Hongsan Sheng, Philip Orlik, Alexander M.
  Haimovich, Leonard J. Cimini, Jr. Jinyun Zhang,
  On the Spectral and Power Requirements for
  Ultra-Wideband Transmission, ICC 2003, vol1,
  738-742.
• 4 Dr. Jeffrey Reed, Dr. R. Michael Buehrer, Dr.
  Dong S. Ha, Introduction to UWB Impulse Radio
  for Radar and Wireless Communications, ISCAS
  2004, vol 4, 129-132.
• 5 Yves-Paul Nakache, Andreas F. Molisch,
  Spectral Shape of UWB Signals Influence of
  Modulation Format, Multiple Access Scheme and
  Pulse Shape, VTC 2003 Spring, vol 4, 2510-2514.
• 6 Zhenzhen Ye, Madhukumar A. S, Francois Chin,
  Power Spectral Density and In-Band Interference
  Power of UWB Signals at Narrowband Systems, ICC
  2004, vol 6, 3561-3565.
• 7 Kenneth P. Wallace, Ashley Brent Parr, Byung
  Lok Cho, Zhi Ding, Performance Analysis of a
  Spectrally Compliant Ultra-Wideband Pulse
  Design, IEEE Transactions on Wireless
  Communications, vol 4, no. 5, Sep. 2005,
  2172-2181.