What is cellular communication, without which a modern person cannot imagine life? This is the type of connection in which the last channel is wireless. The network is distributed over land areas called cells, each of which is served by at least one fixed location transceiver, but most commonly by three cellular or base transceiver stations. They provide the cell with network coverage that can be used to carry voice, data, and other types of content.
How does it work?
What is cellular in action? A cell usually uses a different set of frequencies from neighboring ones to avoid interference and ensure a guaranteed quality of service in each cell (cell principle). When combined, these cells provide radio coverage over an extended geographic region. This allows a significant number of portable transceivers (for example, mobilephones, tablets and laptops equipped with mobile broadband modems, pagers, etc.) communicate with each other and with fixed transceivers and phones anywhere on the network via base stations, even if some transceivers pass through multiple cells during transmission.
Cellular communication has a number of useful features:
- Higher capacitance than one large transmitter, since the same frequency can be applied to multiple channels if they are in different cells.
- Mobile devices consume less power than when connected to a single transmitter or satellite because cell towers are closer.
- Larger coverage than a single terrestrial transmitter as additional cell towers can be added indefinitely and are not limited in visibility.
How advanced is this today?
Major telecommunications service providers have deployed cellular networks for voice and content transmission over most of the inhabited territory of the Earth. This allows mobile phones and computing devices to connect to the standard telephone network and the public Internet.
Regions of mobile operators can be different - from the territory of the country to a small object. Private cell networks can be used for research or for large organizations and parks, such as sending calls to local public security agencies or a taxi company.
Which mobile operator is the leader today? Today, each country has its own providers. In Russia, MTS and Megafon occupy the first place in terms of prevalence.
Concept
What is cellular communication and how does it work? In a cellular radiocommunication system, the land area to be provided with this service is divided into cells in a pattern that depends on terrain and reception characteristics. It may be approximately hexagonal, square, round, or some other regular shape, although hexagonal honeycombs are standard. Each of these cells is assigned a set of frequencies (f1 - f6) that the respective radio base stations have. A group of frequencies can be reapplied in other cells, provided that similar frequencies are not reused in neighboring cells, as this may cause co-channel interference.
The increased throughput on a cellular network compared to a single transmitter network was due to the mobile switching system developed by Amos Joel of Bell Labs, which allowed multiple subscribers in the same area to use the same frequency when switching calls. If there is one simple transmitter, only one call can be used on any given frequency. Unfortunately, there is inevitably some level of interference from other cells that use the same frequency. This means that in a standard FDMA system, there must be at least one gap between cells that reuse the same frequency.
How did this technology come about?
The first commercial 1G cellular network was launched in Japan by Nippon Telegraph and Telephone (NTT) in 1979, initially in the Tokyo metropolitan area. Within five years, it was expanded to cover the entire population of Japan, becoming the first nationwide 1G network.
Cellular coding
To understand what cellular communication is, you need to understand its standards. To distinguish signals from several different transmitters, the following varieties of multiple access have been developed:
- time division division (TDMA);
- frequency division (FDMA);
- Code Division Division (CDMA);
- Orthogonal Frequency Division (OFDMA).
In TDMA, the transmit and receive timeslots used by different users in each cell are different.
In FDMA, the transmit and receive frequencies used by different users in each cell are different.
The CDMA principle is more complex but achieves the same result: distributed transceivers can select one cell and listen to it.
TDMA is used in combination with FDMA or CDMA in some systems to provide multiple channels in a single cell coverage area.
Modern trend
What is LTE cellular in a tablet? Recently, systems based on orthogonal frequency division multiple access, such asLTE, frequency reuse 1.
Because such systems do not spread the signal over the frequency band, inter-cell radio resource management is important for coordinating resource allocation between different cells and for limiting inter-cell interference. There are various methods of Inter-Cell Interference Coordination (ICIC) already defined in the standard.
Coordinated scheduling, multi-site MIMO or multi-site beamforming are other examples of inter-cell radio resource management that may be standardized in the future.
Broadcast messages and signals
What is a cell phone? The definition is given above. Almost every such system has some kind of broadcasting mechanism. This can be used directly to distribute information to multiple mobile phones. For this purpose, cellular amplifiers are also used.
Typically, for example, in mobile telephony systems, the most important use of broadcast information is to set up channels for one-to-one communication between a mobile transceiver and a base station. This is called a cellular signal. Three different signaling procedures are commonly used: serial, parallel, and selective.
The details of the paging process vary somewhat from network to network, but there is usually a limited number of cells in which a phone resides (this group is called a coverage area in a GSM or UMTS system, or a routing area if a session is involved).data package; in LTE, cells are grouped into a tracking area).
Signaling occurs by sending a broadcast message to all these cells. Signaling messages can be used to convey information. This occurs in pagers, in CDMA systems for sending SMS messages, and in a UMTS system where it allows for low downlink delay in packet connections.
Movement between cells and data transmission
What is a modern type of cellular communication? In a cellular communication system, when distributed mobile transceivers move from cell to cell during continuous communication, switching from one cell frequency to another is done electronically without interruption and without the base station operator or manual switching. This is called mobile data. Typically, a new channel is automatically selected for the mobile device at the new base station that will serve it. The device then automatically switches from the current channel to the new one and communication continues.
The exact details of moving cellular communications from one base station to another vary considerably from system to system.
GSM network architecture
The most common example of a cellular network is a mobile (cellular) phone network. This is a portable telephone that receives or makes calls through a cell site (base) or transmission tower. Radio waves are used to transmit signals to or from a mobile phone.
ModernCellular networks use cells because radio frequencies are a limited common resource. Cellular stations and telephones change frequency under computer control and use low power transmitters so that a normally limited number of radio frequencies can be used by many subscribers simultaneously with less interference.
How the connection works
The cellular network is used by the mobile operator to achieve both coverage and capacity for its subscribers. Large geographic areas are divided into smaller cells to avoid line-of-sight signal loss and to support a large number of active phones in that area. All coverage areas are connected to telephone exchanges (or switches), which, in turn, are connected to the public telephone network.
What is cellular as a modem? In fact, this is a similar connection that transmits packets of information via the Internet.
In cities, each cell site can have a range of up to approximately 0.80 km, while in rural areas this value can reach up to 8 km. It is possible that in open areas, the user can receive signals from a cell site at a distance of up to 40 km.
Because almost all mobile phones use GSM, CDMA and AMPS cellular communications, the term "cellular phone" is used interchangeably with "mobile". But it is worth considering some differences between these devices.
What is cellular communicationon an iPhone? This is the ability to connect to the network using two standards at the same time - GSM and CDMA. However, satellite phones are mobile devices that do not communicate directly with a terrestrial cell tower, but can do so indirectly via satellite.
What communication formats can be used?
There are a number of different digital cellular technologies, including:
- Global System for Mobile Communications (GSM).
- General Packet Radio Service (GPRS).
- CDMAOne.
- CDMA2000 data optimized (EV-DO).
- Enhanced data rates for GSM (EDGE).
- Universal Mobile Telecommunications System (UMTS).
- Digital Enhanced Wireless Communications (DECT).
- Digital AMPS (IS-136 / TDMA).
- Integrated Digital Enhanced Network (iDEN).
The transition from the existing analog to digital standard was very different in Europe and the US. As a result, many digital standards have appeared in the US, and Europe and many countries have moved closer to GSM. This explains the peculiarity of the work of iPhones on the network.
Cellular network structure
A simple representation of a cellular network in terms of radio communication consists of elements such as:
- A network of radio base stations that form a base station subsystem.
- The main circuit-switched network that exists to handle voice and text calls.
- Packet-switched network designed to handle mobile data.
- Public switched telephone network for connecting subscribers to a wider telephone network.
This network is the backbone of the GSM system. It performs many functions to ensure that customers receive the desired service, including mobility management, registration, call setup, and handover.
Each phone connects to the network using an RBS (radio base station) in the sector of the corresponding cell, which in turn connects to the Mobile Switching Center (MSC). The MSC connects to the public switched telephone network (PSTN). The link from the phone to the RBS is defined as uplink and the return path is defined as downlink.
How is data transmitted?
Radio channels use the transmission medium efficiently through the use of the following multiple access and multiplexing schemes:
- frequency division (FDMA);
- time division division (TDMA);
- Code Division Division (CDMA);
- Space Divisional (SDMA).
Small cells, which have a smaller coverage area than base stations, are classified as follows:
- Microcell - less than 2 kilometers.
- Picocell - less than 200 meters.
- Femtocell - about 10 meters.
What is cellular communication for children? This term is usually understood as special "children's" tariffs with special service packages.
Cellular transmission in networksmobile communications
When the phone user moves from one cell area to another during a call, the mobile station will look for a new channel to connect so as not to interrupt the call. Once it is found, the network instructs the mobile device to switch to the new channel and switch the call to it at the same time.
With CDMA format, multiple phones share a specific radio channel. The signals are separated using a pseudo noise code (PN code) specific to each device. When a user moves from one cell to another, the phone establishes a radio link with multiple locations (or sectors of the same location) at the same time. This is known as "soft handover" because, unlike traditional cellular technologies, there is no single defined point where the phone switches to a new cell. Therefore, when applying this standard, cellular and Internet amplifiers are used.
In IS-95 inter-frequency handovers and older analog systems such as NMT, it is usually not possible to directly check the target channel during communication. In this case, other methods must be used, such as control beacons in IS-95. This means that when looking for a new channel, there is almost always a short break in communication, with the risk of an unexpected return to the old one.
If there is no permanent connection, or it may be interrupted, the mobile device may spontaneously move from one cell to another and then notify the base station with the strongest signal.
Choicecellular frequencies in mobile networks
The effect of frequency on cell coverage means that different frequencies are better suited for different purposes. Low frequencies such as 450 MHz NMT serve very well for rural coverage. GSM 900 (900 MHz) is a suitable solution for small urban coverage.
GSM 1800 (1.8 GHz) is starting to be limited to structural walls. UMTS at 2.1 GHz is very similar in coverage to GSM 1800. Depending on the characteristics of the region, mobile operators set different coverage areas and frequencies.
Higher frequencies are a disadvantage when it comes to coverage, but a decisive advantage when it comes to bandwidth. Small cells covering, for example, one floor of a building become possible, and the same frequency can be used for cells that are practically neighbors.
Coverage and service areas
The service area of a cell can also change due to interference from transmitting systems both within and around it. This is especially true in CDMA based systems. The receiver needs a certain signal-to-noise ratio, and the transmitter should not transmit at too high a power so as not to interfere with other transmitters.
As the interference (noise) increases due to the increase in received power from the transmitter, the signal becomes corrupted and eventually becomes unusable. In CDMA-based systems, the impact of interference from other mobile transmitters in the same cell on the coverage area is very noticeable.
Coating examplescellular coverage can be seen by examining some of the coverage maps provided by real providers on their websites, or by looking at independent crowdsourced maps such as OpenSignal. They show which mobile operator operates in a particular territory. In some cases they may mark the location of the transmitter, in others it may be calculated by determining the point of greatest coverage.
Cellular repeater is used to expand the coverage area of a cell over a large area. They range from broadband repeaters for residential and office use to smart or digital repeaters for industrial use.
Each cellular provider has its own range of numbers, usually differing by code. It can be used to determine which region and mobile operator the caller has.
