Doc.: IEEE 15-05-0344-01-004a TG4a June 30th, 2005 Gian Mario Maggio & Philippe Rouzet (STM)Slide 1 Project: IEEE P802.15 Working Group for Wireless Personal

June 30th, 2005

Gian Mario Maggio & Philippe Rouzet (STM)Slide 1

doc.: IEEE 15-05-0344-01-004a

TG4a

Project: IEEE P802.15 Working Group for Wireless Personal Area Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Networks (WPANs)

Submission Title: TG4a Review of Proposed UWB-PHY Modulation Schemes and Selection Criteria

Date Submitted: June 30th, 2005Source: Gian Mario Maggio & Philippe Rouzet (STMicroelectronics)Contact: Gian Mario MaggioVoice: +41-22-929-6917, E-Mail: [email protected]: Review of modulations/waveforms for TG4a UWB-PHY standard and

proposed selection criteriaPurpose: To provide information for further investigation on and selection of the

modulation/waveforms for the UWB-PHYNotice: 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.

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IEEE 802.15.4a:UWB-PHY Modulation

UWB-PHY Modulation SubgroupGian Mario Maggio & Philippe Rouzet

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List of Contributors/Documents

• Gian Mario Maggio & Philippe Rouzet - STMicroelectronics (#15-05-0217-00-004a, #15-05-0243-00-004a, #15-05-0325-00-004a)• Laurent Ouvry et al. – CEA-LETI (#15-05-0354-01-004a)• Michael Mc Laughlin – Decawawe (#15-05-0359-00-004a)• Matt Welborn – Freescale (#15-05-0240-02-004a)• Francois Chin et al. – I2R (#15-05-0231-03-004a)• Huang-Ban Li et al. – NICT (#15-05-0300-00-004a)• Ismail Lakkis & Saeid Safavi – Wideband Access (#15-05-0250-03-004a, #15-05-0355-00-004a) • Phil Orlik, Andy Molisch et al. - MERL (#15-05-0291-00-004a)

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Topics for Discussion

1. Pulse shaping2. Modulation formats3. Waveform design4. Design parameters5. Adaptive modulation & coding6. Selection Criteria

7. Receiver Architecture8. Simulation Results

ACTION LIST UWB-PHY GROUP

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UWB-PHY: Introduction

• Impulse-radio based (pulse-shape independent)

• Support for different RX architectures: – Coherent– Differentially-coherent– Non-coherent

• Support for multiple rates• Support for SOP

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Parameter Definition

Chip The minimum time resolution of a UWB signal, whose rate is considered as the minimum sampling rate of the signal (complying with the Nyquist sampling theorem), i.e. closest allowable distance between successive pulses

Pulse A radiated short transient UWB signal whose time duration is associated with the reciprocal of its UWB -10 dB BW , i.e. the shortest waveform

Effective PulseWidth

An interval which is defined by the effective portion of the pulse energy with a time duration which is the reciprocal of the -10 dB BW of the UWB signal

Burst Group of Pulses

Symbol Group of Bursts

Channel Separation

The difference between the center frequencies of each channel (its relation to chip rate is not yet defined)

PRF The frequency of repetition of Pulses if there is one pulse per Burst. If there is more than one Pulse per Burst the PRF is defined as the frequency of repetition of Bursts (group of pulses)

PRI Reciprocal of PRF

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Illustration of Pulse and Chip Definitions

One Pulse

One Chip

PULSE: shortest waveform

CHIP: closest allowable distance between successive pulses

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Symbol (1 or more bursts)

EffectivePulse

Duration

-3 dB

-10 dB

-20 dB

-30 dB

-40 dB

-50 dB

-60 dB

-70 dB

3 dB BW

10 dB BW

Pulse Repetition Interval (PRI, assuming one burst per symbol)

Inverse Relation PRF

Burst(1 or more pulses)

Pulse

Inverse Relation

ChipDuration

Symbol Duration

Burst DurationPulse Duration

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Pulse Shaping Pulse shape:

a) Gaussianb) Raised cosinec) Chaotic d) Chirp….• Optional: Variable pulse shapes with SSA (Soft

Spectrum Adaptation)Pulse duration: Lower bound set by bandwidth

occupation (e.g. 500 MHz); Upper bound may be set according to design considerations

Pulse amplitude: Peak-to-peak voltage limited by CMOS technology

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Definitions

• Coherent RX: The phase of the received carrier waveform is known, and utilized for demodulation

• Differentially-coherent RX: The carrier phase of the previous signaling interval is used as phase reference for demodulation

• Non-coherent RX: The phase information (e.g. pulse polarity) is unknown at the receiver - operates as an energy collector- or as an amplitude detector

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Pros/Cons of RX Architectures

Coherent+ : Sensitivity+ : Use of polarity to carry data+ : Optimal processing gain achievable- : Complexity of channel estimation and RAKE receiver

Differentially-Coherent (or using Transmitted Reference)+ : Gives a reference for faster channel estimation (coherent

approach)+ : No channel estimation (non-coherent approach)- : Asymptotic loss of 3dB for transmitted reference (not for DPSK)

Non-coherent+ : Low complexity+ : Acquisition speed- : Sensitivity, robustness to SOP and interferers

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Modulation Format(s)

• Simple, scalable modulation format• One mandatory mode plus one or more

optional modulation modes• Modulation compatible with multiple

coherent/non-coherent receiver schemes Flexibility for system designer

• Time hopping (TH) for spectral smoothing and to permit multiple access

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Time Hopping-IR: Basics

Ts

Tc

Tf

+1

-1

• Each symbol represented by sequence of very short pulses• Each user uses different PN sequences (for multiple access)• Spectrum mostly determined by pulse shape

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Waveform Design

• Combination of (outer) TH and BPPM, combined with BPSK/DBPSK

• Guarantee coexistence of coherent and non-coherent RX architectures:– Non-coherent receivers just look for energy in the early or

late slots to decode the bit (BPPM); OOK receiver may be used to demodulate BPPM symbol as well

– Coherent and differentially-coherent receivers, in addition, understand the fine symbol structure (BPSK or DBPSK)

• Principle: Non-coherent and differentially-coherent modes should not penalize coherent-RX performance

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RX Coexistence

Rake Receiver

Finger Np

Rake ReceiverFinger 2


Summer

Td

0

Coherent RX

Differentially-Coherent RX

TX

( )2

Non-Coherent RX

Pulse Gen.

TH SeqBPSK symbol mapper

BPSK symbol mapper

Delay

Central Timing Control

Multipl

exer

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Mitigation of Peak-Voltage through Multi-Pulses

Tf=PPI

Tf=PPI

IS « EQUIVALENT » TO

ppV = peak-to-peak voltage

ppV/2M = 4

M = 1

Tf=PPI

ppV/sqrt(2)

M = 2

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BPPM Symbol Structure

1. Doublet-based symbolRealization 1a: TH-IR + TR(the whole TR symbol is BPPM modulated)

Realization 2a: TR + Inner TH (apply TH code to each frame)

Realization 3a: Diff. encoding + Inner TH (doublets with memory from previous bit)

2. Burst-based symbolRealization 2a: Generalized TR(one reference pulse, multiple information pulses)

Realization 2b: “CDMA-like” burst(burst of pulses, modulated by a spreading code)

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(1) Transmitted-Reference: Basics

• First pulse serves as template for estimating channel distortions• Second pulse carries information• Drawback: Waste of 3dB energy on reference pulses

Tddata

Ts

TcTf

+1

-1

reference

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(1a) Example - Signal Waveforms

Ts

« 11 »

« 01 »2-PPM + TR baseM = 2(with two bits/symbol) « 10 »

« 00 »

(coherent decoding possible) 2-PPM + 16 chips 2-ary TH code

• Time hopping code is (2,2) code of length 8/16, can be exploited by non-coherent RX• Effectively, 28 or 216 codes to select for channelization for non-coherent scheme

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(1a) Detailed Symbol Structure

Ts

« 0 »

Td

negative

positive

Same polarity : bit = 0

ThInner time hop of Tdelta = 2 Th

Outer time hop of Tc = Tf/2 = n*Th


Tc

Tf

Tdelay

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(1b) Example - Signal Waveforms

Ts

« 11 »

« 01 »2-PPM + TR baseM = 2

One bit/symbol « 10 »

« 00 »

(coherent decoding possible) 2-PPM + 16 chips 2-ary TH codeor 2-PPM + 8 chips 4-ary TH code

• Time hopping code is (2,2) code of length 8/16, can be exploited by non-coherent RX• Effectively, 28 or 216 codes to select for channelization for non-coherent scheme

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(1b) Detailed Symbol StructureTs

« 0 »

Tx

Td negative

positive


ThInner time hop of Tdelta = 2 Th+ inner polarity hop

Outer time hop of Tc = Tf/2 = n*Th


Tc

Tf

Tx Tdelay

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(1c) Differential Encoding: Basics

Ts

+1 -1 +1 -1 +1 -1

-1 -1 +1 +1 -1 -1

0 0 1 1 0 0 1

b0 b4b3b2b1 b5b-1

Tx Bits

Reference Polarity

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(1c) Example - Signal Waveformsbi-1 = 1, bi = 1

bi-1 = 0, bi = 1

bi-1 = 0, bi = 0

bi-1 = 1, bi = 0

• Use of doublets with memory from previous bit (encoding of reference pulse with previous bit)

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(2a) Generalized TR

TH PatternTH Code 1,1 1,1 0,1 0,0 1,0 0,1Data 1,1 1,1 1,1 1,1 1,1 0,0

Pulse Shift, polarity invert

τΔ + τdelay

Enhanced Mode

D« 1 1 »

« 1 0 »

D D τdelay +τΔ

τΔ τdelay τΔ + τdelayτdelayτΔτΔ + τdelay τΔ + τdelay

Basic Mode (as seen by non-coherent)

« 1 »τdelay +τΔD D D

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(2b) “CDMA-Like” BurstSimilar signal using 31-pulse sequence

Can use coherent or non-coherent receiver Can use PPM/OOK by sending pulse burst in

Either first or second bit location

One BPPM symbol

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(2b) Example 1: 31-Chip Code

Symbol Cyclic shift to right by n chips, n=

31-Chip value

00 0 + - - 0 0 0 + - 0 + + + 0 + 0 - 0 0 0 0 + 0 0 - 0 - + 0 0 - -

01 8 - 0 - + 0 0 - - + - - 0 0 0 + - 0 + + + 0 + 0 - 0 0 0 0 + 0 0

11 16 - 0 0 0 0 + 0 0 - 0 - + 0 0 - - + - - 0 0 0 + - 0 + + + 0 + 0

10 24 - 0 + + + 0 + 0 - 0 0 0 0 + 0 0 - 0 - + 0 0 - - + - - 0 0 0 +

• Can support both coherent and non-coherent pulse compression

• Add 33 zero chips to get baseline mode for non-coherent receivers

Note: In general, careful code design is needed for spectral shaping

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(2b) Example 2: Spreading via Scrambling

• Scrambling = time varying spreading• Use a single (set) scrambler of length (ex: 32768) and assign a

different offset (of 16 or 32) to different nodes• For ternary modulation invert sequence when transmitting a 0• Number of users supported is 1024• Perfect co-channel interference rejection• Support virtually any data rate from 16MHz to 32 Kbps for a PRF of

16MHz• Spectrum is virtually flat (no back-off)

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(2b) Example 2: Ternary Modulator

Scramblerspreader

PRF rate (ex: 16MHz)

Data @ Data-Rate (ex: 2Mbps) On-off pulses @

PRF rate (2Mbps) On-off to Ternary1 : +/-0: 0

Ternary pulses @ PRF rate (2Mbps)

0 1 1 0 1 0 0 1 1 0 0 0 1 1 0 1

1 0

0 1 1 0 1 0 0 1 0 1 1 1 0 0 1 0

Data bits

Scrambler output

On-off pulses

0 + - 0 - 0 0 + 0 + + - 0 0 - 0Ternary pulses

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(2b) Example 2: Ternary Receiver

BPF LNA ( )2 1 bitADC

On-off toBPSK

Scramblerdespreader

BPSKcorrelator

On-off toBPSK

+ - - - + + - +

8 -8

0 1 1 0 1 0 0 1 0 1 1 1 0 0 1 0

Correlator output

BPSK Scrambler output

Received on-off pulses

- + + - + - - + - + + + - - + -On-off to BPSK

- + + - + - - +

1b ADC : requires threshold training during preamble3b ADC : does not requires thresholding (soft correlator)

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(2b) Example 2: BPSK Modulator/Receiver

• ADC from 1 bit to multiple bits• BPSK correlator• Time varying spreading improves interference rejection

tremendeously

BPF LNALow Rate

Limiter

Scramblerdespreader

BPSKcorrelator

On-off toBPSK

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Design Parameters (1/3) • Pulse Repetition Period (PRP)

– Realization #1:1a) PRP = 100 ns1b) PRP = 40 ns1c) PRP = 40 ns

• Burst Repetition Period (BRP)– Realization #2:

2a) BRP ≥ 200 ns2b) BRP = 436 ns

• Inter-pulse interval:– Minimum: ~5 ns (technology constraint)– Realization #1: ~20 ns– Realization #2(b): ~4.5 ns

Note (TR): Max realizable analog delay ~10 ns

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Design Parameters (2/3)

• Time-hopping:– TH code (outer): 2-ary (or M-ary in general, for

better SOP support) of length 4-16; granularity level ~Tf/2 (or Tf/M)

– Inner TH code (Realization #1b,c): Apply inner TH code (frame-by-frame) down to 2 ns (or multiples) granularity level

• Polarity hopping: May be applied on top, for spectral smoothing

purposes and/or signals separation

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Design Parameters (3/3)

• Channelization– Coherent schemes: Use of TH codes and polarity

codes– Non-coherent schemes: Use of TH codes (polarity

codes for spectrum smoothing only)Realization 2b): CDMA

• Multi-access capabilities:– Max # of coexisting users within piconet

• SOP support:– Up to 6 SOP/band

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Adaptive Modulation & Coding

1. Adaptive modulation: Enhanced modes (available for coherent receiver)

2. Adaptive PRP: Two PRP values supported

3. Adaptive processing gain: Variable TH code length (variable number of pulses/bit)

4. Adaptive coding rate (e.g. by acting on the puncturing associated with a convolutional code)

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Optional: Encoding of “Extra”-Bits

• Example: Rate-½ convolutional encoder– Produce multiple coded bits from each data bit

• Special case of convolutional code is a “systematic” code– First coded bit is same as input data bit– Second coded bit is computed by encoder

• Mapping coded bits to waveform– Map first coded bit (systematic bit) into position for BPPM– Map second coded bit into TR symbol

• Can be extended to more general (non-systematic) codes very easily

x2

x1=bkbk

ConvolutionalEncoder

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(3) CS-UWB

Time

Am

plitu

de

Am

plitu

de

Frequency

Time

Fre

quen

cy

Pulse signal

• Chirp Signaling-UWB can be generated by passing a pulse signal through a distributed delay line (DDL) such as a SAW DDL:

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(3) Correlated Processing• Correlated processing produces not only high

precision ranging but also robustness against noise and multipath

Cor

rela

tor

outp

ut

Correlated processing

Time shift[s]

The wide the bandwidth, the sharp the peak.

B: 3-dB bandwidth of chirpT: time interval of chirp

T

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(3) Advantages of Chirp Signaling

• High capacity for SOP – Plenty of source with chirp– Combination with FDM and/or CDM

• Additional link margins – Low peak-to-average ratio

• Robustness against interference and multipath– Excellent correlation characteristics

• Potential high precision ranging. – Excellent correlation characteristics

• An selectivity for FFD and RFD – Chirp vs. non-chirp

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Proposed Selection Criteria (in decreasing priority order)

1. PER (packet error rate) performance @1Mb/s with 15.4a channel models, CMOS-compatible peak-to-peak voltage, rate ½ convolutional code (constraint length up to 5; more needs justification):

1.a) Coherent receiver 1.b) Diff. coherent receiver 1.c) Non-coherent receiver

2. SOP isolation (at least 2 SOP/band; up to 6 SOP)3. Spectrum: SPAR (spectral peak-to-average ratio)

4. Receiver flexibility: Support for coherent, diff. coherent and non-coherent RX

5. Scalability: Trade-off performance vs. complexity

6. Resilience to NBI (narrow-band interference)

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ANNEX(Extra-Slides: Support for Discussion)

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Coherent Receiver: RAKE Receiver

Rake ReceiverFinger Np

Demultiplexer Rake ReceiverFinger 2


Summer

Channel Estimation

Convolutional Decoder Data

Sink

Sequence Detector

• Addition of Sequence Detector – Proposed modulation may be viewed as having memory of length 2• Main component of Rake finger: pulse generator• A/D converter: 3-bit, operating at symbol rate• No adjustable delay elements required

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Differentially-Coherent Receiver(for Transmitted Reference)

Td

0

MatchedFilter

Convolutional Decoder

• Note: Addition of Matched Filter prior to Delay & Correlation operations improves output SNR and reduces noise-noise cross terms

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Non-Coherent Receiver (Energy Collector)

Band MatchedBand Matched

LNALNALNALNA BPFBPF

TrackingTrackingThresholThreshol

ds ds settingsetting

TrackingTrackingThresholThreshol

ds ds settingsetting

DumpDumpLatchLatchDumpDumpLatchLatch

RA

ZR

AZ

DUMPDUMP

ControlledControlledIntegratorIntegrator

ADCADC

BPPM Demodulation BPPM Demodulation branchbranch

RAZRAZ

x2 x2r(t)

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LNALNALNALNA BPFBPF

De-Spreading TH Codes

r(t) TH Sequence Matched

Filter

Bit Demodulation Bit Demodulation


LNALNALNALNA BPFBPFr(t) TH

Sequence Matched Filter

Bit Demodulation Bit Demodulation

Case I - Coherent TH de-spreading

ADCADC

ADCADCb(t)

soft info

Case II – Non-coherent / differential TH despreading

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• Idea: Transmitted-reference BPSK symbol can be decoded by a non-coherent detector (like OOK symbol)

• Advantages: Differential and non-coherent receiver may coexist• Concept can be generalized to N-ary TR-BPSK

TR-BPSK Non-Coherent Detection

Pulse MatchedPulse Matchedf(t) s(t)

r(t)“0”

“1”“1”

“0”

LNALNALNALNA

DelayDelayDD

DelayDelayDD

BPFBPF

D

Non-Coherent DetectorNon-Coherent Detector(Energy Collection)(Energy Collection)

-SynchroSynchroTrackingTracking

ThresholdThresholds settings setting

SynchroSynchroTrackingTracking

ThresholdThresholds settings setting

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TR-BPPM Schemes Comparison (1/2)

Notes:• Results are theoretical calculations• Assumes ideal ”impulse” UWB pulses in

AWGN channel• Different TR-BBPM options are considered

with different number of pulses per pulse train• Multipath fading simulations can be performed

to back up theory

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TR-BPPM Schemes Comparison (2/2)

• Parameters:– PPI slot - slot inside each TH chip containing a

burst of pulses including reference pulses

– Np represents the number of pulses in each PPI slot

– The energy E per PPI slot is kept constant

– The pulse energy Ep = E/Np

– TW represent the time-bandwidth product

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Pulse Repetition Structures- Scheme 1TR-BPPM with doublets

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Pulse Repetition Structures - Scheme 2TR-BPPM single reference

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Pulse Repetition Structures - Scheme 3Auto Correlation BPPM with doublets

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Pulse Repetition Structures - Scheme 4Auto Correlation BPPM single reference

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Pulse Repetition Structures - Scheme 5Auto Correlation BPPM alternate

• Scheme 5: “AC Alternate” performs better then all the other pulse repetition structures• AC generally performs better than TR• “AC alternate” and “AC with doublets” require a single delay

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Overall Block Diagram With Optional CS

Coding &modulation Coding &

modulation SpreadingSpreading

Pre-SelectFilter

LNALNA

Transmitter

Receiver

CHIRPCHIRP

De-CHIRP

De-CHIRP

PulseshapingPulse

shaping GAGA

Local oscillator

Local oscillator

BW = 500MHz or 2GHz

Additional circuits to DS-UWB as an option

Ranging data

Comm.data

LPFLPF

LPFLPF

GAGA

GAGA

1 or 2-bit ADC

1 or 2-bit ADC

1 or 2-bitADC

1 or 2-bitADC

Sync.Sync.Local

oscillatorLocal

oscillator

Decision/FEC

decoder

Decision/FEC

decoder

I

QTime base

Peak detection

Ranging data

Calculation

Comm.data

Ranging processing