Operating Manual Vol 1 - ES Documentation

Digital Standard GPSSMIQ2.20 Digital Standard GPSWhen equipped with the options Modulation Coder (SMIQB20), Data Generator (SMIQB11) and DigitalStandard GPS (SMIQB51), SMIQ can generate the signal of a GPS satellite. Section 2.20.1 provides anintroductory overview of the Global Positioning System (GPS). Section 2.20.2 then describes theassociated control functions. For more detailed information on generating GPS signals, refer to section2.20.3.2.20.1 Description of Global Positioning System (GPS)The Global Positioning System consists of several satellites circling the earth in low orbits. The positionof a receiver on the earth can be determined by carrying out delay measurements of at least four signalsemitted by different satellites.Being transmitted on a single carrier frequency, the signals of the individual satellites can bedistinguished by means of correlation (Gold) codes (with GPS, these codes are known as C/A codes).Information on time and satellite orbit is contained in the navigation data emitted by each satellite. In thiscase, the C/A codes are used as spreading codes (see CDMA) for the navigation data.Each GPS satellite emits an individual navigation data sequence spread by the C/A code assigned to itat the carrier frequency L1 = 1.57542 GHz. A GPS signal of this type (see Table 2-33 GPS systemparameters), which allows basic receiver function tests to be carried out, can be generated by SMIQ forone satellite.Table 2-33GPS system parametersCarrier frequencySignal level, after antennaDoppler shiftSymbol rate (C/A code)C/A codesModulationInformation data rate (navigation data)Frame structure of navigation data1.57542 GHzApprox. –125 dBm to [1] and [2], depending on receiveconditions-10 kHz to +10 kHz settable1.023 Msps1 to 37 settable, 1023 chips per C/A codeBPSK50 Hz25 frames consisting of 5 subframes where1 subframe consists of 10 words,1 word consists of 30 data bits,1 data bit consists of 20460 C/A code chips.Use of navigation dataThe C/A code used is fundamental to the simulation of GPS signals. The C/A code can be set from 1 to37 in the operating menu and specifies the satellite to be simulated.In addition to this, navigation data play an extremely important role, since they are essential forcalculating the positions of the four satellites, which are the minimum prerequisite for localizationpurposes. However, even if only one satellite is available (as simulated by SMIQ), pseudo navigationdata can be used to check the decoding of navigation information (such as GPS time, almanac andephemeris) in addition to the recognition of the C/A code.Current almanac data can be downloaded via the Internet. Once converted into navigation data via PCapplication software available on the Rohde & Schwarz homepage (www.rohde-schwarz.com,Application Note 1GP46, AlmanacUploader), the data can be transferred to SMIQ as a data list. Thisensures that any navigation data records can be used for GPS signal generation in SMIQ.1125.5555.03 2.334E-9