**Cellular Mobile Communication**
Cellular mobile communication is a wireless networking technology that enables communication between devices and the network, allowing users to stay connected while on the move. Its key characteristic is the mobility of the terminal, which supports seamless handoff and automatic roaming across different cells within a local network. The services provided by a cellular network include voice, data, and video transmission, supported by components such as the base station subsystem and the mobile switching subsystem.
**Classification of Cellular Mobile Communication**
Common cellular systems can be categorized into three types: macrocells, microcells, and picocells. Each has unique features tailored for different coverage and capacity needs.
**1. Macrocell Technology**
In the early stages of network deployment, operators focused on creating large macrocells to achieve wide geographical coverage. A typical macrocell covers a radius of 1 to 25 kilometers. Within this area, there are two common issues: "blind spots," where signal strength is weak due to obstacles, and "hot spots," where high traffic density leads to congestion. These problems are often addressed using repeaters or cell splitting. However, these solutions have limitations—expanding coverage may reduce quality, while improving quality may decrease capacity. As user numbers grow, macrocells are split into smaller ones, but further reduction in size increases costs and interference. To address these challenges, microcell technology was introduced.
**2. Microcell Technology**
Microcell technology offers smaller coverage areas (30–300 meters), lower power consumption, and easier installation. It is ideal for improving coverage in hard-to-reach areas like subways or basements and for increasing capacity in high-traffic zones such as shopping malls or stadiums. When used together with macrocells, microcells form a multi-layer network, with macrocells covering large areas and microcells enhancing performance in specific locations. They operate independently in terms of system configuration and use separate broadcast channels.
**Cellular Mobile Communication System**
A cellular mobile communication system consists of three main components: the Switched Network Subsystem (NSS), the Radio Base Station Subsystem (BSS), and the Mobile Station (MS). The NSS handles call routing and user data management, while the BSS manages wireless communication with the MS. The interface between the NSS and BSS is called the "A" interface, and the one between the BSS and MS is the "Um" interface.
The GSM system, designed by Northern European operators, features open interfaces to allow interoperability between different manufacturers' equipment. The block diagram of the GSM system includes the MSC, VLR, HLR, AUC, EIR, BSC, BTS, and MS. Additionally, the system includes a Short Message Service Center (SMSC) for sending and receiving messages and a Voice Mailbox for handling missed calls.
**Switched Network Subsystem (NSS)**
The NSS is responsible for managing user data, mobility, and security. Key components include:
- **MSC (Mobile Switching Center):** Controls voice exchange and serves as an interface between the mobile network and other public networks.
- **VLR (Visitor Location Register):** Stores temporary information about visiting users.
- **HLR (Home Location Register):** Keeps permanent records of all registered users.
- **AUC (Authentication Center):** Generates authentication parameters to secure user identity.
- **EIR (Equipment Identity Register):** Tracks and blocks unauthorized devices.
**Wireless Base Station Subsystem (BSS)**
The BSS includes the BSC and BTS. The BSC controls multiple BTSs, managing resources, handover, and power control. The BTS handles wireless transmission, encryption, and channel management.
**Mobile Station (MS)**
The mobile station consists of the mobile terminal and the SIM card. The terminal processes voice and data, while the SIM card stores user information and ensures secure access to the network.
**Operation and Maintenance Subsystem (OMC)**
The OMC monitors and manages the entire GSM network, providing fault detection and status reporting. Although the interface between OMC and MSC is not yet fully standardized, it plays a critical role in maintaining network reliability.
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