Positioning Technology Gps/a-gps/lbs/wifi Positioning Introduction __lbs

Positioning Technology Gps/a-gps/lbs/wifi positioning IntroductionSource: Site Finishing Author: 08lr.cn update: May 03, 2013 popularity: 9 this week: 19 this month: 34 total: 2,134 times

In life, we often see the so-called mobile phone positioning of the application, for the tracking technology can not be incredible, we will think: How to do this? With today's positioning technology, a certain degree of precision and accurate tracking can be achieved, even beyond your imagination. All sorts of positioning techniques are already built into your smartphone, and as the mobile Internet comes into our lives.

GPS satellite positioning: The core of mobile phone positioning

Talk about mobile phone positioning, I believe many people immediately think of "GPS satellite positioning." Indeed, GPS positioning system can be said to be the earliest, the development of the most mature, the most widely used positioning technology. The full name of the GPS is "navigation satellite Timing and Ranging/global Position system", which is the satellite measuring time ranging navigation/global Positioning System.

How exactly is the satellite positioned? In fact, very simple, the satellite signal contains information roughly including satellite map orbit information and accurate time signal (atomic clock calibration), through the formula of speed, time and distance, and then auxiliary four point positioning principle can determine the user's position.

GPS satellites running in space, each constantly broadcast their current position coordinates to the world through satellite signals. Any GPS receiver can easily receive this information through an antenna and can read the information. and calculating the distance requires a very simple formula, distance = Speed x time. Here, the speed is using an absolute speed--the speed of light. Each GPS satellite broadcasts its own location, and when it sends the location information, it attaches the timestamp when the packet is issued. When a GPS receiver receives a packet, subtracting the time from the timestamp with the current time is the time it takes for the packet to be transmitted in the air. Know the packet in the air transmission time, then multiply its transmission speed, is the packet in the air transmission distance, that is, the satellite to the GPS receiver distance. In theory, it only needs to search for 4 satellites to locate them accurately.

However, GPS positioning also has a lot of shortcomings, such as GPS signals by the weather and location of the impact of large, GPS terminals stored in the orbit Ephemeris usually not more than 4 hours, so that people develop a A-GPS.

A-gps: Send an assistant to GPS.

A-gps, the English language is all called "Assisted Global Positioning System", the Chinese meaning is "auxiliary GPs".

In fact, the positioning of A-gps and GPS is the same, but only with the help of the network. The mobile base station is connected to the A-GPS server, A-gps services to preserve the satellite complete trajectory data, base station and A-GPS server connection, you can get the base station location (base station latitude and longitude are recorded) above the satellite running orbit Ephemeris, and then the two data through GSM, CDMA and other protocols sent to your mobile phone, real-time update on the GPS chip Ephemeris, so that GPS positioning speed and precision are greatly improved, even if the cold start can be quickly positioned.

In addition, we can use another workaround: Download the long-lasting ephemeris. GPS chips calculate and store the Ephemeris can only be deduced to 4 hours of satellite orbit, so through the Internet from the A-GPS server download the current position (this position is to the GPS chip to obtain "the last positioning of latitude and longitude" Information obtained) satellite data over a number of days (long-lasting ephemeris) can be stored on a mobile phone to speed up the search speed. For example, the EPO technology included in MediaTek MTK6589 Four's nuclear smartphone program is such a long-lasting ephemeris aid technology. and SIRFIII chip add Instancefix function is also let you to the GPS chip upload long-term ephemeris. GPS two times positioning can refer to this information, quickly lock and decode satellite signals, do not require a long time to scan and lock work.

But this long-lasting Ephemeris also has one of the biggest flaws----can't get "current position" in real time. If you have a long lasting ephemeris in Beijing and then travel to Shanghai, the Ephemeris still fails, and you must first make a lengthy "cold start" position.

Although A-gps has a better performance than traditional GPS, it does not fully compensate for the shortcomings of traditional GPS, such as the problem of indoor positioning is still not satisfactorily resolved.

Mobile Base Station positioning lbs: Mobile phone signal can be positioned.

Mobile phone base station positioning service is also called Mobile location service, that is, mobile Internet circle, the famous Lbs--location Based service.

It is through the mobile communication operator's network to obtain the mobile terminal user's position information (latitude and longitude coordinates), under the support of the electronic map platform, provides the user with the corresponding service one kind of business.

The general principle is: mobile phone to measure the downlink pilot signal of different base stations, to get Toa (time of arrival, arrival moment) or Tdoa (Times difference of Arrivalm, arriving at different base stations), The position of the mobile phone can be computed based on the measurement results and the coordinates of the base station (generally using the trigonometric Formula estimation algorithm). Take TDOA positioning technology as an example: by mobile phone signal to neighboring a number of base stations (two-dimensional space positioning at least 3 base stations), using the characteristics of the hyperbola (two focus to the distance difference between the curve is a fixed value) in the 22 base station to draw a double curve, the intersection of two sets of curves is the position of mobile phone, The positioning precision has a great influence on the geometric position of the base station distribution.

Like Google mobile phone maps and other types of mobile phone map software in the rough positioning and so on are using the base station positioning to achieve. The positioning technology does not require the mobile phone to have GPS positioning capability, but the precision depends on the distribution density and coverage of the base station, the more the number of base stations, the higher the measurement accuracy. As the base station location and density problem, positioning accuracy can be from 100 meters to thousands of meters floating, generally in the city can be used as a reference, a little remote area is a big error.

WiFi Location: "Supernatural" positioning technology

If you don't know the WiFi location technology, then you must have experienced a situation where you find that a smartphone that does not support 3G or does not have a SIM card, or that enters flight mode to turn off the mobile signal, can pinpoint its location on Google Maps if you open WiFi at home.

How this is done. It is obviously impossible to rely on IP to query. In fact, the key behind this is WiFi positioning technology. In fact, Wi-Fi positioning technology, its principle and base station positioning similar. We all know that each wireless AP has a globally unique MAC address, which relies on detecting the MAC address of all the wireless network base stations (WiFi Access Point) around the neighborhood to compute the location of the MAC address in the database. This method still needs to have network to do database query to complete the positioning. So the question is: This wireless network base station MAC address corresponds to the longitude and latitude of the database, how to establish it. The infrastructure is built on Google Street View cars.

The WiFi location database is called Skyhook, collecting wireless access points and mobile base station information

Google Street View car, in addition to filming Street View, building 3D model data, but also to do one thing: along the road to collect all the public wireless router MAC address and cell phone base station ID, and then the latitude and longitude recorded together.

In fact, when you use the mobile terminal + Google Map Locator program, is also helping to do this-when WiFi and cell phone base positioning or GPS to open simultaneously, handheld devices with mobile phone base station positioning or GPS positioning of the two ways to get the current coordinates, and then through WiFi search to the nearby No line from the MAC address, from the background to Google's database to do updates, so no Street View car measurement to obtain the location data. ios/Android mobile phone users in the "use of wireless network positioning" will be prompted to allow Google's positioning service mobile phone anonymous location data, that is the meaning.

All the above information to the server, the server will do this information processing, filtering out the obvious error information, with these input information through an algorithm, processing a location information record, there is a database inside. When these records are more and more, the location that can be queried is more and more accurate. With such a large database, but also to call on each mobile terminal to help update the maintenance of the database, and probably only Google.

Summarize

GPs and solid, base station positioning, WiFi positioning, such as the emergence of simple positioning technology, opened up the entire mobile positioning Service market. It is with these technologies, mobile Internet social Network "communication, sharing", E-commerce, "Eat, drink, play, music, buy" services really into our daily life.