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RCB-F9T - Integration manual

receiver obtains some credible timing information from a satellite or an aiding message, it will jump
to an estimate of GNSS time.

3.7.2 Navigation epochs

Each navigation solution is triggered by the tick of the 1 kHz clock nearest to the desired navigation
solution time. This tick is referred to as a navigation epoch. If the navigation solution attempt is
successful, one of the results is an accurate measurement of time in the time-base of the chosen
GNSS system, called GNSS system time. The difference between the calculated GNSS system time
and receiver local time is called the clock bias (and the clock drift is the rate at which this bias is
changing).

In practice the receiver's local oscillator will not be as stable as the atomic clocks to which GNSS
systems  are  referenced  and  consequently  clock  bias  will  tend  to  accumulate.  However,  when
selecting the next navigation epoch, the receiver will always try to use the 1 kHz clock tick which it
estimates to be closest to the desired fix period as measured in GNSS system time. Consequently
the number of 1 kHz clock ticks between fixes will occasionally vary. This means that when producing
one fix per second, there will normally be 1000 clock ticks between fixes, but sometimes, to correct
drift away from GNSS system time, there will be 999 or 1001.

The GNSS system time calculated in the navigation solution is always converted to a time in both
the GPS and UTC time-bases for output.

Clearly when the receiver has chosen to use the GPS time-base for its GNSS system time, conversion
to GPS time requires no work at all, but conversion to UTC requires knowledge of the number of
leap seconds since GPS time started (and other minor correction terms). The relevant GPS-to-UTC
conversion parameters are transmitted periodically (every 12.5 minutes) by GPS satellites, but can
also be supplied to the receiver via the UBX-MGA-GPS-UTC aiding message. By contrast when the
receiver has chosen to use the GLONASS time-base as its GNSS system time, conversion to GPS
time is more difficult as it requires knowledge of the difference between the two time-bases, but as
GLONASS time is closely linked to UTC, conversion to UTC is easier.

When  insufficient  information  is  available  for  the  receiver  to  perform  any  of  these  time-base
conversions precisely, pre-defined default offsets are used. Consequently plausible times are nearly
always generated, but they may be wrong by a few seconds (especially shortly after receiver start).
Depending on the configuration of the receiver, such "invalid" times may well be output, but with
flags indicating their state (e.g. the "valid" flags in UBX-NAV-PVT).

u-blox receivers employ multiple GNSS system times and/or receiver local times (in order
to support multiple GNSS systems concurrently), so users should not use UBX messages
reporting GNSS system time or receiver local time. It is recommended to use messages that
report UTC time and other messages are retained only for backwards compatibility reasons.

3.7.3 iTOW timestamps

All the main UBX-NAV messages (and some other messages) contain an iTOW field which indicates
the GPS time at which the navigation epoch occurred. Messages with the same iTOW value can be
assumed to have come from the same navigation solution.

Note  that  iTOW  values  may  not  be  valid  (i.e.  they  may  have  been  generated  with  insufficient
conversion data) and therefore it is not recommended to use the iTOW field for any other purpose.

The original designers of GPS chose to express time/date as an integer week number
(starting with the first full week in January 1980) and a time of week (often abbreviated
to TOW) expressed in seconds. Manipulating time/date in this form is far easier for digital
systems than the more conventional year/month/day, hour/minute/second representation.

UBX-19003747 - R04

 

3 Receiver functionality

Page 26 of 54

Early production information

Содержание RCB-F9T

Страница 1: ...high accuracy timing board Integration manual Abstract This document describes the features and application of RCB F9T a multi band GNSS timing board o ering nanosecond level timing accuracy www u bl...

Страница 2: ...t to intellectual property rights Reproduction use modi cation or disclosure to third parties of this document or any part thereof without the express permission of u blox is strictly prohibited The i...

Страница 3: ...e evaluation 17 3 3 Interfaces 17 3 3 1 UART interface 17 3 4 Prede ned PIOs 18 3 4 1 RESET_N 18 3 4 2 TIMEPULSE 18 3 5 Antenna supervisor 18 3 5 1 Antenna voltage control ANT_OFF 18 3 5 2 Antenna sho...

Страница 4: ...y 43 4 2 1 VCC Main supply voltage 43 4 2 2 RCB F9T VCC_ANT Antenna power supply 44 4 3 Antenna 44 4 4 EOS ESD precautions 45 4 4 1 ESD protection measures 45 4 4 2 EOS precautions 46 4 4 3 Safety pre...

Страница 5: ...existing and new users should read this section to understand the new messages employed Most of the following sub sections should be familiar to existing users of u blox positioning products however...

Страница 6: ...with its di erential timing mode In di erential timing mode correction data is exchanged with other neighboring ZED F9T timing receivers via a communication network In di erential timing mode the RCB...

Страница 7: ...in u center and within this document Within u center a con guration group is identi ed as Group name and the con guration item is identi ed as the item name under the Generation 9 Con guration View A...

Страница 8: ...how often the message is output For periodic output messages the rate relates to the event the message is related to For example the UBX NAV PVT navigation position velocity and time solution is rela...

Страница 9: ...2 messages are not supported by this standard To modify the RTCM input output settings see the con guration section in the u blox RCB F9T Interface description 2 3 1 5 2 List of supported RTCM input...

Страница 10: ...into Survey in mode CFG TMODE MODE SURVEY_IN the following items are required Con guration item Description CFG TMODE MODE Receiver mode disabled survey in or xed CFG TMODE SVIN_MIN_DUR Survey in min...

Страница 11: ...PE1005_UART1 Output rate of the RTCM 3X TYPE1005 message on port UART1 RTCM base station message CFG MSGOUT RTCM_3X_TYPE1077_UART1 Output rate of the RTCM 3X TYPE1077 message on port UART1 RTCM GPS MS...

Страница 12: ...and their details can be seen in Table 6 and Table 7 below Platform Description Portable default Applications with low acceleration e g portable devices Suitable for most situations Stationary Used i...

Страница 13: ...algorithm uses a constant altitude to compensate for the missing fourth SV When a SV is lost after a successful 3D x min four SVs available the altitude is kept constant at the last known value This i...

Страница 14: ...rse over ground from position at very low speed The output of the low speed course over ground lter is published in the UBX NAV PVT message headMot eld UBX NAV VELNED message heading eld NMEA RMC mess...

Страница 15: ...B F9T Integration manual Figure 2 Position publication in static hold mode Figure 3 Flowchart of the static hold mode UBX 19003747 R04 3 Receiver functionality Page 15 of 54 Early production informati...

Страница 16: ...0 1 m s then the course over ground value becomes inaccurate too In this case the course over ground value is frozen i e the previous value is kept and its accuracy is degraded over time These frozen...

Страница 17: ...Outside The position lies outside of the geofence with the con gured con dence level Unknown There is no valid position solution or the position uncertainty does not allow for unambiguous state evalu...

Страница 18: ...EA and or UBX protocol The RCB F9T active antenna supervisor block diagram is shown in the Figure 1 The antenna supervisor is monitoring active antenna current consumption and based on that antenna op...

Страница 19: ...enabled by default in the RCB F9T 3 5 2 Antenna short detection ANT_SHORT_N To set short circuit detect ON CFG HW ANT_CFG_SHORTDET 1 Result MON RF in u center Antenna status OK Antenna power status O...

Страница 20: ...riod receiver will re test the short condition by enabling ANT_OFF LOW If a short is not present it will report antenna condition is ok GNTXT 01 01 02 ANTSTATUS OK 25 MON RF in u center Antenna status...

Страница 21: ...ance activity In order to protect customers against the impact of such outages u blox runs at least two instances of the AssistNow Online Service on independent machines Customers have a choice of req...

Страница 22: ...line Service uses a simple stateless HTTP interface Therefore it works on all standard mobile communication networks that support internet access including GPRS UMTS and Wireless LAN No special arrang...

Страница 23: ...after the other If the communication link is fast and or the receiver is busy trying to acquire new signals it is possible that the internal bu ers will over ow and some messages will be lost In order...

Страница 24: ...section below If this value is not provided the server assumes an accuracy of 300 km Must be in range 0 to 6000000 tacc Numeric seconds Optional The timing accuracy see the Time parameters tacc and la...

Страница 25: ...lient should establish an accurate sense of time itself e g by calibrating its system clock using a local NTP service and then modify the time data received from the service as appropriate 3 7 Clocks...

Страница 26: ...lites but can also be supplied to the receiver via the UBX MGA GPS UTC aiding message By contrast when the receiver has chosen to use the GLONASS time base as its GNSS system time conversion to GPS ti...

Страница 27: ...in the confirmedDate and confirmedTime ags in the UBX NAV PVT message If these ags are set the time validity can be con rmed by using an additional independent source meaning that the probability of...

Страница 28: ...to 0 and e ectively ignored Which master clock the UTC time is referenced to is output in the message UBX NAV TIMEUTC The preferred variant of UTC time can be speci ed using CFG NAVSPG UTCSTANDARD con...

Страница 29: ...the system the rst ambiguous date will be in 2124 Therefore u blox 9 receivers using Protocol Version 24 and above regard the date information transmitted by GLONASS BeiDou and Galileo to be unambiguo...

Страница 30: ...inst a reference timing source In order to get the best timing accuracy with the antenna a xed and accurate position is needed If relative time accuracy between multiple receivers is required do not m...

Страница 31: ...select an appropriate UTC version itself based on the GNSS con guration using in order of preference USNO if GPS is enabled SU if GLONASS is enabled NTSC if BeiDou is enabled and nally European if Ga...

Страница 32: ...e of the generated pulse as soon as receiver has calculated a valid time from a received signal Only used if the corresponding item is set to use another setting in locked mode user delay The cable de...

Страница 33: ...mitigate it Threat u blox solution Over air signal integrity Spoo ng detection mitigation Jamming detection mitigation GNSS receiver integrity Secure boot Secure rmware update Table 11 u blox security...

Страница 34: ...the receiver detects that the noise has risen above a preset threshold the receiver reports Warning If in addition there is no current valid x the receiver reports Critical The monitor has four state...

Страница 35: ...between di erent GNSS the most important step in parsing a UBX RXMSFRBX message is to identify the form of the data This should be done by reading the gnssId eld which indicates which GNSS the data w...

Страница 36: ...10 1 2 2 GPS L2C For GPS L2C signals each reported subframe contains the CNAV message as described in the GPS ICD The ten words are arranged as follows Figure 12 GPS L2C subframe words 3 10 1 3 GLONAS...

Страница 37: ...rds are arranged as follows Figure 13 GLONASS subframe words In some circumstances especially on startup the receiver may be able to decode data from a GLONASS SV before it can identify the SV When th...

Страница 38: ...E5 bl bQ signals both transmit the I NAV message but in di erent con gurations The UBX RXM SFRBX structures for them are as follows 3 10 1 5 1 Galileo E1 C B For Galileo E1 C B signals each reported...

Страница 39: ...ileo E5 bI bQ signals each reported subframe contains a pair of I NAV pages as described in the Galileo ICD Galileo pages can either be Nominal or Alert pages For Nominal pages the eight words are arr...

Страница 40: ...he structure of the eight words will be slightly di erent as indicated by the Galileo ICD 3 10 1 6 SBAS For SBAS L1C A signals each reported subframe contains eight 32 data words to deliver the 250 bi...

Страница 41: ...ssage GNSS Signal gnssId sigId numWords period GPS L1C A 0 0 10 6s SBAS L1C A 1 0 8 1s GPS L2CL 0 3 10 12s GPS L2CM 0 4 10 12s Galileo E1 C 2 0 8 2s Galileo E1 B 2 1 8 2s Galileo E5 bl 2 5 8 2s Galile...

Страница 42: ...ssible See Multiple GNSS assistance Hot start In hot start mode the receiver was powered down only for a short time 4 hours or less so that its ephemeris is still valid Since the receiver does not nee...

Страница 43: ...6 TP1 O Time pulse1 LVCMOS 7 TP2 O Time pulse2 LVCMOS 8 GND Ground Table 14 RCB F9T pin assignment 4 2 Power supply The u blox RCB F9T timing board has two power supply pins VCC and VCC_ANT 4 2 1 VCC...

Страница 44: ...recommends using an active antenna with RCB F9T If an active antenna needs to be implemented in an application case it is recommended that an OEM active antenna module be used that meets our speci ca...

Страница 45: ...d voltage whereas bipolar semiconductors are more susceptible to thermal overstress The following design guidelines are provided to help in designing robust yet cost e ective solutions To avoid overst...

Страница 46: ...0950 1 In addition to external limited power source only Separated or Safety Extra Low Voltage SELV circuits are to be connected to the module including interfaces and antennas For more information ab...

Страница 47: ...self One reason is that the frequency band above 1 GHz is not well regulated with regards to EMI and even if permitted signal levels are much higher than GNSS signal power Notably all types of digital...

Страница 48: ...frequency The main sources are wireless communication systems such as LTE GSM CDMA WCDMA Wi Fi BT etc Measures against out of band interference include maintaining a good grounding concept in the des...

Страница 49: ...ng an antenna patch connect ground of the device When handling the RF pin do not come into contact with any charged capacitors and be careful when contacting materials that can develop charges e g pat...

Страница 50: ...0x2005000c E1 0 UTC UTC time reference Table 16 RCB F9T speci c UART baud rate antenna supervisor and time pulse 1 default con gurations B Glossary Abbreviation De nition ANSI American National Stand...

Страница 51: ...on manual Abbreviation De nition SBAS Satellite based Augmentation System SV Space Vehicle a satellite UBX u blox QZSS Quasi Zenith Satellite System UBX 19003747 R04 Appendix Page 51 of 54 Early produ...

Страница 52: ...on doc no UBX 19003606 3 Radio Resource LCS Protocol RRLP 3GPP TS 44 031 version 11 0 0 Release 11 For regular updates to u blox documentation and to receive product change noti cations please registe...

Страница 53: ...dvance information R02 18 Jun 2019 tkoi Early production information R03 16 Jan 2020 tkoi Early production information Updated type number R04 25 Feb 2020 jhak Updated minimum and maximum gains in Ant...

Страница 54: ...m E mail info_cn u blox com Support support_cn u blox com Regional O ce China Chongqing Phone 86 23 6815 1588 E mail info_cn u blox com Support support_cn u blox com Regional O ce China Shanghai Phone...

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