Mobile positioning technology for cellular systems

1. Development and application of mobile positioning technology

The origin of radio location technology can be traced back to the beginning of the last century, the military demand of the Second World War and the digital cellular mobile communication system which began to be popularized in the late 80 promoted the development of the technology in military and civilian fields respectively. GPS and Loran C system are typical positioning systems, they use radio location method to meet different positioning accuracy requirements. With the rapid development of the advanced technology in the field of military application, such as CDMA and cellular network, the localization technology of cellular mobile communication system has already been studied abroad.　　The E911 specification, developed by the FCC in 1996, required all mobile operators to provide emergency services at a 67% probability, thus speeding up the progress of the technology and the global development of location Service (LCS) based on radio positioning technology. The rapid growth of China's mobile communication market has laid a solid foundation for the development and popularization of mobile positioning system in China. Beijing Mobile uses the Motorola's LCS solution to provide a variety of location services for individuals and business users in the mobile network, mainly including relatives and friends location inquiries, user location authorization and city information inquiries. Since the beginning of 2001, mobile operators in Fujian Mobile, Shanxi and Yunnan have signed a mobile location commercial contract with Nokia. Recently, Unicom Guomai with Japan's renowned location service Content solutions provider Navitime signed a cooperation agreement to jointly develop a CDMA2000 1x based location services.

2. Mobile positioning Technology

Using appropriate positioning technology to obtain location information is the prerequisite for the realization of location services, according to different criteria, the cellular network positioning technology has the following classification methods:

(1) According to the position of the location system in different space, can be divided into space-based Positioning System (GPS), ground positioning system and the hybrid positioning System three kinds. GPS system is widely used in the world for its high precision and all-weather features, and it plays an important role in the management of vehicle dispatching. The traditional wide area radio direction locating system belongs to the ground positioning system. A-gps system is a combination of GPs and cellular network products, high positioning accuracy, overcome the GPS in the building and urban areas of the shortcomings of the existing blind spot, is the future of cellular positioning technology standards the most powerful competitor.

(2) According to the location parameters of different locations, can be divided into network-based positioning and based on terminal positioning two. CELL_ID technology based on cell identification has been applied in mature. The arrival time difference (TDOA) combined with the CDMA system can provide positioning within 50m, which is the most rapidly developing positioning technology at present. The enhanced Observation time localization technique (E-OTD) is the most promising cellular location technology in GSM system, but it needs to change the soft and hard structure of terminal, so it is not widely used at present. (Computer science)

(3) According to the different parameters of positioning, can be divided into field strength measurement (SSOA), enhanced field strength measurement method/Multipath Fingerprint method (essoa/fingerprint), Arrival angle Measurement (AOA), Arrival/Time difference measurement (TOA/TDOA) and mixed parameter positioning method.

2.1 cell_id Technology

The positioning system identifies the terminal location according to the community or base station in which the user is located within the network. The terminal may be anywhere in the cell, so positioning accuracy depends entirely on the size of the cell. At present, domestic GSM network base station density is very large, cell_id cell positioning accuracy can be as high as 100-150m, such a level of precision enough to meet the requirements of most application services. Suburbs and rural areas of the community radius is much larger than the urban area radius, so the location accuracy of urban cell_id is far higher than the suburbs and rural areas. The CDMA system does not need to set the dense base station, the urban area radius is generally around 1-2km, at this time the cell_id precision is not superior to the 500m, such precision can not satisfy most user's request. Therefore, some improvement techniques, such as Cell_id+sector-id, Cell_id+ta and Cell_id+rtt technology, have appeared on the basis of cell_id, although these technologies can improve the positioning accuracy to some extent, but the improvement effect is not obvious.

CELL_ID and its improved technology is the simplest way to realize the terminal location of cellular network, which requires less financial, human and material resources, less network resources, convenient implementation and short response time, and can be used in all cellular networks and get gsm/gprs/wcdma/ CDMA2000 and other technologies are low in location, with different location precision, it is usually used as auxiliary location means to provide auxiliary information for precise positioning and to realize initial positioning.

2.2 TDOA, EOTD, Otdoa and E-flt Technologies

TDOA technology was first used in radar systems, and GPS positioning systems are now using this technology. It utilizes clock synchronization between base stations and user signals to different base stations at different times. The location algorithm is used to calculate the position. The positioning technology can be applied to all kinds of mobile communication systems (AMPS, GSM, wideband and narrowband CDMA), especially for CDMA systems, the CDMA system expands the signal spectrum to a wide range by spread spectrum, which makes the system have strong resistance to multipath. CDMA is a non power sensitive system, and the signal attenuation has less influence on the precision of time measurement.

The TDOA is measured by the network equipment and is positioned and calculated without the participation of the terminal. The enhanced forward link triangulation (E-flt) technology is measured by the terminal position parameters, and then sent back to the network to complete the location calculation, at present the E-flt only supports the cellular system of the CDMA system. The E-OTD and Otdoa are measured by the terminals, and the position calculation is done according to the terminal or network, the former is the specific positioning technology developed for the GSM/GPRS system, the latter can only be used in WCDMA system.

These four kinds of positioning techniques are advantageous to the time difference parameter determination position, the digital model is same, the localization precision is affected by the system timing precision. Whether based on the terminal or the network, the base station must be strictly synchronized, to ensure that the timing error of the system itself does not affect the positioning result obviously. IS-95 CDMA and CDMA2000 belong to the synchronous system, which can ensure the timing accuracy of the base station by GPs synchronization. Gsm/gprs and WCDMA belong to asynchronous network, must add high precision and high stability Timing unit (atomic species or GPS clock) in each base station, or increase timing unit LMU between base stations to realize clock unification. In addition, in the CDMA system, the system of positioning by the time difference is affected by the "testability", in which the reverse power control can seriously affect the positioning of the TDOA, and the forward power control has a great influence on the Otdoa.

2.3 A-gps Technology

GPS technology has been widely used in the world since it was put into use since the late 70, because of its all-weather, high-precision positioning performance. The use of GPS equipment is one of the important prerequisite for the receiver and the satellite between the direct path, which makes GPs in the building-intensive urban areas and inside the building there is a signal reception blind area. The new A-GPS technology integrates GPS high-precision positioning and cellular network high density coverage characteristics, that is, to ensure the accuracy of cellular positioning within the city, but also to expand the coverage of the GPS, A-GPS can through the air interface of the cellular network to enable the terminal to obtain the effective parameters of the satellite. In addition, the A-GPS response time is significantly faster than the traditional GPS. The initial capture time of GPs is longer, usually 30s-15min, depending on the relative position of the satellite and the terminal, A-GPS can reduce the initial capture time to 5-10s. The compatibility of A-GPS technology system is very strong, if the GPS function module is added in the network, the basic positioning function can be realized. The implementation of the positioning process is not necessarily connected with the air interface standard, so GPS positioning technology can provide location service for all cellular networks conveniently and quickly. Qualcomm has developed a miniaturized chipset UEM5100 that integrates GPS positioning functions and has been used in Gpsone systems launched by subsidiaries Snaptrack. With the progress of chip manufacturing technology, GPS system itself positioning accuracy and cost reduction, A-GPS will eventually replace a variety of traditional wireless positioning technology, cellular mobile communication system to provide positioning services, the main technical means.