Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our User Agreement and Privacy Policy.

Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our Privacy Policy and User Agreement for details.

Like this presentation? Why not share!

- Satellite navigation lecture 2 by TU Delft OpenCour... 3460 views
- Satellite Navgation Lecture 1 by TU Delft OpenCour... 4960 views
- Satellite Navigation: Lecture 4 -_g... by TU Delft OpenCour... 2431 views
- Satellite Navigation: Lecture 5 -_g... by TU Delft OpenCour... 2528 views
- Satellite Navigation: Lecture 10 - ... by TU Delft OpenCour... 2141 views
- Satellite Navigation: Lecture 7 - p... by TU Delft OpenCour... 1827 views

3,565 views

3,502 views

3,502 views

Published on

No Downloads

Total views

3,565

On SlideShare

0

From Embeds

0

Number of Embeds

1

Shares

0

Downloads

175

Comments

0

Likes

1

No embeds

No notes for slide

- 1. Satellite NavigationPrinciple and performance of GPS receiversAE4E08 GPS Block IIF satellite – Boeing North AmericaChristian TiberiusCourse 2010 – 2011, lecture 3
- 2. Today’s topics• Introduction – basic idea• Link budget• Signal de-modulation• Receiver architecture• Measurement precision topics in part III and IV of Misra&Enge book, instead …: GPS Receiver Architectures and Measurements c on exp cise o of s sition by Michael S. Braasch and A.J. van Dierendonck ubje ct Proceedings of the IEEE, Vol. 87, No. 1, January 1999 pp. 48-64 2Satellite Navigation (AE4E08) – Lecture 3
- 3. Receiver architecture overview of a GNSS receiver – main building blocks its purpose? output: - pseudorange code measurement - carrier phase measurement - Doppler measurement - C/N0 measurement (signal strength)Satellite Navigation (AE4E08) – Lecture 3
- 4. GPS receiver architecture - functionality basic idea Red-crowned amazon from: Misra and EngeSatellite Navigation (AE4E08) – Lecture 3
- 5. The GPS Signal - recapFREQUENCY DOMAIN TIME DOMAIN Binary Phase Shift Keying (BPSK) modulation CARRIER (spread spectrum (SS) modulation) CARRIER with Pseudo Random Noise (PRN) f0 = 1.5 GHz f code sequences: PRN-CODE( sin x ) 2 - SPECTRUM 1 1 0 0 0 0 1 1 1 • C/A code on L1 - 1.023 Mbits/sec x SPREAD • P(Y) code on L1 and L2 - 10.23 Mbits/sec SPECTRUM SIGNAL f0 = 1.5 GHz 2.046 MHz 2.046 MHz sin x 2 ( ) - SPECTRUM CA CODEsee also Figure 2.5 in Misra&Enge x P CODE 1227.6 MHz 1575.42 MHz f 20.46 MHz 20.46 MHz L2 SIGNAL L1 SIGNAL Satellite Navigation (AE4E08) – Lecture 3
- 6. The GPS Signal at the Receiver Antenna• Signal delayed due to the travel time • speed of light in vacuum “ “ • atmospheric delays• Signal has undergone a Doppler shift (freq)• Signal is very weak (amplitude) • ordinary spherical weakening (~158 dB) • atmospheric absorption (small, 1-2 dB) typical signal-to-noise ratio (SNR) for the C/A code signal is ~1/80 (-19dB) well below noise level dB? see § 2.3.3 Misra&Enge Satellite Navigation (AE4E08) – Lecture 3
- 7. Link budget - 1 Table 1 from IEEE-article C/A-code at 1575.42 MHz satellite antenna: directs signal in beam (not omni-directional) EIRP: 478.63 W (or 26.8 dBW) 26.8 dBW = 10 log10 478.63 W ⎛ λ ⎞ 2 spherical spreading free − space loss factor = ⎜ ⎟ factor = 5.73 * 10-19 ⎝ 4πR ⎠ -182.4 dB = 10 log10 5.73e-19Satellite Navigation (AE4E08) – Lecture 3 includes effective area of (omni-directional) receiver antenna - see § 10.2 Misra&Enge AE = λ2/4π
- 8. Power density of received GNSS signal from: Misra and EngeSatellite Navigation (AE4E08) – Lecture 3
- 9. Link budget - 2 atmospheric loss: -2 dB -2 dB = 10 log10 0.63 (hence factor of 0.63) ⇒ received signal power: 26.8 dBW 478.63 W -182.4 dB x 5.73 * 10-19 -2.0 dB x 0.63 + -157.6 dBW 1.738 * 10-16 Wnoise power at receiver: 1.413*10-14 W (or –138.5 dBW) in 2 MHz bandwidth -138.5 dBW = 10 log10 1.413e-14 W Satellite Navigation (AE4E08) – Lecture 3
- 10. Link budget - 3 signal power [W] Signal-to-Noise ratio (SNR) SNR = noise power [W] signal power: -157.6 dBW 1.738 * 10-16 W noise power: -138.5 dBW / 1.413 *10-14 W -at receiver on Earth SNR: -19.1 dB 0.0123 Fig. 6 (a) from IEEE-articleraw GPS signal?‘nothing’ to see !⇒ signal indeed far below noise-floor 1 millisecond of received signal - sampled at 5 MHz (amplified & filtered) Satellite Navigation (AE4E08) – Lecture 3
- 11. Signal de-modulation• tracking• work-out on the blackboard …Satellite Navigation (AE4E08) – Lecture 3
- 12. Correlation Demo is on blackboard.Satellite Navigation (AE4E08) – Lecture 3
- 13. Correlation • shift s1(t) τ =0 • multiply s2(t-τ) • integrate τ =0 s1(t).s2(t-τ)∫ s1(t).s2(t- τ) ⎯⎯ τ →Satellite Navigation (AE4E08) – Lecture 3
- 14. Correlation • shift s1(t) τ = 0.5 • multiply s2(t-τ) • integrate τ = 0.5 s1(t).s2(t-τ)∫ s1(t).s2(t- τ) ⎯⎯ τ →Satellite Navigation (AE4E08) – Lecture 3
- 15. Correlation • shift s1(t) τ =1 • multiply s2(t-τ) • integrate τ =1 s1(t).s2(t-τ)∫ s1(t).s2(t- τ) ⎯⎯ τ →Satellite Navigation (AE4E08) – Lecture 3
- 16. Correlation • shift s1(t) τ = 1.5 • multiply s2(t-τ) • integrate τ = 1.5 s1(t).s2(t-τ)∫ s1(t).s2(t- τ) ⎯⎯ τ →Satellite Navigation (AE4E08) – Lecture 3
- 17. Correlation • shift s1(t) τ =2 • multiply s2(t-τ) • integrate τ =2 s1(t).s2(t-τ)∫ s1(t).s2(t- τ) ⎯⎯ τ →Satellite Navigation (AE4E08) – Lecture 3
- 18. Correlation • shift s1(t) τ = 2.5 • multiply s2(t-τ) • integrate τ = 2.5 s1(t).s2(t-τ)∫ s1(t).s2(t- τ) ⎯⎯ τ →Satellite Navigation (AE4E08) – Lecture 3
- 19. Correlation • shift s1(t) τ =3 • multiply s2(t-τ) • integrate τ =3 s1(t).s2(t-τ)∫ s1(t).s2(t- τ) ⎯⎯ τ →Satellite Navigation (AE4E08) – Lecture 3
- 20. Correlation s1(t) • shift • multiply s2(t-τ) • integrate s1(t).s2(t-τ)∫ s1(t).s2(t- τ) ⎯⎯ τ →Satellite Navigation (AE4E08) – Lecture 3
- 21. Two stages of receiver operation• acquisition (searching)• tracking (following) – providing measurementsSatellite Navigation (AE4E08) – Lecture 3
- 22. Receiver block diagram Fig. 5 from IEEE-article next slide …Satellite Navigation (AE4E08) – Lecture 3
- 23. Fig. 7 from IEEE-article baseband processing In-phase cos sin I and Q channel, to avoid Quadrature-phase lack of signal when ϕ=0, π/2, π, 3π/2 baseband signal processing block diagram = block 3 in Fig. 5.Satellite Navigation (AE4E08) – Lecture 3
- 24. code trackingDelay Lock Loop (DLL) code tracking controls delay pseudorangeSatellite Navigation (AE4E08) – Lecture 3
- 25. carrier phase trackingPhase Lock Loop (PLL) *)actually Costas-loop carrier tracking controls frequency carrier phase (Doppler shift)*) sometimes also Carrier Tracking Loop (CTL) Satellite Navigation (AE4E08) – Lecture 3
- 26. data nav. msg. when PLL is locked in data (nav. msg.) can be extractedSatellite Navigation (AE4E08) – Lecture 3
- 27. GNSS receiverDLL + PLL per signal, per satellitetoday’s high-end GPS receiver has typicallybetween 24 and 48 channels: multi-constellation GNSS receiver: - CA-code signal on L1 much more! - P(Y)-code signal on L1 - P(Y)-code signal on L2to track up to 12-16 GPS satellites simultaneouslygenerally each satellite is tracked independently(each GPS satellite has its own unique PRN ranging code (pulse sequence)) Satellite Navigation (AE4E08) – Lecture 3
- 28. Link budget – de-spreading signal power at receiver: 1.738*10-16 W (or –157.6 dBW) What if we could confine ourselves to a much smaller bandwidth …? noise power at receiver: 3.54*10-19 W (or –184.5 dBW) in 50 Hz bandwidth -184.5 dBW = 10 log10 3.54e-19 W signal power: -157.6 dBW 1.738 * 10-16 W noise power: -184.5 dBW / 3.54 *10-19 W -at receiver on Earth SNR: +26.9 dB 490 then, GPS signal has been raised well above noise floor !! Satellite Navigation (AE4E08) – Lecture 3 ⇒ read data when tracking
- 29. Signal to Noise Ratio (SNR) signal power [W]Signal-to-Noise ratio (SNR) SNR = noise power [W] in the same band (of course total noise power depends on bandwidth considered)normalize SNR to 1 Hz bandwidth:carrier to noise density ratio c/no = SNR * Blogarithmic scale [dB-Hz] C/No = 10 log10 c/no see example in eq. (16) IEEE-articleto present signal strength independent of spreading / de-spreading stage Satellite Navigation (AE4E08) – Lecture 3
- 30. Performancesignal key-parameters• power: C/No (code and phase)• (PRN-code) chip-rate (code)• (carrier) wavelength (phase)• signal bandwidth (code) but transmitted bandwidth not infinitenext to receiver parameters as: e.g. antenna gain, and (code and carrier) tracking loop bandwidthsSatellite Navigation (AE4E08) – Lecture 3
- 31. Measurement precision: code BL σc ≈ λc standard deviation in [m] 2 c / nowith BL code tracking loop bandwidth (0.1 - 5 Hz) c / no carrier-to-noise density ratio λc PRN code ‘wavelength’ [m] (1 chip = 293 m for CA-code)measurement noise due to thermal noise, coherent DLL,for standard 1-chip Early-Late spacing (and assuming infinite signal bandwidth)Satellite Navigation (AE4E08) – Lecture 3
- 32. Measurement precision: phase BP λ σP ≈ standard deviation in [m] c / no 2π with BP carrier tracking loop bandwidth (5 - 15 Hz) to accommodate c / no carrier-to-noise density ratio vehicle / platform dynamics (and local oscillator noise) λ wavelength [m] (~0.20 m) measurement noise due to thermal noise (and neglecting squaring loss)Satellite Navigation (AE4E08) – Lecture 3
- 33. Summary and outlookStudy:• IEEE-paper by Braasch&VanDierendonck (Blackboard)Next: GPS measurements and error sourcesAssignment 1 Future GNSS (deadline 2 December)Satellite Navigation (AE4E08) – Lecture 3

No public clipboards found for this slide

×
### Save the most important slides with Clipping

Clipping is a handy way to collect and organize the most important slides from a presentation. You can keep your great finds in clipboards organized around topics.

Be the first to comment