Transcript October 2001 doc.: IEEE 802.15-01/478r0 Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs) Submission Title: [Low Rate Sensitivity] Date Submitted: [10

October 2001
doc.: IEEE 802.15-01/478r0
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:[[email protected]]
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.
Submission
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
Low Rate Sensitivity:
IEEE 802.15.4
D09 PHY Changes Leading to “LowRate” Sensitivity Loss
Paul Gorday
Oct. 10, 2001
Submission
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
PHY Changes in d09
Symbol Structure
Previous Symbol Definition
I-Channel
32-chip CPM symbol
···
Q-Channel
32-chip CPM symbol
···
Ts = 32 µs
Rs = 31.25 kbaud
d09 Symbol Definition
I-Channel
Q-Channel
32-chip
CPM
symbol
···
···
Ts = 16 µs
Rs = 62.5 kbaud
Submission
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
PHY Changes in d09
Chip Modulation
Previous Chip Modulation
Ts = 32 µs
I-Channel
Q-Channel
cI0
cI1
cQ0
cI2
cQ1
cI30
cQ2
cI31
cQ30
1 µs
cQ31
Complex Chip Rate = 1 Mchip/s
d09 Chip Modulation
Ts = 16 µs
I-Channel
Q-Channel
c0
c2
c1
1 µs
Submission
c30
c3
c31
Complex Chip Rate = 1 Mchip/s
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
PHY Changes in d09
Symbol 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.
I-Channel
Q-Channel
32-chip
CPM
symbol
32-chip
CPM
symbol
···
···
Ts = 32 µs
Submission
Rs = 31.25 kbaud
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
PHY Changes in d09
Base 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
Submission
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
PHY Changes in d09
Low 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
Submission
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
PHY Changes in d09
Low 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
Submission
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
PHY Changes in d09
Summary
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?)
Submission
Paul Gorday, Motorola
October 2001
doc.: IEEE 802.15-01/478r0
BER Curves
Conventional DSSS Decoding
Simulated IEEE 802.15.4 PHY performance in ideal AWGN channel
0
10
Theory (16-ary)
4 bits/symb (New)
4 bits/symb (Old)
Theory (2-ary)
1 bit/symb (New)
1 bit/symb (Old)
-1
10
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
BER
-2
10
-3
10
-4
10
0
Submission
2
4
6
8
Eb/No (dB)
10
12
14
Paul Gorday, Motorola