Electronic Tracker positioning at present and in the future
Positioning with data link is not the same as referenced positioning (a method that allows measurements from more than one receiver to be combined and processed together in order to enhance accuracy), This external information includes measurements from other receivers, but it also includes other information which can be used to improve not only accuracy, but also other parameters in the specification, such as TTFF and sensitivity. It is very important for many applications to be able to provide instant positioning, i.e. to avoid the necessity of tracking a satellite signal and reading a navigation message. It takes up to 36 s to read a complete navigation message for a GPS L1 signal to ensure the decoding necessary for positioning data. If navigation message data are available through some other data link, it is still necessary to decode a time mark from the navigation message, which may require up to 6 s. BGPS (and AGPS before that) are very important for many applications because they allow instant positioning using just a snapshot of data.
It is often impossible to track a satellite signal indoors and therefore it becomes impossible to decode the navigation message, even partially. This is because moving indoors will change the multipath, and therefore the tracking will most likely be interrupted, even if it was possible in the first place. When using the Small GPS Tracking Device in cellular phone applications, the cellular phone cannot be used at the same time as GPS because of interference. This means that a user has to wait until all the data from the navigation message have been acquired. In one sentence, The terms “carrier differential GNSS” and “AGNSS” came from different sides of the GNSS industry: the former has been developed as a precise positioning method in satellite geodesy field, whereas the latter was developed much more recently for cellular phone applications. Both technologies use externally supplied information: in the first case, differential corrections to enhance accuracy, and in the second, assist data, which are used to enhance the TTFF, sensitivity, and other parameters in the receiver specification.
Whether it is proper to combine these two technologies in one device depends on whether it would be feasible to have one device that could benefit from both technologies and to provide all the information on the same data link. This tendency to combine precise applications with mobile applications started some time ago. In this blog, we look at various information that is externally supplied in real time and discuss how this information is used in a receiver. Usually, this subject is considered in relation to a specific field and therefore to a specific receiver type. The theory behind AGPS was first summarized and given to the scientific community by Frank van Diggelen, who authored various AGPS-related technologies, in Indoor GPS tutorials at ION GPS-2001. All this information has been extended and now comprises a textbook. Reference provides additional information on AGPS implementation. There are two different approaches taken for the application of external information.
One concept is to use this information on the rover side. The other concept, which can be called network-based or sometimes reversed positioning, is to provide some data from a rover to the server and allow the server to calculate the rover’s position. Reversed positioning allows us to implement geodetic techniques without load on a handset processor.
Electronic Tracker can be used for cellular phones and also for fleet management, animal tracking systems, etc. It can be realized in two ways.
(A) A rover sends chunks of DIF records to a server, or keeps them in memory. We look at the latter approach in detail in Chapter 9. In this case, the rover receiver is only equipped with a front end, because all baseband functions are on the server side. This method is sometimes referred as tracking with RF logs.
(B) A rover sends to a server code phase measurements, which are processed on the server using all the available information at the server, such as navigation message and so on. This method is sometimes referred as tracking with positioning logs. Note that in this case code phase measurement may not be converted to pseudoranges.
The rover estimate of the time at which it receives the signal is also required in both cases. In rover-based positioning, the rover may also send some information to a server. For example, for open sky application in the case of VRS corrections, which we will consider later in this chapter, the rover may send its code-phase-based positioning. Using this position, the server calculates the carrier-phase corrections for this particular rover and sends them back. This allows an improvement in rover positioning accuracy from meters to centimeters.
More information about GPS Tracking Devices at http://www.jimilab.com/blog/ .
It is often impossible to track a satellite signal indoors and therefore it becomes impossible to decode the navigation message, even partially. This is because moving indoors will change the multipath, and therefore the tracking will most likely be interrupted, even if it was possible in the first place. When using the Small GPS Tracking Device in cellular phone applications, the cellular phone cannot be used at the same time as GPS because of interference. This means that a user has to wait until all the data from the navigation message have been acquired. In one sentence, The terms “carrier differential GNSS” and “AGNSS” came from different sides of the GNSS industry: the former has been developed as a precise positioning method in satellite geodesy field, whereas the latter was developed much more recently for cellular phone applications. Both technologies use externally supplied information: in the first case, differential corrections to enhance accuracy, and in the second, assist data, which are used to enhance the TTFF, sensitivity, and other parameters in the receiver specification.
Whether it is proper to combine these two technologies in one device depends on whether it would be feasible to have one device that could benefit from both technologies and to provide all the information on the same data link. This tendency to combine precise applications with mobile applications started some time ago. In this blog, we look at various information that is externally supplied in real time and discuss how this information is used in a receiver. Usually, this subject is considered in relation to a specific field and therefore to a specific receiver type. The theory behind AGPS was first summarized and given to the scientific community by Frank van Diggelen, who authored various AGPS-related technologies, in Indoor GPS tutorials at ION GPS-2001. All this information has been extended and now comprises a textbook. Reference provides additional information on AGPS implementation. There are two different approaches taken for the application of external information.
One concept is to use this information on the rover side. The other concept, which can be called network-based or sometimes reversed positioning, is to provide some data from a rover to the server and allow the server to calculate the rover’s position. Reversed positioning allows us to implement geodetic techniques without load on a handset processor.
Electronic Tracker can be used for cellular phones and also for fleet management, animal tracking systems, etc. It can be realized in two ways.
(A) A rover sends chunks of DIF records to a server, or keeps them in memory. We look at the latter approach in detail in Chapter 9. In this case, the rover receiver is only equipped with a front end, because all baseband functions are on the server side. This method is sometimes referred as tracking with RF logs.
(B) A rover sends to a server code phase measurements, which are processed on the server using all the available information at the server, such as navigation message and so on. This method is sometimes referred as tracking with positioning logs. Note that in this case code phase measurement may not be converted to pseudoranges.
The rover estimate of the time at which it receives the signal is also required in both cases. In rover-based positioning, the rover may also send some information to a server. For example, for open sky application in the case of VRS corrections, which we will consider later in this chapter, the rover may send its code-phase-based positioning. Using this position, the server calculates the carrier-phase corrections for this particular rover and sends them back. This allows an improvement in rover positioning accuracy from meters to centimeters.
More information about GPS Tracking Devices at http://www.jimilab.com/blog/ .
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