Cellular network service function introduction
**Cellular Network**
A cellular network, also known as a mobile network, is a type of communication infrastructure that divides the coverage area into small hexagonal regions called cells. Each cell is equipped with a base station that handles wireless communication within its area. This structure resembles a honeycomb pattern, hence the term "cellular." The system allows for efficient use of radio frequencies and supports seamless mobility for users as they move between cells.
Cellular networks can be categorized into analog and digital systems, based on how information is transmitted. Analog networks were used in early mobile communications, while modern systems rely on digital technology for better quality, security, and capacity.
**Components of a Cellular Network**
A typical cellular network consists of three main parts: the mobile station, the base station subsystem, and the network subsystem.
- **Mobile Station (MS):** This refers to the user device, such as a mobile phone or other portable communication equipment.
- **Base Station Subsystem (BSS):** Includes the Base Transceiver Station (BTS) and the Base Station Controller (BSC). The BTS handles wireless communication, while the BSC manages connections and controls the BTS.
- **Network Subsystem:** This includes the Mobile Switching Center (MSC), which acts as the central control unit, and other databases like the Home Location Register (HLR) and Visitor Location Register (VLR), which store user and device information.
**Cellular Structure and Frequency Reuse**
The concept of cellular networks relies heavily on dividing a large area into smaller hexagonal cells. This approach allows for the use of low-power transmitters instead of a single high-power one, reducing interference and improving efficiency.
One key principle in cellular networks is **frequency reuse**, where the same set of channels can be used in different cells if they are far enough apart. The number of cells in a cluster determines the frequency reuse factor. For example, with a regular hexagonal layout, the number of cells in a cluster (N) can be calculated using formulas like N = i² + ij + j², where i and j are integers. Common values include 3, 4, 7, 9, and 12.
**Why Hexagons?**
Hexagons are preferred in cellular network design because they provide the most efficient way to cover an area without gaps or overlaps. Among squares, equilateral triangles, and hexagons, the hexagon offers the largest area for the same perimeter, making it ideal for maximizing coverage with minimal overlap.
**Cellular Coordinates**
Each cell can be identified using a coordinate system, often represented as (i, j). For example, a cell might be labeled as (2, 1), helping in tracking and managing network resources efficiently.
**Channel Allocation**
In FDMA (Frequency Division Multiple Access) systems, channels are assigned based on signal strength and distance. There are two main types of channel allocation:
- **Static Channel Allocation:** Each cell is assigned a fixed set of channels, making it simple but less flexible.
- **Dynamic Channel Allocation:** Channels are allocated on demand by the MSC, allowing more efficient use of resources and reducing call blocking, though it requires real-time coordination between base stations.
**Key Functional Units**
- **Base Transceiver Station (BTS):** Manages wireless communication and connects to the BSC.
- **Base Station Controller (BSC):** Controls the BTS and manages handovers between cells.
- **Mobile Switching Center (MSC):** Acts as the core of the network, handling call routing and user management.
- **Home Location Register (HLR):** Stores permanent user data.
- **Visitor Location Register (VLR):** Temporarily stores data about users visiting a particular area.
- **Authentication Center (AUC):** Verifies user identity to prevent unauthorized access.
- **Equipment Identity Register (EIR):** Keeps track of mobile devices to block illegal ones.
- **Operation and Maintenance Center (OMC):** Monitors and maintains the entire network.
By combining these components and principles, cellular networks provide reliable, scalable, and efficient mobile communication services that support millions of users worldwide.
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