DS-UWB-responses-to-MB-OFDM-voter-NO-comments

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission Title
DS-UWB Proposal Update Date Submitted July
2004 Source Reed Fisher(1), Ryuji Kohno(2),
Hiroyo Ogawa(2), Honggang Zhang(2), Kenichi
Takizawa(2) Company (1) Oki Industry
Co.,Inc.,(2)National Institute of Information and
Communications Technology (NICT) NICT-UWB
Consortium Connectors  Address (1)2415E.
Maddox Rd., Buford, GA 30519,USA, (2)3-4,
Hikarino-oka, Yokosuka, 239-0847, Japan
Voice(1)1-770-271-0529, (2)81-468-47-5101,
FAX [phone], E-Mail(1)reedfisher_at_j
uno.com, (2)kohno_at_nict.go.jp, honggang_at_nict.go.jp,
takizawa_at_nict.go.jp Source Michael Mc
Laughlin Company decaWave, Ltd. Voice353-1-2
95-4937, FAX -, E-Mailmichael_at_decawave.com
Source Matt Welborn Company Freescale
Semiconductor, Inc Address 8133 Leesburg Pike
Vienna, VA USA Voice703-269-3000,
E-Mailmatt.welborn_at_freescal.com Re
Abstract Technical update on 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.
2
Outline

• Merger 2 Proposal Overview
• DS-UWB option of Common Signaling Mode (CSM)
  MB-OFDM
• Complexity/Scalability of UWB implementations
• Spectral control options for DS-UWB
• Performance

3
Overview of DS-UWB Proposal

• One of the goals of Merged Proposal 2 is DS-UWB
  and MB-OFDM harmonization interoperability
  through a Common Signaling Mode (CSM)
• High rate modes using either DS-UWB or MB-OFDM
• Best characteristics of both approaches with most
  flexibility
• A piconet could have a pair of DS and a pair of
  MB devices
• CSM waveform provides control interoperation
  between DS-UWB and MB-OFDM
• All devices work through an 802.15.3 MAC
• User/device only sees common MAC interface
• Hides the actual PHY waveform in use

4
The Common Signaling ModeWhat Is The Goal?

• The common signaling mode (CSM) allows the
  802.15.3 MAC to arbitrate between multiple UWB
  PHYs
• It is an etiquette to manage peaceful
  coexistence between the different UWB PHYs
• Multiple UWB PHYs will exist in the world
• DS-UWB MB-OFDM are first examples
• CSM improves the case for international
  regulatory approval
• Common control mechanism for a multitude of
  applications
• Planned cooperation (i.e. CSM) gives far better
  QoS and throughput than allowing un-coordinated
  operation and interference
• CSM provides flexibility/extensibility within the
  IEEE standard
• Allows future growth scalability
• Provides options to meet diverse application
  needs
• Enables interoperability and controls interference

5
What Does CSM Look Like?One of the MB-OFDM bands!
Proposed Common Signaling Mode Band (500 MHz
bandwidth) 9-cycles per BPSK chip
DS-UWB Low Band Pulse Shape (RRC) 3-cycles per
BPSK chip
3978
Frequency (MHz)
3100
5100
MB-OFDM (3-band) Theoretical Spectrum
6
CSM Specifics

• We have designed a specific waveform for the CSM
• BPSK modulation for simple and reliable
  performance
• Length 24 spreading codes using 442 MHz chip rate
• Harmonically related center frequency of 3978 MHz
• Rate ½ convolutional code with k6
• Provides 9.2 Mbps throughput
• Extendable up to 110 Mbps using variable code and
  FEC rates
• 802.15.3 MAC works great with CSM
• CSM can be used for control and beaconing
• Negligible impact on piconet throughput (beacons
  are lt1)
• Requires negligible additional cost/complexity
  for either radio
• MB-OFDM already has a DS mode that is used for
  synchronization
• This proposal is based on DS-UWB operating with a
  26 MHz cell-phone crystal
• Very low cost yet terrific phase-noise and
  accuracy (see GSM spec)

7
Overview of DS-UWB Proposal

• DS-UWB proposed as a radio for handheld with
• low-cost,
• ultra high-rate,
• ultra low-power,
• BPSK modulation using variable length spreading
  codes
• Scales to 1 Gbps with low power - essential for
  mobile handheld applications
• Much lower complexity and power consumption

8
Overview of DS-UWB Proposal

• Two wide 50-bandwidth contiguous bands
• Each captures unique propagation benefits of UWB
• Bandwidth and Center Frequency Programmable

• Low band provides long wavelet
• High band provides short wavelet
• Wavelet 3 cycles, packed back-to-back

3
4
5
6
7
8
9
10
11
GHz

• Wavelets are modulated with BPSK or QPSK
• Symbol is made with an N-chip code sequence
• Code is ternary (1, 0, -1)

N-chips

• Result is Not-spiky in either Time or Frequency
  Domain

volts
time
9
DS-UWB Signal Generation
Scrambler
K6 FEC Encoder
Conv. Bit Interleaver
Input Data
Bit-to-Code Mapping
Pulse Shaping
Static Center Frequency
Gray or Natural mapping
K4 FEC Encoder
4-BOK Mapper
Transmitter blocks required to support optional
modes

• Data scrambler using 15-bit LFSR (same as
  802.15.3)
• Constraint-length k6 convolutional code
• K4 encoder can be used for lower complexity at
  high rates or to support iterative decoding for
  enhanced performance (e.g. CIDD)
• Convolutional bit interleaver protects against
  burst errors
• Variable length codes provide scalable data rates
  using BPSK
• Support for optional 4-BOK modes with little
  added complexity

10
Data Rates Supported by DS-UWB
Data Rate FEC Rate Code Length Range (AWGN)
28 Mbps ½ 24 29 m
55 Mbps ½ 12 23 m
110 Mbps ½ 6 18.3 m
220 Mbps ½ 3 13 m
500 Mbps ¾ 2 7.3 m
660 Mbps 1 2 4.1 m
1000 Mbps ¾ 1 5.1 m
1320 Mbps 1 1 2.9 m
Similar Modes defined for high band
11
DS-UWB Architecture Is Highly Scaleable

• DS-UWB provides low scalable receiver
  complexity
• ADC can range from 3 bits to 1 bit for super-low
  power implementation
• Rake pipeline DFE can be optimized to trade off
  power cost in multipath
• 16 fingers _at_ 220, 5 fingers _at_ 500, 2 fingers _at_
  1326Mbps
• Time duration of DFE scales (shrinks) at shorter
  range higher rates.
• FEC can scale w/data rate (k6 k4) or be
  turned-off for ultra low power
• DFE effectiveness and simplicity proven in
  shipping chips 3 of area

12
UWB System Complexity Power Consumption

• Two primary factors drive complexity power
  consumption
• Processing needed to compensate for multipath
  channel
• Modulation requirements (e.g. low-order versus
  high-order)
• DS-UWB designed to operate with simple BPSK
  modulation for all rates
• Receiver functions operate at the symbol rate
• Optional 4-BOK has same complexity and BER
  performance
• MB-OFDM operates at fixed 640 Mbps (raw)
• Designed to operate at high rate, then use
  carrier diversity (redundancy) and/or strong FEC
  to combat multipath fading
• Diversity not used above 200 Mbps

13
Fundamental Design Approach Differences

• Signal bandwidth leads to different operating
  regimes
• DS-UWB uses 1.326 GHz bandwidth
• MB-OFDM data BW is 412.5 MHz (100 tones x 4.125
  MHz/tone)
• Modulation bandwidth induces different fading
  statistics
• DS-UWB (single carrier UWB) results in
  frequency-selective fading with relatively low
  power fluctuation (variance)
• MB-OFDM (multi-carrier) creates a bank of
  parallel channels that experience flat fading
  with a Rayleigh distribution (deep fades)
• Motivations for different choices
• Different energy capture mechanism (rake vs. FFT)
• Different ISI compensation (time vs. frequency
  domain EQ)
• These fundamental differences affect both
  complexity flexibility
• Significant impact on implementation, especially
  at high rates

14
Analog Complexity
MB-OFDM Analog Components DS-UWB Analog Components
Similar characteristics Antenna Pre-select filter LNA Antenna Pre-select filter LNA
Different characteristics Switchable UNII filter Hopping Frequency Gen Band filter to reject adjacent channels Static UNII filter Static Frequency Gen Band filter with no adjacent channels

• Equivalent analog components have similar
  complexity

15
Implications of Switchable UNII Filter(slide
copied from Doc 03/141r3,p12)

• MB-OFDM is proposed to use the UNII band for Band
  Group 2
• If the operating BW includes the U-NII band, then
  interference mitigation strategies have to be
  included in the receiver design to prevent analog
  front-end saturation.
• Example Switchable filter architecture.
• When no U-NII interference is present, use
  standard pre-select filter.
• When U-NII interference is present, pass the
  receive signal through a different filter (notch
  filter) that suppresses the entire U-NII band.

• Problems with this approach
• Extra switches ? more insertion loss in RX/TX
  chain.
• More external components ? higher BOM cost.
• More testing time.

16
Band-Select Filter Complexity
DS-UWB Filter
Bandwidth of DS-UWB gt 1500 MHz
Uses single fixed bandwidth filter provides
rejection for OOB noise RFI

• MB-OFDM filter complexity
• depends on requirements to reject
• adjacent-band signal energy
• Depends on whether design
• is using the guard tones for
• real data or just PN modulated
• noise

Data tones Guard tones
17
MB-OFDM Band-Select Filter Complexity

• If guard tones are used for useful data, band
  filter must have very steep cut-off
• Transition region is very narrow
• Only 5 un-modulated tones between bands (21 MHz)
  
• SOP performance also affected by filter design
  rejection of adjacent band MAI for SOP
• If guard tones not used for data, then filter
  constraint is relaxed
• Transition region is a wider (15 tones 62 MHz)
• Energy in guard band is distorted (not useful)
• May not meet FCC UWB requirement for 500 MHz

Tight filter constraint
Filter must reject MAI for SOP
Relaxed filter constraint
Data tones Guard tones Filter response
18
Comparison of DS-UWB to MB-OFDM Digital Baseband
Complexity for PHY

• Gate count estimates are based on MB-OFDM
  proposal team methodology detailed in IEEE
  Document 03/449r2
• Gate counts converted to common clock (85.5 MHz)
  for comparison
• Explicit MB-OFDM gates counts have only been
  reported by proposers for a 110/200 Mbps
  implementation
• Other estimates of MB-OFDM Viterbi decoder and
  FFT engine are provided in IEEE Document 03/343r0
• Estimates for MB-OFDM 480 Mbps mode complexity
  are based on scaling of FFT engine, equalizer and
  Viterbi decoder
• MB-OFDM estimates of 480 Mbps power available in
  03/268r3
• Details available in IEEE Document 04/164r0
• Estimates for MB-OFDM 960 Mbps mode details are
  based on linear scaling of decoder and FFT engine
  to 960 Mbps
• Assumes 6-bit ADC for 16-QAM operation
• DS-UWB gate estimates are detailed in IEEE
  Document 03/099r4
• Methodology for estimating complexity of
  16-finger rake, equalizer and synchronization
  blocks are per MB-OFDM methodology

19
DS-UWB MB-OFDM Digital Baseband Complexity
Component MB-OFDM(Doc 03/268r3 or 03/343r1)110 Mbps DS-UWB16-Finger Rake 220 Mbps Raw 3-Bit ADC DS-UWB32-Finger Rake 220 Mbps Raw 3-Bit ADC
Matched filter Rake DS or FFT OFDM 100K 26K 45K
Viterbi decoder 108K 54K 54K
Synchronization 247K (Freq Domain) 30K 30K
Channel estimation 247K (Freq Domain) 24K 24K
Other Miscellaneous including RAM 247K (Freq Domain) 30K 30K
Equalizer 247K (Freq Domain) 20K 20K
Total gates _at_ 85.5 MHz 455K 184K 203K

• Gate counts are normalized to 85.5 MHz Clock
  speeds to allow comparison
• Based on methodology presented by MB-OFDM
  proposal team (03/449r3)
• Other details of gate count computations in
  Documents 04/099 and 04/256r0

20
Digital Baseband Complexity Comparison at 1 Gbps
Component MB-OFDM 960 Mbps using 16-QAM DS-UWB 2-Finger Rake 1.326 Gbps 3-bit ADC width DS-UWB 5-Finger Rake 1.326 Gbps 3-bit ADC width
Matched filter rake or FFT 225K 26K 45K
Viterbi decoder 432K 0K 0K
Synchronization 297K (Freq Domain) 30K 30K
Channel estimation 297K (Freq Domain) 24K 24K
Other Miscellaneous including RAM 297K (Freq Domain) 30K 30K
Equalizer 297K (Freq Domain) 50K 50K
Total gates _at_ 85.5 MHz 954K 160K 179K

• Assumptions MB-OFDM using 6-bit ADC, FFT is
  2.25x Viterbi is 4x of low rate. DS-UWB
  operating with no FEC at 1.362 Gbps

21
Optional Improvement for Interference Mitigation
(Approach 1)Analog type of SSA- Notch generation
by using a simple analog delay line

• Example Just Two taps delay line

The output signal x(t) is given by
where p(t) is a pulse signal , and d is delayed
time by a delay line D.
By assuming that coefficients w0 and w1 is time-
invariant, then its signal in frequency domain
is given by

Now, we set w01 and w1a (a is in real value),
we obtain
A notch is generated at a frequency fn where
X(fn)20, then
The solutions are given by
,
however, the coefficient a can take only real
value. Therefore,
(m1,2,3,)
As you can see, the coefficient a takes 1 or -1.
It leads simple implementation.
The right figure is an example a is set to 1 and
d is set at 0.116nsec.
22
Optional Improvement for Interference Mitigation
(Approach 2) Analog type of SSA- Notch
generation by using a spreading code

• DS-UWB systems

Tx model 2
Tx model 1
x(t)
b(t)
x(t)
b(t)
X
X
X
X
X
X
X
fc
c(t)
fc
c(t)
p(t)
p(t)
cl(t)
long code
Spreading code
Carrier frequency
Pulse signal
Spreading code
Carrier frequency
Pulse signal
(Scrambler)
Assumption Chip rate of a long code is the same
as bit rate.
c(t)-1 -1 -1 1 1 -1 1 1
cl(t), c(t)-1 -1 -1 1 1 -1 1 1
Example
Example

• Narrow and Repetitive

• Narrow and Repetitive

4.3GHz (EES)
4.3GHz (EES)
Note These notches are diminished by a bi-phase
modulation.
23
Optimization of coding rate and spreading factor

• Original VS-DS-UWB

(Have you already optimized the combinations ?)
Data rate FEC Rate Code Length Range (AWGN)
110Mbps 1/2 6 18.3m
220Mbps 1/2 3 12.9m
gt
gt

• The other combinations

Data rate FEC Rate Code Length Range (AWGN)
110Mbps 1/4 3 13.9m
110Mbps 1/3 4 16.1m
110Mbps 3/4 9 16.9m
220Mbps 1/3 2 11.4m
220Mbps 2/3 4 12.9m
FEC Rate1/2 53,75
FEC Rate1/3 47,53,75
Constraint length is fixed to 6
FEC Rate1/4 53,67,71,75
24
Received Power as a Function Of Node Separation

• Real World DS-UWB Measurements Demonstrate Unique
  Benefits of UWB
• Not on a 1/R4 curve -- Small dips, no deep fades
• Very robust in highly cluttered environments
• Lower power and minimized potential for
  interference

0
Measured DS-UWB
-3
-6
-9
-12
dB
-15
-18
-21
-24
-27
-30
feet
4
6
8
10
12
14
16
18
20
22
24
26
25
UWB Fading Distributions Are Key
Large proportion of deep fades cause bit errors
0.1
4 MHz MB-OFDM carrier BW fading
0.08
0.06
PDF - 4 MHz Fading
0.04
0.02
0
1.368 GHz BW DS-UWB Fading
0.4
PDF - 1.368 GHz Fading
NO deep fades!
0.2
DS-UWB Has NO Raleigh Fading
0
Received Energy (dB)
26
Many MB-OFDM Tones Suffer Heavy Fading
True coherent UWB like DS-UWB yields significant
fading statistics advantage
100

• MB-OFDM tones suffer heavy fading
• MB-OFDM does not coherently process the bandwidth
• FEC across tones is used

25 of Narrow Band Channels are Faded by 6 dB or
more
25
MB-OFDM
P (Received Energy lt x)
DS-UWB
10-1
4 MHz BW
75 MHz BW
1.4 GHz BW
Theoretical Rayleigh
10-2
-20
-15
-10
-5
0
5
X (dB)
27
MB-OFDM Performance Loss Due to Fading

• MB-OFDM performance worsens as data rate
  increases
• DS-UWB maintains performance within 1 dB of
  optimal with low complexity RAKE

110 MbpsRate 11/32 FECwith 2x Diversity MB-OFDM
1.3 dB Loss
200 MbpsRate 5/8 FECwith 2x Diversity MB-OFDM
3.5 dB Loss
480 MbpsRate 3/4 FECwith No Diversity MB-OFDM 6
dB Loss
-3
10
4 MHz BW CM-3
Simple Diversity Sum OFDM
-4
10
MRC OFDM
MRC OFDM
BER
AWGN
AWGN
6 dB
-5
10
AWGN
1.3 dB with MRC
3.5 dB
-6
10
2
2.5
3
3.5
4
4.5
3
4
5
6
7
8
9
10
5
6
7
8
9
10
11
12
13
14
SNR (dB)
SNR (dB)
SNR (dB)
28
DS-UWB Takes Full Advantage of UWB
PropagationDS-UWB Performance Excels As Speed
Goes Up
Performance Difference is Natural Consequence of
Channel Physics
DS-UWB
Performance
0
dB
-1
11/32 FEC2x Diversity
The Faster the Radio,The More DS is Better
-2
5/8 FEC2x Diversity
-3
DS-UWB Naturally Fits Needs of Multi-Media
Handheld Devices
3/4 FECNo Diversity
-4
MB-OFDM
-5
-6
100
150
200
250
300
350
400
450
500
Mbps
Speed
29
DS-UWB Uses RAKE Receiver with EqualizerFor
Optimum Energy Capture and BER

• Use of RAKE is flexible in receiver, not
  transmitter
• Short range (CM-1) does not need RAKE -- only 4
  dB loss from ideal
• No-Rake DS is less power outperforms MB-OFDM
  (by 2 dB at 480 Mbps)
• Media Server can use 16-finger RAKE and capture
  all but 1 dB of available energy in CM-3 Very
  high performance

Captured Energy (dB)
30
DS-UWB Complexity Takes Advantage Of
PropagationDS-UWB Power Excels More More As
Data Rate Goes Up

• As UWB Gets Faster
• DS Gets Simpler
• MB-OFDM Requires Higher Emissions, More
  Complexity

High Cost Complexity
MB-OFDM
DS-UWB
Simpler Lower Cost
Speed
As Range Speed DS (Gets Simpler) MB-OFDM (Gets More Complex)
Signal gets Big Adapts Uses less processing Gain Shorter codes 3 2 1 bits ADC as speed goes up Less bits in processing Frozen Reqs more processing gain to get to high data rate regardless of SNR Higher order QAM More bits in ADC/DAC, FFT/IFFT
Rayleigh Fading AdaptsTurn FEC Off, (or leave it out)or Use Small (k4) FEC Frozen Serious FEC Required Speed of K7 FEC at high rates killer power space _at_ 1Gbps
Delay Spread goes Down AdaptsDFE covers less time FrozenBand Plan Fixed
31
Multipath Performance for 110 Mbps
110 Mbps 90 Outage Range (meters) Mean of Top 90 Range (meters)
CM1 13.5 16.9
CM2 11.7 14.6
CM3 11.4 13.4
CM4 10.8 13.0
Simulation Includes 16 finger rake with
coefficients quantized to 3-bits 3-bit A/D (I
and Q channels) RRC pulse shaping DFE trained
in lt 5us in noisy channel Front-end filter for
Tx/Rx 6.6 dB Noise Figure Packet loss due to
acquisition failure
32
Multipath Performance for 220 Mbps
220 Mbps 90 Outage Range (m) 8-finger rake 90 Outage Range (m) 16-finger rake Mean of Top 90 Range (m) 8-finger rake Mean of Top 90 Range (m) 16-finger rake
CM1 8.4 - 10.2 -
CM2 5.8 7.2 8.2 8.8
CM3 4.9 7.0 6.2 8.4
Simulation Includes 8 finger (16 finger) rake
with coefficients quantized to 3-bits 3-bit A/D
(I and Q channels) RRC pulse shaping DFE
trained in lt 5us in noisy channel Front-end
filter for Tx/Rx 6.6 dB Noise Figure Packet
loss due to acquisition failure
33
Multipath Performance for 500 Mbps
500 Mbps 90 Outage Range (m) Mean of Top 90 Range (m)
CM1 3.0 4.8
CM2 1.9 3.2
Simulation Includes 16 finger rake with
coefficients quantized to 3-bits 3-bit A/D (I
and Q channels) RRC pulse shaping DFE trained
in lt 5us in noisy channel Front-end filter for
Tx/Rx 6.6 dB Noise Figure Packet loss due to
acquisition failure
34
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

35
Multipath SOP Distance Ratios
Test Transmitter Channels 1-5 Single Interferer
Channels 6-10 Second Interferer Channel 99 Third
Interferer Channel 100
110Mbps 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)

36
Conclusions

• Our vision A single PHY with multiple modes to
  provide a complete solution for TG3a
• Base mode that is required in all devices, used
  for control signaling CSM for beacons and
  control signaling
• Higher rate modes also required to support 110
  200 Mbps
• Compliant device can implement either DS-UWB or
  MB-OFDM (or both)
• Increases options for innovation and regulatory
  flexibility to better address all applications
  and markets
• DS-UWB is shown to have equal or better
  performance to MB-OFDM in all modes and multipath
  conditions for a fraction of the complexity
  power

37

• Back-up slides

38
Notch generation by using a spreading code

• DS-UWB systems

Frequency domain
Tx model
x(t)
b(t)
X
X
X
fc
c(t)
p(t)
Output spectrum is given by convolution
Carrier
Spreading code
Pulse signal
Spectrum of a spreading code
Example
Spectrum of a pulse signal
Convolution
39
Notch generation by using a spreading code

• Experimental result by UWB Test bed

MATLAB results
UWB testbed outputs
40
All-Digital Architecture DS-UWB Receiver
1-16 Rake Fingers (or more)
Variable Rate FEC (or no FEC)
Variable Equalizer Span
1 to 3 bits ADC Resolution
Pre-Select
GA/ VGA
ADC at Chip Rate
Filter
LPF
De-interleave FEC Decode
LNA
DFE
Rake
ADC at Chip Rate
GA/ VGA
LPF
Cos
Agile Clock
Synch/ Track Logic
Sin

• DS-UWB Digital architecture provides scalable
  receiver complexity
• ADC can range from 3 bits to 1 bit for super-low
  power implementation
• Rake DFE can be optimized to trade off power
  cost in multipath
• FEC can scale data rate or be turned-off for low
  power operation
• DFE effectiveness and simplicity proven in
  shipping chips

41
Scalability to Varying Multipath Conditions

• Critical for handheld (battery operated) devices
• Support operation in severe channel conditions,
  but also
• Ability to use less processing ( battery power)
  in less severe environments
• Multipath conditions determine the processing
  required for acceptable performance
• Collection of time-dispersed signal energy (using
  either FFT or rake processing)
• Forward error correction decoding Signal
  equalization
• Poor receiver always operates using worst-case
  assumptions for multipath
• Performs far more processing than necessary when
  conditions are less severe
• Likely unable to provide low-power operation at
  high data rates (500-1000 Mbps)
• DS-UWB device
• Energy capture (rake) and equalization are
  performed at symbol rate
• Processing in receiver can be scaled to match
  existing multipath conditions
• MB-OFDM device
• Always requires full FFT computation regardless
  of multipath conditions
• Channel fading has Rayleigh distribution even
  in very short channels
• CP length is chosen at design time, fixed at 60
  ns, regardless of actual multipath

42
Interference Issues (1)

• Hopped versus non-hopped signal characteristics
• ITS and FCC studies are underway
• Goal is to see if interference characteristics of
  MB-OFDM are acceptable for certification (using
  DS-UWB/noise/IR for comparison)
• Use of PN-modulation to meet 500 MHz BW
• Recent statements by NTIA emphasize importance of
  minimum
• Desire is to ensure protection for restricted
  bands
• DS-UWB bandwidth is determined by pulse shape and
  pulse modulation
• Spectrum exceeds 1500 MHz
• MB-OFDM bandwidth for data and pilot tones is 466
  MHz, guard tones are used to increase bandwidth
  to 507 MHz
• Guard tones carry no useful information, only
  to meet BW reqt.
• See authors statements in 802.15-03/267r1 (July
  2003, page 12)

43
NTIA Comments on Using Noise to meet FCC 500 MHz
BW Requirement

• NTIA comments specifically on the possibility
  that manufacturer would intentionally add noise
  to a signal in order to meet the minimum FCC UBW
  500 MHz bandwidth requirements
• Furthermore, the intentional addition of
  unnecessary noise to a signal would violate the
  Commissions long-standing rules that devices be
  constructed in accordance with good engineering
  design and manufacturing practice.
• And
• It is NTIAs opinion that a device where noise
  is intentionally injected into the signal should
  never be certified by the Commission.
• Source NTIA Comments (UWB FNPRM) filed January
  16, 2004
• available at http//www.ntia.doc.gov/reports.html
  

44
FCC Rules Regarding Unnecessary Emissions

• FCC Rules in 47 CFR Part 15 to which NTIA refers
• 15.15 General technical requirements.
• (a) An intentional or unintentional radiator
  shall be constructed in accordance with good
  engineering design and manufacturing practice.
  Emanations from the device shall be suppressed as
  much as practicable, but in no case shall the
  emanations exceed the levels specified in these
  rules.