1. doc.: IEEE 802.15-<doc#>
<month year>
doc.: IEEE <doc#>
July 2005
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Coding for TG4a]
Date Submitted: [July 2005]
Source: [Matt Welborn (1), Michael McLaughlin (2), & Shariar Emami (1)]
Company [(1) Freescale Semiconductor, Inc, (2) decaWave, Ltd.]
Address [8133 Leesburg Pike, Vienna VA 22182]
Voice:[ ], FAX: [], freescale.com, or
Re: [Response to Call for Proposals]
Abstract: [This document describes a proposal for the TG4a baseline draft standard.]
Purpose: [Proposal Presentation for the IEEE a standard.]
Notice: This document has been prepared to assist the IEEE P 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 P
Welborn, Freescale
<author>, <company>

2. Support for Coherent and Non-Coherent Modulation
July 2005
Support for Coherent and Non-Coherent Modulation
Two different sets of requirements
Non-coherent receiver only uses energy detector, cannot resolve phase relative to reference carrier
Coherent receiver can also resolve phase
Idea:
Encode data non-coherently for PPM/OOK
Add redundant encoding of data in phase of pulses
How would this work?
Welborn, Freescale

3. Encode data at two levels
July 2005
Encode data at two levels
Data bits map into PPM constellation
Map “zero” into
Map “one” into
Now map data into pulse phase as well
How do we do this?
Create a redundant mapping using a systematic convolutional code
Welborn, Freescale

4. Use a Systematic Code to Compute a Redundant Bit
July 2005
Use a Systematic Code to Compute a Redundant Bit
x1=bk bk
Convolutional
Encoder x2
Rate-½ convolutional encoder
Produce multiple coded bits from each data bit
Encoder itself is very low complexity
Special case of convolutional code is a “systematic” code
First coded bit is same as input data bit
Second coded bit is computed by encoder
Code can be chosen to have desired constraint length (TBD) & code gain (not limited to a specific constraint length)
Mapping coded bits to waveform
Map first coded bit (systematic bit) into position for BPPM
Map second coded bit into phase
Can be extended to more general (non-systematic) codes very easily
Welborn, Freescale

5. Non-Coherent and Coherent Demodulation
July 2005
Non-Coherent and Coherent Demodulation
X1 = 0, X2 = 0
X1 = 1, X2 = 0
X1 = 0, X2 = 1
X1 = 1, X2 = 1
Non-coherent receiver only sees position
Demodulates only x1
No Viterbi decoding required (easy since x1=bk)
Achieves no coding gain, assumes bk = x1  Done.
Coherent receiver demodulates position and phase
Decodes x1 & x2
Viterbi decoding used to estimate original bit, bk
Achieves coding gain of original rate ½ code
Welborn, Freescale

6. Another way to look at this Mapping
July 2005
Another way to look at this Mapping
4-BOK (coherent)
constellation
2-PPM
constellation
2-PPM
constellation
Non-coherent receiver
cannot see these
OOK
constellation
Encoding two coded bits requires a 4-point signal constellation
Each axis represents one of two possible positions (orthogonal axes)
Phase of pulse determines sign of constellation point on axis  4-BOK
Non-coherent receiver is insensitive to phase – see only two points in constellation  2-PPM
Support for OOK receiver is possible by demodulating only one of the two dimensions (i.e. just look at first position: pulse or not?)
Welborn, Freescale

7. Ternary Modulator II (from 15-05-428r0)
July 2005
If a guard of 2 pulses is used:
Welborn, Freescale

8. Using multiple pulses per symbol
July 2005
Using multiple pulses per symbol
Tsymbol
Can use multiple pulses per each “burst”
Four shown as an example
Can using “scrambling” on pulses to whiten spectrum
Can also include “guard” pulses if desired
Also need to ensure that “average” pulse rate is kept sufficiently high
Welborn, Freescale

9. What about a Differential Recevier?
July 2005
What about a Differential Recevier?
Differential receiver cannot discern absolute phase, just the phase difference between two pulses
Same polarity
Opposite Polarity
Same polarity, inverted
Opposite Polarity, inverted
Welborn, Freescale

10. Extending the “Punctured Code” Concept
July 2005
Extending the “Punctured Code” Concept
Now we need three levels of encoding
“Pulse” position – detectable by non-coherent receiver
“Relative” phase – detectable by differential receiver
“Absolute” phase – detectable by coherent receiver
Extend the previous concept to use a rate-1/3 code
Encoder maps one input data bit to three output bits
Could choose to use one “systematic” bit of the three
Decode only phase
Can decode the “rate 1” punctured code (only systematic bit - trivial)
Decode position & relative phase
Have two of every three “coded bits”
Can treat the code as a rate 1/3 code, punctured to rate ½
Perform decoding and get moderate coding gain
Decode all three (Position, relative & absolute phase)
Use full viterbi decoder to get best performance & coding gain
Welborn, Freescale