September 2004
doc.: IEEE 802.15-04/504r0
Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [DS-UWB Responses to TG3aVoter NO Comments – Equalizer, SOP, ADC, RFI]
Date Submitted: [September 2004]
Source: [Matt Welborn, John McCorkle,& Michael McLaughlin]
Company [Freescale Semiconductor, Inc & DecaWave, Ltd.]
Address [8133 Leesburg Pike]
Voice:[703-269-3000], E-Mail:[matt.welborn @freescale.com]
Re: []
Abstract: [Response to NO voter comments and feedback regarding the DS-UWB (Merger #2) Proposal]
Purpose: [Provide technical information to the TG3a voters regarding DS-UWB (Merger #2) Proposal]
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
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Topic: Equalization
• Typical comments
– A single carrier receiver requires a decision based equalizer (DFE)
for meeting reasonable performance. Under severe multipath
scenarios (non line of sight) such equalizers introduces an error
propagation effect
– lack of sufficient high fidelity simulations of equalizer performance
– Current evidence shows that DFE works well at very high SNRs
(9.6 and 12.6 dB). Must show evidence that DFE will not suffer from
error propagation at realistic operating points such at ~1 dB
– I believe that a big application area for UWB will be in personal and
portable devices. I have not been convinced that the DS-SS
proposal will provide good performance in the face of changing
propagation conditions, potential due to device movement or
movement of people and objection in the propagation path. I have
not seen an explanation and a simulation of how the equalizer will
quickly adapt
Submission
Slide 2
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Responses: Equalization
• Comments – Fully Resolved
– There is no need for an adaptive equalizer. The
system is assumed to see a psuedo-stationary
channel for the duration of the packet.The
equalizer re-trained for each packet.
• At 110 Mbps, packets will be < 0.1ms in duration
– Equalizer performance is demonstrated in systemlevel simulations
– Our simulations show that although error
propagation is present, it does not significantly
reduce the range achieved by DS-UWB
Submission
Slide 3
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
DS-UWB in Multipath
• Indoor multipath channels provide several challenges
for UWB systems
– Multipath fading
– Inter-symbol interference (ISI)
– Energy capture
• Effects are well-understood and are analyzed as
trade-off between performance versus complexity
• DS-UWB minimizes fading and provides scalable
energy capture
• Other approaches can provide good energy capture
at the expense of significant multipath fading
Submission
Slide 4
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Compensating for ISI
•
ISI occurs as a result of non-uniform channel frequency response
– Multipath delay spread exceeds the symbol interval
•
ISI is compensated for using an equalizer
– Linear equalizer (digital filter)
– Decision-feedback equalizer (DFE)
•
•
If left uncompensated, ISI can cause high BER & error floor phenomenon
Equalizer technology is widely used in many types of systems
– Telephone modems
– WLAN (e.g. 802.11b)
– HDTV
•
OFDM systems use frequency domain equalization to compensate for
phase and amplitude response of channel
– If delay spread exceeds CP length, residual ISI compensation would require
additional time-domain equalization
Submission
Slide 5
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Example of ISI Effects on BER
Uncoded Equalization Performance on CM3-15, 16 Finger Rake
-1
No Equalization
9-Tap Least-Squares DFE
AWGN Channel
Log10 BER
-2
-3
-4
-5
-6 5
10
15
20
Eb/No
• Un-equalized system experiences high BER and error floor
• 9-tap DFE with 16-finger rake performance approaches AWGN
Submission
Slide 6
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Eye diagram at Eb/No = 5 dB
Noise dominates ISI
Uncoded Equalization Performance on CM3-15, 16 Finger Rake
-1
16 Rake, No DFE, Eb/No = 5
No Equalization
9-Tap Least-Squares DFE
AWGN Channel
-1.5
1
-2
0.5
-2.5
-3
Log10 BER
0
-0.5
-3.5
-4
-1
-4.5
100
200
300
400
500
600
700
800
900 1000 1100
-5
-5.5
16 Rake, Post DFE, Eb/No = 5
-6
1
5
10
15
Eb/No
0.5
0
-0.5
-1
100
200
Submission
300
400 500 600 700 800
Received BPSK Symbols
900 1000 1100
Slide 7
Welborn, Freescale & McLaughlin, DecaWave
20
September 2004
doc.: IEEE 802.15-04/504r0
Eye diagram at Eb/No = 10 dB
Noise/ISI at similar levels
Uncoded Equalization Performance on CM3-15, 16 Finger Rake
-1
No Equalization
9-Tap Least-Squares DFE
AWGN Channel
-1.5
-2
16 Rake, No DFE, Eb/No = 10
-2.5
1
Log10 BER
-3
0.5
0
-3.5
-4
-4.5
-0.5
-5
-1
-5.5
100
200
300
400
500
600
700
800
900 1000 1100
-6
16 Rake, Post DFE, Eb/No = 10
5
10
15
Eb/No
1
0.5
0
-0.5
-1
100
200
Submission
300
400 500 600 700 800
Received BPSK Symbols
900 1000 1100
Slide 8
Welborn, Freescale & McLaughlin, DecaWave
20
September 2004
doc.: IEEE 802.15-04/504r0
Eye diagram at Eb/No = 15 dB
ISI dominates AWGN
Uncoded Equalization Performance on CM3-15, 16 Finger Rake
-1
No Equalization
9-Tap Least-Squares DFE
AWGN Channel
-1.5
16 Rake, No DFE, Eb/No = 15
-2
1
-2.5
0.5
Log10 BER
-3
0
-3.5
-4
-0.5
-4.5
-5
-1
-5.5
100
200
300
400
500
600
700
800
900 1000 1100
-6
5
10
15
Eb/No
16 Rake, Post DFE, Eb/No = 15
1
0.5
0
-0.5
-1
100
200
Submission
300
400 500 600 700 800
Received BPSK Symbols
900 1000 1100
Slide 9
Welborn, Freescale & McLaughlin, DecaWave
20
September 2004
doc.: IEEE 802.15-04/504r0
Eye diagram at Eb/No = 20 dB
ISI dominates AWGN
Uncoded Equalization Performance on CM3-15, 16 Finger Rake
-1
16 Rake, No DFE, Eb/No = 20
No Equalization
9-Tap Least-Squares DFE
AWGN Channel
-1.5
-2
1
-2.5
0.5
Log10 BER
-3
0
-3.5
-4
-4.5
-0.5
-5
-1
-5.5
100
200
300
400
500
600
700
800
900 1000 1100
-6
5
10
15
Eb/No
16 Rake, Post DFE, Eb/No = 20
1
0.5
0
-0.5
-1
100
Submission
200
300
400 500 600 700 800 900 1000 1100
Received BPSK Symbols
Slide 10
Welborn, Freescale & McLaughlin, DecaWave
20
September 2004
doc.: IEEE 802.15-04/504r0
Responses: Equalization
• Comments – Fully Resolved
– There is no need for an adaptive equalizer. The
system is assumed to see a psuedo-stationary
channel for the duration of the packet.The
equalizer re-trained for each packet.
• At 110 Mbps, packets will be < 0.1ms in duration
– Equalizer performance is demonstrated in systemlevel simulations
– Our simulations show that although error
propagation is present, it does not significantly
reduce the range achieved by DS-UWB
Submission
Slide 11
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Topic: Simultaneous Piconets (SOP)
• Typical comments:
– SOP numbers are inconsistent with any of the sanity checks.
Please revise numbers via full level simulation. Do not
assume that the interference is white Gaussian noise and
shift curves. To verify numbers are based on simulations,
please provide each curve used in the averaging process
– Isolation between interfering piconets occupying the lower
band needs to be better than the stated d_int/d_ref = 0.66 for
2-3 uncoordinated interfering piconets in some applications
- I would like to see evidence of how this can be met
Submission
Slide 12
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
SOP Mechanism
• SOP performance values reported for DS-UWB were
based on full simulations of all interfering signals (not
based on statistical signal distributions)
• SOP mechanism is based on spread-spectrum
techniques
– Other piconet signals look like uncorrelated noise
• Analysis results show PHY layer interference ratios
– Equivalent to “fully loaded” piconets
– Actual MAI will depend on MAC & actual traffic loading
– 15.3 MAC co-existence mechanisms (child & neighbor
piconets) can allow co-existence at much shorter ranges
Submission
Slide 13
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
SOP Performance
• DS-UWB also has the potential for enhanced SOP
performance using advanced receiver architectures
– MAI is not truly random noise, but has structure
– Different piconet codes & chip rates are known
• Multi-user detection (MUD) techniques could allow for
significant SOP performance improvements
Submission
Slide 14
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
AWGN SOP Distance Ratios
Test
Distance
1 Interferer
Distance Ratio
2 Interferer
Distance Ratio
3 Interferer
Distance Ratio
110 Mbps
15.7 m
0.65
0.92
1.16
220 Mbps
11.4 m
0.90
1.28
1.60
500 Mbps
5.3 m
2.2
3.3
-
• AWGN distances for low band
• High band ratios expected to be lower
– Operates with 2x bandwidth, so 3 dB more processing gain
Submission
Slide 15
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Multipath SOP Distance Ratios
Test Transmitter: Channels 1-5
Single Interferer: Channels 6-10
Second Interferer: Channel 99
Third Interferer: Channel 100
110
Mbps
1 Interferer
Distance Ratio
2 Interferer
Distance Ratio
3 Interferer
Distance Ratio
CM1
0.66
0.86
1.09
CM2
0.64
0.91
1.14
CM3
0.72
0.97
1.24
• High band ratios expected to be lower (3 dB more processing gain)
Submission
Slide 16
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Topic: ADC Issues
• Typical comments
– [DS-UWB must demonstrate] a receiver structure
would be suggested that can achieve range
comparable with the MBOA proposal, with a digital
sampling rate of no more than 528Mbit/s
– The Silicon implementation feasibility is
substantiated satisfactorily. ----The Silicon
implementation size/power/complexity claims of
the ADC/DAC/FEC/ Rake/equalizer at high speed
do not agree with general knowledge…
Submission
Slide 17
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
ADC Power Requirements & Scaling
• ADC complexity is a function of both sample rate and bit width
• Concerns of comments seem to be that ADC requirements are much
higher for DS-UWB than for alternative approaches (e.g. MB-OFDM)
because clock rate is higher
• ADC performance is described by “efficiency quotient”
– EQ = power / 2^ (ENOB * BW)
• ENOB = effective number of bits & BW = input bandwdith
• This agrees with ADC scaling estimates based on MB-OFDMproposed methodology
– Available in IEEE Document 03/343r1 describing MB-OFDM complexity
and power consumption
• DS-UWB digital receiver architecture can use a fixed bit width for all
data rates up to 1.326 Gbps
• MB-OFDM proposes to use 4-5 bits at 528 MHz
Submission
Slide 18
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
ADC Relative Complexity & Bounds
• Relative complexity (power)
– 528 MHz @ 4 bits  0.8x 1326 MHz @ 3 bits
– 528 MHz @ 5 bits  1.6x 1326 MHz @ 3 bits
• Both approaches can likely scale to lower resolution
ADCs with some sacrifice in performance
• Research on the lower bounds for ADC resolution
indicates that OFDM-UWB will have “error floors” for
low ADC resolution (not true for single-carrier UWB)
– “Digital Architecture for an Ultra-Wideband Radio Receiver,” Raul
Blazquez, Fred S. Lee, David D. Wentzloff, Puneet P. Newaskar,
Johnna D. Powell, Anantha P. Chandrakasan, Microsystems
Technology Laboratory, Massachusetts Institute of Technology,
VTC 2003
Submission
Slide 19
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Topic: Interference Rejection
• Comments
– Authors of Merged #2 showed heuristic arguments
for performance in the presence of narrowband
interferers. The selection criteria ask for simulation
results. Authors need to do simulations.
– I find the DS approach hard to achieve good
performance under narrow band interferers. I will
change my vote if I get explanation how this
approach can function under narrow band
interferers
Submission
Slide 20
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Topic: Interference
• Comments – Fully Resolved
– Selection Criteria clearly ask for analysis or
simulation results
– Detailed analysis shows that DS-UWB provides
robust performance against RFI through UWB
processing gain
• Additional implementation mechanisms available to
significantly improve RFI rejection
Submission
Slide 21
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Interference Criteria
•
Interference criteria (03/031r11):
–
•
•
When this interferer is present, using simulation results,
analysis, or technical explanations, determine the average
received interference power, PI, that can be tolerated by
the receiver, after it has executed any interference
mitigation algorithms, while still maintaining a PER less
than 8% for 1024 byte packets
Minimum criteria: PI - Pd> 3 dB (Pd is the received
power which is defined here as 6 dB above the
receiver sensitivity level)
Out-of-Band Interference from Intentional or
Unintentional Radiators
–
Submission
Proposers should report the minimum out-of-band rejection
in dB provided by the proposed system. This will provide a
minimum standard for out-of-band interferer immunity
Slide 22
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
NarrowBand Interference (NBI)
Radio Frequency Interference (RFI)
3-Cases
RFI
Mild
Processing Gain Adequate
Out-of-Band
BPF
Moderate
LNA does Not saturate
Processing Gain inadequate
Severe
LNA saturates
Must Filter
DS-UWB
1% (40 MHz) Notch Filter
=2% of DS-UWB band
No added
complexity needed
2% = small impact
Submission
Slide 23
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Moderate RFI
Moderate
LNA does Not saturate
Processing Gain inadequate
See calculation next page
DS-UWB
SIR < -3.06 dB
Notch
Filter
LOW COMPLEXITY
Only 4 MAC’s
per symbol
per tone!
Submission
MB-OFDM
SIR < ? dB
Digital RFI
Extraction
10+ dB gain
Erasure Detection
& Erasure decoding
(same as turning tone off)
SIR < -13 dB
SIR < -7 dB
Slide 24
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Narrow-Band Interference
• DS-UWB receivers with 3-bit ADC architectures
– Simulations with no active NBI compensation indicate about 3 dB Ito-S is to be expected
– Simple analysis with NO ACTIVE COMPENSATION (worst case):
• Required Eb/No is 5.0 dB for rate-½ FEC code
• Assume 1.5 dB implementation loss (based on simulation results)
• Total noise-per-bit is –87 dBm = -174dBm/Hz + 10log(110MHz) + (6.6
dB NF)
• Sensitivity = -87+5+1.5= 80.5
• Sensitivity + 6dB (per spec) = signal power (S) = -74.5 dBm
• Allowable (I+N) = -74.5 - 5.0 - 1.5 = -81 dBm (assume I is noise-like at
slicer)
• Allowable I is therefore 10*log(10^(-81/10)-10^(-87/10)) = -82.24 dBm
• At 110 Mbps, processing gain is 12:1 over (I+N) in signal bandwidth 
10.8 dB gain (worst case)
– Processing gain is a function of tone frequency – depends on pulse shape. At
band edges, gain is much higher
• Allowable I-to-S is therefore -81.24 + 10.8 -(-74.5) = 3.06 dB I-to-S
– Result for high-band operation is 6.0 dB allowable I-to-S
• 3 dB better than low band operation because 2x signal bandwidth
provides 3 dB more processing gain
Submission
Slide 25
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Digital RFI Removal
•
•
•
•
Real signal and noise from hardware
A/D samples fed into Matlab
6 bits used to represent basis functions
Data processed in 128 sample blocks
Before (SIR = 5 dB)
Submission
After (SNR = 15 dB)
Slide 26
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Quantized RFI Suppression Performance Vs.
Frequency Error
15
3 Bits
4 Bits
5 Bits
6 Bits
7 Bits
8 Bits
Input SNR:15.0dB
SIR:6.0dB
14.5
14
Output SNR (dB)
13.5
13
12.5
12
11.5
11
10.5
10
Submission
0
50
100
150
Frequency Error (kHz)
Slide 27
200
250
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Spectrum Before Extraction
40
Fd = 114e6
Power Spectrum Magnitude (dB)
30
Resolution:
Fd/1024 =
111 kHz
20
10
0
-10
-20
Submission
0
1
2
3
Frequency
4
5
Slide 28
Welborn, Freescale & McLaughlin, DecaWave
7
x 10
September 2004
doc.: IEEE 802.15-04/504r0
Spectrum After Extraction
40
Fd = 114e6
Power Spectrum Magnitude (dB)
30
Resolution:
Fd/1024 =
111 kHz
20
10
0
-10
-20
Submission
0
1
2
3
Frequency
4
5
Slide 29
Welborn, Freescale & McLaughlin, DecaWave
7
x 10
September 2004
doc.: IEEE 802.15-04/504r0
BACKUP
Submission
Slide 30
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
Bounds on ADC Resolution
From “Digital Architecture for an Ultra-Wideband Radio Receiver,” Raul
Blazquez, Fred S. Lee, David D. Wentzloff, Puneet P. Newaskar, Johnna D.
Powell, Anantha P. Chandrakasan, Microsystems Technology Laboratory,
Massachusetts Institute of Technology, VTC 2003.
Submission
Slide 31
Welborn, Freescale & McLaughlin, DecaWave
September 2004
doc.: IEEE 802.15-04/504r0
DS-UWB Avoids the UNII Band
• DS-UWB already excludes bands used by
most likely high power interferers (UNII
bands: WLAN, radars, DSRC, cordless
phones, etc
Submission
Slide 32
Welborn, Freescale & McLaughlin, DecaWave