Q1. Is GPS sent straight to GPS receiver?
A1. Yes, it is not. The GPS signal in the receiver is straight, but it is definitely not a GPS satellite sending a straight signal to the receiver. The reason is that the line-of-sight brings you the illusion that it is literally line-of-line. -sight
It is called visual line, so some people use this as a GPS signal to spread so I think this is incorrect; GPS satellite signals are broadcast, everyone receives it, when the signal arrives at the receiver At the same time, it will also go to other locations. Correctly, a signal broadcasted by a satellite is received by your receiver. We will use this distance as a known condition for pseudo-range (seudo
This is also true for several other satellites. The point where all the great circles meet is the location of the receiver. These pseudoranges are a big ball in 3D space. This is called the distance position line in positioning. That is to say, when the receiver receives this GPS signal, all points in the 3-degree space that are equal distances from the satellite are called distance position lines. (The other position line is called azimuth position line, For example, if you have a lighthouse, and you are at the 090 degree of the lighthouse, which is also known as the east, all the points drawn along the line drawn by 90 readings may be your position, so this line is the azimuth position. Lines, there is a position line called hyperbola with the opportunity to introduce you again), satellite signal to the receiver is a straight line from the right distance, but the satellite signal is from the distance position line as the signal status of the broadcast.
Q2. The speed of positioning?
A2. This is what I answered in another article
There are three reasons why GPS can be quickly positioned for success when it is turned on:
1. Ephemeris data, trajectory data of all satellites
2. Last valid position
3. The time now
The principle is that the BASEBAND of the GPS receiver can calculate the position of any satellite on the orbit of the Earth’s equator at an angle of 55 degrees based on the satellite ephemeris data. Which time is it? It is based on the current time of your GPS receiver. If the GPS has the current time, it can calculate the reference time from the ephemeris data creation time, and calculate the orbit to your current time satellite, but the satellites are seen in different places. The group will definitely be different, so the GPS must refer to the last valid position, and then calculate the current location, all the satellite numbers at the current time. At this time, the GPS internal comparator will only generate the PRN code of the calculated satellite, and all the receivers The channel will only lock these satellites, so it can be located quickly.
There are a few common questions that people often have
Long time no use of GPS, positioning becomes slow, why?
1. RTC overflow: RTC (Real time)
Clock) is a counter that helps when GPS is turned off, but some brand ICs use COUNTER which is too small, so it will lose time after overflow.
2. The ephemeris data expires, and the ephemeris data are divided into two types: fine and coarse, finely effective for about half an hour, rough for about 1 to 2 weeks, and rough ephemeris data can be broadcasted by any satellite. At 12.5 minutes, the fine ephemeris data cycle is 30 seconds, but the fine ephemeris data of each satellite can only be broadcast by the satellite.
3. The battery for backing up the above three elements is dead, and the data is lost and becomes a cold boot.
After I used the shutdown in A, I took a plane to B. I found that GPS could not be located. Why?
Because the last valid position is different, this time can be solved by clearing the last valid position or cold start.
Q3. Some navigation software has a function to set GPS sensitivity?
A3. Can you really set it? Of course not, because every GPS
The IC's setting commands are all different, so the navigation software absolutely does not have the ability to adjust the GPS sensitivity, but I understand why he wrote so is to make the user more understand, in fact, the software's function is to do filtering Action, you will find that when using the navigation software to travel through the junction, it will wait in the same place, to confirm the path is in or exceed the set distance to display the timely position to avoid errors The direction is also the same. When the difference between the directions at the moment is too large, it will not be accepted. When the direction is determined to be the walking direction, the map will be rotated, so if there is no filtering action, at some point in time In the jungle, you will find that the map has been spinning around.
Q4. Fast positioning is not easy?
A4, will you? If the speed of light travels, of course, but relative to the 20,183 km of GPS, your speed has little effect on it, and the impact is also on some satellites. I have answered in other articles, I intend to To be clear, when the receiver captures and tracks GPS signals, the receiver is synchronized with its signals in frequency and time in order to demodulate navigation messages. This is called a two-dimensional signal reconstruction procedure. The receiver is adjusted on the frequency axis. Frequency to compensate for the Doppler shift and the receiver on the time axis to generate the PRN code and GPS
The PRN code synchronization achieves the maximum positive correlation. If the GPS carrier frequency is not well locked, the lock code will be difficult to generate in the just-mentioned 2D reconstruction process. If the code cannot be locked, the carrier tracking will also be affected by the balanced modulator. It is not easy to track the carrier, so the two need to coordinate with each other to get a fast positioning, and the reason why the speed is not easy to locate is because .... When you are on some roads, your direction of travel, the shadow of the turning building. .. will let the GPS receiver lock in some satellites again. For example, when you receive satellite number 1, the receiver will get the number 1 Ephemeris (precise ephemeris data)
Cycle time is 30 seconds, including satellite reference time, clock frequency drift, clock drift clock offset, average angle, angular velocity difference, ascending angle, orbital inclination..... a lot I can't remember, I used to write programs to count those There is no way to remember that all of them are written while referring to some papers.) The result is that the signals of the demodulation process are instantly obscured by the obstacles of high and low levels in the car's progress. Of course, the data of the satellite may not be used correctly to perform navigation calculations. When you stop, the receiver is not at risk of being obscured by movement. Of course, positioning is faster, if there are more than 3 good and normal satellites!
Q5GPS positioning error how to calculate?
A5. In the navigation software, there are two errors in the satellite data field followed by a value
In fact, that value is called the DOP value (precision dilution or error amplification factor). What is the meaning of that value? Let me tell everyone! Afterwards, everyone will know how to read it.
In fact, there are too many kinds of error classification, but some of you will not even know what that is. For example, people who know the positioning algorithm will know that there is a kind of difference that cannot be eliminated, that is, residual error, and some errors. If the ionosphere error is the most obvious, it is also the largest source of error for GPS positioning. After the SA (Selection Error) is lifted, the so-called SA... If it is already gone we do not need to explain it. In those days, people doing GPS research wrote a lot of papers on error correction in order to eliminate SA, but after Xiao Ke lifted the SA interference, the value of all the papers became... very worthless, of course there are some useful Differential applications... sorry for pulling away
Closer to home...
Error = Measurement Error X DOP
Explanation
Measuring error = measuring GPS signal error, which is the error of the position line I mentioned above, what does that mean? For example, if you have a lighthouse 1km away from you, then drawing a circle around the lighthouse with a radius of 1km is the so-called distance line, but... How do you know that the axiom is 1km? It may have been 980 meters, it may be 1020 meters, so the 40 meters from the middle of 980 to 1020 is your measurement error. The distance from the azimuth means that you are in the east of the lighthouse, which is 090 degrees. Where do you know you must be at 90 degrees? You may be at one of the 088- 092 degrees, which is the measurement error.
DOP=Chinese is converted to longitude dilution with GDOP, PDOP, VDOP, HDOP and TDOP. Explain... (Too many words
It is too tortured. What does the DOP mean? I explain to you that I have a boat in the middle of the parish. There is an A lighthouse in the north, which is 000 degrees north, which is 90 degrees in the east. Where there is a B lighthouse, assuming that their measurement error is 4 degrees, that is +-2 degrees, the two azimuth position lines drawn over will overlap in this boat's position to form a square range, which is an error Summation, if we move the B pole to the northeast, that is 045 degrees, the same measurement error will be drawn from the side of the ship. At this time, the area of ​​the range formed by the overlapping of the B lighthouse and the A lighthouse is certain. It is bigger than B lighthouse when it is 90 degrees eastward. This is the error caused by the difference in the spatial geometry formed by the location.
Error=The so-called error is multiplying the measurement error by the precision dilution value, which is the range formed by the overlap of the position line I mentioned above. We return to the topic of GPS. When the DOP is 1, it means that there is no DOP error at all because Any number multiplied by 1 or himself, is it possible that DOP is 1? In the case of GPS satellites, unless there are three satellites with a difference of 120 degrees each and the altitude is 0 degrees, and the receiver has a satellite with a zenithal altitude of 90 degrees, then the DOP is 1, but I have never seen it. After that, except for the previous simulations, but... When the GPS altitude is too low, the signal propagation on the ground will cause various delays, reflections, etc., so the measurement error will be amplified. Some GPS
The IC will exclude satellites whose satellite height is below 5 or 10 degrees, etc.. In short... if the measurement error becomes smaller, the DOP value will become larger. To make the DOP value smaller, the measurement error will be Bigger...
and so
Later you see the error displayed by the navigation software (in fact it is the DOP value), that is to say assuming that the position of your GPS receiver at this point in time, in fact, contains the measurement error, and that DOP value Is the multiple of your error
For example, if your measurement error is 20 meters and the DOP value is 1.5, then your error is 30 meters, and your correct position is centered on your current position, with a radius of 30 meters. Draw a circle, and your real position may be at any point in this circle.