IEEE 802'15 PHY Proposal

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Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
Enhanced COBI-16 with Offset QPSK for 802.15.4b
High Rate Alt-PHY Date Submitted 13 Mar,
2004 Source Francois Chin, Yuen-Sam Kwok, Lei
Zhongding Company Institute for Infocomm
Research, Singapore Address 21 Heng Mui Keng
Terrace, Singapore 119613 Voice 65-6874-5687
FAX [phone] E-Mail chinfrancois_at_i2r.a
-star.edu.sg Re Response to the call for
proposal of IEEE 802.15.4b, Doc Number
15-04-0239-00-004b Abstract This presentation
compares all proposals for the IEEE802.15.4b PHY
standard. Purpose Proposal to IEEE 802.15.4b
Task Group 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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Motivation

• It is desirable choose a code sequences that
  will lead to efficient transmission and low
  implementation complexity. In particular, it
  should
• Avoid spikes in frequency spectrum
• Simplify correlation operations
• Enable simple frequency offset and DC
  compensation

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Motivation

• As such, it is desirable that the code sequences
  have the following properties
• All sequences contain an equal number of ones and
  zeros in total
• All sequences contain an equal number of ones and
  zeros in the even numbered chips (I phase)
• All sequences contain an equal number of ones and
  zeros in the odd numbered chips (Q phase)
• Total phase rotation in I / Q plane accumulates
  to 0 degree over the complete symbol
• The first 8 symbols are shifted versions of each
  other
• The last 8 symbols have inverted odd numbered
  chips (Q phase) when compared to the 8 first
  symbols, have the exact inverted baseband phase

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Motivation

• The COBI-32 code sequences satisfy all the 6
  requirements.
• Challenge
• Can we find a shorter 16-chip code sequences
  that give better bandwidth and, at the same time,
  satisfy all the 6 requirements?

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YES!!
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Proposed Symbol-to-Chip Mapping (Enhanced
16-chip COBI Code Set ?16)
The sequences are related to each other through
cyclic shifts and/or conjugation (i.e., inversion
of odd-indexed chip values)
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COBI-16 Sequences ?16

• The proposed code set satisfy all 6
  requirements!!!
• Another Root Sequence, with identical
  performance, is also found through exhaustive
  search
• 1 0 1 0 0 1 0 0 0 1 1 1 1 1 0 0 (Root A47C)
• Which is a direct left-right flip of previous
  root sequence
• IN FACT, other base sequence can be established
  by
• Any combination of cyclic shifts, bit inversion
  sequence flips of the base sequence (3E25 hex)

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TX PSD (915 MHz), RBW 16 kHz
Meet ETSI Mask
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TX PSD (915 MHz), RBW 100 kHz
Meet ETSI Mask
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TX PSD (868 MHz)Roll-off 0.2, RBW 16 kHz
Meet ETSI Mask
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TX PSD (868 MHz)Roll-off 0.2, RBW 100 kHz
Meet ETSI Mask
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TX PSD (868 MHz)Roll-off 0.2, RBW 16 kHz
Not Meet ETSI Mask
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TX PSD (868 MHz)Roll-off 0.6, RBW 16 kHz
Not Meet ETSI Mask
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TX PSD (868 MHz)Roll-off 0.6, RBW 16 kHz
Not Meet ETSI Mask
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TX PSD (868 MHz)Roll-off 0.2, 16-Tap _at_ 2x
sampling

• To meet ESTI mask with 40ppm crystal, small
  roll-off factor 0.2 has to be employed
• The proposed tap weights are

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EVM
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Preamble Structure
Preamble structure is the same as of 15.4
standard
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Auto-correlation of un-modulated COBI-16
Snapshot Of Normalized Correlation Values with 6
octet as example
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Cross-correlation of Enhanced COBI-16
There is a performance cost to pay for this
quasi-orthogonality as compared to another
orthogonal code, like DSSS Lets quantify the
loss
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Simulation models
Discrete exponential channel model -Sampled
version of diffuse channel model offer by Paul
with 4x sampling rate PER calculated on 20
bytes PPDUs with preamble
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System Performance

• Simulation parameters assumptions
• Flat fading 250ns rms delay spread Rayleigh
  Channel model
• O-QPSK modulation half sine pulse Transmit
  filtering Raised cosine (roll-off 0.2)
• 20 octets in each packet
• 20,000 packets for Monte-Carlo simulation
• Sync SFD error taken into account
• 2x oversampling
• Non-coherent demodulation

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868 MHz AWGN (Non-coherent)
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915 MHz AWGN (Non-coherent)
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Non-Coherent Receiver (with Tx Filter r0.2)
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Synchronisation False Alarm (915 MHz Band)
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Synchronisation Miss Detection(915 MHz Band)
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Synchronisation False Alarm (868 MHz Band)
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Synchronisation Miss Detection(868 MHz Band)
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Summary

• enhanced COBI-16 can satisfy the stated 6
  criteria that will
• Avoid spikes in frequency spectrum
• Simplify correlation operations
• Enable simple frequency offset and DC
  compensation