MGA Webinar Series : 8
GNSS Raw Data Measurement from Android Device
Background Information
Dinesh ManandharCenter for Spatial Information ScienceThe University of Tokyo
Contact Information: dinesh@iis.u-Tokyo.ac.jp
6th Dec 2018
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

Slide : 1

Background Information : GPS Signal Structure
900 Phase Reversex154

L1 Carrier, 1575.42Mhz∑x1/10

X1, Clock10.23Mhz

C / A Code, 1.023Mhz

x1/204600

Navigation Data, 50Hz

L1 Band GPS Signal

P Code, 10.23Mhz
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

Slide : 2

GPS

Architecture of a GNSS Receiver
Convert toLower Frequency
Defined bySampling Frequency and IF

Antenna

AGC

Pre-Amp(LNA)

DownConverter

A/D Converter

Replica Signal
Generator
Frequency
Generator

Oscillator
Ref. Clock 10.23MHz

Output fromBase-band
Signal Processing

GPS RF signal at1575.42MHz

Digital Signal Output

Baseband Signal
Processing

Acquisition

Tracking

Position Output(PVT)

To find out visible satellites,
approximate Doppler
and Code-phase
To continuously demodulate the signal
to extract the navigation data bits
Done by using DLL, FLL and PLL.
Outputs from Acquisition
are used as input for Tracking

Generate Pseudorange, Doppler etc
Extract Ephemeris orSatellite Orbit related Data
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp Extract Clock related data
Navigation Data

Slide : 3

GPSArchitecture of a GNSS Receiver
Position Output(PVT)

Convert toLower Frequency
Defined bySampling Frequency and IF

Antenna

AGC

Pre-Amp(LNA)

Down
Converter

A/D Converter

Replica Signal
Generator
Frequency
Generator

Oscillator
Ref. Clock 10.23MHz

Output fromBase-band
Signal ProcessingGPS RF signal at1575.42MHzDigital Signal Output

Baseband Signal
Processing

Acquisition

Tracking

RAW Data
Data necessary to compute
Pseudorange, Carrier Phase,Doppler, TimeError etc

To find out visible satellites,
approximate Doppler
and Code-phase
To continuously demodulate the signal
to extract the navigation data bits
Done by using DLL, FLL and PLL.
Outputs from Acquisition
are used as input for Tracking

Generate Pseudorange, Doppler etc
Extract Ephemeris orSatellite Orbit related Data
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp Extract Clock related dataNavigation Data

Slide : 4

Acquisition of GPS L1C/A Signal

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

Slide : 5

Acquisition Output shown for Doppler Frequency
File: LS2.dat, SV: GPS, PRN ID:8
CodePhase: 2339, Doppler: -5100Hz, CohInt.: 2, NonCohInt: 5414039Signal Power, dB

38373635343332Acquisition Output for Maximum Code Phase Value
31-5900-4900-3900
Doppler Frequency, Hz

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp-3000
Slide : 6

Acquisition Output shown for Code Phase (PRN Code Chip Delay)
File: LS2.dat, SV: GPS, PRN ID:8
CodePhase: 2339, Doppler: -5100Hz, CohInt.: 2, NonCohInt: 5414039Signal Power, dB

3837363534
33
32
Acquisition Output for Maximum Doppler Value
312220

2250

2280

2310
2340
Code Phase

2370

2400

2430

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

Slide : 7

GPS Signal Tracking• Tracking Loops (PLL & DLL) are used to continuously lock theincoming signal and demodulate it by using the carrier
frequency and code phase values detected in Acquisition.
• PLL• Phase Lock Loop
• To Track the Carrier Frequency• DLL• Delay Lock Loop
• To Track the Code Phase (PRN Code Delays)
Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

Slide : 8

GPS Signal Tracking Output
Navigation Data Bits
1’s and 0’s

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

Slide : 9

SNR & C/No
• SNR

• Signal to Noise Ratio, unit is dB• S: Signal Power in dBm or dBW• N: Noise power in a given bandwidth in dBm or dBW• C/No• Carrier to Noise Density, unit is dB-Hz• C: Carrier power in dBm or dBW• No: Noise power density in dBm-Hz or dBW-Hz• SNR = C/No-BW (BW = bandwidth of the Front End)• If BW = 4Mhz = 10*log10(4000000) = 66dB
• If C/No = 48dB-Hz• SNR = C/No-BW = 45-66 = -21dB• Noise Density (No) at Room Temperature (290K): -204dBW/Hz• Received Power (GPS L1C/A Signal) at Antenna: -158.5dBW• C/No = -158.5-(-204) = 45.5dB-Hz

Dinesh Manandhar, CSIS, The University of Tokyo, dinesh@iis.u-tokyo.ac.jp

Slide : 10