Pseudo range measurementPseudo range measurement refers to the technology and method of measuring the distance between the observation station and the satellite, including clock error and atmospheric refraction delay, by using the correlation technology between the pseudo-random code transmitted by the satellite and the copied code of the receiver when using the global positioning system for navigation and positioning.
Chinese name
Pseudo range measurement
Foreign name
pseudo-range measurement
Field
Surveying and Mapping
Purpose
Navigation with low precision requirements
Related concepts
Clock difference, etc
Status
One of the key technologies of satellite navigation system
The measured distance contains clock error and atmospheric refraction delay, rather than "real distance", so it is called pseudo distance.In order to realize pseudo range positioning, the measured pseudo range is used to form an equation set with the unknown 3D coordinates of the receiver antenna phase center and the satellite clock differenceleast square methodSolve to obtain the three-dimensional coordinates of the receiver antenna phase center, and reduce them to the three-dimensional coordinates of the measuring station.Since the equations contain 4 unknowns, there must be more than 4 pseudo ranges obtained by pseudo range measurement.This method can be used not only for static positioning when the receiver is fixed on the ground station, but also for dynamic positioning when the receiver is placed on a moving carrier.But the latterAbsolute positioningLow precision, it can only be used for navigation with low precision requirements.
Pseudo range measurement involves many physical quantities such as clock offset, true range, equipment delay, observation time, etc. In order to achieve accurate evaluation of the uncertainty of pseudo range measurement and the stability of equipment delay, it is necessary to clarify their basic concepts and definitions, which is particularly important under high dynamic conditions.[1]
Clock difference
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Space reference point of clock difference and time
Clock difference refers to the difference between two clocks at the same time.In modern high-tech applications, the accuracy of time measurement has reached the nanosecond or even picosecond level.Precise time signals are usually represented by pulse signals, such as 1 pps, 10 pps and 100 pps representing 1 pulse signal, 10 pulse signals and 100 pulse signals in 1 second respectively.As we all know, signal propagation takes time, so the so-called clock face must specify its time space reference point, that is, the time given by a clock must indicate which space reference point is relative to the device, such as the 1pps port of the atomic clock or the 50m cable port of the 1pps output, etc.
True distance
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In radio measurement, the signal is transmitted through the transmitting antenna and received by the receiving antenna after space propagation.The so-called signal space propagation delay refers to the time spent by the signal in the process of space propagation.The signal space propagation delay reflects the real distance traveled by the signal, which can be simply called the true distance.
Equipment transmission delay
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The equipment transmission delay is defined as the difference between the signal leaving the local clock face at the time of the transmission antenna phase center and the characteristic time value of the transmission signal (such as the corresponding time of the pseudo noise code chip).It is not necessarily the signal propagation time from the code generator to the phase center of the transmitting antenna.It depends on the selection of the local time reference point.If the time reference point of the transmitting station is defined at the output port of the code generator, it is the signal propagation time from the code generator to the phase center of the transmitting antenna.
Device receiving delay
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The equipment receiving delay is defined as the difference between the nominal signal receiving time (local clock face time) of the receiver and the local clock face time when the signal actually reaches the phase center of the receiving antenna.
Pseudo range
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Pseudo range can be defined as the difference between the local receiving time (local clock face time) of the signal and the characteristic time value carried by the signal.
significance
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satellite navigation system The basic principle of the operation is that the user receives navigation signals from at least four satellites at the same time, so as to measure more than four pseudo range observations. When the satellite coordinates, satellite clock offset and relative equipment delay deviation between different frequency points of the satellite are known, calculate their own three-dimensional coordinates and clock offset.Therefore, pseudo range is the most basic observation of satellite navigation system, and the observation accuracy of pseudo range directly determines the navigation and positioning accuracy of the system.High precision pseudo range measurement technology is one of the key technologies of satellite navigation system.[2]
The development of high-precision pseudo range measurement technology first needs to solve the problems of uncertainty of pseudo range measurement and stability evaluation of equipment delay.Since the measurement accuracy of pseudo range not only depends on the pseudo range receiver, but also is related to the signal source, and the inherent equipment delay of signal transmitting equipment and signal receiving equipment is difficult to be accurately separated from the pseudo range measurement, therefore, the delay stability of pseudo range measuring equipment and the evaluation of the uncertainty of pseudo range measurement are technical issues worthy of in-depth discussion.
Accuracy evaluation
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The pseudo range measurement is closely related to the time delay of the device. If the time delay of the device changes with time, it is difficult to accurately separate them.Since the transmitting and receiving delay of equipment not only depends on the pseudo range receiver, but also is related to the signal source, it further increases the difficulty of evaluating a single equipment.Therefore, it is assumed that the transmission delay of the signal source is stable.[3]
aboutReceiverThe receiving delay must be stable and the pseudo range observation time must be accurate.If the transmission delay of the signal source is stable, the average value of the transmission and reception delay of the equipment can be simply deducted in the receiver evaluation process, and the rest can be comprehensively evaluated as the measurement error.
It should be noted that the stability of equipment delay and the precision of pseudo range measurement are often related to the measurement conditions such as the motion characteristics, ambient temperature, signal strength of the transceiver. Therefore, to make the calibration results universal and reliable, the measurement of pseudo range must cover as many technical states as possible, such as power on/off, static, low dynamic, high dynamic, and multiple signal receiving strengths.
In order to deduct the influence of the transmission delay of the signal source, two receivers of the same model manufactured by the same manufacturer can be observed simultaneously to construct a statistical observation independent of the transmission delay.
Improve accuracy
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(1) Pseudo rangeClock difference, equipment delay, etcBasic physical quantityIt is closely related and is a function of time, so its definition must be strictly self consistent.In a broad sense, the device delay is not necessarily the real delay, they depend on the choice of time reference point.In general, the value can be positive or negative.
(2) When the 1pps output port of the device is selected as the local time reference point, the combined transmit receive delay can be measured by directly measuring the clock difference.The relative difference between the transmission delay (or reception delay) of two transmitting (or receiving) devices can be obtained by measuring the combined delay with a reference receiving (or transmitting) device.
(3) For the receiver, the precision of pseudo range measurement, the stability of equipment delay and the calibration error of pseudo range measurement time are closely related.Because these errors are difficult to be strictly separated, in practical applications, the average value of the transmission and reception delay of the equipment can be simply deducted by the clock difference measurement method, and the remaining part can be used as the measurement error to comprehensively evaluate the receiver.
(4) To ensure the universality of the test results and obtain the device delay value with high reliability, the pseudo range and clock difference measurement must traverse various technical states as far as possible, such as power on/off, static, low dynamic, high dynamic and multiple signal receiving strengths.
