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October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Low Rate Sensitivity]
Date Submitted: [10 October, 2001]
Source: [Paul Gorday] Company: [Motorola]
Address: [8000 W. Sunrise Blvd., M/S 2141, Plantation, FL 33322]
Voice:[(954) 723-4047], FAX: [(954) 723-3712], E-Mail:[paul.gorday@motorola.com]
Re: [IEEE 802.15.4 PHY Baseline; Doc. IEEE 802.15-01/358r0]
Abstract: [This presentation describes the effect on low rate sensitivity of a proposed change to the TG4 PHY.]
Purpose: []
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.
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
Low Rate Sensitivity:IEEE 802.15.4
D09 PHY Changes Leading to “Low-Rate” Sensitivity Loss
Paul Gorday
Oct. 10, 2001
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
PHY Changes in d09Symbol Structure
32-chip CPM
symbol · · ·
· · ·I-Channel
Q-Channel
Ts = 16 µs
d09 Symbol Definition
Rs = 62.5 kbaud
Previous Symbol Definition
32-chip CPM symbol
32-chip CPM symbol · · ·
· · ·I-Channel
Q-Channel
Ts = 32 µs
Rs = 31.25 kbaud
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
PHY Changes in d09Chip Modulation
I-Channel
Q-Channel
Ts = 16 µs
d09 Chip Modulation
Complex Chip Rate = 1 Mchip/s1 µs
c0 c2 c30
c1 c3 c31
Previous Chip Modulation
I-Channel
Q-Channel
Ts = 32 µs
Complex Chip Rate = 1 Mchip/s1 µs
cI0 cI
1 cI2 cI
31
cQ0 cQ
1 cQ2 cQ
31
cI30
cQ30
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
PHY Changes in d09Symbol Structure (cont’d)
Previous Symbol Definition• Complex Symbol defined as two “real” 32-chip CPM symbols (I and Q) • Required two orthogonal PN codes
d09 Symbol Definition• Complex Symbol defined as one “real” 32-chip CPM symbol• Requires one PN code• Allows greater frequency drift since PN sequence spans less time
Alternative d09 Symbol Definition• For consistency, we could have defined a complex symbol as two “real” 32-chip symbols that are sequential in time, but this seems less simple.
32-chip CPM
symbol · · ·
· · ·I-Channel
Q-Channel
32-chip CPM
symbol
Ts = 32 µs
Rs = 31.25 kbaud
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
PHY Changes in d09Base Rate Mode
In both modulation methods:• Each 32-chip CPM symbol represents 4 bits of data, and it both cases the net bit rate is Rb=250 kbps.• Each 32-chip CPM symbol is selected from a set of 24 = 16 “nearly orthogonal” code words. Thus with non-coherent detection, performance closely resembles 16-ary non-coherent orthogonal modulation (curves available from almost any communications textbook).
Simulated performance of the new modulation• Eb/No = 7.5 dB at 10-4 BER• 0.5 dB improvement (differential coding removed, I/Q cross-correlation reduced).• Receiver sensitivity (assuming 15 dB noise figure)
Sens. (dBm) = -174 + (NF)dB + (Eb/No)dB + 10log(Rb) = -174 + 15 + 7.5 + 10log(250000) = -97.5
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
PHY Changes in d09Low Rate Mode
Previous modulation method:• Each 32-chip CPM symbol represents 1 bit of data, but within a complex symbol, the I and Q component carried the same bit. The net bit rate was 31.25 kbps.• Each 32-chip CPM symbol is selected from a set of 21 = 2 “nearly orthogonal” code words. Thus with non-coherent detection, performance closely resembles binary non-coherent orthogonal modulation.• The 3 dB penalty from repeating each bit on I and Q was offset by coherently combining the I and Q correlation results prior to making the symbol decision.
Simulated performance of the old modulation• Eb/No = 13.5 dB at 10-4 BER• Receiver sensitivity (assuming 15 dB noise figure)
Sens. (dBm) = -174 + (NF)dB + (Eb/No)dB + 10log(Rb) = -174 + 15 + 13.5 + 10log(31250) = -100.5
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
PHY Changes in d09Low Rate Mode (cont’d)
New modulation method:• Each 32-chip CPM symbol represents 1 bit of data. New net bit rate is 62.5 kbps.• Each 32-chip CPM symbol is selected from a set of 21 = 2 “nearly orthogonal” code words. Thus with non-coherent detection, performance closely resembles binary non-coherent orthogonal modulation.• Symbol repetition was removed.
Simulated performance of the new modulation• Eb/No = 13 dB at 10-4 BER• 0.5 dB improvement (differential coding removed, I/Q cross-correlation reduced)• 3 dB loss (removal of symbol repetition)• Receiver sensitivity (assuming 15 dB noise figure)
Sens. (dBm) = -174 + (NF)dB + (Eb/No)dB + 10log(Rb) = -174 + 15 + 13 + 10log(62500) = -98
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
PHY Changes in d09Summary
High Rate• Net bit rate is the same as before• Sensitivity gain of 0.5 dB due to removal of differential coding and reduced I/Q cross-correlation.
Low Rate• Net bit rate increased due to removal of symbol repetition• Sensitivity gain of 0.5 dB due to removal of differential coding and reduced I/Q cross-correlation.• Sensitivity loss 3 dB due to removal of symbol repetition
Possible corrections for Low-Rate sensitivity loss• Put symbol repetition back in. Needs to be verified by simulation.• Run in high-rate mode (i.e., 4 bits/symbol), but use additional FEC coding to achieve “low-rate” sensitivity gain. (Complexity?)
October 2001
Paul Gorday, Motorola
doc.: IEEE 802.15-01/478r0
Submission
0 2 4 6 8 10 12 14
10-4
10-3
10-2
10-1
100
Eb/No (dB)
BE
R
Simulated IEEE 802.15.4 PHY performance in ideal AWGN channel
Theory (16-ary)4 bits/symb (New)4 bits/symb (Old)Theory (2-ary)1 bit/symb (New)1 bit/symb (Old)
BER CurvesConventional DSSS Decoding
Notes: (1) Theoretical refers to M-ary
non-coherent orthogonal signaling
(2) “New” refers to the latest d09 version
(3) “Old” refers to all earlier versions