Data transfer in the vehicle monitoring system - DDF technology
A rare example of the fact that a patent in Russia can actually work in the field of GPS. DDF is an abbreviation of Dynamic Data Flow. It is patented as an invention in Russia and the USA (RF Patent 2010127419, US Patent 8,498,774 B2) and is used in the LOCARUS monitoring system.
With its help, GPRS-traffic from monitoring devices, the required amount of memory in the device, communication session time, as well as DDF virtually no restrictions on the number of monitored parameters of the vehicle, attachments and cargo.
The initial goal was, of course, traffic - when the DDF was developed, the prices for data transfer were significantly higher than today. Since the development proceeded in parallel with the development of a new monitoring device, it was also decided to maximize the possibilities of connecting sensors.
How do satellite monitoring devices usually work? Periodically or by event (going beyond the virtual “circle”, passing a given distance, changing course, going beyond the geofence, triggering the sensor, sending an SMS, etc.), the device forms a so-called “point”: a data set that includes coordinates, time, sometimes the course and speed, sensor readings. With the development of the system, with the advent of new devices / firmware, such a premise can change the format, for example, one format serves to transfer the readings of the fuel level sensors, the other to transfer the temperature readings from the microgrid of thermal sensors.
In any case, the format of the data and the number of their sources is strictly determined at the stage of protocol development. To change something in it means to doom all the groups of applied developers to torment, and to curse themselves. If the developer has decided that there can be a maximum of two submersible fuel level sensors - then the third and fourth sensors will never be able to supply the integrator. If the developer decided once that the data on the air pressure in the air suspension of the tractor is not needed, then they will never be transferred to the application software. Changes to the “normal” protocol are epochal for the mass producer and painful for the consumer.
In the DDF protocol, they essentially refused to record the track “points”. The question: “How many points fit in the memory of the LOCARUS device?” Does not have a definite answer, it all depends on the operating conditions of the device.
So, data compression. But compressing data with conventional methods of mathematical compression is highly undesirable. Because in this case the most important quality of the monitoring system will be lost - efficiency! Mathematical methods effectively work on a sufficiently large data array, and we need to transfer (sometimes) almost continuously!
Thus, the developers came to the idea of ​​separating the supporting and intermediate frames. In the reference frames, the transmission frequency of which is configured in accordance with the task, but usually is 300 seconds, the absolute values ​​of all monitored parameters are transmitted. Coordinates, date-time, course, number of visible satellites, supply voltage and backup battery, and all declared sensors. And you can claim as many sensors as you like, only bandwidth considerations and traffic charges can limit the user. In intermediate frames, increment values ​​are transmitted. The increment of time from the last reference frame and the increment of the indication of any of the values.
Since the maximum possible period between reference frames is constrained forcibly, based on the actual values ​​of the vehicle speed, the dimension of the recording field for the increment of coordinates can be limited. The dimension of the time recording fields is also limited, and the dimension of the recording fields of the other monitored parameters (we call them “logical channels”) is selected by the user during configuration.
Logical channels are universal, and externally differ exclusively in dimension. The application program uses the configuration file generated when setting up the device in order to understand - in which channel the speed comes, and in which - the fuel level.
The formation of an intermediate frame occurs in accordance with the settings. They offer the user to determine the minimum transmission period and the amount of change needed to form a frame. For the transfer of coordinates, the dependence on the change in the course by a given value is also introduced.
That is, we get an extremely flexible system. With the correct settings, a standing in place car with the engine off transmits only reference frames every 5 minutes. The dispatcher does not lose touch with the car, but at the same time we have scant GPRS traffic.
When moving, the support frames are transmitted, plus (for a car equipped with fuel level and temperature sensors in the refrigerator):
- pressing the alarm button or triggering alarm sensors, instantly
- increments of coordinates when changing course (usually 3-5 degrees.)
- fuel level changes as consumed
- temperature changes, if they occurred and exceeded the established threshold of sensitivity to changes
In fact, a highly specialized data compression algorithm has been implemented, applied to a specific area - satellite monitoring of land and water transport. In aviation, the DDF will not operate “as is” - at least you need to revise the speed range.
Of course, the implementation of DDF protocol decryption on the server side is much more complicated than any other. Hence, the low prevalence of LOCARUS devices is technologically difficult to adapt to third-party software. However, consumers appreciate the flexibility of configuration and the quality of work in weak networks. The quality of this comes from the fact that the terminal takes much less time to transfer data after entering the GSM coverage area, or when the network is busy.
With its help, GPRS-traffic from monitoring devices, the required amount of memory in the device, communication session time, as well as DDF virtually no restrictions on the number of monitored parameters of the vehicle, attachments and cargo.
The initial goal was, of course, traffic - when the DDF was developed, the prices for data transfer were significantly higher than today. Since the development proceeded in parallel with the development of a new monitoring device, it was also decided to maximize the possibilities of connecting sensors.
How do satellite monitoring devices usually work? Periodically or by event (going beyond the virtual “circle”, passing a given distance, changing course, going beyond the geofence, triggering the sensor, sending an SMS, etc.), the device forms a so-called “point”: a data set that includes coordinates, time, sometimes the course and speed, sensor readings. With the development of the system, with the advent of new devices / firmware, such a premise can change the format, for example, one format serves to transfer the readings of the fuel level sensors, the other to transfer the temperature readings from the microgrid of thermal sensors.
In any case, the format of the data and the number of their sources is strictly determined at the stage of protocol development. To change something in it means to doom all the groups of applied developers to torment, and to curse themselves. If the developer has decided that there can be a maximum of two submersible fuel level sensors - then the third and fourth sensors will never be able to supply the integrator. If the developer decided once that the data on the air pressure in the air suspension of the tractor is not needed, then they will never be transferred to the application software. Changes to the “normal” protocol are epochal for the mass producer and painful for the consumer.
In the DDF protocol, they essentially refused to record the track “points”. The question: “How many points fit in the memory of the LOCARUS device?” Does not have a definite answer, it all depends on the operating conditions of the device.
So, data compression. But compressing data with conventional methods of mathematical compression is highly undesirable. Because in this case the most important quality of the monitoring system will be lost - efficiency! Mathematical methods effectively work on a sufficiently large data array, and we need to transfer (sometimes) almost continuously!
Thus, the developers came to the idea of ​​separating the supporting and intermediate frames. In the reference frames, the transmission frequency of which is configured in accordance with the task, but usually is 300 seconds, the absolute values ​​of all monitored parameters are transmitted. Coordinates, date-time, course, number of visible satellites, supply voltage and backup battery, and all declared sensors. And you can claim as many sensors as you like, only bandwidth considerations and traffic charges can limit the user. In intermediate frames, increment values ​​are transmitted. The increment of time from the last reference frame and the increment of the indication of any of the values.
Since the maximum possible period between reference frames is constrained forcibly, based on the actual values ​​of the vehicle speed, the dimension of the recording field for the increment of coordinates can be limited. The dimension of the time recording fields is also limited, and the dimension of the recording fields of the other monitored parameters (we call them “logical channels”) is selected by the user during configuration.
Logical channels are universal, and externally differ exclusively in dimension. The application program uses the configuration file generated when setting up the device in order to understand - in which channel the speed comes, and in which - the fuel level.
The formation of an intermediate frame occurs in accordance with the settings. They offer the user to determine the minimum transmission period and the amount of change needed to form a frame. For the transfer of coordinates, the dependence on the change in the course by a given value is also introduced.
That is, we get an extremely flexible system. With the correct settings, a standing in place car with the engine off transmits only reference frames every 5 minutes. The dispatcher does not lose touch with the car, but at the same time we have scant GPRS traffic.
When moving, the support frames are transmitted, plus (for a car equipped with fuel level and temperature sensors in the refrigerator):
- pressing the alarm button or triggering alarm sensors, instantly
- increments of coordinates when changing course (usually 3-5 degrees.)
- fuel level changes as consumed
- temperature changes, if they occurred and exceeded the established threshold of sensitivity to changes
In fact, a highly specialized data compression algorithm has been implemented, applied to a specific area - satellite monitoring of land and water transport. In aviation, the DDF will not operate “as is” - at least you need to revise the speed range.
Of course, the implementation of DDF protocol decryption on the server side is much more complicated than any other. Hence, the low prevalence of LOCARUS devices is technologically difficult to adapt to third-party software. However, consumers appreciate the flexibility of configuration and the quality of work in weak networks. The quality of this comes from the fact that the terminal takes much less time to transfer data after entering the GSM coverage area, or when the network is busy.
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Source: https://habr.com/ru/post/207614/
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