The space segment currently consists of 28 operational satellites orbiting the earth. They orbit at a height of almost 21,000 km above the earth's surface. Any one satellite completes its orbit in around 12 hours. Due to the rotation of the Earth, a satellite will be at its initial starting position after approximately 24 hours.
GPS receivers collect signals from satellites in view. They display the user's position, velocity, and time, as needed for their marine, terrestrial, or aeronautical applications. Some display additional data, such as distance and bearing to selected waypoints or digital charts.
Yes, GPS receivers can work anywhere on Earth, providing their antennas have a good view to the sky above.
NMEA 0183, or NMEA for short, stands for National Marine Electronics Association, a US standards committee that defines data message structure, contents and protocols to allow the GPS receiver to communicate with other pieces of electronic equipment. NMEA 0183 is a standard data communication protocol used by GPS receivers.
Acquisition time is the time it takes for a GPS receiver to acquire satellite signals and determine the initial position. The time may vary depending how much satellite information was already received during the last boot up, and how much of that data is usable. During this time, GPS is receiving data such as satellites’ ephemeris, almanac, and other critical information in the form of navigation messages.
Latest GlobalTop GPS engines will automatically determine the updating and refreshing timing. The time required for update typically depends on the current calculation stage and environment. If the GPS module has not been operated before or has not been in operation for a very long time, the minimum time required to receive all data in the GPS navigation message (including RTC, ephemeris and almanac) is 12.5 minutes. It is hard to say for a receiver that already contains partial messages, because the GPS engine will automatically determine which data it needs and which data it will need to update.
The receiving time may also be depended on receiving conditions, because it takes 30 seconds to receive 1 page of the GPS navigation message (for a total of 25). If the data for a particular page is missed due to bad reception, it must wait for another cycle.
AGPS can be used to speed up this process.
There are several ways to increase the accuracy of GPS receivers through DGPS (WAAS, EGNOS) and RTCM: By comparing the GPS signal received with a precisely known location, it is possible to increase the GPS module’s position accuracy to around 2.5 m.
DGPS is a technique used to improve positioning or navigation accuracy by determining the positioning error at a known location and subsequently incorporating a corrective factor into the position calculations of another receiver operating in the same area and simultaneously tracking the same satellites. It is a system of beacons which broadcasts signals to help increase the accuracy of GPS positioning.
WAAS (Wide Area Augmentation System) is a network of 25 reference station (WRS, Wide Area Ground Reference Station) that receive GPS signals. They have been surveyed exactly in terms of their position. Each reference station determines actual and target pseudo-range deviation.
The precisely processed DGPS correction values are transmitted to two geo-stationary satellites (Inmarsat) and beamed back to earth on the GPS L1 frequency. The WAAS signals are received by GPS receivers equipped for this task and further processed.
Currently, WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit.
EGNOS (European GEO-stationary Navigation Overlay System) is satellite-based augmentation system for existing GPS and Glonass satellite navigation systems. A European network of GPS/Glonass receivers has been built up to receive the corresponding satellite signals and relay these to central data processing stations.
Similar to WAAS, the signals received are evaluated by taking into account the exact known position of receiving stations. In this way, correction data can be determined that is ultimately broadcast to users via geo-stationary communications satellites. With the help of these corrections positional accuracy can be significantly increased.
AGPS stands for “Assisted Global Positioning System“. It is method of using pre-calculated orbital data such as emphasis and almanac for each satellite to speed up acquisition time. AGPS is supported on selected GlobalTop GPS modules. Please see software service for more details.
GlobalTop GPS module only provides the coordinates of its current location. No map is included with the GPS module.
GPS antenna module comes pre-installed with a finely tuned GPS antenna not found in GPS module. If you have RF design experience and experience in antenna fine tuning, the GPS modules without antenna is a good choice for its added flexibility. Otherwise, it is best to choose antenna modules as they are relatively easier to work with.
Please see comparison table located in the product page for more information.
Yes! We have evaluation kit available for all GlobalTop GPS modules. Please contact us for more details.
USB port is the standard connections for our evaluation kit, which can be connected to a Windows-based PC and controlled using with GlobalTop GPS applications. The USB port is a virtual COM port made possible by SL CP210X USB Bridge IC that is connected to UART port located on the GPS module. So essentially, the computer is communicating directly with the UART port of the GPS module.
First, place the test module inside test chamber designed to avoid noise interference. Then, use a multi-channel GPS simulator and set it to 12 channels satellite view. Afterwards, start broadcasting the RF signals with RF power set to -130 dBm. Lastly, boot up the test modules for 1000 times and record the time needed for first fix.
Place and boot-up the test module inside test chamber designed to avoid noise interference. Then, use a multi-channel GPS simulator with external LNA. Lastly, start decreasing the broadcasting RF signals until the test module can no longer fix onto positions.
The data outputted from both port are an exact duplicate. It is just one is in UART format, and the other in USB virtual COM port format.
The maximum ratings are as follow:Altitude: 18,000mVelocity: 515m/sAcceleration: 4G
Customer who purchased GPS standalone module must incorporate antenna design into its consideration, and will need to use proper RF knowledge in order to prevent any internal interference.
On the other hand, GPS antenna module has a simple passive antenna integrated that makes it easier to work with, but user still have to exercise with caution (please refer to application note).
Assuming both module and its related systems are well designed, GPS standalone module will have the edge in terms of GPS reception because:
Mini GPS Tool: Application for our GPS module where you can temporarily change GPS settings and check firmware serial number.
AGPS Tool: Tool for downloading and updating AGPS data to GlobalTop GPS module.
Other tools are available by request, such as firmware flashing tool.
PMTK protocol is a set of commands that can be sent to GlobalTop MTK GPS modules to control and change its attributes and settings. The document for the set of PMTK commands is available upon request.
Update rates below 5Hz can be set temporarily using Mini GPS Tool, anything above will need to be set via PMTK command. The change will not be permanent and you will need to request a new firmware if you wish to set a particular update rate as default.
GlobalTop software supports desktop Windows based operation system such as Windows Xp, Windows Vista, and Windows 7.
It is a fail-safe mechanism in case the new setting causes major instability to the GPS module itself or to the entire system. You can always request a new firmware if you have found a new setting that best suited your device.
Having the flash memory built inside the GPS module allows us to write custom firmware and have your desired setting set as factory default.
It is possible that you have an earlier version of GPS module with “Allow change of baud-rate” disabled, please contact technical support for more details.
Please take a look at the PMTK Command document and see command PMTK314.
Please see “Software Service” for more details. The type of customizations we can make ranges from power saving, increase processing efficiency, to outputting data typically not found in NMEA such as distances between two points. You can also contact us if you wish to have a special firmware feature customized.
One is MTK USB driver, which is typically used with MT3329 based GPS module because it has a built-in USB Bridge IC. The other is SL CP210x USB driver, which is typically used with GPS Evaluation Kit.
GPS drift is the “drifting” of position coordinates when the GPS receiver is at a standstill. GlobalTop uses a special firmware feature called “Navigation Speed Threshold” to filter out unwanted information to decrease the drifting. For more information, please take a look at our software service page.
Yes! Please ask our support for more details.
Either by using Mini GPS Tool (available for download from GlobalTop website) and query the firmware version at the “About” Tab, or by sending “$PMTK605*31<CR><LF>” command to GPS module.
First, double check that commands can be given to GlobalTop GPS module or that you can query GPS firmware version using mini-GPS tool or through MTK command.
Quick Flashing Introduction:
If you are having trouble with flashing, you can try the force flash method:
GlobalTop module does not support any RTK modes within the RTCM commands.
Version of RTCM SC104 supported
SC104 V2.0, V2.1, V2.2, V2.3 and V3.0:
Type 1: Differential GPS Corrections
Type 2: Delta Differential GPS Corrections
Type 3: GPS Reference Stations Parameters
Type 9: GPS Partial Correction Set
Under international treaty CoCom (Coordinating Committee for Multilateral Export Controls) and the subsequent Wassenaar Arrangement, a civilian GPS module must not be operable under these two conditions at the same time in order to prevent it being used as a part of ballistic missile (ICBM). GlobalTop offers altitude unlimiter firmware customization to remove one of such restriction without breaking the international and local laws.
Running 10Hz with SBAS will most likely stress the ARM processor inside GlobalTop GPS module to its limit. We have observed random packet loss with both settings enabled and we do not recommend enabling 10Hz and SBAS at the same time.
There are still ways around to enable it if user is ok with the packet loss, but it is not recommended.
Due to intensive calculation when using magnetic variation function, 10Hz output will not be supported if it is enabled.
Please refer to the following document.
Link
GlobalTop GPS module does not support these modes.
Yes, it is. We have mimic u5 series’ NMEA sentence to match the output of a particular brand of GPS module. You can find the differences between the u5 series and other GlobalTop GPS modules below.
Yes, we do have an application note document available upon request. It contains design notices that users will need to watch out for before actually working with GPS modules. Please download this document from the download page.
There are several issues that may affect the acquisition time. Generally, it will be best if you can start the GPS receiver and antenna under clear sky because initially satellite data such as ephemeris and almanac must be transmitted to the GPS receiver during acquisition phase. The amount of time required is dependent on how much of the satellite data already stored inside the flash memory of the GPS module is usable.
Once the position is fixed, you can move it to an area where the reception is poorer as the tolerance for GPS signal clarity is less strict due to the way ultra-sensitive GPS modules are designed.
There are several possible causes which may lead to decrease in GPS sensitivity during circuit design & layout. These include “unclean” power supply (ripple voltage must be controlled under 50mVpp), layout path, ground restrictions and placement. Please refer to our newest applications note for more details.
There are several possibilities to why the GPS module failed to turn on:
1. Maybe the input voltage to VCC is incorrect, makes sure the voltage falls within the required range specified on the data sheet.
2. Vbackup is not connected. It is necessary to connect VCC for certain module types.
They are there to reduce the amount of radiation per part of EMC requirement. Please do not exceed the recommended value by too much as this will have an adverse effect on signal quality. More information about damping resistors can be found on our application note.
By supplying VBackup with power, it can retain satellite information that has been already received after the module is powered off. This can help to speed up the acquisition time during the next start-up. In addition, user will be able to retain adjusted settings (through Mini GPS Tool or PMTK Command) as well.
GlobalTop does not provide sub-meter accuracy GPS that are typically found in expensive survey equipment.
Generally, GPS accuracy can be increased by insuring the GPS module is used in an open sky environment. It is best if the GPS module is not used beside a large water body such as lake or ocean, or other tall constructions to lower the chance of multi-path signals.
User can also use DGPS (WAAS, EGNOS) and RTCM (on selected models) to increase GPS accuracy. By comparing the GPS signal received to a precisely known location, it is possible to increase the accuracy to around 2.5M. It is not sub-meter quality, but it is the best GlobalTop can offer for now.
GlobalTop provides the USB driver for desktop based Windows operating system such as Windows XP, Windows 2000, Windows Vista, and Windows 7. Windows CE is not supported. Please contact us if you are interested in Linux drivers.
Cold Start is performed every time when the GPS module is turned off without backup power supply connected. It is the longest starting time out of the three and usually takes 35 seconds in average under open sky environment. During Cold Start, almanac and ephemeris data has to be downloaded first from the GPS satellites to GPS module before a position fix can be acquired.
Assuming that a proper backup power source is provided, GPS module will perform Hot Start if the GPS module is powered on any time within the 2-hour time frame after GPS was previously turned off, as the ephemeris and almanac data is still stored inside the its flash memory.
Warm Start is performed if the above module is started after the 2-hour time frame, as part of its satellite data has to be refreshed.
Currently it is not possible to put the GPS module to sleep via software command. However, user can just switch off the power to the main power input (VCC) while keeping the backup power active (VBACKUP). This has the same effect as putting the module to sleep.
GPS module is likely to cease to function when it is connected to an unstable or wrong power source. GPs module is also likely to fail to turn on if incorrect connection is made at one of its I/O port such as TX, RX and 3D-Fix pins.
Double check with our reference design included in the respected data sheet and makes sure the power and configuration is correct.
If the GPS module still remains unresponsive, you can try reviving the GPS module with the force flash method. Please see question “3.14 Firmware cannot be flashed successfully using GlobalTop GPS tool, what’s wrong?” for instruction on force flashing the GPS module. Please contact GlobalTop technical support for more details.
High Voltage: 2.8~3.1V, Source current 14 mA Low Voltage: 0~0.4V, Sink current 14 mA
Even though GlobalTop GPS module is able to obtain -165dBm of sensitivity, please beware that this sensitivity is labeled as “tracking sensitivity”; or the sensitivity when GPS module has already successfully established a position fix.
You can test this by placing the GPS module nearby an open window until it has obtained a position fix, and then slowly move it away from the window. You should find that the GPS module will still be able to report a position even by then.
Also, your system and housing design will inevitably affect/degrade the GPS reception.
The SPI port on GlobalTop GPS module is currently only used as a part of data logger solution, where the flash memory is connected directly to. It cannot output NMEA data via the SPI port.
GlobalTop GPS external antennas have magnets on the bottom so they can adhere onto the roof of the car.
GPS external antenna varies by the type of connector (MMCX/MCX/SMA) and cable length (2m/5m).
Because the one built in is often passive and may not be adequate for use under reception poor areas or when the GPS receiver is blocked out from the sky. On the other hand, External Antenna is active and can be freely moved to a place where it has a good view to the sky.
Yes it is!
