LocationUpdate汇总

1、.Location UpdateTypes of Location Update· Location Registration (power on)· Generic· PeriodicLocation registration takes place when a mobile station is turned on. This is also known as IMSI Attach because as soon as the mobile station is switched on it informs the Visitor Location Reg

2、ister (VLR) that it is now back in service and is able to receive calls. As a result of a successful registration, the network sends the mobile station two numbers that are stored in the SIM (Subscriber Identity Module) card of the mobile station:Location Area Identity (LAI) + Temporary Mobile Subsc

3、riber Identity (TMSI). The network, via the control channels of the air interface, sends the LAI. The TMSI is used for security purposes, so that the IMSI of a subscriber does not have to be transmitted over the air interface. The TMSI is a temporary identity, which regularly gets changed.A Location

4、 Area Identity (LAI) 位置区识别码is a globally unique number.LAI用于移动用户的位置更新。LAIMCCMNCLAC MCC移动国家号，与IMSI中的MCC一样具有3个数字，用于识别一个国家，中国为460。 MNC移动网号，识别国内GSM网，与IMSI中的MNC的值是一样的。 LAC位置区号码，识别一个GSM网中的位置区。LAC最大长度为16Bit，理论上可以在一个GSM/VLR内定义65536个位置区。A Location Area Code (LAC) is only unique in a particular network.Every

5、time the mobile receives data through the control channels, it reads the LAI and compares it with the LAI stored in its SIM card. A generic location update is performed if they are different. The mobile starts a Location Update process by accessing the MSC/VLR that sent the location data.A channel r

6、equest message is sent that contains the subscriber identity (i.e. IMSI/TMSI) and the LAI stored in the SIM card. When the target MSC/VLR receives the request, it reads the old LAI which identifies the MSC/VLR that has served the mobile phone up to this point. A signalling connection is established

7、between the two MSC/VLRs and the subscribers IMSI is transferred from the old MSC to the new MSC. Using this IMSI, the new MSC requests the subscriber data from the HLR and then updates the VLR and HLR after successful authentication.Figure 2.25 Network Elements involved in location updatePeriodic l

8、ocation update is carried out when the network does not receive any location update request from the mobile in a specified time. Such a situation is created when a mobile is switched on but no traffic is carried, in which case the mobile is only reading and measuring the information sent by the netw

9、ork. If the subscriber is moving within a single location area, there is no need to send a location update request.Figure 2.26 Example of Periodic Location UpdateA timer controls the periodic updates and the operator of the VLR sets the timer value. The network broadcasts this timer value so that a

10、mobile station knows the periodic location update timer values. Therefore, when the set time is up, the mobile station initiates a registration process by sending a location update request signal. The VLR receives the request and confirms the registration of the mobile in the same location area. If

11、the mobile station does not follow this procedure, it could be that the batteries of the mobile are exhausted or the subscriber is in an area where there is no network coverage. In such a case, the VLR changes the location data of the mobile station to “unknown”.Figure 2.27Location Update procedures

12、HandoverIn a mobile communications network, the subscriber can move around. How can we maintain the connection in such cases? To understand this, we must study the process of handing over the calls.Maintaining the traffic connection with a moving subscriber is made possible with the help of the hand

13、over function. The basic concept is simple: when the subscriber moves from the coverage area of one cell to another, a new connection with the target cell has to be set up and the connection with the old cell has to be released. There are two reasons for performing a handover:1. Handover due to meas

14、urements occurs when the quality or the strength of the radio signal falls below certain parameters specified in the BSC. The deterioration of the signal is detected by the constant signal measurements carried out by both the mobile station and the BTS. As a consequence, the connection is handed ove

15、r to a cell with a stronger signal.2. Handover due to traffic reasons occurs when the traffic capacity of a cell has reached its maximum or is approaching it. In such a case, the mobile stations near the edges of the cell may be handed over to neighbouring cells with less traffic load.The decision t

16、o perform a handover is always made by the BSC that is currently serving the subscriber, except for the handover for traffic reasons. In the latter case the MSC makes the decision. There are four different types of handover and the best way to analyse them is to follow the subscriber as he moves:Int

17、ra cell - Intra BSC handoverThe smallest of the handovers is the intra cell handover where the subscriber is handed over to another traffic channel (generally in another frequency) within the same cell. In this case the BSC controlling the cell makes the decision to perform handover.Figure 2.28Intra

18、 Cell - Intra BSC HandoverInter cell - Intra BSC handoverThe subscriber moves from cell 1 to cell 2. In this case the handover process is controlled by BSC. The traffic connection with cell 1 is released when the connection with cell 2 is set up successfully.Figure 2.29 Inter Cell - Intra BSC handov

19、erInter cell - Inter BSC handoverThe subscriber moves from cell 2 to cell 3, which is served by another BSC. In this case the handover process is carried out by the MSC, but, the decision to make the handover is still done by the first BSC. The connection with the first BSC (and BTS) is released whe

20、n the connection with the new BSC (and BTS) is set up successfully.Figure 2.30Inter Cell - Inter BSC HandoverInter MSC handoverThe subscriber moves from a cell controlled by one MSC/VLR to a cell in the domain of another MSC/VLR. This case is a bit more complicated. Considering that the first MSC/VL

21、R is connected to the GMSC via a link that passes through PSTN lines, it is evident that the second MSC/VLR can not take over the first one just like that. The MSC/VLR currently serving the subscriber (also known as the anchor MSC), contacts the target MSC/VLR and the traffic connection is transferr

22、ed to the target MSC/VLR. As both MSCs are part of the same network, the connection is established smoothly. It is important to notice, however, that the target MSC and the source MSC are two telephone exchanges. The call can be transferred between two exchanges only if there is a telephone number i

23、dentifying the target MSC.Figure 2.31Inter Cell - Inter MSC HandoverSuch a situation makes it necessary to generate a new number, the Handover Number (HON). The generation and function of the HON are explained in the following text.The anchor MSC/VLR receives the handover information from the BSS. I

24、t recognises that the destination is within the domain of another MSC and sends a Handover Request to the target MSC via the signalling network. The target MSC answers by generating a HON and sends it to the anchor MSC/VLR, which performs a digit analysis in order to obtain the necessary routing information. This information allows the serving MSC/VLR to connect the target MSC/VLR. When the two MSCs are connected, the call is transferred to