doc.: IEEE 802.15-<doc#> <month year> doc.: IEEE 802.15-<doc#> July 2005 Project: IEEE P802.15 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:[703-269-3000], FAX: [], E-Mail:[matt.welborn @ freescale.com, or michael@decawave.com] Re: [Response to Call for Proposals] Abstract: [This document describes a proposal for the TG4a baseline draft standard.] Purpose: [Proposal Presentation for the IEEE802.15.4a standard.] 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. Welborn, Freescale <author>, <company>

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

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

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

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

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

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

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

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

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