The dipper PK GPS, who is stronger in the end?2018-04-11 20:25:02 93 ℃
production: Science and technology, China's
production: Dong Gong
producer: the Chinese Academy of Sciences Computer Network Information Center
read the article, you have already used Beidou, you don't know! "", a lot of small partners suddenly realized that the original dipper has been deep in the daily life.
but the new question comes again: the Beidou and GPS, who is stronger? Can the dipper be able to "throw away" GPS and locate it independently?
Beidou PK GPS, who can win?
as a member of the GNSS (Global Navigation Satellite System global navigation satellite system) club, navigation and positioning is the basic function. First look at the positioning function is how to compare the process of
receiver using satellite positioning can be abstracted into at least four two-dimensional points on a blackboard (satellite), with each point as the center, respectively, to draw a circle with chalk (the distance to the satellite receiver measurement), the overlap region is the powder of handwriting the positioning results. Because of the existence of a variety of errors, the result of each satellite is more like a piece of chalk than a line without a width. Effect of
thickness of the chalk by various error mechanisms, comparison of Beidou and GPS, mainly is the atomic clock stars on the different precision compass two generation is the use of rubidium atomic clock, GPS is using cesium atomic clock combination rubidium atomic clock, at this point GPS is better, it is more powder handwriting some fine. And now the three generation compass is the use of hydrogen atomic clock , frequency accuracy from 5 * 10-13 to 6 * 10-14, frequency stability by 2 * 10-14 (1D) increased to 6 x 10-15 (1D), compared with the two generation satellites to a high level, the reaches the leading level in the world , the positioning accuracy will be further improved.
is not only affected by the thickness of the chalk painting, apparently more round, which the satellite number of overlapping area is small, it is more accurate positioning, but if these points are concentrated in the side, even if overlapping, overlapping they draw the powder of handwriting will become great, and these the more dispersed, draw the powder handwriting overlap is lower, also said that the receiver positioning result is more accurate also. The parameter of the position distribution is the PDOP value called , the lower the representation is the better the distribution, the more accurate the positioning result is .
, when the Beidou generation did locate slowly, and the accuracy was somewhat worse, how did all more than 10 years pass? Others felt that the Beidou is not good enough to say, "what satellites are less", "still built", "accuracy is far away from GPS".
actually started from the two generation of the Beidou. The constellation is designed for the Asia Pacific region, which is different from the MEO mode in the US. It adopts the GEO+IGSO+MEO mode. Has the advantages of high precision and fast in key service areas with fewer satellites, the disadvantage is the high latitude area is not good for GEO reception, accuracy factor value is too large, there is the other side of the earth not received, with the increase of Beidou satellite, these problems will be resolved later.
even so, in the three generation is not used today, to see how the accuracy of Beidou. Now, we Chinese in the north to pick a point:
52.4476 degrees north latitude, North enough of it, the official announcement of the two generation Beidou service area but only between North and south latitude 55 degrees, how to position this visibility day 24 hours of Beidou Satellite:
as can be seen, all day long available in more than 10 degrees of elevation of the Beidou satellite at least 8 stars, who said that the star come?
GNSS "big brother" club now compared to GPS satellite visibility here:
is not found visible satellite number as the compass? The feeling is not like "can make a GPS defeat in the China Beidou" news......
, of course, it's not advisable to be arrogant. There are always some Beidou's false news of "spike GPS", which is not good for people to know Beidou. in addition to using their own safety navigation system, GNSS Club four who can't please seckill who, shortly before the sign "beauty in the compass and GPS signal compatibility and interoperability joint statement", mutual backup more harmonious......
said the number of Beidou satellite positioning, but not only the number of stars, eat constellation set loss, here received the compass GEO elevation is too low, the geometric distribution is poor, so the accuracy factor:
Beidou GDOP reached the maximum 6 and the maximum fluctuations, compared to GPS of it 4.4:
this is because the satellite GEO hanging above the equator, received here elevation is less than 30 degrees, the IGSO satellite orbit at an angle of 55 degrees, go to this is the "8" type trajectory of the head, so most of the area 1, 4 quadrant basic not what star, plus these factors lead to the big dipper DOP was larger, but to meet the accuracy of 10m still have no problem.
, so you have to say that Beidou is less acceptable than GPS. Of course, with the three generation of networking, this gap will soon disappear, and multiple MEO will be fine. Below is the distribution of the GPS satellite track:
next, we pick a point in China South:
26.6940 degrees north latitude, longitude 109.9688 degrees, the visual coordinate is in Hunan, here is how the Beidou satellite visibility:
at least ten stars visible, look at GPS:
is the same as the old, little difference between North and south, the focus is on the DOP value, can a war? The DOP value of Beidou is as follows:
is the largest no more than 3.4, then look at GPS:
can ignore the especially high point, which is basically within 4.4, but obviously Beidou is smoother.
has been able to maintain a good distribution in all day long each period, because this can stabilize the received GEO Beidou satellite and IGSO satellite signal, MEO satellite accounted for only a few, but not like GPS is composed of MEO, with the change of time will be constantly changing in positioning satellites, and less calculation in Beidou the process of change in the introduction of a large number of satellite positioning error results and jump at low elevation, more atmospheric satellite elevation is lower signal passes through the error caused by the more, but also more affected by multipath fading, and other factors are also greater.
GEO all day long here visible Beidou satellite, IGSO satellite and MEO satellite visible more than half, do not stay in one place, is around the earth in their own circle, so they will continue to repeat, one after another from the low elevation into the scope of vision, rose to a certain height, then reduce the cycle of elevation leave the field.
integrated these factors from the positioning accuracy, the Beidou is certainly not less than the GPS. so as in northern engineer. I want to Tucao: at the present stage in Beidou test in Guangdong and Heilongjiang in the test is two concepts completely well, the same things to Hainan just to go to Harbin, is very strenuous...... After the three generation of network, we will not have to eat this loss.
on the whole, in the current two generation Beidou service area, the number of visible star compass than GPS all day long, most of the region is better than in the constellation distribution on GPS, but considering the problem of atomic clock precision difference in high latitude and constellation distribution, or the reliable compass and GPS comparable, is practical the measurement results. But now the construction of the three generation networking is in progress. The number of Beidou satellites is increasing steadily, and the most critical atomic clock problem has been solved in the three generation. By that time, we won't be modest.
who says the dipper can't stand on its own? However some people dislike me
: "GPS is the main location, your home is only used to make up the numbers of Beidou GPS, they don't have independent position, not GPS you Beidou nothing." And wait for you to say QZSS, can't you use the country to spend money on this? The truth of
is obvious, but it's not easy to prove it. Why? Is the objective existence of the satellite receiving channel for mobile phone users open hardware, unless the chip bottom control instruction, the so-called "GPS" is not a real close receiving channel, but not admissible GPS positioning results, can not ensure the validation requirements of "Beidou Positioning can be independent, after all the underlying algorithm of the chip is not controllable. In case, design of navigation chip are stolen by GPS guide how to do?
proof method is to use a special microwave darkroom - GNSS test darkroom! The principle of
GNSS testing darkroom is similar to that of ordinary microwave anechoic chamber. It's all about shielding electromagnetic waves outside. The signals emitted from darkroom will not reflect on the wall, but the key protection frequency bands are different. Compared to the microwave anechoic chamber test or large radar array antenna, GNSS test chamber clean area not too big, because the GNSS receiver size is not large, the most important difference is that the GNSS navigation signal simulator, and a complete set of evaluation system, with this set of things can be simulated at any point on the earth GNSS satellite in the sky. Want to send what what signal signal is sent, to which position can send what, just move, want to stop, and can evaluate the positioning device under test results, the accuracy of test results are given authority.
can ensure that only receive the Beidou satellite signal in the darkroom, power is also consistent with the calibration to open, can eliminate all uncontrollable factors, if in this case can positioning, it can prove that the mobile phone has the ability of "Beidou Positioning independent" . Results:
is certainly not what the suspense: "
, Beidou received" 9 star in the location, no GPS, no auxiliary, Beidou satellite is really "independent". Beidou is in the world. After the completion of the three generation of the Beidou generation network in 2020, at any point on the planet, we can rely on Beidou to complete the location independently.
"science popularization China" is a scientific authoritative brand that China Association for science and technology is carrying out scientific communication with all sectors of society.
this article is produced by the combination of science and technology in China, and reprinted to indicate the source.
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