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

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Project IEEE P802.15 Working Group for Wireless
Personal Area Networks Submission Title Pulse
code proposal Date Submitted June
2005 Source Dan Raphaeli, Gidi Kaplan
Company SandLinks Ltd. Address Hanehoshet 6
Tel Aviv Israel Voice, E-Mail
danr_at_eng.tau.ac.il Re Abstract
Purpose Contribution to 802.15
TG4a 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.
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A Burst Sequence Proposal for Coherent Pulse
Compression

• Dani Raphaeli Gidi Kaplan
• Sandlinks
• June 3rd, 05

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Terminology

• Terminology - as agreed lately over the
  reflector
• Pulse a single UWB pulse (on the order of 1-2
  nsec)
• Burst a sequence of L UWB pulses (each pulse
  possibly modulated, the whole sequence has some
  code). Possibly, L may be between 11 to 33.
• Symbol - for data or ranging comprises of M
  bursts.
• Each pulse has energy of
• Ep Es/(LM)
• where Es is the symbol energy.

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Burst Code Selection Criteria

• Signal Spectrum Flatness.
• Autocorrelation Goodness.
• Length.
• Complexity of generation and correlation.
• Ability to provide SOP separation

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Optimization of Sequence

• The sequences which give almost ideal
  autocorrelation, and therefore a flat spectrum
  are called barker sequence.
• The largest known binary barker sequence is of
  length 11 in binary form 10110111000
• Larger sequences, even of length much larger,
  e.g. 32, cannot yield as good autocorrelation as
  the above.

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Consequences of not good autocorrelation

• As a first result of moderate autocorrelation,
  the spectrum will have peaks.
• Since FCC limits measure the peak in the spectrum
  - the effect is a decrease in the allowed power
  level (at the transmitter).
• Barker sequence have only 1dB peaks. Other
  sequences have larger peaks up to 5dB (see
  15-05-0240-02-004a)
• Note to assure this good spectrum, care must be
  taken to modulate the bursts with good sequence
  and random like data

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Spectrum of Barker-11
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Consequences of not good autocorrelation

• Another consequence of moderate autocorrelation
  - the autocorrelation sidelobes will be high
• The effect is a ghost multipath, leading to
  reduced performance or failures in ranging
• Barker sequence have only -20dB sidelobes.

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Using sequences with perfect periodic
autocorrelation

• There exist some sequences with good periodic
  autocorrelation PN codes, Ipatov sequences
• The problems is that in order to take advantage
  of this property, the sequence should be sent
  repetitively without a gap or without modulation,
  limiting their usefullness
• Although such periodic sequence can be used in
  the preamble, it will make an adverse effect on
  the spectrum resulting in peaks in the
  repetition frequency.

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Supporting multiple Piconets

• Can one practically achieve physical piconet
  seperation using a short code?
• Codes with no crosscorrelation cannot exist if
  codes are non synchronized
• Due to Near-far effect one cannot use CDMA type
  separation in 4a application unless the code is
  very large (e.g. l000 pulses) or alternatively,
  there is effective time hopping code with very
  large discrete resolution. Both approaches lead
  to complicated receiver
• Conclusion SOP should be differentiated
  logically if more than 3 needed. Not a big issue
  in 4a, where traffic is low.