What is a cell phone? It is a system that uses a large number of low power wireless transmitters to create cells, the main geographic coverage area of a wireless communication system. Variable power levels allow cell sizes to be determined according to subscriber density and regional needs.
When mobile users move from cell to cell, their conversations are "transferred" between these areas to ensure uninterrupted service. Channels (frequencies) used in one such unit can be reused in another at some distance.
Cellular is…
Cellular refers to the Enhanced Mobile Phone Service (AMPS), which divides a geographic region into areas called cells. The purpose of this split is to make the most of the limited number of transmission frequencies.
Cellular is a form of communication technology that allows mobile phones to be used.
Mobile phoneis a bi-directional radio that provides simultaneous transmission and reception.
Cellular mobile communication is based on the geographical division of the communication coverage area. Each cell is allocated a certain number of frequencies (or channels), which allow a large number of subscribers to simultaneously conduct conversations.
The common element of all generations of mobile communication technologies is the use of certain radio frequencies (RF) as well as frequency reuse. This allows you to provide services to a large number of subscribers while reducing the number of channels (bandwidth). It also allows you to create wide networks by fully integrating advanced mobile phone capabilities.
The increase in demand and consumption, as well as the development of various types of services, has accelerated the rapid technological development of modern networks, as well as the continuous improvement of the cellular devices themselves.
How mobile communication works
Each mobile phone uses a separate temporary radio channel to communicate with the cell site. This site supports communication with many phones at the same time using one channel per phone. Channels use a pair of cellular frequencies:
- Direct line for transmission from cell site.
- Reverse line so that the cell site can receive calls from users.
Radio energy dissipates over distance, so mobile phones must stay close to the base station to keep in touch. Basic structure of mobilenetworks includes telephone systems and radio services.
The principle of cellular communication (for dummies)
The process begins with the activation of the chip by entering the PIN code of the inserted SIM card. Then the cellular signal is transmitted over the control channels. The answer of the called number is transmitted over a free control channel to the antenna of the base station, from where it is transmitted to the mobile switching center.
The switching center is looking for a base station with the maximum cell phone signal strength of a cellular subscriber and switches the conversation to it.
Early architecture of the telephone system
The traditional mobile service was structured similarly to television broadcasting: one very powerful transmitter, located at the highest point in the area, would broadcast up to a radius of fifty kilometers.
The cellular concept structured the telephone network differently. Instead of using one powerful transmitter, many low-power transmitters have been placed throughout the cellular coverage area.
For example, by dividing an area into one hundred different areas (cells) with low power transmitters using twelve conversations (channels), the system capacity could theoretically be increased from twelve conversations or voice channels using one powerful transmitter to twelve hundred conversations (channels) using one hundred low power transmitters.
City area configured as traditionalmobile phone network with one powerful transmitter.
Mobile communication system using cellular concept
Interference problems caused by mobile devices using the same channel in adjacent areas have proven that all channels cannot be reused in every cell. Although it affected the effectiveness of the original concept, frequency reuse has become a viable solution to the problems of mobile telephony systems.
Engineers found that the effect of interference was not related to the distance between zones, but to the ratio of distance to power (radius) of the zone transmitters. By reducing the zone radius by fifty percent, service providers can quadruple the number of potential customers in the zone.
Systems based on areas with a radius of one kilometer will have a hundred times more channels than systems based on areas with a radius of ten kilometers. Speculation led to the conclusion that by reducing the radius of the zone to a few hundred meters, it was possible to serve millions of calls.
The cellular concept uses variable low power levels, allowing cells to be matched to subscriber density and area needs. As the population grows, cells can be added to accommodate this growth.
Cellular frequencies used in one cluster of cells can be reused in other cells. Conversations can be passed from cell to cell to maintain a constanttelephone connection when the user moves between them.
Cellular radio equipment (base station) can communicate with mobile phones as long as they are within range. Radio energy dissipates over distance, so mobile phones must be within the operating range of the base station. Like the early mobile radio system, the base station communicates with mobile phones via a channel.
The channel consists of two frequencies: one for transmitting to the base station and one for receiving information from the base station.
Cell System Architecture
Increasing demand and the poor quality of existing services have prompted mobile service providers to explore ways to improve the quality of service and support more users on their systems. Since the amount of frequency spectrum available for mobile cellular use was limited, efficient use of the required frequencies was necessary to cover communications.
In today's cellular telephony, rural and urban areas are divided into areas according to specific service rules. Deployment parameters such as number of divisions and cell sizes are determined by engineers experienced in cellular architecture.
Provisioning for each region is planned according to the engineering plan, which includes cells, clusters, frequency reuse and handover.
The cell is the basic geographical unit of the cellular system. These are the base stationstransmitting a signal through small geographic areas, which are represented as hexagons. The size of each varies according to the landscape. Due to limitations imposed by natural terrain and artificial structures, the true shape of the cells is not a perfect hexagon.
A cluster is a group of cells. No channel is reused in the cluster.
Because only a small number of radio frequencies were available for mobile systems, engineers had to find a way to reuse radio channels to carry more than one conversation at a time. The decision taken by the industry was called scheduling or frequency reuse. Frequency reuse was realized by restructuring the architecture of the mobile telephone system into the concept of cellular communications.
Cellular standards are as follows: the concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area. Cells are assigned a channel group that is completely different from neighboring similar units. Their coverage area is called an imprint. This footprint is bounded by a boundary so that the same group of channels can be used in different cells that are far enough apart that their frequencies do not interfere.
Cells with the same number have the same set of frequencies. If the number of available frequencies is 7, the frequency reuse factorequals 1/7. That is, each cell uses 1/7 of the available cellular channels.
Obstacles in the development of cellular communications
Unfortunately, economic considerations made the concept of building complete systems with many small areas impractical. To overcome this difficulty, system operators developed the idea of cell splitting. When a service area becomes full of users, this approach is used to divide one area into smaller ones. Thus, urban centers can be subdivided into as many areas as needed to provide an acceptable level of service in high-traffic regions, while larger, less expensive cells can be used to cover outlying rural areas.
The last hurdle in the development of the cellular network is related to the problem that arose when a cellular subscriber moved from one cell to another during a call. Since adjacent areas do not use the same radio channels, the call must either be dropped or transferred from one radio channel to another when the user crosses the line between adjacent cells.
Because call drop is not allowed, a handover process has been created. A handoff occurs when a mobile phone network automatically transfers a call to another radio channel when the mobile device traverses adjacent cells.
During a conversation, the two parties are on the same voice channel. When the mobile device leaves the coverage area of thiscell site, reception becomes weak. At this point, the cell site in use requests a handover. The system switches the call to a higher frequency channel at the new site without dropping the call or alerting the user. The call continues as long as the user is talking and the caller does not notice the handoff.
Cellular System Components
The cellular system offers mobile and portable telephone exchanges the same service as fixed exchanges over conventional wired loops. It is capable of serving tens of thousands of subscribers in a large metropolis. The cellular communication system consists of the following four main components that work together to provide mobile phone services to subscribers:
- Public Switched Telephone Network (PSTN).
- Mobile telephone exchange (MTSO).
- Cell site with antenna system.
- Mobile Subscriber Station (MSU).
PSTN consists of local area networks, exchange area networks and long distance networks that connect telephones and other communication devices around the world.
MTSO is the central office of mobile communications. It houses a communications switching center (MSC), field control and relay stations to switch calls from cell sites to wireline central offices (PSTN).
The term "cell site" is used to refer to the physical location of the radio equipment that provides cell coverage. The list of hardware located in the cell site includes power supplies,interface equipment, RF transmitters and receivers and antenna systems.
The mobile subscriber unit consists of a control unit and a transceiver that transmits and receives radio transmissions to and from the cell site. Three types of MSUs are available:
- Mobile phone (typical transmission power 4.0W).
- Portable (0.6W typical transmission power).
- Transportable (Typical transmission power is 1.6W).
Cell towers harmful
Cellular communication is a big breakthrough in science and technology of its time, which was not without consequences. The cell phone industry continues to claim that cell towers are not a he alth hazard, but fewer people believe that these days.
Are cell towers harmful? Unfortunately, the correct answer is yes. Microwaves can interfere with your body's electromagnetic fields, causing many potential he alth problems:
- Headaches.
- Memory loss.
- Cardiovascular stress.
- Low sperm count.
- Birth defects.
- Cancer.
There is strong evidence that electromagnetic radiation from towers is harmful to he alth.
Example: A study on the effect of a cage tower on a herd of dairy cattle was carried out by the government of the state of Bavaria in Germany, the results were published in 1998. The erection of the tower caused adverse he alth effects, resulting in a perceptible fallmilk yield. The move of cattle restored the milk yield. Moving them back to their original pasture recreated the problem.
Cellular communications in Russia
Out of 100 possible Russian cellular codes, 79 are used and 21 are free. Free codes are in reserve and do not yet belong to any operator.
More than 80 cellular communication companies are registered in the Russian Federation, providing their services on the territory of the country. Mobile operators have dialing codes in 9xx format. Cellular phone numbers are ten digits and start with +79xx or 89xx.
The largest operators include: MTS (Mobile TeleSystems), Beeline (Vympel-Communications), MegaFon, Tele2 (T2-Mobile). The Big Three operators (MTS, Beeline and MegaFon) own a whole series of numbers.
