Location business in WCDMA network
Http://www.chinatelecom.com.cn November 03, 2003 China Telecom Group Beijing Research Institute Yu Wei Xing Yanxia
Abstract This article mainly introduces location services in the WCDMA system, including the principles and features of three positioning techniques, core network network structures and interfaces and location services. Keywords: LCS Cell ID OTDOA A-GPS Location Business 1. Foreword Mobile Communications is one of the most competitive industries in recent years, operators are increasingly needed to improve competitiveness, LCS businesses (Location Services, Location business is a commonly optimized mobile value-added business. According to Strategics Group's forecast, in 2004, there will reach 360 million US dollars in 2004. The so-called location service refers to the location technology to determine the position of the mobile terminal and provide a variety of location-based application value-added services. At present, a simple location-based service is available in the 2G system. With the acceleration of the commercial process of the 3G network, the location service will be able to rely on the broadband and high speed characteristics of the 3G network, become more colorful. The implementation method of location services in the WCDMA system will be specifically described below. 2, the positioning technology WCDMA R99 specification defines three positioning techniques: the positioning technology of Cell ID (cell recognition), OTDOA (Observed Time Difance Of Arrival), and network-assisted GPS positioning technology, the following respectively Introduction. 2.1 Positioning technology based on Cell ID This is the most basic positioning method for all cellular networks. It does not require mobile station to provide any positioning measurement information, and there is no need to change the current network. It only needs to add a simple location process processing on the network side, and thus the most easily implemented, this positioning technology has been widely used in various mobile networks. use. Its positioning principle is simple: the network is locked according to the location and cell of the mobile station current service base station. If the cell is a full-to-directional cell, the location of the mobile station is in a circle of the radius of the radius in the serving base station, and the radius is covered with a radius; if a small partition sector, the mobile station can be further determined within a range of a certain sector coverage. Obviously, this positioning method is completely dependent on the size of the mobile station, from several hundred meters to tens of kilometers. In rural areas, the coverage of the cell is large, so the positioning accuracy of the Cell-ID is very poor. The area of the urban environment is small, and the general cell radius is 1 ~ 2km. For the bustling urban area, it is possible to use a microcell, the cell radius may go to a few hundred meters, and the positioning accuracy of the Cell-ID will be improved as a few. 100 meters. Since the Cell-ID positioning does not require the positioning measurement of the mobile station, and the positioning signaling transmission of the air interface is rare, the positioning response time is shorter, generally within 3s. 2.2 OTDOA Technology OTDOA (Observed Time Difference Of ArriVal is a way of positioning under 3G networks. There is also a similar positioning method in the GSM network, called E-OTD (Enhanced Observed Time Diference). The principle of this method is shown in Figure 1. The basic principle of this positioning method is that the mobile station measures the downlink pilot signal of different base stations to obtain TOA (TIME O F ArriVal, arrival time) of different base stations, that is, the so-called pilot phase measurement. According to the measurement result and combined with the coordinates of the base station, the position of the mobile station can be calculated using a suitable positional estimate.
As shown in the figure, it is assumed that the A base station is referenced, according to the pilot phase measurement result provided by the mobile station, it is possible to obtain a difference between the downlink pilot signal of the B base station relative to the A base station, which is described as TDOAAB, multiplied by light speed to obtain a base station and The B base station reaches the spread distance difference, which can be obtained by the A base station and the B base station as a basis. Also, another pair of surfaces based on the A base station and the C base station can be obtained according to TDOAAC. The two-faceted junction is the location of the mobile station. The actual positional estimation calculation requires the case where the multi-base station (3 or more) positioning is considered, so the algorithm is more complicated. In general, the number of base stations measured by the mobile station, the higher the measurement accuracy, the more obvious the positioning performance improvement. Using this method, a base station that is required to measure mobile comparable simultaneously issues a downlink pilot signal. Therefore, all base stations in the network must achieve time synchronization. Generally, the base station can be achieved by installing a GPS receiver or connected to a time synchronization network in a base station. OtDOA's positioning accuracy is higher than the Cell ID method, but its accuracy is affected by the environment, and the mobile station can be positioned within 10-20 meters in suburbs and rural areas; due to higher buildings, radio wave propagation environments due to high buildings in the city Not good, the signal is difficult to directly from the base station to the mobile station, generally to reflect or reflect, the TOA of the downlink pilot signal has an error, so the positioning accuracy will affect, the positioning range is approximately 100-200 meters. General situation The OTDOA positioning response time is around 3 to 6 s. 2.3 Network Assisted GPS Location A-GPS (Assisted Global Positioning Systems) is a referred to as a network-assisted GPS positioning, which requires network and mobile stations to receive GPS information. Its basic principle is that the network provides auxiliary GPS information to the mobile station, including accessibility information of GPS pseudorange measurements (such as GPS capture assistance information, GPS positioning auxiliary information, GPS sensitivity assist information, GPS satellite work status, etc.) and mobile stations Position calculation auxiliary information (such as GPS columns, correction data, GPS epicard, GPS navigation, etc.), use this information, mobile station can quickly capture satellite, and receive measurement information, then send measurement information to the network The positioning service center, which calculates the location where the mobile station is currently located. Since the location calculation is completed in the network, the GPS reception implementation complexity of the mobile station is greatly reduced, and power consumption can be reduced. In an open environment, such as suburban or rural, multipath and occlusion are negligible, and the positioning accuracy of A-GPS can reach around 10m or better; if the mobile station is in the urban environment, there is no blocking and non-abutment, positioning Accuracy will be around 30 to 70m; if the mobile station is in indoor or other multipath and occlusion, the mobile station is difficult to capture enough satellite signals, and the A-GPS will not be able to complete the positioning. This is its maximum limitability. . Compared to the first two positioning techniques, the response time of the A-GPS positioning method is slightly longer, in the case of cold start, the positioning response time of the A-GPS is 10s ~ 30s; in normal operation, the response time is about 3 to 10 s . The above introduction is the three basic positioning techniques specified in R99, which can be used in different situations, and the positioning method based on the Cell ID can be used at a lower positioning accuracy; the OTDOA method can be high and the terminal and the terminal and When the network does not have a GPS receiving device; the network assisted GPS positioning method is suitable for the positioning accuracy requires high and the terminal and the network have a GPS receiving device. In addition, these methods can be mixed simultaneously to make up for the shortcomings of each other. For example, use Cell-ID and OTDOA technology, you can get better positioning effects in rural and dense urban areas.
In the early days of WCDMA network, there is no GPS device, and the LCS business is not rich, and the network will mainly use the first two methods to provide location services; with the development and maturity of the network, the application of network-assisted GPS positioning technology will have Increased, the network will use multiple positioning techniques to provide LCS services for different applications and different users in different situations. 3, the next figure below is the network structure of the 3GPP implementation of the LCS service, and the LCS function entity on the wireless access network is the LMU (Location Measurement Unit, Location Measurement Unit) and SMLC (Serving Mobile Location Center, Service Mobile Location Center) Where the LMU can be set separately or with the Node B, the SMLC can be a separate device or a function block and the RNC as an RNC, depending on the implementation of the manufacturer. The LCS function entity on the core network is mainly GMLC (GMLC (Gateway Mobile Location Center), which is connected to LCS clients; other core network dollars HLR, MSC / MSC Sever, SCP and SGSN Need to have the ability to support location services. The above functional entity is responsible for the LMU, responsible for wireless signal measurement, resulting in SMLC calculating location information; SMLC selects the appropriate positioning technology based on the QoS of the service, and the location information of the UE is in the form of latitude latitude by the MSC in the form of the latitude. The SGSN of the packet domain is sent to the GMLC; the GMLC is a gateway for external applications to obtain UE location information, including authentication, authorization, authorization, authorization of the client to geographic coordinates, to the client and The user's bill, accept the client's request and make a corresponding response. The LCS client is a functional entity that interacts with the LCS server in order to obtain the mobile station location information. It can be external to the mobile network, and the general situation LCS customers are available in network operators or other third parties. Location-related applications, it can be accessed in two ways to GMLC, one is to access the LE interface using the MLP (Mobile Location Protocol) protocol, MLP is a GMLC and specific application recommended by Open Mobile Alliance OMA (Open Mobile Alliance) The agreement between the other access method is to access the standard API (Application Program Interface) interface provided by OSA (Open Service Access), which is the trend of hierarchical network development, but currently unified business platform construction There is also a difficulty, the OSA API protocol is also yet to be improved, so this approach is not as easy as the former method. According to the needs of different applications, the LCS client can issue two position requests to the GMLC, instant location request LIR (Location Immediate Request), and delay position request LDR (Location DeferRed Request), including the information of the target UE, information information, Business type and QoS and other business related information. The corresponding GMLC will reply to instantly respond (IMMEDIATE RESPONSE), which contains the geographic coordinates of the target UE, and the LCS client provides different applications based on this result.
