What is a base station?

In telecommunications, a base station is a fixed transceiver that is the main communication point for one or more wireless mobile client devices.

A base station serves as a central connection point for a wireless device to communicate. It further connects the device to other networks or devices, usually through dedicated high bandwidth wire or fiber optic connections. Base stations are generally a transceiver, capable of sending and receiving wireless signals; otherwise, if they only transmitted signals out, they would be considered a transmitter or broadcast point. A base station will have one or more radio frequency (RF) antennas to transmit and receive RF signals to other devices.

Base stations are also central points that all clients connect to in a hub and spoke style network; it would not be a client among similar peers. Generally, if client devices wanted to communicate to each other, they would communicate both directly with the base station and do so by routing all traffic through it for transmission to another device.

What is a base station and wireless network?

Wireless systems use a network of radio base stations to provide service for mobile phones and other wireless devices.  Base stations send and receive low powered radio signals to and from mobile phones, and provide the connection to the main telephone network.   A mobile network is usually configured in a cellular grid format.

Base stations need to be located close to mobile phone users to provide good quality reception. 

What different types of base stations are there?

• Macro cells – towers, masts and poles providing wide are coverage.
• Micro cells – small antennas at street level providing local area coverage.
• Pico cells – very small antennas providing dedicated coverage spots.

What is the role of base station which is used in cellular mobile communication?

A base station is a radio transmitter/receiver, including an antenna, used in a mobile telecommunications network. The base station maintains the communication between the network and the mobile users through a radio link. The geographic area covered by a base station is called a cell.

What do base stations look like?

Base stations usually consist of a small equipment cabinet or hut, and antennas mounted on a support structure.

The antenna support structure can vary considerably.  Typical examples are: 

• Buildings
• Light poles
• Towers or masts

Base station antennas are usually located on the most suitable structure in the area for example an existing building, tower or structure.  Sometimes a new tower or mast is required if there are no existing structures.  Each base station is connected to the main telephone network either via a microwave link using a small dish antenna, or via optical fibre cable.

How do mobile network operators decide where to site base stations?

To provide a good quality mobile service, base stations need to be located where people use their mobile phones.  A mobile network is typically designed on a “cell grid” basis covering a geographic area.  Base stations are located either in the centre of each cell or on the corner of a group of cells.   The number of base stations required for a given area will depend on the terrain and number of people using mobile phones.

The radio signals that base station antennas transmit are primarily transmitted from the centre of the antenna outwards.  This means that the antennas need to be placed in locations where there are no obstructions, such as building rooftops and masts.

In built-up and mountainous areas with many buildings, trees and obstructions, it is likely that more base stations will be required to provide service to the local community. In rural areas with fewer obstructions, less base stations will be required.

How many base stations are required in a given area?

Mobile networks have a finite capacity which means the ability to cater for simultaneous phone calls.  The more people using mobile phones, the more capacity is required and this usually means more base stations closer together.  Mobile networks must be designed according to the local population and number of people using the network.

FUNCTIONS OF BASE STATION IN GSM COMMUNICATION

The BTS and the BSC communicate across the specified Abis interface, enabling operations between components that are made by different suppliers. The radio components of a BSS may consist of four to seven or nine cells. A BSS may have one or more base stations. The BSS uses the Abis interface between the BTS and the BSC. A separate high-speed line (T1 or E1) is then connected from the BSS to the Mobile MSC.

The Base Transceiver Station (BTS)

The BTS houses the radio transceivers that define a cell and handles the radio link protocols with the MS. In a large urban area, a large number of BTSs may be deployed.

The BTS corresponds to the transceivers and antennas used in each cell of the network. A BTS is usually placed in the center of a cell. Its transmitting power defines the size of a cell. Each BTS has between 1 and 16 transceivers, depending on the density of users in the cell. Each BTS serves as a single cell. It also includes the following functions:

• Encoding, encrypting, multiplexing, modulating, and feeding the RF signals to the antenna
• Transcoding and rate adaptation
• Time and frequency synchronizing
• Voice through full- or half-rate services
• Decoding, decrypting, and equalizing received signals
• Random access detection
• Timing advances
• Uplink channel measurements

The Base Station Controller (BSC)

The BSC manages the radio resources for one or more BTSs. It handles radio channel setup, frequency hopping, and handovers. The BSC is the connection between the mobile and the MSC. The BSC also translates the 13 Kbps voice channel used over the radio link to the standard 64 Kbps channel used by the Public Switched Telephone Network (PSDN) or ISDN.

It assigns and releases frequencies and time slots for the MS. The BSC also handles intercell handover. It controls the power transmission of the BSS and MS in its area. The function of the BSC is to allocate the necessary time slots between the BTS and the MSC. It is a switching device that handles the radio resources. Additional functions include:

• Control of frequency hopping
• Performing traffic concentration to reduce the number of lines from the MSC
• Providing an interface to the Operations and Maintenance Center for the BSS
• Reallocation of frequencies among BTSs
• Time and frequency synchronization
• Power management
• Time-delay measurements of received signals from the MS

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