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LEP> SCN. High Data Rate Transmission System for Micro UAVs. Fabien MULOT: Internship ONERA-SUPAERO Vincent CALMETTES: Research SUPAERO. LEP> SCN. Plan of the presentation. Context of the study Video quality VS data rate trade-off

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slide1

LEP> SCN

High Data Rate Transmission System for Micro UAVs

Fabien MULOT: Internship ONERA-SUPAERO

Vincent CALMETTES: Research SUPAERO

slide2

LEP> SCN

Plan of the presentation

  • 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
slide3

LEP> SCN

b

a

c

a. Reflection

b. Shadowing

c. Line of Sight

Context of the study

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

Monitoring

Base station

slide4

LEP> SCN

Context of the study

  • Transmission Band
    • ISM band 2400 - 2483,5 MHz
  • Regulation

http://www.anfr.fr

("Tableau National de Répartition des Bandes de Fréquences“)

slide5

LEP> SCN

Context 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
slide6

LEP> SCN

Channel

Video monitoring

Reception Scheme

Video Source

Transmission Scheme

Video quality VS data rate

trade-off

slide7

LEP> SCN

D

Video quality VS data rate trade-off

302 Ko

10 Ko

A

  • 2 modes of transmission
    • 14 i/s low quality A
    • 3.3 i/s high quality D
    • Bit rate: 1.12 Mbits.s-1

42 Ko

slide8

LEP> SCN

1.12 Mbits.s-1

Channel ?

Video monitoring

Reception Scheme

Transmission Scheme

JPEG Coding

Characterisation of the

micro-UAV transmission channel

slide9

LEP> SCN

Micro-UAV transmission channel

  • Path loss
    • A = (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
slide10

LEP> SCN

X(t)

1

2

n

1(t)

2(t)

n(t)

Y(t)

Micro-UAV transmission channel

  • Statistic model
  • C) channel Model
  • A) Statistic Power Delay Profiles
  • B) Tap Delay Line Model
slide11

LEP> SCN

Deep Fades

Example of a 4 MHz occupied bandwidth for video transmission

Micro-UAV transmission channel

  • 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

slide12

LEP> SCN

1.12 Mbits.s-1

Multipath

Shadowing

Frequency Selecticve

Suited Reception Scheme

Channel Decoding

JPEG

Decoding

Channel

Coding

JPEG Coding

Modulation

Micro-UAV transmission channel

  • Issues:
    • Frequency selective channel
    • Inter Symbol Interferences
  • Solutions:
    • Channel coding
    • Suited transmission techniques
slide13

LEP> SCN

1.12 Mbits.s-1

Multipath

Shadowing

Frequency Selctive

Suited Reception Scheme

Channel Decoding

JPEG

Decoding

Channel

Coding

JPEG Coding

Modulation

Fade Mitigation Techniques

Channel coding

slide14

LEP> SCN

Puncturing

Reed Solomon

(204/188)

External

Interleaver

Convvolutional Code

[177/188]

Internal

Interleaver

Channel Coding

  • Objective: Spreading and correction of the bursts of errors
  • Architecture
  • Target BER: 10-7 => SNR=3.5 dB
  • Pe=Pr.D4/(Ge.Gr)
slide15

LEP> SCN

1.12 Mbits.s-1

2. Mbits.s-1

Multipath

Shadowing

Frequency Selective

Suited Reception Scheme

Channel Decoding

Channel

Coding

JPEG

Decoding

JPEG Coding

Modulation

Fade Mitigation Techniques

Transmission & Reception Techniques

slide16

LEP> SCN

Training sequence generator

QPSK Mapping

JPEG source coding

SRRC

Filtering

Coding

+Puncturing

Channel

SRRC

Filtering

JPEG decoding

Decoding

+ deinterleaving

Demapping

Adaptive filtering

QPSK + Equalization

  • Architecture
    • Channel coding
    • SSRC Roll Off = 0.4
    • Equalizer
  • Bandwidth: 1.5 Mhz
slide17

LEP> SCN

Multipath

Shadowing

1.12 Mbits.s-1

2. Mbits.s-1

0.8 Msymb.s-1

MLSE

1024 states

Channel

Coding

Channel Decoding

JPEG

Decoding

JPEG Coding

QPSK

QPSK

1.5 Mhz

QPSK + Equalization

  • Equalization
    • LMS algorithm
      • Channel impulse response <= 1symbol
    • MLSE using a Viterbi algorithm
      • Several Symbols
      • Mk Complexity
      • 1024 state trellis
slide18

LEP> SCN

Guard Interval Insertion

2N points padding

P/S

CP

S1(k)..Sn(k)

Channel

I

F

F

T

Coding

Symbol

mapping

S/P

OFDM emitter

Frequency

0

0

OFDM

  • Advantage:
    • Transmission of high data rate while keeping a non frequency selective channel.
    • Bandwidth efficient
  • Architecture
    • Channel coding mandatory
    • OFDM Symbol duration =50 µs
    • 10 times the channel impulse response
slide19

LEP> SCN

0.8 Msymb.s-1

1.12 Mbits.s-1

2. Mbits.s-1

20 Ksymb

Multipath

Shadowing

OFDM 64 pts FFT

Channel

Coding

OFDM 64pts IFFT

Channel Decoding

JPEG

Decoding

JPEG Coding

QPSK

QPSK

1.3 Mhz

OFDM

  • Taking into account
    • The symbol duration 50µs
    • the length of the cyclic prefix
    • The data rate after coding
    • The insertion of training symbols for equalization
    • 64 points FFT
    • Bandwidth: 1.3Mhz
slide20

LEP> SCN

Power

Noise

Spread signal

Frequency

Narrow Band Information signal After Despreading

Power

Spread Noise

Frequency

Up sampling

QPSK

Mapping

SRRC

Filtering

Coding

IQ Spreading code

IQ Scrambling code

DSSS + Rake

  • Advantages of Direct Sequence Spread Spectrum:
    • Rake uses time diversity
    • Resistant to noise and interference
  • Architecture
    • OVSF spreading codes
    • PN scrambling sequence
    • Rake receiver
slide21

LEP> SCN

Descramble Despread

Integrate and Dump

Channel estimation

Path Search

g*(t-1)

y(t-1)

1

∫dt

g*(t-2)

y(t-2)

2

∫dt

IQ demapper

y(t)

g*(t-3)

y(t-3)

3

∫dt

g*(t-4)

y(t-4)

4

∫dt

MRC

DSSS + Rake

  • Rake Receiver Architecture
slide22

LEP> SCN

51.2 Msymb.s-1

0.8 Msymb.s-1

1.12 Mbits.s-1

2. Mbits.s-1

Multipath

Shadowing

Channel

Coding

Channel Decoding

JPEG Coding

JPEG Decoding

QPSK

DSSS

QPSK

Rake

72.6 Mhz

DSSS + Rake

slide23

LEP> SCN

Future studies and developments

slide24

LEP> SCN

LEP> SCN

ATHEROS AR5005uX

USB 2.0

Interface

Baseband

Processor

Transceiver

FPGA

Baseband

Processor

Transceiver

External

PA

ATHEROS

5523

ATHEROS

5112

ATHEROS

5523

ATHEROS

5112

Future studies and developments

  • Evaluation of a system based on existing commercial technologies:
  • WI-FI [802.11b]
    • DSSS
    • 1 to 11 Mbps
  • WI-FI [802.11g]
    • OFDM
    • 1 to 54 Mbps

? FEC ?

slide25

LEP> SCN

LEP> SCN

Thank you

Questions ?

slide26

Analog VS Digital

  • Digital Camera
  • JPEG processing to deduce the bandwidth
  • Onboard storage of the data is possible
  • Digital signals are more resistant against multipath distortions
    • I.e Use of COFDM
  • Already existing technologies working in the ISM band
  • Dynamically reconfigurable system parameters
  • No need to adjust to tune the transmitter board
  • Analog transmission requires more power