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High Data Rate Transmission System for Micro UAVs

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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High Data Rate Transmission System for Micro UAVs

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  1. LEP> SCN High Data Rate Transmission System for Micro UAVs Fabien MULOT: Internship ONERA-SUPAERO Vincent CALMETTES: Research SUPAERO

  2. 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

  3. 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

  4. 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“)

  5. 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

  6. LEP> SCN Channel Video monitoring Reception Scheme Video Source Transmission Scheme Video quality VS data rate trade-off

  7. 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

  8. LEP> SCN 1.12 Mbits.s-1 Channel ? Video monitoring Reception Scheme Transmission Scheme JPEG Coding Characterisation of the micro-UAV transmission channel

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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)

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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

  22. 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

  23. LEP> SCN Future studies and developments

  24. 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 ?

  25. LEP> SCN LEP> SCN Thank you Questions ?

  26. 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

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