Notes on Digital Communication Principles (II)-GSM System

Notes on Digital Communication Principles (ii) --- GSM System

1. GSMSystem Structure

It demonstrates a typical GSM system:

1)
Mobile (MS)

The mobile station is a device used by users in the public GSM mobile communication network and the only device in the entire GSM system that users can directly access.

Apart from what we usually call telephone components, another important component of the Mobile Station is the user identification module (SIM), which is basically an ISO
The standard "smart" card contains all information related to users and some wireless interfaces, including authentication and encryption information. Sim must be inserted to all mobile devices that use the GSM standard.
Card, only when handling abnormal emergency calls, you can operate the mobile station without a SIM card.

2)
Base Station Subsystem (BSS)

The Base Station Subsystem directly connects to the mobile station through wireless interfaces, and is responsible for wireless sending and receiving and wireless resource management.

On the other hand, the base station subsystem is connected to the Mobile Business Exchange Center (MSC) in the network subsystem (NSS) to achieve communication between mobile users or between mobile users and fixed network users, transmit System signals and user information. Of course
In addition, you must establish a communication connection between the BSS and the operation support subsystem (OSS.

The Base Station Subsystem is composed of two functional entities: the base station receiving and sending station (BTS) and the Base Station Controller (BSC. In fact, a base station controller can control dozens of BTS based on traffic demands. BTS
You can directly connect to the BSC, or use the remote control connection method of the base station interface device (BIE) to connect to the BSC
Connected. It should be noted that the base station subsystem should also include the Code Converter (TC) and the corresponding sub-multiplexing equipment (SM ). In more cases, the Code Converter is placed in the BSC
And MSC, it has many advantages in networking flexibility and reducing the number of transmission device configurations.

3)
Network subsystem

The network subsystem (NSS) mainly includes the exchange function of the GSM system and the database functions required for user data and mobility management and security management.
Communication between mobile users and between GSM users and other communication network users plays a management role.

• Mobile Business Exchange Center (MSC)

The Mobile Business Exchange Center MSC can be divided into three databases: belonging user Location Register (HLR), access user Location Register (vlr), and authentication center (AUC) obtain all data required to process user location registration and call requests. Conversely, MSC
It also requests to update some data of the database based on the latest information.

• Access user Location Register (vlr)

The access user Location Register (vlr) serves mobile users in the control area and stores information about registered mobile users in the control area, vlr obtains and stores necessary data from the HLR location of the mobile user. Once a mobile user leaves the control area of the vlr, it registers again in another vlr. The original vlr will cancel the mobile user data temporarily recorded. Therefore, vlr can be viewed as a dynamic user database. Vlr functions are always integrated in each MSC.

• User Location Register (HLR)

The user Location Register (HLR) is the central database of the GSM system, which stores the data of all existing mobile users controlled by the HLR. One HLR can control several mobile exchange areas and the entire mobile communication network. All important static data of mobile users is stored in HLR.
This includes data such as mobile user identification numbers, access capabilities, user categories, and supplementary services. HLR also stores and provides dynamic information about the MSC region where mobile users actually roam. In this way, any incoming call can be selected immediately
Path to the called user.

• Authentication center (AUC)

The GSM system adopts special security measures, such as user authentication and confidentiality of voice, data, and signal information on wireless interfaces. Therefore, the authentication center (AUC) Stores authentication information and encryption keys to prevent unauthorized users from accessing the system and ensure the security of mobile user communication through wireless interfaces. AUC
A function unit part of HLR, dedicated to GSM
System security management.

• Mobile device recognition register (EIR)

The mobile device identification register (EIR) stores the international mobile device identifier (IMEI) of mobile devices by checking the White List, black list, or gray list, the table lists the IMEI of the mobile devices that are permitted to use, that are to be monitored for failures, and that are not allowed to be used for theft.
Identification code, so that the operation department can take timely preventive measures for MS devices that are stolen or that are in danger of normal network operation due to technical faults or misoperations, to ensure the uniqueness and security of the mobile devices used in the network.

• Operation Support subsystem (OSS)

The operation support subsystem (OSS) needs to complete many tasks, including mobile user management, mobile device management, and network operation and maintenance. Mobile User management includes user data management and call billing. User data management is generally performed by the user Location Register (HLR ).
Is one of the NSS functional entities. User Identification Card Sim
Management can also be considered as part of user data management. However, as a relatively independent user identification card SIM management
The management requirements and modes of are completed using dedicated SIM personalized devices. Call billing is applicable to the mobile service exchange center MSC that can be accessed by mobile users.
And gmsc respectively. You can also use HLR
Or independent billing devices to centrally process billing data.

2. GSMSystem Parameters