Perspective of Eastern Global Satellite Navigation Systems

Transcription

1 POSTER 2015, PRAGUE MAY 14 1 Perspective of Eastern Global Satellite Navigation Systems Jiří SVATOŇ Dept. of Radioengineering, Czech Technical University, Technická 2, Praha, Czech Republic svatoji2@fel.cvut.cz Abstract. Accurate positioning is a strategic information. Beside of American GPS and Russian Glonass another countries on east are developing own satellite navigation systems. The Chinese BeiDou and Indian IRNSS are potentially most interesting systems for us. Although the first plans for an independent Chinese satellite navigation system could be dated in an end of previous century first satellites were launched after 2007 and its first signal specification was publicized in Very interesting is Indian Regional Navigation Satellite System IRNSS. Satellites were launched since 2013 and its signal specification is known since half of year IRNSS specifies the first public signal out of L-band as a first GNSS systems. Our contribution describes our experience with these systems and with a first reception of satellite navigation system signal in S-band. Keywords GNSS, IRNSS, BeiDou 2, Compass, S-band, acquisition. 1. Introduction Multi-frequency and multi-constellation reception of a different independent systems is a current trend in satellite navigation receiver s development. Accuracy is improved due a higher number of satellites on the sky [1]. Multiconstellation receiver is more reliable in compare with a GPS only, frequency diversity is a protection against a jamming. Existing GNSS systems are traditional application of L-band. Usage of an additional band for the Radio Navigation Satellite Service (RNSS) purpose has been considered since The first ideas were connected with the development of the European navigation system Galileo but has not been used yet. S-band has been used for a first regional generation of BeiDou since 2000, was allocated to the GNSS purpose in 2003 and has been used for purpose of IRNSS since We are able to observe some satellites from its constellations. We describes our experience with BeiDou 2 (which specifies signals in L-band only) and with reception of IRNSS signal in L and S-band in our contribution. The second paragraph of our contribution describes BeiDou 2 and IRNSS properties and parameters for their observation in a part of Central Europe. The third paragraph is dedicated to the description of our experimental platform for the S-band signal reception of IRNSS and for results presentation. The fourth paragraph is a conclusion. 2. New satellite navigation systems The next two satellite navigation systems, BeiDou 2 and IRNSS has been on the scene since 2007, 2013 respectively. Both were built for a regional coverage initially. They use a different geostationary or called inclined-geostationary satellites orbits besides of medium orbit for a regional coverage. So it s the most important difference against a conventional GPS or Glonass MEO only constellation. Both systems are specified below. 2.1 BeiDou 2 China has been used first generation of own regional navigation system since This system uses MHz frequency. First satellite of second generation for a Global coverage system was launched in This generation BeiDou 2 was called as Compass for some time. Full operational capability constellation consists of 35 satellites (Tab. 2.). Twenty-seven satellites will be on Medium Earth Orbit (MEO), five on geostationary (GEO) and three on inclined-geostationary (IGSO is a GSO orbit with non-zero inclination). Current constellation in year 2015 consists of fifteen satellites. Most of them were launched from 2010 to No satellites were launched in 2013 and This can be explained by preparations for launch of new series of satellites from third generation, which is scheduled for launch from Signal Carrier Chip rate Modulation name [MHZ] [Mchip/s] type B1 1561,098 2,046 QPSK B ,742 2,046 QPSK B2 1207,140 10,23 QPSK B3 1268,52 10,23 QPSK B1-BOC 1575,42 1,023 MBOC(6,1,1/11) B2-BOC 1207,14 5,115 BOC(10,5) B3-BOC 1268,52 2,5575 BOC(15,2.5) L5 1176,45 10,23 QPSK Tab. 1. BeiDou 2 signals plan

2 2 J. SVATOŇ, PERSPECTIVE OF EASTERN GLOBAL SATELLITE NAVIGATION SYSTEMS A big amount of signals were planned (Tab. 1.) but official B1 signal specification was publicized in December 2011 [2]. Reception on B1 and then on B2 carrier frequency was confirmed on our department in 2012 [3]. Official B2 signal specification for was publicized later in December 2013 [4]. Longitude [ E] Launch M1 MEO April 13, 2007 M2 MEO out of order M3 MEO April 29, 2012 M4 MEO April 29, 2012 M5 MEO September, 2012 M6 MEO September, 2012 G1 140 January, 2010 G2 21 April, 2009 G3 110 June, 2010 G4 160 October, 2010 G5 59 February, 2012 IGSO1 120 July, 2010 IGSO2 120 December, 2010 IGSO3 120 April, 2011 equation (1). A PRN code C SPS is similar to the Gold code and is chipped at Mcps with 1 ms period. The Navigation message D SPS is modulo 2 added to data which are transmitted by 50 symbols per second rate. c sps SSPS t CSPS i DSPS i rectt t it, c, sps (1) i The main difference on reception in S-band is a higher propagation loss in compare with L-band. The Tab. 4. specifies the minimum received power level of a signal at the Earth s surface (0 dbi RHCP antenna is used). The power of the IRNSS L5 signal is almost comparable with similar GPS signals, but the signal in the S-band is about 4 db weaker than the signals usually received in the L-band [6]. Signals in both bands were experimentally received. The next two satellites are to be released in early 2015 (March and April). The complete full operational capability constellation of seven satellites is scheduled to be in the orbits by The three satellites at the GEO orbit will be located at 32.5ºE, 83º E and 131.5º E. Four IGSO satellites will cross the equator on 55º E and º A (two in each plane). The satellite lifespan is scheduled for 10 years. The weight of the satellite is around 1400 kg and its solar panels supply it with power of about 1660 Watts. IGSO4 92 July, 2011 IGSO5 95 December, 2011 Tab. 2. BeiDou 2 satellites constellation in Position with commercial receiver on B1 frequency was determined on antenna on faculty roof in Position error was estimated to 22 m. 2.2 Indian Regional Navigation System Second is Indian IRNSS. The IRNSS is expected to determine the position more accurately than 20 m in the Primary Service Area. The Primary Service Area is bounded by the 1500 km distant the India border. The Extended Service Area is also defined and is bounded from 50 to 30 N and from 30 to 130 E. Its European part exceeds the Turkey and Ukraine areas. Our experience from Central Europe is described in third paragraph. The first IRNSS space vehicle was launched in 2013 and first three satellites from its seven satellites constellation (Tab. 3. and Fig. 1.) were launched by the end of The IRNSS Interface Control Document (ICD) was officially published in June 2014 in its first version [5]. This ICD defines two carrier frequencies: the L5 ( MHz with 24 MHz bandwidth) [6] and the IRNSS-S ( MHz with a 16.5 MHz bandwidth). Two different services are defined: the Standard Positioning Service (SPS) and the Restricted Service (RS). Each carrier is modulated by three signals: by the SPS - BPSK (1), the RS - Data Channel BOC (5,2) and the Pilot Channel BOC (5,2). The SPS signal is defined by the Fig. 1. IRNSS FOC constellation Earth plot Longitude [ E] Inclin. [ ] RAAN [ ] Tab. 3. IRNSS FOC constellation. Launch 1A (±2) 135 July, B (±2) 310 April, C 83.0 ± October,2014 1D (±2) 135? March, E (±2) 310? April, F 32.5 ± By end G ± By end 2016

3 POSTER 2015, PRAGUE MAY 14 3 From a current constellation a geostationary satellite 1C is observable from Prague at low elevation from 2 to 9. The first two IGSO satellites 1A and 1B reaches good elevation of up to 49 and at least one of them is always observable from our laboratory in Prague. The remaining satellites 1D and 1E will be also observable from our location in a the future, but for a shorter period of the day. Only 1F will be visible from Central Europe from the future GEO satellites 1F and 1G. Nevertheless it means that constellation would be able to determine a 2D position during the whole day in Central Europe from the spring 2015 [7]. Fig. 2. IRNSS S-band experimental reception system 3. Signal reception and acquisition 3.1 L-band reception L-band B1(I) BeiDou 2 signals were confirmed by post-processing acquisition on complex envelop samples sampled by a software defined radio receiver in Then the B1 and B2 signals were tracked real-time by the same receiver later in The compliance of broadcasted signals in both band B1(I) and B2(I) was confirmed [3] before official publication of B2 specification. IRNSS L5 signal was acquired by a post-processing method too in autumn Ranging code generator structure was confirmed. Methods and results are presented below and in a Fig S-band reception For IRNSS S-Band signal acquisition the postprocessing method was chosen again. But different frequency band (16 MHz bandwidth around central frequency MHz) requires a specific radio-front end. The Rohde and Schwarz FSQ 3 signal analyzer was used as an acquisition system for signal samples. The 44 MHz sampling frequency and the 50 MHz resolution filter were used. The analyzer uses three inter-frequency stages. The first one is for a mirror reception cancellation. The digitalization is implemented in the third stage with the help of a cascade of interpolators and decimators. Signal in S-band is little bit weaker than in L-band (Tab. 4.) so better front-end parts are required. IRNSS central frequency is MHz, so specific SAW filter was utilized [7]. Own extra-low noise amplifier [9] was utilized too. Block schematic picture you find on a Fig. 2 and its frequency characteristic on Fig. 3. Signal Modulation Min. P R [dbw] Tab. 4. IRNSS received power on Earth surface. Max. P R [dbw] L5 - SPS BPSK (1) S - SPS BPSK (1) Fig. 3. S-band front-end frequency characteristic 3.3 L-band reception The signal was sampled via the analyser. The ambiguity function of the signal acquisition was computed with the equation (2) respectively (3). Where R(τ, f d) is the crosscorrelation function between the received signal s(t) with Doppler frequency f d and PRN code replica C SPS. The functions F and F -1 (9), (10) are Fourier transformation and the inverse-fourier transformations, respectively [8]. * j2 fd d SPS 1 j2 fdt R, f s t C t e dt (2) jt F : S( ) s t e dt (4) 1 : ( ) (5) 2 1 jt F s t S e d R, f F F s( t) e F C ( t) (3) d The presented functions are results of a non-coherent integration process. An integration time 22 ms was used in the L5-band and 360 ms in the S-band. The result presented in Fig. 4. are acquisitions of all three IRNSS satellites in both bands. Signals were received with C/N 0 from 30 to 39 db. The S-band signals have worse C/N 0 because of the lower gain of the analogue parts and due to the lower received power level. This means that the longer integration time is required. Geostationary satellites signals have better C/N 0 than the satellites on inclined-geostationary orbits. SPS *

4 4 J. SVATOŇ, PERSPECTIVE OF EASTERN GLOBAL SATELLITE NAVIGATION SYSTEMS L5 IRNSS 1A L5 IRNSS 1B L5 IRNSS 1C S IRNSS 1A S IRNSS 1B S IRNSS 1C Fig. 4. IRNSS L-band and S-band satellite signal acquisition function 4. Conclusion Both new eastern satellite navigation systems were experimentally received. BeiDou 2 is able to be used for navigation even in Central Europe. Three IRNSS satellites were received in L and S-band. Our contribution is based mainly on the new experience with the experimental reception of the signal in the S-band in the area of Central Europe. Quality front-end with good filtration system for the suppression of near-out-band interferences (Wi-Fi) and low noise figure amplifiers are required for the S-band reception due to the lower received power level and C/N 0 at the antenna output. We expect that IRNSS will be probably useable for 2D positioning in central part of Europe in the first half of the year 2015, however with the poor DOP. But the main advantage of this system is evaluation of reception in new band. Acknowledgements The submitted paper has arisen during the work on the project which has been financially supported by the Technology Agency of the Czech Republic under grant No. TE This work was also supported by the Student Grant Agency of the Czech Technical University in Prague, grant No. SGS14/150/OHK3/2T/13. References [1] SVATOŇ, J., POPP, J. '"Multi-constellation GNSS systems, Signals and Receivers," In Proceedings of the 9th International Student Conference on Electrical Engineering POSTER Prague (Czech Republic), 2014, p [2] BeiDou 2 Signal in Space ICD, version v1.0. China Satellite Navigation office, [3] KACMARIK, P. et al., Dual-frequency Tracking of Compass Signals: Compass Implementation to the Witch Navigator Receiver, Xian (China), 2012 [4] BeiDou 2 Signal in Space ICD, version v2.0. China Satellite Navigation office, [5] IRNSS Signal In Space ICD. Version 1.0. Bangalore, 2014DOBEŠ, J. et al Using the Sensitivity Analysis of the Noise Spectral Density for Practical Circuit Design IEEE International Symposium on Circuits and Systems (ISCAS). p [6] Thombre, S. et al Tracking IRNSS Satellites. InsideGNSS. online: [7] SVATON, J., VEJRAŽKA, F., Experiments with Reception of IRNSS Satellite Navigation Signals in the S and C Frequency Bands. In Proceedings of the 11th International conference TRANSNAV Gdynia (Poland), 2015, p [8] BRADFORD, P.W. SPILKER, J. and ENGE, P Global positioning system: theory and applications. AIAA Washington DC. [9] DOBEŠ, J. et al. Using the Sensitivity Analysis of the Noise Spectral Density for Practical Circuit Design IEEE International Symposium on Circuits and Systems (ISCAS), 2014, p

5 POSTER 2015, PRAGUE MAY 14 5 About Authors... Jiří SVATOŇ was born in Žďár nad Sázavou (Czech republic). He is a post gradual student of CTU in Prague at Department of Radioengineering. Have a MSc. From wireless communications. He is interested in construction of radio systems and signal processing. His PhD studies are devoted to study and optimization of multi-constellation receivers.