Come on, Coptic, turn from: https://bbs.feng.com/read-htm-tid-7709847.html
Blue-Hong Zhongtian
nearly see a lot of FY on the mobile phone positioning means and principles, especially the principle of WiFi assist positioning do not understand, so finishing a bit of the previous writing of a popular science, sent to the forum, science a bit ~ ~
The full text is long, the long wen phobia patient is cautious into.
first of all, to elaborate on these things:1, GPS positioning. 2, base station positioning. 3, WiFi auxiliary location. 4, aGPS positioning. 5, GLONASS positioning. 6, Beidou positioning. 7, positioning example. from 4s onwards, the iphone has 1, 2, 3, 4, 5 total five ways of positioning.
1. GPS positioning GPS is a familiar noun, it is a way of positioning by the United States to study. The system consists of 31 satellites running on the track (the numbers are unclear) and the ground terminals. in orbit satellites, many satellites flying in space, their orbits are regular: No matter where you are in the world, at least at the same time there are 4 satellites at the top of your head, in fact, we have little relationship. The ground terminal, in fact, is our popular GPS, it can receive your head of those flying satellite signals, and then based on the signal to calculate your current position. Common terminal has car navigation GPS, mobile phone built-in GPS and hiking outdoor GPs and so on. The accuracy of the general civil class is about 10 meters. When using GPS, it is necessary to be able to receive GPS satellite signals outdoors, and the room is basically hopeless. It is characterized by: do not need a SIM card, do not need to connect the network, as long as in the outdoors, almost anywhere can be accurately located. But the GPS after the start of the search for satellites more time, generally takes about 2 minutes (commonly known as cold start).
2, Base station positioning This is a late emergence of a technology, its principle is relatively simple. The landlord originally heard is in 2006, China Mobile launched a mobile phone map using the base station positioning, or Saipan system, experience is simply weak explosion . mobile phone after inserting SIM card boot, need to search around the base station information (is to find signal), usually in the place of the signal, mobile phone can search for more than one base station, just like your notebook in the community can find more than one open router. The phone will then automatically select the best signal from these base stations (if the base station a) connection is registered. Is the rest of the base station all right? No, the phone still searches for them, once you leave base station a for a certain distance, the signal of base station A is inferior to base station B, and the cell phone will automatically switch to base station B. This is why the same standby day, you on the train than at home power consumption more reason, the phone needs to constantly search, connect the base station. when the mobile phone network coverage to a certain extent, the base station positioning has emerged. the principle is as follows: As we all know, the farther away from the base station, the worse the signal, so the intensity of the signal can approximate the distance from the base station. Well, because the base station is China Unicom and other operators established, so they can determine the exact location of each base station, when the phone simultaneously search for at least three base station signal (now the network coverage this is very easy one thing), mobile phone In addition to connect the signal of the best, at the same time according to the base station signal strength, Approximate distance from the base station is estimated. Because the base station location is determined, so it is easy to determine the location, only need to base station as the center point, the distance is a radius to draw a circle, but at least three base station signal can be. What, it sounds like you're in a neighborhood. Refresh three times position draw round to find the sister paper around? because of the base station positioning, the signal is easily disturbed, so the innate decision on its positioning of the inaccuracy, the accuracy of about 150 meters, the basic can not drive navigation. positioning conditions must be in the location of the base station signal, the phone is in the SIM card registration status (flight mode to open WiFi and unplug the SIM card is not), and must receive 3 base station signal, whether indoors or not. However, the positioning speed is super fast, once the signal can be positioned, the main purpose is no GPS without WiFi in the case of a quick general understanding of your location (such as can make the weather forecast where to go to where to update). Also, if you don't have a base station location packet in your phone, you need to be connected.
3, wifi auxiliary location In fact, the full name is not called this, called the WiFi assistance under what location, but as a medical student I think or call WiFi dependency positioning better understanding: WiFi dependence, as the name implies, There must be WiFi around! This technology seems to be originally proposed by Google, the purpose is to solve the indoor precision positioning, the principle of similar base station positioning. Google's engineers think so: A WiFi hotspot coverage is only dozens of meters, the majority of the world's WiFi hotspots are fixed location, they have a unique MAC address (a code, the role of similar hot Shen Fen zheng number), If you apply the principle of base station positioning, then you can get quite accurate position information. However, there are so many WiFi hotspots in the world, you can not run to various countries, knocking open the door to measure it? Google has thought of his artifact-Google Maps. If your home has a wireless router you set up, often turn on, your neighbor is on the balcony with a mobile phone to play Google Maps, just his mobile phone wifi is open, but not connected to your home hotspot. When your neighbor uses GPS to locate the map accurately, Google server will record the surrounding WiFi hotspot information. Just right, your router is on, and then it is recorded to the database: a certain province of a city in a certain district of the east Side (in fact, with latitude and longitude) has a MAC address for 12-2e-3f-4a-09-3d WiFi hotspot. A few days later you plan to eat Sichuan, so even on your router to open Google Maps to search, when you are surprised to find that the GPS is not open, but your location is precisely located in a certain province of a city of a certain district of the east side of a building. What is this for? This is the WiFi dependency location: After you open the Google Map, will upload the surrounding WiFi hotspot information, and then 2-2e-3f-4a-09-3d upload to the server, the server according to this address feedback your neighbor with GPS positioning the latitude and longitude to you, so as to achieve accurate matching position. When n more than n people in the world repeat the above positioning, Google can build up a rich and powerful WiFi hotspot location database. does that sound a little scary? You can rest assured.. knowing the principle and then determining its positioning conditions is not difficult: 1. WiFi must be turned on, regardless of whether a hotspot is connected or not. 2, mobile phone must be able to surf the internet, mobile data or WiFi network can be. (don't expect Google to allow mobile phone-built-in location information for these hotspots, which is a fortune) The advantage of this way is that the ① positioning accuracy is high, the location of WiFi dense crowd is quite accurate, ② speed, the WiFi around ③ even if not connected to the location. The downside is obvious: ①wifi depends! ———— cannot be located without opening WiFi, ② must be networked. There are many advantages to WiFi targeting, which is why many FY use targeting often jumps out to ask if WiFi is turned on.
4. aGPS positioning aGPS is the abbreviation of assisted Global Positioning System-assisted GPS, which is a technology developed after the mobile phone starts to build up the built-in device. On this noun, some domestic "small partners" easily confuse it with the location of the base station. aGPS Positioning, there must be a GPS module exists, if there is no GPS module, this positioning is not what role. since the GPS cold start, the search star speed is very slow, about 2 minutes to search. What is cold start? Is the GPS satellite location information is emptied (for example, ①gps first use ②gps battery ③ shutdown state to move more than 1000 kilometers of distance or continuous shutdown more than 4 hours), the GPS needs 1.1 points of the search satellite signal, more than 30 satellites, who knows what is above the top of the head, search Bai, Search the South and search the north.... So the speed of the search star is very slow and slow. aGPS is to use the base station in general to locate your location, and then send this location through the network to the server, the server according to this location will pass through your head of the satellite parameters (which several, frequency, location, elevation and other information) feedback to your mobile phone, Your mobile phone GPs can be very purposeful to search satellites, at this time your search star speed greatly increased, a few seconds can be positioned. For example, a GPS search star is like finding a Pepsi in a big supermarket. cold start, is this supermarket is very strange, you do not know where the food cold drink area, need 1.1 points to find. aGPS, it's like you called the supermarket manager, and he told you that Pepsi is on the second floor, southwest corner, near the building.. The difference between the speed of the search stars is obvious. So, aGPS consumes a lot of traffic? Not much, each location, only more than 10 KB of traffic, once the location is successful, the rest of the work will be handed over to the GPS module processing, no consumption of traffic. Why is there a lot of traffic in the argument? Probably these little friends did not download offline maps ...Therefore, the advantage of aGPS is to search the star positioning fast, no matter how to start, the second set. The disadvantage is, must be networked, if your machine can not surf the internet, or mobile phone stop around and no wifi, it is impossible to apply AGPS to achieve the second effect. Also, aGPS need a specific server, you do not expect to change the server to www.CCTV.com still have a second effect . to summarize:aGPS is a method of auxiliary GPS positioning, support GPS, not necessarily support aGPS (for example, some antique machine can not surf the internet). Support AGPS, must support the GPS, but this GPS module is not necessarily built into the phone, it may be necessary to purchase an additional external Bluetooth GPS module (this disgusting model is very few, the general Mark aGPS Basic is the built-in GPS module). such as Apple's super-formal company, the official website parameters are written aGPS and GLONASS. What do you mean? is the built-in GPS module, which assists in positioning and also supports the GLONASS of another navigation system. Why Apple's aGPS on the internet will cause a discussion, because the early mobile phone built-in GPS chip cost is very high precision is not good, some manufacturers have come up with the external GPS module This behavior, so like Zhongguancun this it station parameters on the separation of GPs and AGPS to refer to the built-in GPS and auxiliary positioning, It's a selling point. So, I think the Apple label is the best. PS: Since the GPS has a cold start, there is a hot start, what is the hot start? Is cold start search star after its star calendar is not lost, the condition is as follows ① last shutdown position information (latitude and longitude, height) known (so in the garage shut down the next time must be cold start); ② current time, annual calendar, Ephemeris known (requires real-time clock support) ③ distance from the last shutdown time of not more than 4 hours (the time is too long, the ephemeris changed, that is, the previous satellite can not see).
5, GLONASS positioning Glonass is a Russian development of a set of positioning system, the principle of the same as GPS, but also with a lot of flying satellites in the sky to locate. The difference is that the ①glonass chip is more expensive than the GPS, ② it anti-jamming performance, cloudy and rainy high-rise chasm place GPs may flying blind, GLONASS is still able to work normally; ③ the Northern hemisphere has better positioning accuracy than GPS; ④ search stars faster. at present GLONASS is mainly found in high-end models, such as the Apple series, HTC one, etc., are gps+glonass dual system navigation, accuracy is quite high, navigation can be accurate to the driveway.
6, Beidou positioning Simple point is the domestic GPS, Chip is said to be more expensive than GLONASS, positioning accuracy than gps,glonass are better, but in view of domestic media urine sex still remains to be seen. At present the largest user is the Chinese military, the civilian aspect is very not popular, depends on the policy in the transport company strong buy strong sell. There is a bright spot is that the Beidou generation can use the satellite on the head to send text messages, in the absence of mobile phone signal is very practical, there is a signal when the basic useless. Civilian can have this function hard to say, the military has active exposure "I'm here you hit meyou're going to hit me."Suspicion.
7, positioning examples to write this part of the purpose is to better let everyone understand the working conditions of various positioning methods, HTC One as an example: ① is the most power to plug in SIM card, open WiFi, networking, start GPs and GLONASS. Set all of the above positioning methods in one, except that made. ② turn off the GPS option. Gps,glonass and aGPS are not, base station, WiFi location is fair. ③ off WiFi, mobile data open, base station only location. ④ start airplane mode, all positions are stopped. ⑤ open WiFi, networking, only WiFi location work.
iphone due to all of the above positioning methods are set in the "privacy" option, so after switching off the positioning switch, all the above positioning functions all stop.
How the phone is positioned
