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Encyclopedia > Cellular network

A cellular network is a radio network made up of a number of radio cells (or just cells) each served by a fixed transmitter, known as a cell site or base station. These cells are used to cover different areas in order to provide radio coverage over a wider area than the area of one cell. Cellular networks are inherently asymmetric with a set of fixed main transceivers each serving a cell and a set of distributed (generally, but not always, mobile) transceivers which provide services to the network's users. A cleverly mounted base station on top of an Electricity pylon. ... The term base station can be used in the context of land surveying, wireless computer networking, and wireless communications. ... A transceiver is a device that has both a transmitter and a receiver which are combined in to one. ...


Cellular networks offer a number of advantages over alternative solutions:

  • increased capacity
  • reduced power usage
  • better coverage

A good (and simple) example of a cellular system is an old taxi driver's radio system where the taxi company will have several transmitters based around a city each operated by an individual operator. Taxicab, short forms taxi or cab, is a type of public transport for a single passenger, or small group of passengers, typically for a non-shared ride. ...

Contents

General characteristics

The primary requirement for a network to be succeed as a cellular network is for it to have developed a standardised method for each distributed station to distinguish the signal emanating from its own transmitter from the signals received from other transmitters. Presently, there are two standardised solutions to this issue: · frequency division multiple access (FDMA) and; · code division multiple access (CDMA). FDMA, or frequency-division multiple access, is the oldest and most important of the three main ways for multiple radio transmitters to share the radio spectrum. ... Code division multiple access (CDMA) is the current name for the cellular technology originally known as IS-95. ...


FDMA works by using varying frequencies for each neighbouring cell. By tuning to the frequency of a chosen cell the distributed stations can avoid the signal from other cells. The principle of CDMA is more complex, but achieves the same result; the distributed transceivers can select one cell and listen to it. Other available methods of multiplexing such as polarization division multiple access (PDMA) and time division multiple access (TDMA) cannot be used to separate signals from one cell to the next since the effects of both vary with position and this would make signal separation practically impossible. Time division multiple access, however, is used in combination with either FDMA or CDMA in a number of systems to give multiple channels within the coverage area of a single cell. A transceiver is a device that has both a transmitter and a receiver which are combined in to one. ... Time division multiple access (TDMA) is a channel access method for shared medium (usually radio) networks. ... Time division multiple access (TDMA) is a channel access method for shared medium (usually radio) networks. ...


In the case of the aforementioned taxi company, each radio has a knob. The knob acts as a channel selector and allows the radio to tune to different frequencies. As the drivers move around, they change from channel to channel. The drivers know which frequency covers approximately what area, when they don't get a signal from the transmitter, they also try other channels until they find one which works. The taxi drivers only speak one at a time, as invited by the operator (in a sense TDMA). Taxicab, short forms taxi or cab, is a type of public transport for a single passenger, or small group of passengers, typically for a non-shared ride. ... FreQuency is a music video game developed by Harmonix and published by SCEI. It was released in November 2001. ...


Broadcast messages and paging

Practically every cellular system has some kind of broadcast mechanism. This can be used directly for distributing information to multiple mobiles, commonly, for example in mobile telephony systems, the most important use of broadcast information is to set up channels for one to one communication between the mobile transreceiver and the base station. This is called paging. Cellular redirects here. ...


The details of the process of paging vary somewhat from network to network, but normally we know a limited number of cells where the phone is located (this group of cells is called a Location Area in the GSM or UMTS system, or Routing Area if a data packet session is involved). Paging takes place by sending the broadcast message to all of those cells. Paging messages can be used for information transfer. This happens in pagers, in CDMA systems for sending SMS messages, and in the UMTS system where it allows for low downlink latency in packet-based connections. It has been suggested that this article or section be merged with pager. ... General Information Generically (as a multiplexing scheme), code division multiple access (CDMA) is any use of any form of spread spectrum by multiple transmitters to send to the same receiver on the same frequency channel at the same time without harmful interference. ... This article describes the technical methods for providing the text messaging service. ... Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) mobile phone technologies. ...


Our taxi network is a very good example here. The broadcast capability is often used to tell about road conditions and also to tell about work which is available to anybody. On the other hand, typically there is a list of taxis waiting for work. When a particular taxi comes up for work, the operator will call their number over the air. The taxi driver acknowledges that they are listening, then the operator reads out the address where the taxi driver has to go. This page is a candidate for speedy deletion. ...


Frequency reuse

Example of frequency reuse factor or pattern 1/4

The increased capacity in a cellular network, compared with a network with a single transmitter, comes from the fact that the same radio frequency can be reused in a different area for a completely different transmission. If there is a single plain transmitter, only one transmission can be used on any given frequency. Unfortunately, there is inevitably some level of interference from the signal from the other cells which use the same frequency. This means that, in a standard FDMA system, there must be at least a one cell gap between cells which reuse the same frequency. Image File history File links Frequency_reuse. ... Image File history File links Frequency_reuse. ... Capacity may mean one of the following: Capacity, when used with the mathematics meaning, is another word for volume Legal capacity refers to the legal ability to engage in certain acts, such as making a contract Cranial capacity is a measure of the volume of the interior of the skull... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...


The frequency reuse factor is the rate at which the same frequency can be used in the network. It is 1/K (or K according to some books) where K is the number of cells which cannot use the same frequencies for transmission. Common values for the frequency reuse factor are 1/3, 1/4, 1/7, 1/9 and 1/12 (or 3, 4, 7, 9 and 12 depending on notation).


In case of N sector antennas on the same base station site, each with different direction, the base station site can serve N different cells. N is typically 3. A reuse pattern of N/K denotes N sector antennas per site. Common reuse patterns are 3/3, 3/9 and 3/12.


If the total available bandwidth is B, each cell can only utilize a number of frequency channels correspodning to a bandwidth of B/K, and each base station site can use a bandwidth of BN/K.


Code division multiple access-based systems use a wider frequency band to achieve the same rate of transmission as FDMA, but this is compensated for by the ability to use a frequency reuse factor of 1, for example using a reuse pattern of 3/3. In other words, adjacent base station sites use the same frequencies, and the different base stations and users are separated by codes rather than frequencies. Frequency division is in this case typically only used to separate cells (sector antennas) at the same base station site. Code division multiple access (CDMA) is the current name for the cellular technology originally known as IS-95. ...


Depending on the size of the city, a taxi system may not have any frequency-reuse in its own city, but certainly in other nearby cities, the same frequency can be used. In a big city, on the other hand, frequency-reuse could certainly be in use.


Movement from cell to cell and handover

The use of multiple cells means that, if the distributed transceivers are mobile and moving from place to place, they also have to change from cell to cell. The mechanism for this differs depending on the type of network and the circumstances of the change. For example, if there is an ongoing continuous communication and we don't want to interrupt it, then great care must be taken to avoid interruption. In this case there must be clear coordination between the base station and the mobile station. Typically such systems use some kind of multiple access independently in each cell, so an early stage of such a handover (handoff) is to reserve a new channel for the mobile station on the new base station which will serve it. The mobile then moves from the channel on its current base station to the new channel and from that point on communication takes place. The exact details of the mobile system's move from one base station to the other varies considerably from system to system. For example, in all GSM handovers and W-CDMA inter-frequency handovers the mobile station will measure the channel it is meant to start using before moving over. Once the channel is confirmed okay, the network will command the mobile station to move to the new channel and at the same time start bi-directional communication there, meaning there is no break in communication. In CDMA2000 and W-CDMA same-frequency handovers, both channels will actually be in use at the same time (this is called a soft handover or soft handoff). In IS-95 inter-frequency handovers and older analog systems such as NMT it will typically be impossible to measure the target channel directly whilst communicating. In this case other techniques have to be used such as pilot beacons in IS-95. This means that there is almost always a brief break in the communication whilst searching for the new channel followed by the risk of an unexpected return to the old channel. In telecommunication, the term handoff refers to the process of transferring an ongoing call or data session from one channel connected to the core network to another. ... Global System for Mobile communications (GSM: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. ... W-CDMA (Wideband Code Division Multiple Access) is a type of 3G cellular network. ... CDMA2000 is a hybrid 2. ... Soft handover has been introduced in the CDMA digital cellular standard. ... Interim Standard 95 (IS-95), is the first CDMA-based digital cellular standard pioneered by Qualcomm. ... NMT may mean: Nordic Mobile Telephone New Mexico Tech non-metallic conduit boots with a non-metallic toe Northwest Marine Technology NMT Medical NMT Corporation Toronto New Media Trainers Alliance NMT International Shipping Network Management Technologies NMT Group National Mobile Television Nuremberg Military Tribunals National Meningitis Trust Not More Then...


If there is no ongoing communication or the communication can be interrupted, it is possible for the mobile station to spontaneously move from one cell to another and then notify the network if needed.


In the case of the primitive taxi system that we are studying, handovers won't really be implemented. The taxi driver just moves from one frequency to another as needed. If a specific communication gets interrupted due to a loss of a signal then the taxi driver asks the controller to repeat the message. If one single taxi driver misses a particular broadcast message (e.g. a request for drivers in a particular area), the others will respond instead. If nobody responds, the operator keeps repeating the request.


The effect of frequency on cell coverage means that different frequencies serve better for different uses. Low frequencies, such as 450 MHz NMT, serve very well for countryside coverage. GSM 900 (900 MHz) is a suitable solution for light urban coverage. GSM 1800 (1.8 GHz) starts to be limited by structural walls. This is a disadvantage when it comes to coverage, but it is a decided advantage when it comes to capacity. Pico cells, covering e.g. one floor of a building, become possible, and the same frequency can be used for cells which are practically neighbours. UMTS, at 2.1 GHz is quite similar in coverage to GSM 1800. At 5 GHz, 802.11a Wireless LANs already have very limited ability to penetrate walls and may be limited to a single room in some buildings. At the same time, 5 GHz can easily penetrate windows and goes through thin walls so corporate WLAN systems often give coverage to areas well beyond that which is intended. Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) mobile phone technologies. ... IEEE 802. ...


Moving beyond these ranges, network capacity generally increases (more bandwidth is available) but the coverage becomes limited to line of sight. Infra-red links have been considered for cellular network usage, but as of 2004 they remain restricted to limited point-to-point applications. This article does not cite any references or sources. ... See also: line of sight in gaming, referring to visibility of units. ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. ... 2004 is a leap year starting on Thursday of the Gregorian calendar. ...


Cell service area may also vary due to interference from transmitting systems, both within and around that cell. This is true especially in CDMA based systems. The receiver requires a certain signal-to-noise ratio. As the receiver moves away from the transmitter, the power transmitted is reduced. As the interference (noise) rises above the received power from the transmitter, and the power of the transmitter cannot be increased any more, the signal becomes corrupted and eventually unusable. In CDMA-based systems, the effect of interference from other mobile transmitters in the same cell on coverage area is very marked and has a special name, cell breathing. Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering concept defined as the ratio of a signal power to the noise power corrupting the signal. ...


Old fashioned taxi radio systems, such as the one we have been studying, generally use low frequencies and high sited transmitters, probably based where the local radio station has its mast. This gives a very wide area coverage in a roughly circular area surrounding each mast. Since only one user can talk at any given time, coverage area doesn't change with number of users. The reduced signal to noise ratio at the edge of the cell is heard by the user as crackling and hissing on the radio.


To see real examples of cell coverage look at some of the coverage maps provided by real operators on their web sites; in certain cases they may mark the site of the transmitter, in others it can be located by working out the point of strongest coverage.


Cellular telephony

Cell site

The most common example of a cellular network is a mobile phone (cell phone) network. A mobile phone is a portable telephone which receives or makes calls through a cell site (base station), or transmitting tower. Radio waves are used to transfer signals to and from the cell phone. Large geographic areas (representing the coverage range of a service provider) are split up into smaller cells to deal with line-of-sight signal loss and the large number of active phones in an area. In cities, each cell site has a range of up to approximately ½ mile, while in rural areas, the range is approximately 5 miles. Many times in clear open areas, a user may receive signal from a cell 25 miles away. Each cell overlaps other cell sites. All of the cell sites are connected to cellular telephone exchanges "switches", which in turn connect to the public telephone network or another switch of the cellular company. Download high resolution version (460x780, 59 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (460x780, 59 KB) Wikipedia does not have an article with this exact name. ... For other uses, see Telephone (disambiguation). ... A cleverly mounted base station on top of an Electricity pylon. ... Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... A telephone operator manually connecting calls with patch cables at a telephone switchboard. ... The public switched telephone network (PSTN) is the network of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the network of the worlds public IP-based packet-switched networks. ...


As the phone user moves from one cell area to another, the switch automatically commands the handset and a cell site with a stronger signal (reported by the handset) to go to a new radio channel (frequency). When the handset responds through the new cell site, the exchange switches the connection to the new cell site.


With CDMA, multiple CDMA handsets share a specific radio channel; the signals are separated by using a pseudonoise code (PN code) specific to each phone. As the user moves from one cell to another, the handset sets up radio links with multiple cell sites (or sectors of the same site) simultaneously. This is known as "soft handoff" because, unlike with traditional cellular technology, there is no one defined point where the phone switches to the new cell. General Information Generically (as a multiplexing scheme), code division multiple access (CDMA) is any use of any form of spread spectrum by multiple transmitters to send to the same receiver on the same frequency channel at the same time without harmful interference. ... Pseudorandom noise (PRN) is a signal similar to noise which satisfies one or more of the standard tests for statistical randomness. ...


Modern mobile phones 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 reused by many callers with less interference. CDMA handsets, in particular, must have strict power controls to avoid interference with each other. An incidental benefit is that the batteries in the handsets need less power.


Since almost all mobile phones use cellular technology, including GSM, CDMA, and AMPS (analog), the term "cell phone" is used interchangeably with "mobile phone"; however, an exception of mobile phones not using cellular technology is satellite phones. The Global System for Mobile communications (GSM: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. ... General Information Generically (as a multiplexing scheme), code division multiple access (CDMA) is any use of any form of spread spectrum by multiple transmitters to send to the same receiver on the same frequency channel at the same time without harmful interference. ... Advanced Mobile Phone System or AMPS is the analog mobile phone system standard, introduced in the Americas during the early 1980s. ... ...


Old systems predating the cellular principle may still be in use in places. The most notable real hold-out is used by many amateur radio operators who maintain phone patches in their clubs' VHF repeaters.


There are a number of different digital cellular technologies, including: Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), Code Division Multiple Access (CDMA), Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution (EDGE), 3GSM, Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN). The Global System for Mobile communications (GSM: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. ... General Packet Radio Service (GPRS) is a Mobile Data Service available to users of Global System for Mobile Communications (GSM) and IS-136 mobile phones. ... CDMA2000 is a hybrid 2. ... Evolution-Data Optimized or Evolution-Data only, abbreviated as EV-DO or EVDO and often EV, is one telecommunications standard for the wireless transmission of data through radio signals, typically for broadband Internet access. ... Enhanced Data rates for GSM Evolution (EDGE) or Enhanced GPRS (EGPRS), is a digital mobile phone technology that allows it to increase data transmission rate and improve data transmission reliability. ... Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) mobile phone technologies. ... This article or section does not adequately cite its references or sources. ... IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS). ... Iden is also a village in East sussex, England iDEN Base Radio at a Cell Site Integrated Digital Enhanced Network (iDEN) is a mobile telecommunications technology, it is known to eat little children, developed by Motorola, which provides its users the benefits of a trunked radio and a cellular telephone. ...


See also

Advanced Mobile Phone System (AMPS) is the analog mobile phone system standard developed by Bell Labs, and officially introduced in the Americas in 1983[1][2] It was the primary analog mobile phone system in North America (and other locales) through the 1980s and into the 2000s, and is still... The Base Station Subsystem (BSS) is the section of a GSM network which is responsible for handling traffic and signaling between a mobile phone and the Network Switching Subsystem. ... Instantly sharing media A Sony Ericsson K750 camera phone in use Philippe Kahn Working on and early camera-phone A camera phone is a mobile phone which has a camera built-in and is coupled with a server-based infrastructure that allows the user to share pictures and video with... A compact Clear Voice cellular repeater including a directional antenna, an amplifier and a monopole rebroadcast antenna. ... Code division multiple access (CDMA) is the current name for the cellular technology originally known as IS-95. ... GSM and IS-95 are the two most prevalent mobile communication technologies. ... CDMA2000 is a hybrid 2. ... See http://en. ... Enhanced Data rates for GSM Evolution (EDGE) or Enhanced GPRS (EGPRS), is a digital mobile phone technology that allows it to increase data transmission rate and improve data transmission reliability. ... Evolution Data Only,Evolution Data Optimized, often abbreviated as EVDO, EV-DO, EvDO, 1xEV-DO or 1xEvDO is a wireless radio broadband data protocol being adopted by many CDMA mobile phone providers in Japan, Korea, the United States and Canada, as part of the CDMA2000 standard. ... Global System for Mobile communications (GSM: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. ... HIPERLAN (HIgh PErformance Radio LAN) is a Wireless LAN standard. ... The title of this article is incorrect because of technical limitations. ... Interim Standard 95 (IS-95), is the first CDMA-based digital cellular standard pioneered by Qualcomm. ... IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS). ... Cellular redirects here. ... For other meanings of the abbreviation, see: NMT. NMT (Nordisk MobilTelefoni or Nordiska MobilTelefoni-gruppen, Nordic Mobile Telephone in English) is a mobile phone system that was specified by the Nordic telecommunications administrations (PTTs) starting in 1970, and opened for service in 1981 as a response to the increasing congestion... Professional Mobile Radio (also known as Private Mobile Radio (PMR) in the UK and Land Mobile Radio (LMR) in North America) are field radio communications systems which use portable, mobile, base station, and dispatch console radios and are sometimes based on such standards as MPT1327, TETRA and APCO 25 which... Radio resource management (RRM) is the system level control of radio transmission characteristics in wireless communication systems, for example cellular networks, wireless networks and broadcasting systems. ... In telecommunications, and particularly in radio, signal strength is the measure of how strongly a transmitted signal is being received, measured, or predicted, at a reference point that is a significant distance from the transmitting antenna. ... Spectral efficiency or spectrum efficiency refers to the amount of information that can be transmitted over a given bandwidth in a specific digital communication system. ... Systems engineering techniques are used in complex projects: from spacecrafts to chip design, from robotics to creating large software products to building bridges, Systems engineering uses a host of tools that include modeling & simulation, requirements analysis, and scheduling to manage complexity Systems Engineering (SE) is an interdisciplinary approach and means... Genera More than 150[1] Look up tetra in Wiktionary, the free dictionary. ... Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) mobile phone technologies. ... W-CDMA (Wideband Code Division Multiple Access), a wideband spread-spectrum 3G mobile telecommuncation air interface that utilizes code division multiple access (or CDMA the general multiplexing scheme, not to be confused with CDMA the standard), is a 3G mobile communications standard allied with the GSM standard. ... The notebook is connected to the wireless access point using a PC card wireless card. ... Multiple-input and multiple-output (antennas), or MIMO, (pronounced mee-moh or mai-moh) refers to the use of multiple antennas both at the transmitter and receiver to improve the performance of radio communication systems. ...

External Links


  Results from FactBites:
 
Cellular network - Wikipedia, the free encyclopedia (2385 words)
A cellular network is a radio network made up of a number of radio cells (or just cells) each served by a fixed transmitter, normally known as a (base station).
Cellular networks are inherently asymmetric with a set of fixed main transceivers each serving a cell and a set of distributed (generally, but not always, mobile) transceivers which provide services to the network's users.
The increased capacity in a cellular network, comparing to a network with a single transmitter, comes from the fact that the same radio frequency can be reused in a different area for a completely different transmission.
Cellular network - definition of Cellular network in Encyclopedia (2348 words)
A cellular radio network is a radio network made up of a number of radio cells (or just cells) each served by a fixed transmitter, normally known as a base station.
The primary requirement for a cellular network is a way for the distributed stations to distinguish the signal from its own transmitter from the signal from other transmitters.
The details of the process of paging vary somewhat from network to network, but normally we know a limited number of cells where the phone is located (this group of cells is called a location area in the GSM system).
  More results at FactBites »

 
 

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