CDMA Wireless location technology and its application

This paper describes the main positioning techniques of CDMA system and its characteristics, compares and analyzes various positioning techniques, puts forward the selection scheme, and introduces its bearing application. Keyword CDMA location technology

1 Introduction

Wireless location service is started and developed from the United States. In 1996, the Federal Communications Commission (FCC) forced all wireless service providers to provide the public security service with the user's location information and terminal number when the mobile user started emergency calls, in order to implement emergency relief work for users, and to require that by October 2001, 67% The call positioning accuracy is up to 125m. Since then, Japan, Germany, France, Sweden, Finland and other countries have launched a variety of features of the commercial positioning services.

With the development of wireless systems and the increasing number of mobile users, there is also a growing demand for location-based services, such as public safety, emergency service, location-based billing, asset management, fraud detection and routing wizards, and so on, while different positioning services require varying positioning accuracy, and correspondingly, the required positioning techniques are different, For example, location-based billing requirements are not high positioning accuracy, the use of cell ID (cell identification) positioning technology can be achieved, and the Routing wizard requires a relatively high positioning accuracy, only the use of GPS (Global positioning System) positioning technology and hybrid positioning technology to achieve.

These requirements have greatly promoted the development of positioning technology, after years of research on wireless positioning, has developed a variety of positioning technology, and on this basis, a variety of positioning services and applications have flourished. (Computer science)

2 Main CDMA Location technology

Wireless location technology is to measure the received radio wave parameters, according to the specific algorithm to determine the location of the north-measured objects, the measurement parameters generally include transmission time, amplitude, phase, and arrival angle and so on. The positioning accuracy is mainly determined by the measurement method.

2.1 Technology based on cell ID

In the current CDMA network, BSC transmits the cell ID of the user's base station sector to MSc in the process of location updating, call processing, short message transmission, and switching of mobile stations. This method is simple to implement, the terminal side does not need to make any software and hardware modification, network side does not need to add new I have network entity. But the positioning accuracy is not high, the positioning range and sector coverage is the same, in the densely populated area of urban base station, the radius can reach about 400m, and the location precision is very low in the suburbs where the density of the base station is low, so it can only provide the positioning business which is not high on the positioning precision, such as the charge based on the location of the cell, which cannot realize the

2.2AOA (Angle of arrival)

The position of the mobile user is estimated by two or more base stations by measuring the arrival angle of the receiving signal. The receiver passes the antenna array to measure the incident angle of the electric wave, which makes up a radial connection from the receiver to the transmitter, i.e. the location line, and the two-dimensional position coordinate of the mobile station can be obtained by the intersection point of the two bit line.

The AoA method needs to increase the smart antenna (SA) on the network side to realize; in the environment with more obstacles, because of the multipath effect of wireless transmission, the error increases and the positioning accuracy is low, especially when the mobile station is farther from the base station, the small deviation of the base station's positioning angle will lead to the large error of the location line distance.

2.3TOA (Time of arrival)

is a positioning method based on directional link, which can be used to determine the location of mobile users by measuring the transmission time of mobile station signals to multiple base stations. Only more than three base stations receive the signal of the mobile station, the triangulation algorithm can be used to calculate the position of the mobile station. Toa location accuracy is closely related to the geographical distribution of the base station, and the precision is highest when the intersection angle between the spheres is 90 degrees. However, the error of all receivers is not processed and the errors are large.

2.4TDOA (Time different of arrival)

is another kind of positioning method based on reverse link, by detecting the time difference of the mobile station signal to two base stations to determine the position of the mobile station, the mobile station must be located on the hyperbolic equation with two base stations as the focal point, and it is necessary to establish more than two hyperbolic equations to determine the two-dimensional position coordinate of the mobile station. That is to say, more than three base stations are required to receive the mobile signal, and the intersection of the two hyperbola is the two-dimensional position coordinate of the mobile station.

The Tdoa method does not require to know the time of the signal propagation, but also eliminates or reduces the common error caused by the channel in all receivers, and in general, the positioning accuracy is higher than the Toa method. However, due to the power control caused by the station near the mobile station transmitter power is small, so that the adjacent base station to receive the power is very small, resulting in a relatively large measurement error, that is, the power received by the adjacent base station is very small, resulting in a relatively large measurement error, that is, adjacent base station Snr too small to bring the measurement error. At present, there are some solutions to this situation, such as the E-911 when the mobile station transmission power to the maximum instantaneous, can improve positioning accuracy, but the capacity of CDMA network will have a certain degree of impact.

2.5AFLT (Advanced Forward Link trilateration) technology

It is a kind of positioning method based on the forward link, in the position operation, the mobile phone simultaneously listens for the pilot information of multiple base stations (at least three base stations), uses the code chip Shi Yanlai to determine the distance of the mobile phone to the nearby base station, and finally calculates the user's position by triangulation method.

Aflt positioning technology requires adding new entities to the network, and using pilot information to calculate the location of the mobile station, which includes PDE (Position deltermining Entity) and MPC (mobile positioning Center). There are two main ways for PDE to obtain pilot information:

(1) In accordance with the IS-801 protocol defined by the transmission mode to MSC, and then transmitted to PDE by MSC, this way requires the mobile platform to add support IS-801 protocol features.

(2) using the message of a interface, the parameters for positioning are transmitted to MSC and transmitted by MSC to PDE. In this way, there is no need for the mobile console to support the IS-801 protocol, but the transfer of these parameters is required on the A interface, and messages for passing these parameters have been defined in release version of a interface.

The mobile station needs the software to upgrade, at the same time, according to the PDE obtains the pilot information way difference to decide whether the mobile station needs to support the IS-801 protocol, the network side needs to support the IS-801 protocol, the localization algorithm may put on the mobile platform or the network side. The positioning accuracy is between the cell identification and GPS positioning technology, the location radius is generally 200 to 400m, the maximum can reach 100m. The main factors affecting precision are base station density and terrain environment, such as in the densely populated areas of large cities, where the positioning accuracy is relatively high.