I believe that many people use mobile phones when they have encountered a taxi and are not able to locate them. When the driver meets his name, the map is displayed at the same point, but he is not able to touch the surface. When he drives, the navigation is too late. Missed the export situation.
If you use ultra-precise positioning mobile phone millet 8, the above problems will be solved. Millet 8 as the world's first dual-band GPS support for smart phones, can achieve ultra-precise positioning.
Baidu, Gaode, and Tencent's three major map makers are official positioning technology partners, and all of them also highly value Xiaomi 8, which is known as the groundbreaking innovation and landmark progress of the map navigation industry.
GPS Development History and Basic Positioning Principles
GPS, the global positioning system (Global Positioning System), is a space-based radio navigation system that provides uninterrupted positioning, navigation, and timing services worldwide. Anyone with a receiver can GPS systems Provide him with location and time information. GPS consists of three parts: satellites orbiting the earth; monitoring stations set up on the ground; and user-owned receivers such as smart phones.
The predecessor of the GPS was the US Navy’s 1958 study, which used a satellite system based on Doppler shift technology. It was also the world’s first satellite navigation system that successfully operated, laying the foundation for the development of GPS. In 1973, GPS was The US Department of Defense formally initiated the project and the development process was divided into three phases. The first phase was the feasibility study. The first GPS satellite was launched in 1978. At this stage, a total of four test satellites were launched. The second phase is the comprehensive development and testing. During the period from 1979 to 1984, seven test satellites were successively launched and various types of receivers were developed. The third stage is the practical networking stage, which began in 1985. The first GPS satellite was launched in 1989. Success, GPS was famous in the Gulf War in 1991, and the miniaturization of GPS receivers was successful. In 1995, the United States announced that GPS was in full operation.
The GPS satellite transmits signals received and recognized by the mobile phone from space, which contains the satellite's current position coordinate information and the GPS satellite's own precise time corrected by the atomic clock and relativistic effects. Assume that the time of both the satellite and the mobile phone is precisely synchronized. After receiving the signal from the satellite, the mobile phone subtracts the transmission time carried in the signal from its own time and multiplies it by the ideal transmission speed of the electromagnetic wave, namely, the speed of light. Distance between mobile phone and satellite.
Because of the precise position of the satellite, we have already obtained the distance from the satellite to the mobile phone. Using the distance formula in three-dimensional coordinates and the coordinates of the three satellites, we can form three equations to solve the position of the observation point (X, Y, Z). However, since this conclusion is based on the assumption that each satellite is ideally synchronized with the time base of the mobile phone, in reality, the fourth satellite must be added for calibration. At present, there are 31 GPS satellites in total. At an altitude of 20,200 kilometers above the ground, it orbits the Earth in a 12-hour cycle. At any time, more than four satellites can be observed at any point on the ground.
Limitations of L1 single-frequency GPS handsets
As mentioned above, the key to GPS positioning is to obtain the distance between the mobile phone and the satellite. To calculate the distance, you must know the propagation time of the signal. This data is calculated by the mobile phone. The key point is that the GPS signal will arrive after the launch. What time does the mobile phone take?
First, the accuracy of the L1 band GPS signal is limited
If only the L1 band 1575.42 MHz GPS signal is used for positioning, its bandwidth is small, only 1 MHz. That is, a minimum period of transmission time is 1/106 s=1 μs, multiplied by the speed of light is 300 meters. If the L1 band GPS The signal is likened to a ruler for measuring the distance from a satellite to a mobile phone. Its “minimum scale” is 300 meters, which is the ranging error range of a single L1-band satellite theory. Whether it is an open space or a city with a high number of buildings, L1 This limitation of the band will result in inaccurate positioning.
Second, the L1 band GPS signal is susceptible to reflection interference
In many scenes of buildings, metal, water surface, glass, etc. are all good reflections of GPS signals when they are located in cities or rivers, lakes, and seas. In the above scenario, GPS positioning is used. The mobile phone is not only launched from a GPS satellite, but also passed through a straight line. In addition to the transmitted signal, one or more signals reflected by the surrounding terrain are also received. In this way, multiple signals received by the mobile phone may be superimposed, leading to the inconspicuous direct signal with the shortest distance, thereby reducing satellites and mobile phones. The accuracy of the calculations between the distances can even lead to the disappearance of satellite signals in severe cases. This effect is called in the physics of multipath effects.
It can be seen that in the figure below, because the accuracy of the L1 band signal is 300 meters, which results in the direct signal and the reflected signal being stacked together, the mobile phone will think that the gray received signal is actually received, causing a positioning error.
Third, the L1 band GPS signal is susceptible to ionosphere
In the open area, the main reason for inaccurate positioning is the refraction of the GPS signal caused by the ionosphere in the atmosphere, which increases the transmission time. The ionosphere in the atmosphere is filled with ions and electrons under the irradiation of sunlight, and this electromagnetic wave is the GPS signal. The effect is serious. Studies have found that the ionosphere-induced refraction effect is inversely proportional to the square of the signal bandwidth, that is, the lower the bandwidth, the greater the ionosphere effect.
L1 plus L5 dual-band GPS, Xiaomi 8 achieve ultra-precise positioning
Dual-frequency GPS function, so that millet 8 can use both L1 and L5 GPS signals at the same time for positioning. L5-band GPS signals are more complex than L1-band coding. Both mobile phones and satellites require higher costs. Previously, L5 The frequency bands are mostly used for industrial applications where high accuracy is required, such as oil and gas exploration, aviation safety industry, and Xiaomi 8 is the first consumer product to use dual frequency GPS.
First, the L5 frequency band GPS signal accuracy is higher
Since the bandwidth of the GPS signal in the L5, 1176.45 MHz frequency band is as high as 10 MHz, which is 10 times that of the L1 frequency band, and the minimum periodic transmission time is 0.1 μs, the single satellite positioning distance measurement error is also reduced to 30 meters.
Second, L5 frequency band GPS signal is not susceptible to reflection interference
Therefore, in scenarios where high-rise buildings and other multipath effects are severe, the direct and reflective L5 signals used by Xiaomi 8 are more difficult to superimpose, thereby reducing the impact on positioning accuracy. As shown in the figure below, blue and purple reflected signals are difficult to Affect the green direct signal, millet 8 can get more accurate positioning.
Three, L1, L5 Dual Frequency Controls Eliminates Ionospheric Effects
As for the refraction effect caused by the ionosphere, first, the bandwidth of the L5 band is 10 times that of the L1 band. The error caused by the previous ionosphere is inversely proportional to the square of the bandwidth. The L5 band GPS signal is influenced by the ionosphere and is the L1 band. Part I. Second, because the effect of the ionosphere on the L1, L5 frequency band signals is different, dual-frequency GPS devices such as Xiaomi 8 can be independent of other factors. By comparing the delays of the two signals, the ionospheric band is eliminated by calculation. The error will further improve the GPS positioning accuracy.
Millet 8 dual-band GPS measured: rejection single-frequency mobile phone street
Through actual measurement, it can be seen that when the dual-frequency GPS-enabled millet 8 navigates around the island under the space bridge, the positioning point is almost exactly in accordance with the trajectory path, and the single-frequency GPS mobile phone is greatly disturbed due to the signal interference and blocking of the viaduct. Even once it entered the surrounding building area, this is mainly the limitation of the single-frequency GPS mobile phone in the complex city scene, and the same results are also measured by the same reason Jianwai SOHO.
Space Bridge Location Measurement
Jianwai SOHO Building Site Surveying
Similarly, in the single point positioning of the space bridge, it can be seen that the positioning points of the three test handsets are only coincident with the actual position of the millet 8. However, at present, most single-frequency GPS handsets have different degrees of deviation, that is, when the user uses When the platform is waiting for a car, it is very easy for the driver and the passenger to find each other's problems because of the wrong place marking.
Millet 8 Other Single Frequency GPS Phones
Dual-band satellite positioning, future trends
As mentioned earlier, due to volume, cost, and other factors, dual-band GPS devices are often used in professional fields or military applications where precision is required, even though they are commercially available. However, in recent years, technologies such as automatic driving have been hot, and GPS accuracy has also been proposed. Higher requirements. The International Institute of Electrical and Electronics Engineers predicts that with the continuous improvement of the overall GPS solution, the future of mobile phones for general consumers will gradually spread the dual-band GPS, and ultimately make GPS positioning accurate to 30 cm level.
In addition to GPS in the United States, there are GLONASS in Russia, Beidou in China, Galileo in EU, QZSS in Japan, and Xiaomi 8 supports all major satellite positioning systems. Among these systems, Galieo support is compatible with GPS L1, L5. E1 and E5a bands; As a complement to GPS, QZSS L1 and L5 bands are the same as GPS.
At present, the global support for L1+L5 dual-band positioning satellites has reached 30, and future launch of satellites will also support dual-band. Visible, for higher positioning accuracy, support L1+L5 dual-frequency satellites whether it is a satellite or a smart phone Waiting for the receiver is an inevitable trend in the future. In the moment, on the road to save Lu Chi, the first to support dual-frequency GPS, Galieo, QZSS system, positioning accuracy of the millet 8 can be described as doing my part.
I believe that many people use mobile phones when they have encountered a taxi and are not able to locate them. When the driver meets his name, the map is displayed at the same point, but he is not able to touch the surface. When he drives, the navigation is too late. Missed the export situation.
If you use ultra-precise positioning mobile phone millet 8, the above problems will be solved. Millet 8 as the world's first dual-band GPS support for smart phones, can achieve ultra-precise positioning.
Baidu, Gaode, and Tencent's three major map makers are official positioning technology partners, and all of them also highly value Xiaomi 8, which is known as the groundbreaking innovation and landmark progress of the map navigation industry.
GPS Development History and Basic Positioning Principles
GPS, the global positioning system (Global Positioning System), is a space-based radio navigation system that provides uninterrupted positioning, navigation, and timing services worldwide. Anyone with a receiver can GPS systems Provide him with location and time information. GPS consists of three parts: satellites orbiting the earth; monitoring stations set up on the ground; and user-owned receivers such as smart phones.
The predecessor of the GPS was the US Navy’s 1958 study, which used a satellite system based on Doppler shift technology. It was also the world’s first satellite navigation system that successfully operated, laying the foundation for the development of GPS. In 1973, GPS was The US Department of Defense formally initiated the project and the development process was divided into three phases. The first phase was the feasibility study. The first GPS satellite was launched in 1978. At this stage, a total of four test satellites were launched. The second phase is the comprehensive development and testing. During the period from 1979 to 1984, seven test satellites were successively launched and various types of receivers were developed. The third stage is the practical networking stage, which began in 1985. The first GPS satellite was launched in 1989. Success, GPS was famous in the Gulf War in 1991, and the miniaturization of GPS receivers was successful. In 1995, the United States announced that GPS was in full operation.
The GPS satellite transmits signals received and recognized by the mobile phone from space, which contains the satellite's current position coordinate information and the GPS satellite's own precise time corrected by the atomic clock and relativistic effects. Assume that the time of both the satellite and the mobile phone is precisely synchronized. After receiving the signal from the satellite, the mobile phone subtracts the transmission time carried in the signal from its own time and multiplies it by the ideal transmission speed of the electromagnetic wave, namely, the speed of light. Distance between mobile phone and satellite.
Because of the precise position of the satellite, we have already obtained the distance from the satellite to the mobile phone. Using the distance formula in three-dimensional coordinates and the coordinates of the three satellites, we can form three equations to solve the position of the observation point (X, Y, Z). However, since this conclusion is based on the assumption that each satellite is ideally synchronized with the time base of the mobile phone, in reality, the fourth satellite must be added for calibration. At present, there are 31 GPS satellites in total. At an altitude of 20,200 kilometers above the ground, it orbits the Earth in a 12-hour cycle. At any time, more than four satellites can be observed at any point on the ground.
Limitations of L1 single-frequency GPS handsets
As mentioned above, the key to GPS positioning is to obtain the distance between the mobile phone and the satellite. To calculate the distance, you must know the propagation time of the signal. This data is calculated by the mobile phone. The key point is that the GPS signal will arrive after the launch. What time does the mobile phone take?
First, the accuracy of the L1 band GPS signal is limited
If only the L1 band 1575.42 MHz GPS signal is used for positioning, its bandwidth is small, only 1 MHz. That is, a minimum period of transmission time is 1/106 s=1 μs, multiplied by the speed of light is 300 meters. If the L1 band GPS The signal is likened to a ruler for measuring the distance from a satellite to a mobile phone. Its “minimum scale” is 300 meters, which is the ranging error range of a single L1-band satellite theory. Whether it is an open space or a city with a high number of buildings, L1 This limitation of the band will result in inaccurate positioning.
Second, the L1 band GPS signal is susceptible to reflection interference
In many scenes of buildings, metal, water surface, glass, etc. are all good reflections of GPS signals when they are located in cities or rivers, lakes, and seas. In the above scenario, GPS positioning is used. The mobile phone is not only launched from a GPS satellite, but also passed through a straight line. In addition to the transmitted signal, one or more signals reflected by the surrounding terrain are also received. In this way, multiple signals received by the mobile phone may be superimposed, leading to the inconspicuous direct signal with the shortest distance, thereby reducing satellites and mobile phones. The accuracy of the calculations between the distances can even lead to the disappearance of satellite signals in severe cases. This effect is called in the physics of multipath effects.
It can be seen that in the figure below, because the accuracy of the L1 band signal is 300 meters, which results in the direct signal and the reflected signal being stacked together, the mobile phone will think that the gray received signal is actually received, causing a positioning error.
Third, the L1 band GPS signal is susceptible to ionosphere
In the open area, the main reason for inaccurate positioning is the refraction of the GPS signal caused by the ionosphere in the atmosphere, which increases the transmission time. The ionosphere in the atmosphere is filled with ions and electrons under the irradiation of sunlight, and this electromagnetic wave is the GPS signal. The effect is serious. Studies have found that the ionosphere-induced refraction effect is inversely proportional to the square of the signal bandwidth, that is, the lower the bandwidth, the greater the ionosphere effect.
L1 plus L5 dual-band GPS, Xiaomi 8 achieve ultra-precise positioning
Dual-frequency GPS function, so that millet 8 can use both L1 and L5 GPS signals at the same time for positioning. L5-band GPS signals are more complex than L1-band coding. Both mobile phones and satellites require higher costs. Previously, L5 The frequency bands are mostly used for industrial applications where high accuracy is required, such as oil and gas exploration, aviation safety industry, and Xiaomi 8 is the first consumer product to use dual frequency GPS.
First, the L5 frequency band GPS signal accuracy is higher
Since the bandwidth of the GPS signal in the L5, 1176.45 MHz frequency band is as high as 10 MHz, which is 10 times that of the L1 frequency band, and the minimum periodic transmission time is 0.1 μs, the single satellite positioning distance measurement error is also reduced to 30 meters.
Second, L5 frequency band GPS signal is not susceptible to reflection interference
Therefore, in scenarios where high-rise buildings and other multipath effects are severe, the direct and reflective L5 signals used by Xiaomi 8 are more difficult to superimpose, thereby reducing the impact on positioning accuracy. As shown in the figure below, blue and purple reflected signals are difficult to Affect the green direct signal, millet 8 can get more accurate positioning.
Three, L1, L5 Dual Frequency Controls Eliminates Ionospheric Effects
As for the refraction effect caused by the ionosphere, first, the bandwidth of the L5 band is 10 times that of the L1 band. The error caused by the previous ionosphere is inversely proportional to the square of the bandwidth. The GPS signal in the L5 band is affected by the ionosphere. Part I. Second, because the effect of the ionosphere on the L1, L5 two-band signals is different, dual-frequency GPS devices such as millet 8 can be independent of other factors. By comparing the delays of the two signals, the ionospheric band can be eliminated by calculation. The error will further improve the GPS positioning accuracy.
Millet 8 dual-band GPS measured: rejection single-frequency mobile phone street
Through actual measurement, it can be seen that when the dual-frequency GPS-based millet 8 navigates around the island under the space bridge, the positioning point is almost completely in accordance with the trajectory path, and the single-frequency GPS mobile phone is greatly disturbed due to the signal interference and blocking of the viaduct. Even once it entered the surrounding building area, this is mainly the limitation of the single-frequency GPS mobile phone in the complex city scene, and the same results are also measured by the same reason Jianwai SOHO.
Space Bridge Location Measurement
Jianwai SOHO Building Group Location Measurement
Similarly, in the single point positioning of the space bridge, it can be seen that the positioning points of the three test handsets are only coincident with the actual position of the millet 8. However, at present, most single-frequency GPS mobile phones have different degrees of deviation, which means when the user uses When platforms such as DDT are called for vehicles, it is very easy for drivers and passengers to find problems that cannot be found by each other because of incorrect location marking.
Millet 8 Other Single Frequency GPS Phones
Dual-band satellite positioning, future trends
As mentioned earlier, due to volume, cost, and other factors, dual-band GPS devices are often used in areas with higher accuracy or military expertise even though they are commercially available. However, in recent years, technologies such as automatic driving have been hotter, and GPS accuracy has also been proposed. Higher requirements. The International Institute of Electrical and Electronics Engineers predicts that with the continuous improvement of GPS integrated solutions, future mobile phones for general consumers will gradually become more common with dual-frequency GPS, and eventually make GPS positioning accurate to 30 cm.
In addition to GPS in the United States, there are GLONASS in Russia, Beidou in China, Galileo in EU, QZSS in Japan, and Xiaomi 8 supports all of the above major satellite positioning systems. Among these systems, Galieo support is compatible with GPS L1, L5. E1 and E5a bands; As a complement to GPS, QZSS L1 and L5 bands are the same as GPS.
At present, the global support for L1+L5 dual-band positioning satellites has reached 30, and future launch of satellites will also support dual-band. Visible, for higher positioning accuracy, support L1+L5 dual-frequency satellites whether it is a satellite or a smart phone Receivers, etc., are all inevitable trends in the future. In the present, on the road to save Lu Chi, the first to support dual-frequency GPS, Galieo, QZSS system, positioning accuracy of the millet 8 can be described as doing my part.
