January 2005
doc.: IEEE 802.15-05-0013-01-004a
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [Time-Domain-CFP-Response]
Date Submitted: [4 January, 2005]
Source: [Vern Brethour, Adrian Jennings] Company: [Time Domain Corp.]
Address: [7057 Old Madison Pike; Suite 250; Huntsville, Alabama 35806]
Voice: [Vern: (256) 428-6331; Adrian: (256) 428-6326], E-Mail: [vern.brethour@timedomain.com;
adrian.jennings@timedomain.com]
Re: [802.15.4a CFP]
Abstract: [802.15.4a CFP response from Time Domain. An impulse radio nominally occupying 3 – 5 GHz
with 4 ns chip times using 40 chips/symbol and 300 ns quiet time between symbols.]
Purpose: [Response to WPAN-802.15.4a CFP]
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 individuals or organization. The material in this document
is subject to change in form and content after further study. The contributors reserve the right to add, amend
or withdraw material contained herein.
Release: The contributors acknowledge and accept that this contribution becomes the property of IEEE
and may be made publicly available by P802.15.
Submission
Slide 1
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Time Domain Proposal:
Single Band UWB
Alternate Physical Layer
for TG 802.15.4a
Submission
Slide 2
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Proposal Contents
•
•
•
•
•
General Overview
Proposal Principles
Regulatory Flexibility
Performance
Evaluation Matrix (in backup slides)
Submission
Slide 3
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
General Overview
•
•
•
•
•
•
•
Impulse radio
Single band nominally from 3 to 5 Ghz.
4 ns chip times
40 chips per symbol
300 ns quiet time between symbols
Max symbol integration = 64 (data)
Max symbol integration = 256 (acquisition)
Submission
Slide 4
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Proposal Principles
• The most important part of a proposal is the
signal as it appears on the air. For most signal
definitions, there are many ways to build a
radio, and as many corresponding performance
results. However, as a standard, we can define
a signal which will forever limit the systems
ultimate performance. (For example, by not
using all reasonably available bandwidth.)
Submission
Slide 5
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
The need for robust links
• There is already a 15.4a radio at 2.54GHz.
We must be substantially better than that
radio.
• This proposal provides the opportunity for
maximum performance by occupying as
much bandwidth as reasonable.
Submission
Slide 6
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Regulatory Flexibility
• There are fundamentally two approaches to
UWB regulatory flexibility:
– 1) using multiple bands.
– 2) longer chip times.
• Using long chip times allows for filters if
needed and does little harm if not needed.
Submission
Slide 7
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Regulatory Flexibility
• This proposal occupies all of the spectrum
between the ISM bands and the UNII bands
• This proposal allows ample (4 ns) chip time
to accommodate spectral shaping if
necessary.
• This proposal also allows a future (optional)
band between 6 and 10 GHz.
Submission
Slide 8
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Support for positioning
• There are already radios which do the low
data rate communications job without
positioning.
• Excellent positioning performance will be
the key differentiator for 15.4a.
• Use of as much bandwidth as reasonable
gives the best positioning performance.
Submission
Slide 9
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
What about the “simple radio” approach?
• Vocabulary is important here. Words like
“simplicity” imply virtue. Words like “crude” and
“unsophisticated” might be used by others to
describe the same radio.
• The critical issue is that there will be other users
of the spectrum and the 4a standard must use
spectrum and air time efficiently and effectively.
• A proposed standard which we think implies a
“simple and virtuous” radio might be viewed by
others as spectrally wasteful and unworthy of
letter ballot approval.
Submission
Slide 10
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
What does “simple radio” mean?
• A “simple radio” to our customers doing
system integration, is a radio with the lowest
chip count, the least number of passives and
the most forgiving antenna driver.
• The integration customer does not (and should
not) care how hard we have to work to
implement the design inside of our chip.
Submission
Slide 11
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Performance: the optimistic story.
• A “marketing
style” link
budget looks
very optimistic.
Even for 250
KByte/sec links,
at 100 meters
the link budget
shows over 6dB
of margin.
Submission
Parameter
Value
Value
Information Data Rate
1 Kbps
250 Kbps
Average TX Power
-12 dBm
-12 dBm
Total Path Loss
84.5 dB
(@ 100 meters)
84.5 dB
(@ 100 meters)
Average RX Power
-96.5 dBm
-96.5 dBm
Noise Power Per Bit
-144 dBm
-120 dBm
CMOS RX Noise Figure
8 dB
8 dB
Total Noise Power
-136 dBm
-112 dBm
Required Eb/N0
2.25 dB
2.25 dB
Implementation Loss
6 dB
6 dB
Link Margin
31.25dB
7.25 dB
RX Sensitivity Level
-128 dBm
-104. dBm
Max. Range (AWGN)
3652 m
230 m
Slide 12
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Link Performance: A realistic story.
• Performance predicted by the link budget is
optimistic primarily due to the use of “2”
for the path loss exponent.
• Links inside buildings with interior walls,
will suffer path loss exponents more like
“3”.
Submission
Slide 13
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Link Performance
• A more realistic idea of performance is
available by scaling the results of the
simulations done for 802.15.3a to longer
ranges and lower data rates.
• The 802.15.3a DS proposal uses signaling
similar to this proposal, so I will scale from
simulations reported in 802.15.04.0483r5
(McLaughlin, November 2004).
Submission
Slide 14
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Scaling the DS results:
• The 3a DS radio is simulating an 11.8 meter link
in CM4 at 110 Mbit/sec with a 90% packet
success rate.
• Going from a link distance of 11.8 meters to 100
meters would seem to require less than 20 dB of
additional processing gain. BUT that’s with a path
loss exponent of 2.
• A path loss exponent of 3 requires 28 dB of
processing gain.
Submission
Slide 15
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
How much integration is needed for 28 dB
of processing gain?
• Each time we double the integration, we get
another 3dB of processing gain.
• For 28 dB, we need to do 10 doublings, or
an integration rate of 1024.
• Integration rate 1024 will take the 110
Mbit/sec rate down to 107 Kbit/sec.
Submission
Slide 16
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Noticeable difference:
Data rate
Predicted range
Link Budget with
Path Loss
exponent 2
250 Kbit/sec
245 meters
Scaled
Simulation with
Path Loss
exponent 3
107 Kbit/sec
118 meters
Submission
Slide 17
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Even the Scaled Simulation is a very
optimistic result:
• The DS radio that this prediction rests on is
a very fancy radio:
– 16 Rake taps
– 31 tap decision feedback equalizer
– Constraint length 6 convolutional code with
Viturbi decoder
– RF front end with 6.6 dB noise figure
Submission
Slide 18
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Link budgets do not address acquisition.
• Acquisition will usually be the performance
limiter at long range.
• The Acquisition decision needs an
additional 6 dB of processing gain over data
demodulation.
Submission
Slide 19
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
We must acquire without benefit of a
trained equalizer.
• Equalizers are fine, but only after they have
been trained.
• If the spacing between symbols is too short,
the resulting inter symbol interference
makes trouble for acquisition.
• This proposal uses a relatively long (300 ns)
distance between symbols to handle large
channel delay spreads without an equalizer.
Submission
Slide 20
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Applications need robust links.
• The applications can stand low data rates, so
this proposal uses data symbol integration of
64 and acquisition symbol integration 256.
• The long acquisition integration puts a burden
on crystal tolerance (2 ppm) that not all
vendors will want to deal with, so shorter
integration modes will also be supported.
Submission
Slide 21
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Clear Channel Assessment
• This is a hard problem for all UWB
approaches.
• We should not ignore it.
• Detection of energy at the chipping rate (as in
the 15.3a DS proposal) is doable, but not
reliable.
• We may need relief from the MAC.
Submission
Slide 22
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Simultaneously Operating Piconets
• The long symbol (40 chips) enables good
orthagonality between piocnets.
• Different piconets use slightly different
chipping rates like the 15.3a DS proposal.
• Bits are modulated onto symbols using only
BPSK so all of the symbol orthogonality is
used for piconet isolation.
Submission
Slide 23
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Power control is the key to compatibility
with 15.3a
• This proposal is set up for 100 meter links.
• Many applications will have shorter links.
• For shorter links, we turn down the Tx
power.
• Power control gives superior compatibility
with all services.
Submission
Slide 24
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Proposal Summary
•
•
•
•
•
•
•
Impulse radio
Single band nominally from 3 to 5 Ghz.
4 ns chip times
40 chips per symbol
300 ns quiet time between symbols
Max symbol integration = 64 (data)
Max symbol integration = 256 (acquisition)
Submission
Slide 25
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Backup Slides
Submission
Slide 26
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Evaluation Matrix
Submission
Slide 27
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Self Evaluation – General Solution Criteria
CRITERIA
Evaluation
Unit Manufacturing Cost (UMC) +(no need for an equalizer)
Signal Robustness
Interference
+(due to power control)
Signal Robustness
Susceptibility
+(due to using max bandwidth)
Coexistence
+(due to power control)
Manufacturability
+(due to low peak Tx amplitudes)
Time To Market
+
Regulatory Impact
+ (due to long chip times)
Technical Feasibility
Scalability
+
Location Awareness
+(due to using max bandwidth)
Submission
Slide 28
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Self Evaluation – PHY Protocol Criteria
Submission
CRITERIA
Evaluation
Size and Form Factor
+
Payload Bit Rate
+
Packet Overhead
+
PHY-SAP Throughput
+
Simultaneously Operation Piconets
+(due to the long 40 chip symbol)
Signal Acquisition
+(due to long symbol integration)
System Performance
+
Link Budget
+(due to using max bandwidth)
Sensitivity
+
Power Management Modes
+
Power Consumption
+
Antenna Practicality
+
Slide 29
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Example of a chip waveform
Submission
Slide 30
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Multiple chips make a symbol:
1
2
3
4
5
6
7
8
38 39 40
…………………………
Non-inverted pulses are blue,
Nulled pulses are orange,
Inverted pulses are green.
…………………………...
160 ns
Submission
Quiet time
Slide 31
Vern Brethour, Adrian Jennings (Time Domain)
January 2005
doc.: IEEE 802.15-05-0013-01-004a
Allow plenty quiet time between symbols
…………………………………………….
160 ns
Submission
300 ns
Slide 32
Vern Brethour, Adrian Jennings (Time Domain)