Transcript Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPAN’s)

July 2004
doc.: IEEE 802.15-04-0343r0
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks
(WPAN’s)
Submission Title: [Reasons to vote for the MB-OFDM proposal]
Date Submitted: [July, 2004
Source: [Michael Mc Laughlin] Company [decaWave Ltd]
Address [8133 Leesburg Pike Vienna, VA USA]
Voice:[703-269-3000], E-Mail:[michael@decawave.com]
Re:
Abstract: [Examines the five most popular reasons for voting for the MB-OFDM PHY proposal and
finds that they are actually reasons to vote for the DS-UWB proposal.]
Purpose: [Provide technical information to the TG3a voters regarding PHY proposals.]
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
Slide 1
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Summary of reasons why someone might vote
for MB-OFDM instead of DS-UWB
5.
Complexity: MB-OFDM < 4 x DS-UWB.
4.
Power: MB-OFDM < 4 x DS-UWB.
3.
Range: MB-OFDM almost as good as DS-UWB
on many channels.
2.
OFDM previously chosen for other, different
modulation schemes.
1.
MB-OFDM is backed by TI / Intel /Sony /Philips
and others.
Submission
Slide 2
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Reason 5: Complexity
• MB-OFDM Digital Complexity less than 4 times DSUWB Digital Complexity
– Digital complexity of MB-OFDM is between 2 and 4 times
that of DS-UWB depending on bit rate
• True, but then why not choose lower complexity
proposal
Submission
Slide 3
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Reason 5: Complexity
MB-OFDM
Component
DS-UWB 32-Finger
(Doc 03/268r3) Rake Architecture
Matched filter [rake] or
FFT
100K
45K
Viterbi decoder
108K
54K
Synchronization
Channel estimation
30K
247K
Other Miscellaneous
including RAM
Equalizer
Total gates @ 85.5 MHz
Submission
24K
30K
Freq Domain
20K
455K
203K
Slide 4
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Reason 4: Power Consumption
• MB-OFDM Power less than 4 times DS-UWB Power
– Digital power consumption at a given speed is proportional
to the number of gates
– MB-OFDM proposal is 2 to 4 times digital complexity
complexity for same speed => digital power consumption of
MB-OFDM is between 2 and 4 times that of DS-UWB.
• True, so why not vote for lower power proposal
Submission
Slide 5
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Reason 4: Power Consumption
Channel
DS-UWB
MB-OFDM
DS-UWB
MB-OFDM
Model
220Mbps
200Mbps
500Mbps
480Mbps
Rx Digital
Power
51mW
106mW
57mW
202mW
130nm
Submission
Slide 6
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Reason 3: Range
• MB-OFDM range is almost as good as DS-UWB on
many channels
• Almost is not good enough.
• It is true that MB-OFDM ranges come fairly close to
DS-UWB for the 110Mbps mode, but as conditions
get worse and as bit rates rise, the DS-UWB
advantage increases.
• e.g. DS-UWB outstrips MB-OFDM by more than 60%
for the 220/200Mbps over CM4.
Submission
Slide 7
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Reason 3: Range
DS-UWB
MB-OFDM
DS-UWB
MB-OFDM
Channel
110Mbps
110Mbps
220Mbps
200Mbps
Model
10% Outage
10% Outage
10% Outage
10% Outage
Range
Range
Range
Range
CM1
13.5
11.4
8.4
6.9
CM2
11.7
10.7
7.2
6.3
CM3
11.4
11.5
7.0
6.8
CM4
10.8
10.9
7.1
4.7
Submission
Slide 8
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Reason 2: OFDM used in other standards
• OFDM modulation has previously been chosen for other
different modulation schemes.
And it’s a
big but
• True, e.g. ADSL and 802.11
but the key word here is different.
• In ADSL the fixed channel allows the number of bits per tone to be
varied according to SNR for that part of the channel. This is not
currently possible for wireless systems.
• In 802.11a/g the SNR assumed is very high compared to UWB
and the bandwidth is much lower.
– For both of these reasons, the rayleigh fading effects are far less
damaging.
Submission
Slide 9
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Reason 1: Many large companies
support MB-OFDM
• Giants like Intel/Philips etc. wouldn’t pick an
inferior scheme, right?
• Wrong! They already admitted this when they
abandoned their original Multiband proposal
in favour of TI’s MB-OFDM proposal
Submission
Slide 10
Michael Mc Laughlin, decaWave
July 2004
doc.: IEEE 802.15-04-0343r0
Summary
• The five top reasons for voting for MB-OFDM have
examined and found to actually be reasons to vote
for DS-UWB
• This is without even considering the obvious reasons
not to vote for MB-OFDM (Interference, SOP
performance, Time to Market, Scalability)
• There are no good technical reasons to vote for the
MB-OFDM proposal.
Submission
Slide 11
Michael Mc Laughlin, decaWave