digplanet beta 1: Athena
Share digplanet:

Agriculture

Applied sciences

Arts

Belief

Chronology

Culture

Education

Environment

Geography

Health

History

Humanities

Language

Law

Life

Mathematics

Nature

People

Politics

Science

Society

Technology

Top of a cellular radio tower

A cellular network or mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, known as a cell site or base station. In a cellular network, each cell uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed bandwidth within each cell.

When joined together these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission.

Cellular networks offer a number of advantages over alternative solutions:

• flexible enough to use the features and functions of almost all public and private networks[1]
• increased capacity
• reduced power use
• larger coverage area
• reduced interference from other signals

An example of a simple non-telephone cellular system is an old taxi drivers' radio system, in which a taxi company has several transmitters based around a city that can communicate directly with each other.

## Concept

Example of frequency reuse factor or pattern 1/4

In a cellular radio system, a land area to be supplied with radio service is divided into regular shaped cells, which can be hexagonal, square, circular or some other regular shapes, although hexagonal cells are conventional. Each of these cells is assigned multiple frequencies (f1f6) which have corresponding radio base stations. The group of frequencies can be reused in other cells, provided that the same frequencies are not reused in adjacent neighboring cells as that would cause co-channel interference.

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.

In the simple case of the taxi company, each radio had a manually operated channel selector knob to tune to different frequencies. As the drivers moved around, they would change from channel to channel. The drivers knew which frequency covered approximately what area. When they did not receive a signal from the transmitter, they would try other channels until they found one that worked. The taxi drivers would only speak one at a time, when invited by the base station operator (this is, in a sense, time division multiple access (TDMA)).

## Cell signal encoding

To distinguish signals from several different transmitters, frequency division multiple access (FDMA) and code division multiple access (CDMA) were developed.

With FDMA, the transmitting and receiving frequencies used in each cell are different from the frequencies used in each neighbouring cell. In a simple taxi system, the taxi driver manually tuned to a frequency of a chosen cell to obtain a strong signal and to avoid interference from signals 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.

## Frequency reuse

The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity. As described above, adjacent cells must use different frequencies, however there is no problem with two cells sufficiently far apart operating on the same frequency. The elements that determine frequency reuse are the reuse distance and the reuse factor.

The reuse distance, D is calculated as

$D=R\sqrt{3N},\,$

where R is the cell radius and N is the number of cells per cluster. Cells may vary in radius in the ranges (1 km to 30 km). The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells.[2]

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).[3]

In case of N sector antennas on the same base station site, each with different direction, the base station site can serve N different sectors. N is typically 3. A reuse pattern of N/K denotes a further division in frequency among N sector antennas per site. Some current and historical reuse patterns are 3/7 (North American AMPS), 6/4 (Motorola NAMPS), and 3/4 (GSM).

If the total available bandwidth is B, each cell can only use a number of frequency channels corresponding to a bandwidth of B/K, and each sector can use a bandwidth of B/NK.

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 1/1. 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. While N is shown as 1 in this example, that does not mean the CDMA cell has only one sector, but rather that the entire cell bandwidth is also available to each sector individually.

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 large city, on the other hand, frequency-reuse could certainly be in use.

Recently also orthogonal frequency-division multiple access based systems such as LTE are being deployed with a frequency reuse of 1. Since such systems do not spread the signal across the frequency band, inter-cell radio resource management is important to coordinate resource allocation between different cell sites and to limit the inter-cell interference. There are various means of Inter-cell Interference Coordination (ICIC) already defined in the standard.[4] Coordinated scheduling, multi-site MIMO or multi-site beam forming are other examples for inter-cell radio resource management that might be standardized in the future.

## Directional antennas

Cellular telephone frequency reuse pattern. See U.S. Patent 4,144,411

Although the original 2-way-radio cell towers were at the centers of the cells and were omni-directional, a cellular map can be redrawn with the cellular telephone towers located at the corners of the hexagons where three cells converge.[5] Each tower has three sets of directional antennas aimed in three different directions with 120 degrees for each cell (totaling 360 degrees) and receiving/transmitting into three different cells at different frequencies. This provides a minimum of three channels (from three towers) for each cell. The numbers in the illustration are channel numbers, which repeat every 3 cells. Large cells can be subdivided into smaller cells for high volume areas.[6]

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 transceiver and the base station. This is called paging. The three different paging procedures generally adopted are sequential, parallel and selective paging.

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; in LTE, cells are grouped into Tracking Areas). 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.

## Movement from cell to cell and handover

In a primitive taxi system, when the taxi moved away from a first tower and closer to a second tower, the taxi driver manually switched from one frequency to another as needed. If a communication was interrupted due to a loss of a signal, the taxi driver asked the base station operator to repeat the message on a different frequency.

In a cellular system, as the distributed mobile transceivers move from cell to cell during an ongoing continuous communication, switching from one cell frequency to a different cell frequency is done electronically without interruption and without a base station operator or manual switching. This is called the handover or handoff. Typically, a new channel is automatically selected for the mobile unit on the new base station which will serve it. The mobile unit then automatically switches from the current channel to the new channel and communication continues.

The exact details of the mobile system's move from one base station to the other varies considerably from system to system (see the example below for how a mobile phone network manages handover).

## Mobile phone network

GSM network architecture

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.

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 that area. All of the cell sites are connected to telephone exchanges (or switches), which in turn connect 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.

Since almost all mobile phones use cellular technology, including GSM, CDMA, and AMPS (analog), the term "cell phone" is in some regions, notably the US, used interchangeably with "mobile phone". However, satellite phones are mobile phones that do not communicate directly with a ground-based cellular tower, but may do so indirectly by way of a satellite.

There are a number of different digital cellular technologies, including: Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), cdmaOne, CDMA2000, Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN).

### Structure of the mobile phone cellular network

A simple view of the cellular mobile-radio network consists of the following:

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

Any phone connects to the network via an RBS (Radio Base Station) at a corner of the corresponding cell which in turn connects to the Mobile switching center (MSC). The MSC provides a connection to the public switched telephone network (PSTN). The link from a phone to the RBS is called an uplink while the other way is termed downlink.

Radio channels effectively use the transmission medium through the use of the following multiplexing & access schemes: frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and space division multiple access (SDMA).

### Cellular handover in mobile phone networks

As the phone user moves from one cell area to another cell while a 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 onto the new channel.

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.

In IS-95 inter-frequency handovers and older analog systems such as NMT it will typically be impossible to test the target channel directly while 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 while searching for the new channel followed by the risk of an unexpected return to the old channel.

If there is no ongoing communication or the communication can be interrupted, it is possible for the mobile unit to spontaneously move from one cell to another and then notify the base station with the strongest signal.

### Cellular frequency choice in mobile phone networks

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. UMTS, at 2.1 GHz is quite similar in coverage to GSM 1800.

Higher frequencies are 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.

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, and the transmitter should not send with too high transmission power in view to not cause interference with other transmitters. As the receiver moves away from the transmitter, the power received decreases, so the power control algorithm of the transmitter increases the power it transmits to restore the level of received power. 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.

One can see examples of cell coverage by studying some of the coverage maps provided by real operators on their web sites or by looking at independently crowdsourced maps such as OpenSignal. In certain cases they may mark the site of the transmitter, in others it can be calculated by working out the point of strongest coverage.

### Coverage comparison of different frequencies

The following table shows the dependency of the coverage area of one cell on the frequency of a CDMA2000 network:[7]

Frequency (MHz) Cell radius (km) Cell area (km2) Relative Cell Count
450 48.9 7521 1
950 26.9 2269 3.3
1800 14.0 618 12.2
2100 12.0 449 16.2

## References

1. ^ Raciti, Robert C. (July 1995). "CELLULAR TECHNOLOGY". Nova Southeastern University. Retrieved 2 April 2012.
2. ^ J. E. Flood. Telecommunication Networks. Institution of Electrical Engineers, London, UK, 1997. chapter 12.
3. ^ "Phone Networks". The Reverse Phone. 8 June 2011. Retrieved 2 April 2012.
4. ^ Pauli, Volker; Naranjo, Juan Diego; Seidel, Eiko (December 2010). "Heterogeneous LTE Networks and Inter-Cell Interference Coordination". Nomor Research. Retrieved 2 April 2012.
5. ^ "Cellular Telephone Basics". Privateline.com. 1 January 2006. p. 2. Retrieved 2 April 2012.
6. ^ U.S. Patent 4,144,411Cellular Radiotelephone System for Different Cell Sizes – Richard H. Frenkiel (Bell Labs), filed Sep 22, 1976, issued March 13, 1979
7. ^

• P. Key, D. Smith. Teletraffic Engineering in a competitive world. Elsevier Science B.V., Amsterdam Netherlands, 1999. Chapter 1 (Plenary) and 3 (mobile).
• William C. Y. Lee, Mobile Cellular Telecommunications Systems (1989), McGraw-Hill.

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Cellular_network — Please support Wikipedia.
A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
 357029 videos foundNext >
 Lecture - 22 Cellular NetworksLecture Series on Computer Networks by Prof. S. Ghosh,Department of Computer Science & Engineering, I.I.T.,Kharagpur. For more Courses visit http://nptel.iit... GSM Network Elements - Part 1GSM Network Elements - Part 1. Cellular Network GenerationFor more videos go to this website : www.pecworld.zxq.net. Cellular network - Wiki ArticleA cellular network or mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, kno... Cellular Network Protocols{Computer Hackers}How to be a computer hacker video tutorial educates you on challenging computers & network security, computers were made for humans to control, not otherwise... Why No Cellular Data Network Tab on iPhone 3GS 4 4S 5 iOS 6.0 6.0.1Explanation why you don't have the Cellular Data Network Tab on your iPhone 3GS, 4, 4S or 5 on iOS 6.0 and up. Solution is to jailbreak your iPhone and insta... Fix Missing Cellular Data Network on iPhoneThis will help everyone whos Cellular Data Network is missing in their settings application on the iPhone. Running this will allow iTunes to update the .ipcc... how to fix missing cellular data network on any iphone 3,3gs,4,4sHOW TO FIX MISSING CELLULAR DATA NETWORK ON IPHONE 3,3GS,4 AND 4S. YOU HAVE TO GO TO CYDIA AND ADD ANEW SOURCE THE SOURCE IS hpp://ihacksrepo.com/ them you o... Mobile/Cellular Network Trialing by John Loughney at gogoNET LIVE! 2 IPv6 EventgogoNET IPv6 Video Series. Event, presentation and speaker details below: EVENT gogoNET LIVE! 2: How to do an IPv6 Trial. http://gogonetlive.com November 1 -... Small Cell Backhaul ArchitectureWhile 3G networks typically are deployed with cell site spacing of 3 km, 4G architecture will lead to picocells, especially in dense urban environments. This...
 357029 videos foundNext >
 726 news items
 Digital Media Wire Confirmed: AT&T enables FaceTime over cellular for iPhone 5 customers with ... FierceWireless Tue, 18 Jun 2013 09:47:09 -0700 AT&T Mobility (NYSE:T) has begun enabling Apple's (NASDAQ:AAPL) FaceTime video chatting service over its cellular network for customers who have an LTE-capable iPhone 5 and an unlimited data plan, according to an AT&T spokesman. Geeky gadgets AT&T's unlimited-data users to get FaceTime over cellular network Los Angeles Times Tue, 21 May 2013 08:33:56 -0700 AT&T has been the sole network to ban its unlimited-data users from accessing the video calling feature on its cellular network. Since the feature was released by Apple for its iPhone users in September, Sprint and Verizon have allowed it for their ... AT&T Launches the Cellular Smart Grid Energy Collective Sun, 26 May 2013 06:42:52 -0700 AT&T has already connected individual smart meters via its cellular network. In fact, it linked up the first such mass-scale residential AMI deployment in the United States in 2009 with Texas-New Mexico Power and SmartSynch, the company that Itron ... Range Networks and UC Berkeley Deliver Low Cost Cellular Service to Rural ... MarketWatch (press release) Mon, 20 May 2013 05:02:40 -0700 David Burgess, CEO, Range Networks, Co-Inventor of the OpenBTS Project said:"Underserved markets around the world are looking for solutions that provide affordable, reliable and easy-to-deploy cellular network equipment. We're excited to partner with ... Proposed e-license plates can be altered remotely and may be used to track you ITworld.com Tue, 18 Jun 2013 09:30:16 -0700 Potentially the connected plates might allow a car's location to be tracked via the cellular network. According to the manufacturer, the proposed legislation would require authorities to obtain three court orders to track a car's wearabouts: from the ... Tennessee Combats Menacing Hogs Using Technology Powered by Verizon's ... PR Newswire (press release) Tue, 18 Jun 2013 06:53:41 -0700 This new system is machine-to-machine technology, meaning it's a device that constantly communicates data or video over Verizon's cellular network. "The 4G LTE network allows these types of machine-to-machine solutions to be developed. Before Verizon ... Sprint Completes Spectrum Buy from US Cellular, Gains 420000 Customers Wireless Week Mon, 20 May 2013 08:13:34 -0700 Sprint and its Boost Mobile, Virgin Mobile and payLo prepaid brands are providing special offers and incentives for affected customers that the company says will significantly reduce the cost of acquiring a new device to transition from the U.S ... Hand Hygiene Monitoring Technology: Advice for Product Evaluation and ... Infection Control Today Mon, 17 Jun 2013 14:23:11 -0700 This information is send over a cellular network, combined with published benchmark data to calculate hand hygiene compliance, and presented to users in the form of web-based reports. HandGiene Corp.: The components that make up the HandGiene ...
 Limit to books that you can completely read online Include partial books (book previews) .gsc-branding { display:block; }

Oops, we seem to be having trouble contacting Twitter