Background on Telecommunications Services 

Telecommunications is the transmission of messages over significant distances for the purpose of communication.  In earlier times, telecommunications involved the use of visual smoke signals, semaphores, signal flags and the like.  What began with largely electric modes of telecommunications such as the telegraph, telephone and the teletype has evolved today into wireless communications, beginning in the first decade of the 20th Century.

The basic elements of a telecommunications system are three (3) primary units which are always present in one form of another:-

1. A transmitter: that which takes information and converts it into a signal.

2. A transmission medium, also called the “physical channel”, which carries the signal.

3. A receiver, that takes the signal from the channel and converts it back into usable information.

Sometimes, telecommunications systems are “duplex” (two-way) with a single box of electronics working as both a transmitter and a receiver, or better known as a transceiver. A mobile phone is the classic example of a transceiver.

Cellular Networks
 
A cellular network is a radio network made up of a number of cells, each served by at least one fixed-location transceiver, known as a cell site or base station. When joined together these cells provide radio coverage over a wide geographical area.  This enables a large number of portable transceivers (e.g. pagers, mobile phones, etc.) to communicate with each other and with fixed transceivers and phones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission.

Modern mobile phone networks use cells because radio frequencies are a limited, shared resource. Cell-sites and handsets change frequency under computer control and use low power transmitters so that a limited number of radio frequencies can be simultaneously used by many callers with less interference.

A cellular network is used by the mobile phone operator to achieve both coverage and capacity for their subscribers. Large geographic areas are split into smaller cells to avoid line-of-sight signal loss and to support a large number of active phones in the area.  All of the cell sites are connected to telephone exchanges (or switches), which in turn are connected to the public telephone network.

In cities, each cell site may have a range of up to approximately ½ mile, while in rural areas; the range could be as much as 5 miles.  It is possible that in clear open areas, a user may receive signals from a cell site 25 miles away.

Structure of a Mobile Phone Cellular Network

At its most basic, a cellular mobile-radio network consists of the following components:-

o A network of radio base stations forming the Base Station Subsystem.
o The core circuit switched network for handling voice calls and text.
o A packet switched network for handling mobile data.
o The Public switched telephone network to connect subscribers to the wider telephony network.

This network is the foundation of the GSM system network. There are many functions performed by this network in order to make sure customers get the desired service including mobility management, registration, call set up and handoff.

As the phone user moves from one cell area to another cell whilst a mobile call is in progress, the mobile station will search for a new channel to attach to in order not to drop the call.  Once a new channel is found, the network will command the mobile unit to switch to the new channel and at the same time switch the call to the new channel.  This features the basic “handoff” from one cell to another cell.  Other species of handoff such as the soft handoff and the inter-frequency handoff are beyond the ambit of this report.

The Base Station Subsystem (BSS) is the section of a traditional cellular telephone network responsible for handling traffic and signaling between a mobile phone and a network switching subsystem.  The core of the BSS is the Base Transceiver Station (BTS), which typically contains equipment necessary for the transmission and reception of radio signals, antennas and equipment for encrypting and decrypting communications with the base station controller (BSC). The function of a BTS will vary depending on the cellular technology used and the cellular telephone provider

Radio Transmission Towers

Radio masts and towers are usually tall structures designed and constructed to support antennas for telecommunications and broadcasting.   The terms “mast” and “tower” can be used interchangeably, although a “mast” usually refers to a tower that is held up by guys or stay cables.  A tower, in contrast, is a self-supporting or cantilevered structure.

Towers are usually constructed from a variety of materials, the most common being steel lattice towers, which by design provides great strength, low wind resistance and economy in use of materials, and is usually triangular or square in cross-section.  Apart from steel lattice structures, tubular steel structures are known to be used in the construction of said towers.

Reinforced concrete can also be utilized for the construction of transmission towers, though they are relatively more expensive compared to steel lattice and tubular steel towers.  Fiberglass towers have also been used for narrow-bandwidth equipment, and wooden towers are now rare, but were widely used after World War II.