journées micro-drones 2004. presentation high data rate transmission system for micro uavs lep>...

Journées Micro-Drones 2004. Presentation

High Data Rate Transmission System for Micro UAVs

LEP> SCN

Fabien MULOT: Internship ONERA-SUPAERO

Vincent CALMETTES: Research SUPAERO


Plan of the presentation

LEP> SCN

Context of the study

Video quality VS data rate trade-off

Characterisation of the micro-UAV transmission channel

Fade mitigation techniques

Future studies and developments



Study of a high data rate transmission from a video payload onboard a micro-UAV.

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a. Reflectionb. Shadowingc. Line of Sight

ba

c

Monitoring

Base station


Context of the study Transmission Band

ISM band 2400 - 2483,5 MHz

Regulation

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http://www.anfr.fr("Tableau National de Répartition des Bandes de Fréquences“)


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Objectives of the study Objectives of the study

High data rate source 640x480 pixels grey scale Camera, 8 bits JPEG coded

Image 1Mbits/s target

10-7 BER

Semi urban environment, 1Km max from the emitter to the receiver

0 - 50 Km/h speed

QPSK modulation

Shadowing and multipath resistant transmission



Video quality VS data rate

trade-off

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Video Source

Transmission Scheme

Channel

Reception Scheme

Video monitoring


Video quality VS data rate trade-off

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A

D

2 modes of transmission 14 i/s low quality A 3.3 i/s high quality D

Bit rate: 1.12 Mbits.s-1

302 Ko

42 Ko

10 Ko


Characterisation of the

micro-UAV transmission channel

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JPEG Coding

Transmission Scheme

Channel

?Reception

SchemeVideo

monitoring

1.12 Mbits.s-1


Micro-UAV transmission channel

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Path lossA = (1/d)N N = [3 ….5]

What is shadowing? Particular clutter (buildings dense woods) Scale of 100m 5 to 20dB

What is multipath fading? Reflections, scattering on rough surfaces Constructive and destructive interference Scale of 6.25cm at 2.4Ghz 5 to 40 dB


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B) Tap Delay Line ModelB) Tap Delay Line Model

Y(t)

1 2 n

1(t) 2(t) n(t)

X(t)

A) Statistic Power Delay ProfilesA) Statistic Power Delay Profiles

Statistic model


C) channel ModelC) channel Model


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Channel Characterisation

Use of UMTS standard power delay profiles

Coherence bandwidth Bc: 6KHz<Bc<67KHz depending on the

profiles Frequency selective channel

Channel impulse response: 5µs


25 kHz Coherence Bandwidth Example of a 4 MHz

occupied bandwidth for video transmission

Deep Fades


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Issues: Frequency selective channel Inter Symbol Interferences

Solutions: Channel coding Suited transmission techniques


JPEG Coding

Channel

Coding

Multipath

Shadowing

Frequency Selecticve

Suited Reception

Scheme

JPEG

Decoding

1.12 Mbits.s-1

ModulationChannel Decoding


Fade Mitigation Techniques

Channel coding

LEP> SCN

JPEG Coding

Channel

Coding

Multipath

Shadowing

Frequency Selctive

Suited Reception

Scheme

JPEG

Decoding

1.12 Mbits.s-1



Channel Coding

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Objective: Spreading and correction of the bursts of errorsObjective: Spreading and correction of the bursts of errors

ArchitectureArchitecture

Reed Solomon

(204/188)

External

Interleaver

Convvolutional Code

[177/188]

Internal

InterleaverPuncturing

Target BER: 10Target BER: 10-7-7 => SNR=3.5 dB => SNR=3.5 dB

Pe=Pr.DPe=Pr.D44/(Ge.Gr)/(Ge.Gr)

100M 500M 1Km

0 dB of shadowing 3.9.10-4mw 0.25mw 4mW

-20 dB of shadowing 3.9.10-2mw 25mW 0.4W


Fade Mitigation Techniques

Transmission & Reception Techniques

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JPEG Coding

Channel

Coding

Multipath

Shadowing

Frequency Selective

Suited Reception

Scheme

JPEG

Decoding

1.12 Mbits.s-1


2. Mbits.s-1


QPSK + Equalization

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ArchitectureArchitecture Channel codingChannel coding SSRC Roll Off = 0.4SSRC Roll Off = 0.4 EqualizerEqualizer

BandwidthBandwidth: 1.5 Mhz: 1.5 Mhz

JPEG source coding

Coding+Puncturing

SRRCFiltering

QPSK Mapping

SRRCFiltering

Adaptive filteringDemapping

Decoding+ deinterleaving

JPEG decoding

Training sequence generator

Channel


QPSK + Equalization

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EqualizationEqualization LMS algorithmLMS algorithm

Channel impulse response <= 1symbolChannel impulse response <= 1symbol

MLSE using a Viterbi algorithmMLSE using a Viterbi algorithm Several SymbolsSeveral Symbols MMk k ComplexityComplexity 1024 state trellis1024 state trellis

JPEG Coding

Channel

Coding

Multipath

ShadowingMLSE

1024 states

JPEG

Decoding

1.12 Mbits.s-1

QPSKChannel Decoding

2. Mbits.s-1 0.8 Msymb.s-1

QPSK1.5 Mhz


OFDM

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Advantage: Advantage: Transmission of high data rate Transmission of high data rate

while keeping a non frequency while keeping a non frequency selective channel.selective channel.

Bandwidth efficientBandwidth efficient

ArchitectureArchitecture Channel coding Channel coding mandatorymandatory OFDM Symbol duration =50 µs OFDM Symbol duration =50 µs 10 times the channel impulse 10 times the channel impulse

responseresponse

S1(k)..Sn(k)

S/P00

IFFT

CPSymbolmapping

P/S

2N points padding

Channel

Guard Interval Insertion

Coding

OFDM emitter

Frequency


OFDM

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Taking into accountTaking into account The symbol duration 50µsThe symbol duration 50µs the length of the cyclic prefixthe length of the cyclic prefix The data rate after codingThe data rate after coding The insertion of training symbols The insertion of training symbols

for equalizationfor equalization 64 points FFT64 points FFT Bandwidth: 1.3MhzBandwidth: 1.3Mhz

JPEG Coding

Channel

Coding

Multipath

Shadowing JPEG

Decoding

1.12 Mbits.s-1

QPSK Channel Decoding


QPSK1.3 Mhz

OFDM 64pts IFFT

20 Ksymb

OFDM 64 pts FFT


DSSS + Rake

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Advantages of Direct Sequence Advantages of Direct Sequence Spread Spectrum: Spread Spectrum:

Rake uses time diversity Resistant to noise and

interference

ArchitectureArchitecture OVSF spreading codesOVSF spreading codes

PN scrambling sequencePN scrambling sequence

Rake receiverRake receiver

Power

Frequency

Noise

Spread signal

Power

Frequency

Narrow Band Information signal After Despreading

Spread Noise

IQ Scrambling code

Up sampling

SRRCFiltering

QPSKMapping

IQ Spreading code

Coding


∫dt

∫dt 2

1

∫dt

∫dt

IQ demapper

3

4

Path Search

Descramble Despread

Integrate and Dump

Channel estimation

y(t-1)

y(t-2)

y(t-3)

y(t-4)

y(t)

g*(t-1)

g*(t-2)

g*(t-3)

g*(t-4)

MRC

DSSS + Rake

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Rake Receiver ArchitectureRake Receiver Architecture


DSSS + Rake

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JPEG Coding

Channel

Coding

Multipath

Shadowing JPEG Decoding

1.12 Mbits.s-1

QPSK Channel Decoding


QPSK

72.6 Mhz

DSSS

51.2 Msymb.s-1

Rake



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LEP> SCNLEP> SCN

Evaluation of a system Evaluation of a system based on existing based on existing commercial technologies:commercial technologies:

WI-FI [802.11b] WI-FI [802.11b] DSSSDSSS 1 to 11 Mbps1 to 11 Mbps

WI-FI [802.11g] WI-FI [802.11g] OFDMOFDM 1 to 54 Mbps1 to 54 Mbps

Baseband Processor

Transceiver External PA

ATHEROS

5523

ATHEROS

5112

FPGA

Baseband Processor

Transceiver

ATHEROS

5523

ATHEROS

5112

USB 2.0Interface

ATHEROS AR5005uX

? FEC ?


LEP> SCNLEP> SCN

Thank you

Questions ?


Analog VS Digital

Digital CameraDigital Camera

JPEG processing to deduce the bandwidthJPEG processing to deduce the bandwidth

Onboard storage of the data is possibleOnboard storage of the data is possible

Digital signals are more resistant against multipath distortionsDigital signals are more resistant against multipath distortions I.e Use of COFDMI.e Use of COFDM

Already existing technologies working in the ISM bandAlready existing technologies working in the ISM band

Dynamically reconfigurable system parametersDynamically reconfigurable system parameters

No need to adjust to tune the transmitter boardNo need to adjust to tune the transmitter board

Analog transmission requires more powerAnalog transmission requires more power

journées micro-drones 2004. presentation high data rate transmission system for micro uavs lep>...

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