Page 1CSNC 2012 Integration of COMPASS in a multi-GNSS receiver: frontend design, signal processing issues and results from early operations N. Falk, T. Hartmann, G. Heinrichs, T.Pany, B. Riedl, J. Winkel IFEN GmbH Günter Stangl Austrian Academy of Science Place:Guangzhou, China Session S2 Date&Time:May 17 th, :20 p.m. – 2:45 p.m.

Page 2CSNC 2012 Motivation COMPASS Upcoming GNSS Three frequencies High signal power ICD successively released 11 satellites in orbit Received also outside China IFEN SX-NSR Multi-GNSS PC-based SwRx Used for GNSS/INS integration Scientific experiments Prototype space receivers GNSS reference stations Reflectometry Spectrum monitoring Need to be integrated Introduction RF Front-End Signal Processing Results

Page 3CSNC 2012 Update IGS Reference Site GRAB for COMPASS PC-based software installed at GRAZ 47°4'2"N, 15°29'37"E for IGS Multi-GNSS Experiment GPS L1/L2 daily coordinate repeatability

Page 4CSNC 2012 SX-NSR – Key Components RF Front-End 4 RF bands up to 15 MHz simultaneously GPS L1, L2P, L2C, L5 Galileo E1, E5a, E5b, E6 SBAS L1, L5 GLONASS G1, G2 User specific ≤ 2.5 GHz Frontend coupling for 8 bands Dual antenna operation 1 x high-speed USB2.0 Interfaces to IMU, PPS, clock, baro., … or MHz sample rate External power supply Signal Processing Software Windows personal computer 2GB RAM, SSSE3 capable processor Ultra high sensitivity, ~20-30 channels per CPU core Signal conditioning and pre-processing GNSS baseband processing (acquisition and tracking) for all civil GNSS signals plus GPS L2P Sensor data synchronization and processing Application programming interface for external C/C++ code Introduction RF Front-End Signal Processing Results

Page 5CSNC 2012 GRAB Galileo Performance Introduction RF Front-End Signal Processing Results

Page 6CSNC 2012 Issue 1: RF Frontend Introduction RF Front-End Signal Processing Results

Page 7CSNC 2012 Envisaged Frequency Bands Centre frequencies (front- end no.) Sample rate/No. of bitsBandwidth GPSL1(1), L2(1), L5(1)20.48 bit15 MHz GLONASSG1(2), G2(2)20.48 bit15 MHz GalileoE1(1), E5a(1), E5b(1), E6(2) bit15 MHz COMPASSB1(2), B2(1), B3(1)20.48 bit15 MHz Need 8 frequency bands to track all GNSS: Reuse: L1/E1, L5/E5a, E5b/B2, E6/B3 Introduction RF Front-End Signal Processing Results

Page 8CSNC 2012 Synchronize 2 x NavPort4 Each NavPort-4 frontend supports 4 x ADC MHz (single chip) Decimation for USB transfer Inter – frontend link Synchronizes two NavPort-4 devices by Hardware Connections: Reference clock (10 MHz) interconnection Inter - frontend link Introduction RF Front-End Signal Processing Results

Page 9CSNC 2012 Synchronization Performance Synchronization performance of 2 x NavPort-4 Synchronization guarantee of 475 ps = +/- 14 cm With calibration < 70 ps = +/- 2 cm Cable/RF filter dependent biases Introduction RF Front-End Signal Processing Results

Page 10CSNC 2012 RF Pecularities COMPASS B1 also received quite well through L1 path 2nd order Bessel 15 MHz bandpass at RF (ceramic filter) Useful for applications with limited computational resources Currently E6/B3 share same filter centred on E6 Better to center between E6 and B3 Better to have more than 15 MHz bandwidth Introduction RF Front-End Signal Processing Results

Page 11CSNC 2012 COMPASS Bands at GRAB B2/E5b B1 E6/B3 ok no Introduction RF Front-End Signal Processing Results

Page 12CSNC 2012 Issue 2: Signal Processing Introduction RF Front-End Signal Processing Results

Page 13CSNC 2012 COMPASS Signal Information COMPASS ICD Definies primary codes for B1/B2 Modulation scheme Stanford COMPASS M1 code on B3 Post-correlation Analysis Gives secondary codes Other receiver manufacturers (Trimble, Septentrio) Hints how to retrieve time-of-week RINEX3.txt (Ver. 3.01) How to label COMPASS data Introduction RF Front-End Signal Processing Results

Page 14CSNC 2012 COMPASS Acquisition Cold start mode for all 37 PRNs on B2 (no almanac available) Primary code FFT order 13 = 0.25 chip resolution T coh = 4 ms (averaging data bit, sec. code transistions) Doppler bin = 250 Hz 25 noncoherent integrations Handover to B1, B3 Equivalent correlators: Intel Atom N2600: nVidia GTX 480: COMPASS C3 at GRAB No source code change necessary Introduction RF Front-End Signal Processing Results

Page 15CSNC 2012 COMPASS Carrier Tracking Sync. to secondary code GEO: 11, IGSO/MEO: T coh = 2 ms Costas phase disc, 2 x 1 ms Freq. disc No source code change necessary COMPASS C5 at GRAB Introduction RF Front-End Signal Processing Results

Page 16CSNC 2012 COMPASS Code Tracking Double delta (0.2/0.4 chip for multipath mitigation) MEDLL possible No source code change necessary COMPASS C5 at GRAB Introduction RF Front-End Signal Processing Results

Page 17CSNC 2012 Time-of-Week Time-of-Week needed to output pseudoranges Detected preambel for all COMPASS satellites on B1/B Verification method necessary to avoid false detections Repetition period 300 bits = 6 s for IGSO/MEO 300 bits = 0.6 s for GEO Possible to resolve code ambiguity Satellite range and satellite clock uncertainity << 0.6 s Open question where is t = 0.0 s? Beginng or end of preamble? Somewhere else? Choice needs to be consistent with other receiver manufacturers Introduction RF Front-End Signal Processing Results

Page 18CSNC 2012 Typical Satellite Passes at GRAB Introduction RF Front-End Signal Processing Results

Page 19CSNC 2012 Number of Tracked Satellites at GRAB Introduction RF Front-End Signal Processing Results

Page 20CSNC 2012 RINEX 3.01 RECORD > G G G G G G G G G G G G E E R R R R R R R R R S C C C C C C Data can be downloaded at: ftp://olggps.oeaw.ac.at/pub/igsmgex/ or CDDIS, BKG

Page 21CSNC 2012 CONCLUSIONS COMPASS fits well into a generic tracking scheme Acquisition and tracking without source code changes Fits also well to SX-NSR application programming interface No results yet for B3, the most precise signal Unexpected many satellites tracked in Europe Need to look for applications Interference probably an issue as B1/B3 band have no heritage on GNSS use in Europe