IEEE 802'15 PHY Proposal

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
How Energy Detector handles Inter-Pulse
Interference? Date Submitted 12 May
2005 Source Francois Chin, Lei Zhongding,
Yuen-Sam Kwok, Xiaoming Peng Company Institute
for Infocomm Research, Singapore Address 21
Heng Mui Keng Terrace, Singapore 119613 Voice
65-68745687 FAX [phone] E-Mail
chinfrancois_at_i2r.a-star.edu.sg Re
Abstract Presents signaling options to
achieve precision ranging with both coherent and
non-coherent receivers Purpose To discuss
which signal waveform would be the most feasible
in terms of performance and implementation
trade-offs 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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Objectives

• CMOS technology imposes max PR interval limit
• Inter-pulse interference expected
• Important for energy detector to handle
  inter-pulse interference in order to function in
  various multipath channels

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Ternary Signaling - Synchronisation with Energy
Detector
Pulse Repetition Interval 30ns
1
2
3
31
4
5
6
7
8
30

Non-inverted pulses are blue, Inverted pulses are
green.
Synchronisation / Ranging preamble Binary Base
Sequence repeated For K times


.................
Symbol Interval 940ns
Symbol Interval 940ns
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How Energy Detector despread?
Ternary Seq - - 0 0 0 - 0 0 0 - 0 0
0 0 0 0 - 0 - 0 0 - -
After Square Law Integration in PRI
Unipolar M-Seq 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0
Bipolar M-Seq - - - - - - -
- - - - - - - -
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Synchronisation with Energy Detector in AWGN
Before Depreader Unipolar M-Seq 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0
repeated 4x Despread Sequence Bipolar M-Seq
- - - - - - - - - - - - -
- -
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How Energy Detector handle inter- pulse
interference?
Pulse Repetition Interval 30ns
d5
d1
d2
d3
d4
d6
d7
Ternary signaling Non-inverted pulses are
blue, Inverted pulses are red.
PRI
T8
T5
T6
T7
T1
T2
T3
T4
Lets zoom into the channel details



PRI
T1
T2
T3
T4
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Energy Integration in PRI
_at_ TX Ternary codes
Multipath Channel
d5
d1
d2
d3
d4
d6
d7



Pulse Repetition Interval 30ns
PRI
T1
T2
T3
T4
_at_ RX (assume noiseless case)
Received signal matrix (PRI/column)
Take the 3rd PRI as example
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Energy Integration in PRI
(some noise due to cross terms)
After square-law device at 3rd PRI
Apply integration over PRI Column Sum
The soft ADC value for 3rd PRI

• Each PRI contains partial energy from previous
  pulses

More noise due to cross terms

• Multipath energy spread each PRI

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Energy Detector Sees An Equivalent Unipolar
Sequence after integration in PRI
Pulse Repetition Interval 30ns
d5
d1
d2
d3
d4
d6
d7
Ternary signaling Non-inverted pulses are
blue, Inverted pulses are red.
After Square Law Integration in PRI
cjdj2
Sequence become Unipolar
e1
e2
e3
c5
c1
c2
c3
c4
c6
c7
More Noise due to cross terms

PRI
T1
T2
T3
T4
integrator Output is a convolution of the
equivalent Unipolar Sequence with a PRI-spaced
tap-delay-line channel, each tap comprising
multipath energy within a correponding PRI
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In Multipath Channels
Ternary Seq - - 0 0 0 - 0 0 0 0 0
0 0 0 0 - 0 - 0 0 - -
Unipolar M-Seq 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
Despread Sequence Bipolar M-Seq - - -
- - - - - - - - - - - -
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Sliding Correlator Output _at_ PRI .
Synchronisation in Multipath Channels
Equivalent to
Simple RAKE combining at the despreader output
(in fact, simple summation across despreader
output) can be used to collect energy across PRI
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Summary

• Square Law / Envelope Detector effectively
  convert a ternary sequence to a Unipolar Sequence
• Energy integration in PRI converts the multipath
  channels into a PRI-spaced tap-delay-line channel
  , each tap comprising multipath energy within a
  correponding PRI
• Energy collector / integrator Output is a
  convolution of the equivalent Unipolar Sequence
  with the PRI-spaced tap-delay-line channel
• Simple RAKE combining at the despreader output
  (in fact, simple summation across despreader
  output, no need RAKE coefficients) can be used to
  collect energy across PRI
• Energy Detector can handle inter-pulse
  interference just as normal direct sequence
  spread spectrum systems

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Appendix
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Ternary Bipolar Unipolar Conversion
Ternary
? 0 ? -
Bipolar
This is in fact m-Sequences!
? - ? 0
Unipolar
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Properties of M-Sequence
Transmit Unipolar M-Seq 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
repeated 4x Receive Bipolar M-Seq - - -
- - - - - - - - - - - -

ZERO autocorrelation
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Properties of M-Sequence
Transmit Bipolar M-Seq - - - -
- - - - - - - - - - - repeated
4x Receive Unipolar M-Seq 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0
ZERO autocorrelation
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Properties of M-Sequence
Transmit Bipolar M-Seq - - - -
- - - - - - - - - - - repeated
4x Receive Bipolar M-Seq - - - -
- - - - - - - - - - -
HIGH peak LOW autocorrelation
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How to make use of these properties?
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Synchronisation Preamble

• M-sequences has excellent autocorrelation
  properties
• Synchronisation / Ranging Preamble is constructed
  by repeating the base sequence
• Common Signaling (Mode 1)
• Ternary for e.g. Beacon Packet
• Receiver-specific signaling (Mode 2)
• Ternary for Energy Detector
• Bipolar for Coherent and Differential Chip
  Detectors
• Long preamble for distant nodes is constructed by
  further symbol repetition

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Ranging Code Sequences for different Receiver
Criteria/Target ZERO autocorrelation sidelobes
for best leading edge detection
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Communication Code Sequences for different
Receiver
Criteria/Target Max SNR and min inter-sequence
interference after despreading
22
Snychronisation Code Sequences for different
Receiver
Criteria/Target balance max post-despreading
SNR and low auto-correlation sidelobes