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Mitel GPS Orion-S/-HD Receiver, User Manual

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Document Title: 

 

40 

User’s  Manual for the GPS Orion-S/-HD Receiver 

Document No. 

 

Issue 1.0 

GTN-MAN-0110 

 

June 22, 2003 

 DLR/GSOCNo part of this document shall be reproduced in any form or disclosed to third parties without prior authorization. 

4.4.1.13  F47 – IIP Prediction 

 

MsgID  Chars. 

Format 

Description 

F47 

52 

 

IIP prediction 

 

1 x 

<STX> 

 

3 xxx 

Message Id (=F48) 

 

4 xxxx 

GPS week 

 

12 xxxxxx.xxxxx 

GPS seconds of week [s] (at output) 

 

2 xx 

GPS-UTC [s] 

 

1 x 

Blank 

 

9 sxxx.xxxx 

Longitude [deg] 

 

1 x 

Blank 

 

8 sxx.xxxx 

Latitude [deg] 

 

1 x 

Blank 

 

6 xxxx.x 

Time to impact [s]] 

 

1 x 

Validity flag (0= no IIP pred. available, 1=valid IIP pred. available) 

 

2 xx 

Checksum  

 

1 x 

<ETX> 

 

Example: 

 

<STX>

F471195 45245.5000013  -43.9531  -2.2042  211.31

63<ETX> 

 
 
 

4.4.1.14  F48 – Configuration and Status Parameters 

 

MsgID  Chars. 

Format 

Description 

F48 

48 

 

Configuration and status parameters 

 

1 x 

<STX> 

 

3 xxx 

Message Id (=F48) 

 

4 xxxx 

GPS week 

 

8 xxxxxx.x 

GPS seconds of week [s] (at output) 

 

2 xx 

GPS-UTC [s] 

 

4 xxxx 

Almanac week 

 

5 sxxxx 

Doppler offset [Hz] 

 

1 x 

Mode (0=default,1=rocket,2=orbit) 

 

1 x 

Output format (0=default,1=extended) 

 

1 x 

Update rate of navigation and display task [Hz] (1Hz, 2Hz, 5Hz) 

 

2 xx 

Spare CPU capacity [%] 

 

3 sxx 

Elevation mask [deg] 

 

2 xx 

PDOP mask 

 

8 xxxxxx.x 

Launch time (GPS seconds of week [s])  

 

2 xx 

Checksum  

 

1 x 

<ETX> 

 

Example: 

 

<STX>

F481139216000.1131139  23300226  099216000.1

7C<ETX> 

 
 
 

Summary of Contents for GPS Orion-S/-HD Receiver

Page 1: ...echnology German Space Operations Center GSOC Deutsches Zentrum für Luft und Raumfahrt DLR e V User s Manual for the GPS Orion S HD Receiver O Montenbruck M Markgraf Doc No GTN MAN 0110 Version 1 0 Date June 22 2003 ...

Page 2: ...cription of Change 1 0 June 22 2003 all First release Disclaimer Information in this manual has been compiled with adequate care and represents the best knowledge of the authors Any errors remaining after its release will be fixed upon notifica tion In no way shall DLR or the authors be held liable for direct or indirect damage result ing from missing or erroneous information Furthermore DLR reser...

Page 3: ...itialization 9 3 1 5 Output Selection 10 3 1 6 Pulse per Second Signal 11 3 1 7 Troubleshooting 11 3 2 Special Applications 12 3 2 1 Aiding for Ballistic Trajectories 12 3 2 2 Lift off Signal 13 3 2 3 IIP Prediction 13 3 2 4 Aiding for LEO Satellites 15 3 2 5 Relative Navigation 16 3 2 6 External LNA Power Supply 17 4 Command and Output Message Reference 18 4 1 Overview 18 4 2 Protocol Description...

Page 4: ...ng Parameters Mitel 32 4 4 1 6 F40 Cartesian Navigation Data 33 4 4 1 7 F41 Pseudorange and Range Rate Smoothed 34 4 4 1 8 F42 Pseudorange Carrier Phase and Range Rate Raw 35 4 4 1 9 F43 Channel Status 36 4 4 1 10 F44 Clock Data 38 4 4 1 11 F45 Relative Navigation Data WGS 84 System 39 4 4 1 12 F46 Relative Navigation Data RTN Frame 39 4 4 1 13 F47 IIP Prediction 40 4 4 1 14 F48 Configuration and ...

Page 5: ...This manual provides a user s guide for the DLR s GPS Orion receivers for space and high dynamics applications It describes the hard and software interfaces required for operating the receiver in standalone and embedded applications Information in this document supple ments and supercedes related sections of the GPS Orion Product Brief 1 and the GP2000 Series Demonstrator Board User s Guide 2 It i...

Page 6: ...l Positioning System GSOC German Space Operations Center I F Intermediate Frequency IIP Instantaneous Impact Point IQ In phase and Quadrature correlator output L1 GPS frequency 1575 42 MHz LEO Low Earth Orbit LNA Low noise amplifier MITEL Company name NMEA Nautical Marine Electronics Association NVM Non Volatile Memory ORION Product name PC Personal Computer PLL Phase Locked Loop PPS Pulse per sec...

Page 7: ...n under the rapidly varying signal conditions encountered in typical space missions Key upgrades include enhanced tracking loops a synchronization of measurements to inte ger GPS seconds the provision of precise carrier phase measurements a revised navigation algorithm as well as a software based aiding of the signal acquisition using reference trajec tory data In addition to the above software ch...

Page 8: ...e and rapid signal ac quisition under rapid motion of the host vehicle For satellites in low Earth orbit aiding is pro vided by an analytical orbit model using twoline elements whereas a set of piecewise poly nomials is employed to approximate the trajectory of ballistic vehicles sounding rockets re entry capsules in the HD version Various commands specific to each of these versions are provided t...

Page 9: ...ignal is digitized and sampled to create a digital IF of 1 405 MHz with 2 bit quantization The fundamental reference frequency for the mixing process is provided by a 10 0 MHz TCXO with a specified stability of 2 5 ppm It also used to derive a 40 MHz clock frequency for the correlator The subsequent signal processing is performed in the GP2021 correlator chip 9 which pro vides 12 fully independent...

Page 10: ...f signal 8 Vdd level sense circuit output used as a reset if connected to GND 9 Vdd 5V prime power supply input 10 PPS output optional General physical and electrical parameters of the Orion main board are summarized in Table 2 2 The GPS Orion receiver and its components have not been validated for space applica tions Nevertheless limited information on the radiation hardness of the core chipset s...

Page 11: ...e 2 2 Pins 7 and 8 are cross connected since the Orion receiver does not support a hardware handshake Likewise the three pins 1 4 and 6 are connected among each other Table 2 2 Pin assignment for RS232 Sub D9 connectors Port A and B Pin Description Remarks Schematic 1 DCD Data Channel Received Line Signal Detector Connected with DTR and DSR pins 4 6 2 RxD Receive Data 3 TxD Transmit Data 4 DTR Dat...

Page 12: ...ce board to the PC s COM1 port connect blue cable to ground pin of power supply minus pole of battery The receiver will start to operate once the red cable is connected to the plus pole of the power supply 3 1 2 Precautions To avoid an undesirable behavior or even destruction of the receiver the following handling instructions shall be considered The center pin of the antenna connector provides a ...

Page 13: ...values used for the de fault initialization depend on the particular software r elease and may vary between receivers The ephemeris data are marked as unavailable A boot message identifying the current software version is issued Subsequently the signal tracking is started and the receiver starts outputting a predefined sequence of messages at a 1 Hz rate The same steps are performed when the reset...

Page 14: ... It sets the output interval of a specified message number in multiples of the navigation interval Fur thermore messages can be polled once or disabled completely The data rate selection is available for the F00 03 04 05 08 WinMon messages i e the standard Mitel message set of the original Orion receiver firmware the F40 41 42 43 45 46 47 48 WinMon messages spe cific for the Orion S and or HD rece...

Page 15: ...s may be performed at any time to validate the proper receiver operation The product of the supply voltage and current consumption shall match the nominal power consumption of 2 4 0 1W A lower value may indicate errors in the boot proc ess caused by e g twisted EPROMs or a broken address data line on the main board When connected to a terminal program the receiver shall output a continuous stream ...

Page 16: ... by its start epoch GPS week and seconds and three coefficients per axis To minimize the computational workload in each step a simple 2nd order polynomial 2 0 0 t t c c c t t b b b a a a z y x t z y x z y x z y x r 3 1 is used to approximate the trajectory over discrete time intervals in the WGS84 reference frame Upon differentiation one obtains an associated approximation of the instantaneous Ear...

Page 17: ...iori trajectory polynomials and the time since the reference epoch As such a faulty or outdated navigation solution has no im pact on the initialization of new channels and safe acquisition can even be achieved if during boosted flights that do not allow a linear prediction of the latest state vector On the other hand erroneous values may be predicted in case of a major deviation from the nominal ...

Page 18: ...em and a plane Earth parabolic trajectory model with first order corrections for surface curvature gravity variation and Earth rotation is used to predict the motion up to the intersection with the surface of the Earth 13 Due to its inherent simplicity the analytical IIP model is well suited for real time time compu tations but is still competitive in terms of accuracy Comparisons have demonstrate...

Page 19: ...number of year International designator piece of launch Year of epoch last two digits t0 day of epoch day of year and fractional day 1 2 dn0 dt the time rate of change in the mean mean motion in units of rev d 2 or the ballistic coefficient B depending on ephemeris type 1 6 d 2 n0 dt 2 the second time rate of change in the mean mean motion in units of rev d 3 Adeci mal point is assumed between col...

Page 20: ...e instantaneous visibility conditions and expected Doppler shifts of the GPS satellites 3 2 5 Relative Navigation The Orion S receiver operates a DGPS task providing simple relative navigation of two host vehicles via the exchange of raw navigation solutions To operate the relative navigation fea ture the secondary I O ports port B of two receivers must be connected via a bi directional serial rad...

Page 21: ...use of multiple parallel antennas or the use of miniature anten nas with 3 3V LNA In this case a bias T is employed to block the DC supply of the receiver via a built in capacitor and to insert the external supply voltage via an R F isolating induc tivity to the subsequent antenna line An added advantage of the external DC power supply is the possibility to apply a current limitation and thus prot...

Page 22: ...on and velocity RH cmd WinMon all Set reference position to current position RM obsolete cmd WinMon HD S Select aiding mode RP cmd WinMon all Set reference position RS cmd WinMon all Re select satellite SA cmd WinMon all Save almanac SD cmd WinMon all Set date SM cmd WinMon HD S Choose between standard and extended Mitel format SS cmd WinMon all Select satellite ST cmd WinMon all Set time TA cmd W...

Page 23: ...0 out WinMon HD Reference epoch for trajectory polynomials F51 out in WinMon HD Trajectory polynomials F52 out WinMon S User spacecraft mean elements F99 out WinMon all Debug strings log messages command responses GPGGA out NMEA all Position data PASHR POS out NMEA HD Position and velocity data Ashtech PDLRM IIP out NMEA HD Instantaneous impact point PDLRM XSD out NMEA HD Extended status data PDLR...

Page 24: ...f Transmission 0x03 Fig 4 1 WinMon sentence format and protocol frame for command top and output messages bottom Command identifiers consist of two uppercase alphabetic characters while a message iden tifier is made up of an initial F character and a two digit decimal number2 The sentence checksum is the hexadecimal representation of the exclusive or of all the characters in the sentence excluding...

Page 25: ...sive or of all characters in the header and data field i e in between but excluding the and characters and expressed in up percase hex format C C C C C x x x x x H H CR LF C Alphabetic character uppercase x Data field H Hexadecimal checksum character uppercase CR Carriage return 0x13 LF Line feed 0x13 Fig 4 2 NMEA format definition Aside from the overall protocol the NMEA standard specifically def...

Page 26: ...e GPS Orion receiver scans the primary communication port for WinMon sentences em bedded in the STX ETX frame and starts the command processing if the checksum test is passed Commands that are syntactically correct but do not match a supported command identifier are ignored In this case an F98 command response giving the current time and and error message E id Ignored unsupported command with id d...

Page 27: ...s specified for a given receiver Upon execution the revised settings are acknowledged by one of the following command responses I UR Update rate set to 1Hz I UR Update rate set to 2Hz I UR Update rate set to 5Hz E UR Ignored invalid argument CmdID Chars Format Description UR 7 Update Rate 1x STX 2xx Command Id UR 1x Rate Hz supported values 1Hz 2Hz 5Hz 2xx Checksum 1x ETX Examples STX UR136 ETX Se...

Page 28: ...ersion 0 5 s for 2 Hz version A value of 1 for the output interval is used to deactivate a given message An output interval of 0 requests a one time output polling of the given message Negative message numbers control the output of NMEA type message 1 GPGGA etc Examples STX DR400113 ETX Issue the F40 navigation message at each update STX DR43 10D ETX Deactivate the F43 channel status message STX D...

Page 29: ...ars Format Description MC 7 Media Correction 1x STX 2xx Command Id MC 1x Tropospheric correction 0 disabled 1 enabled 1x Ionospheric correction 0 disabled 1 enabled 2xx Checksum 1x ETX Notes Media corrections are applied only to pseudorange measurements but not to range rate data No corrections are applied for GPS satellites below the horizon 0 elevation The tropospheric range correction is altitu...

Page 30: ... ETX Dump current almanac 4 3 2 2 TE Transmit Ephemeris The TE allows polling of GPS ephemeris data F14 message for one or all GPS satellites In case of an invalid argument the command is ignored and a response I TE Ignored invalid argument is issued CmdID Chars Format Description TE 6 Transmit Ephemeris 1x STX 2xx Command Id TE 2xx PRN of selected satellite 00 requests complete set of 32 ephemeri...

Page 31: ...nitialise the receiver in unaided mode whenever its velocity is larger than 50 m s Execution of the command is acknowledged by an F98 command reply giving the message I PV Updated current position and velocity CmdID Chars Format Description PV 72 Set initial position and velocity 1x STX 2xx Command Id PV 11sxxxxxxxx x x m WGS 84 11sxxxxxxxx x y m WGS 84 11sxxxxxxxx x z m WGS 84 11sxxxxx xxxx vx m ...

Page 32: ...additional 5 kHz window in cold start tracking mode For LEO satellites a window of up to 40 kHz may be required Execution of the command is acknowledged by an F98 command reply of the form I DW Changed Doppler window to 11500Hz Negative input values are ignored and an error message E DW Ignored invalid argument is issued CmdID Chars Format Description DW 72 Set Doppler window 1x STX 2xx Command Id...

Page 33: ...command response with either of the following in formation or errors messages is issued I AM Aiding disabled I AM Aiding for ballistic trajectories enabled I AM Aiding for low Earth orbits enabled E AM Ignored unsupported aiding mode selection CmdID Chars Format Description RM 7 Run Mode 1x STX 2xx Command Id AM 1x Aiding mode 0 unaided 1 ballistic 2 orbit 2xx Checksum 1x ETX Notes The Aiding Mode...

Page 34: ...of the new ele ment set is confirmed by the message I LO Twoline elements line 2 received An inconsistent commanding is reported by an E LO Ignored inconsistent twoline elements error message CmdID Chars Format Description LO 75 Load Orbital Elements 1x STX 2xx Command Id LO 6969 x Twoline elements line 1 or 2 2xx Checksum 1x ETX Examples STX LO1 12345U 01999 A 01309 99984954 00020228 00000 0 4611...

Page 35: ... CmdID Chars Format Description LT 6 Load Trajectory 1x STX 1x STX 2xx Command Id LT 2xx Checksum 1x ETX 4 3 4 7 ET End Trajectory The sequence of trajectory polynomials is terminated by the ET command CmdID Chars Format Description ET 6 End Trajectory 1x STX 2xx Command Id ET 2xx Checksum 1x ETX Example STX ET11 ETX Dump current reference trajectory 4 3 4 8 TT Transmit Trajectory The TE command i...

Page 36: ...essages WinMon Format 4 4 1 Periodic Receiver Data 4 4 1 1 F00 Geographic Navigation Data Mitel See 2 for a complete message description 4 4 1 2 F03 Channel Status Data Mitel See 2 for a complete message description 4 4 1 3 F04 Satellite Summary Mitel See 2 for a complete message description 4 4 1 4 F05 Processing Status Mitel See 2 for a complete message description 4 4 1 5 F08 Operating Paramete...

Page 37: ...er GPS sec ond once the receiver has a achieved continuous 3D navigation fix MsgID Chars Format Description F40 104 Cartesian navigation data 1 x STX 3 xxx Message Id F40 4 xxxx GPS week 12 xxxxxx xxxxx GPS seconds of week s of navigation solution 2 xx GPS UTC s 12 sxxxxxxxx xx x WGS84 m 12 sxxxxxxxx xx y WGS84 m 12 sxxxxxxxx xx z WGS84 m 12 sxxxxx xxxxx vx WGS84 m 12 sxxxxx xxxxx vy WGS84 m 12 sx...

Page 38: ... in F42 Absolute errors are of similar size however due the code carrier divergence in dispersive media ionosphere that necessitates regular resets of the filter smoother The range rate measurements are obtained by fitting a quadratic polynomial to three adjacent carrier phase measurements over an interval of 2 x 0 1 s and evaluating its derivative at the latest instant This procedure is rigorousl...

Page 39: ...ed to GPS time as part of the navigation solution In an S A free environment this model clock usually deviates by no more than 30 0 1 µs from the true GPS time Representative accuracies amount to 0 4 m pseudodrange 0 7 mm carrier phase and 8cm s Doppler based range rate for the Orion S receiver The HD version ex hibits a higher noise of the code ca 1m carrier phase ca 1 5 mm and Doppler measuremen...

Page 40: ...ock has been achieved C Carrier lock has been achieved B Bit lock has been achieved F f Frame lock has been achieved After successful completion of the code search the receiver locks to the carrier fre quency using a frequency locked loop FLL It transitions to the phase locked loop PLL once the bit synchronization has been achieved and further synchronizes the tracking to the frame start of the GP...

Page 41: ...sion C N0 db Hz 41 5 1 1 SNR db 13 0 which is also used to compute C N0 values prior to frame lock SNR values obtained with representative antenna systems range from a minimum of 5 dB to a maximum of 20 dB This corresponds to C N0 values between 33 dB Hz and 49 dB Hz respec tively Example STX F431139172840 21311394751361112 8 3 17210 171211f 9 5 12338 124331F11 6 388 49 389461f14 9 21534 214381F14...

Page 42: ...hars Format Description F44 71 Clock data 1 x STX 3 xxx Message Id F44 4 xxxx GPS week 12 xxxxxx xxxxx GPS seconds of week s at message generation time 2 xx GPS UTC s 8 xxxxxxxx TIC count 8 xxxxxxxx Real Time Clock count s 4 xxxx Extrapolated boot time GPS week 12 xxxxxx xxxxx Extrapolated boot time GPS seconds of week s 6 sx xxx Clock drift µs s 8 xxxxxxxx Time of applicability of clock model TIC...

Page 43: ...Nav 2 xx Number of tracked satellites remote receiver 4 xx x PDOP remote receiver 2 xx Checksum 1 x ETX Example STX F451139172978 0000013 653 26 2342 55 11667 94 0 26231 13 04631 2 648422 6 2 66A ETX 4 4 1 12 F46 Relative Navigation Data RTN Frame MsgID Chars Format Description F46 104 Relative navigation data RTN frame 1 x STX 3 xxx Message Id F46 4 xxxx GPS week 12 xxxxxx xxxxx GPS seconds of we...

Page 44: ...y flag 0 no IIP pred available 1 valid IIP pred available 2 xx Checksum 1 x ETX Example STX F471195 45245 5000013 43 9531 2 2042 211 3163 ETX 4 4 1 14 F48 Configuration and Status Parameters MsgID Chars Format Description F48 48 Configuration and status parameters 1 x STX 3 xxx Message Id F48 4 xxxx GPS week 8 xxxxxx x GPS seconds of week s at output 2 xx GPS UTC s 4 xxxx Almanac week 5 sxxxx Dopp...

Page 45: ...s 3 xxx Time system indicator GPS or UTC 1 x ETX Example STX F502003 4 1 52813 2UTC04 ETX 4 4 2 2 F51 Trajectory Polynomials MsgID Chars Format Description F51 118 Trajectory polynomials 1 x STX 3 xxx Message Id F51 2 xx Running index of polynomial 0 9 10 sxxxxx xxx t_0 s since reference epoch 11 sxxxxxxxx x a_x m WGS 84 11 sxxxxx xxxx b_x m s WGS 84 11 sxxx xxxxxx c_x m s 2 WGS 84 11 sxxxxxxxx x ...

Page 46: ... STX 3 xxx Message Id F52 4 xxxx GPS week of epoch 11 xxxxxxx xxx GPS seconds of week s of epoch 11 xxxxxx xxxx SGP4 mean semi major axis a km 11 xx xxxxxxxx SGP4 mean eccentricity e 9 xxxxx xxxx SGP4 mean inclination i deg 10 xxxxx xxxx SGP4 mean right ascension of ascending node Ω deg 10 xxxxx xxxx SGP4 mean argument of perigee ω deg 10 xxxxx xxxx SGP4 mean mean anomaly M deg 12 xxx xxxxxxxx SGP...

Page 47: ... 4 3 Diagnosis Messages 4 4 3 1 F98 Command Response MsgID Chars Format Description F98 var Command Response 1 x STX 3 xxx Message Id F98 4 xxxx GPS week 8 xxxxxx x GPS seconds of week s at output 1 x Dash 1 x Message type I Info W Warning E Error 1 x Dash 2 xx Command ID 1 x Dash var Text 2 xx Checksum 1 x ETX Examples STX F981139172809 2 I MC Ionospheric correction enabled1C ETX STX F98113917280...

Page 48: ...es int s seconds float 9 000000 00 to 235959 99 single comma C 1 Latitude ddmm mmmmm d degree int m minutes float 10 0000 00000 to 8959 99999 single comma C 1 Latitude Direction C 1 N or S single comma C 1 Longitude dddmm mmmmm d degree int m minutes float 11 00000 00000 to 17959 99999 single comma C 1 Longitude Direction C 1 E or W single comma C 1 Altitude above below WGS84 Earth ellipsoid FFFFF...

Page 49: ...g due to an insufficient number of tracked satellites a re duced sentence is transmitted Quantity Format Units of Chars Range Sentence identifier CCCCC 5 PASHR single comma C 1 Secondary identifier CCCC 3 POS single comma C 1 Not used C 1 0 single comma C 1 Satellites used in Nav fix XX 2 00 12 single comma C 1 Current receiver time hhmmss ss h hours int m minutes int s seconds float 9 000000 00 t...

Page 50: ... 1 UTC time of current IIP predition hhmmss ss h hours int m minutes int s seconds float 9 000000 00 to 235959 99 single comma C 1 IIP validity flag C see note 1 1 1 single comma C 1 Latitude of predicted IIP ddmm mmmm d degree int m minutes float 9 0000 0000 to 8959 9999 single comma C 1 Latitude Direction of pre dicted IIP C 1 N or S single comma C 1 Longitude of predicted IP dddmm mmmm d degree...

Page 51: ...smitted Quantity Format Units of Chars Range Sentence identifier CCCCC 5 PDLRM single comma C 1 Secondary identifier CCC 3 IIP single comma C 1 Current receiver time hhmmss ss h hours int m minutes int s seconds float 9 000000 00 to 235959 99 single comma C 1 IIP validity flag C see note 1 1 0 Commas CCCCCC 6 Total number of characters including sentence header and trailer 27 6 33 Notes 1 IIP Vali...

Page 52: ...n Status C see note 2 1 0 or 2 single comma C 1 Doppler Offset XXXX Hz 5 9999 to 9999 single comma C 1 Elevation Mask XX deg 3 90 to 90 single comma C 1 Spare CPU Capacity XX 2 00 to 99 single comma C 1 Launch Time hhmmss ss h hours int m minutes int s seconds float 9 000000 00 to 235959 99 Repeated for each of 12 channels single comma C 1 PRN XX 2 00 to 32 single comma C 1 Lock Indicator C see no...

Page 53: ... seconds 2 00 or 99 single comma C 1 Receiver clock offset F FFFFFFFFF seconds 12 9 999999999 to 9 999999999 Repeated for each of 12 channels single comma C 1 PRN XX 2 00 to 32 single comma C 1 Smoothed pseudorange FFFFFFFF FF meter 11 00000000 00 to 99999999 99 single comma C 1 Range rate from carrier phases FFFF FF meter secs 8 9999 99 to 9999 99 single comma C 1 Health and validity flag X see n...

Page 54: ... DS3861 Issue 3 1 November 1997 9 GP2021 GPS 12 channel Correlator DS4077 Mitel Semiconductor Issue 2 6 July 1996 10 ARM60 Data Sheet DS3533 Mitel Semiconductor 11 Unwin M J Oldfield M K Underwood C I Harboe Sorensen R The Use of Commercial Technology for Spaceborne GPS Receiver Design ION GPS 1998 pp 1983 Nashville Sep 15 18 1998 12 Montenbruck O Enderle W Schesny M Gabosch V Ricken S Turner P Po...

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