Fiber-optic communication

     Fiber optic communication

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information.Fiber is preferred over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference are required.

Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication, and cable television signals. Researchers at Bell Labs have reached internet speeds of over 100 petabit×kilometer per second using fiber-optic communication.

First developed in the 1970s, fiber-optics have revolutionized the telecommunications  industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in core networks in the developed world.

*The process of communicating using fiber-optics involves the following basic steps:

*creating the optical signal involving

*the use of a transmitter, usually from an electrical signal

*relaying the signal along the fiber, ensuring that the signal does not

*become too distorted or weak
receiving the optical signal

*converting it into an electrical signal

                 
Optical fiber is used by many telecommunications companies to transmit telephone signals, Internet communication and cable television signals. Due to much lower attenuation and interference, optical fiber has large advantages over existing copper wire in long-distance, high-demand applications. However, infrastructure development within cities was relatively difficult and time-consuming, and fiber-optic systems were complex and expensive to install and operate. Due to these difficulties, fiber-optic communication systems have primarily been installed in long-distance applications, where they can be used to their full transmission capacity, offsetting the increased cost. The prices of fiber-optic communications have dropped considerably since 2000.

The price for rolling out fiber to the home has currently become more cost-effective than that of rolling out a copper based network. Prices have dropped to $850 per subscriber[citation needed] in the US and lower in countries like The Netherlands, where digging costs are low and housing density is high.

                  Thecnology

Modern fiber-optic communication systems generally include an optical transmitter to convert an electrical signal into an optical signal to send through the optical fiber, a cable containing bundles of multiple optical fibers that is routed through underground conduits and buildings, multiple kinds of amplifiers, and an optical receiver to recover the signal as an electrical signal. The information transmitted is typically digital information generated by computers, telephone systems and cable television  companies.

The most commonly used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and laser diodes. The difference between LEDs and laser diodes is that LEDs produce incoherent light, while laser diodes produce coherent light. For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient and reliable, while operating in an optimal wavelength range and directly modulated at high frequencies.

In its simplest form, an LED is a forward-biased p-n junction, emitting light through spontaneous emission, a phenomenon referred to as electroluminescence. The emitted light is incoherent with a relatively wide spectral width of 30–60 nm. LED light transmission is also inefficient, with only about 1%[citation needed] of input power, or about 100 microwatts, eventually converted into launched power which has been coupled into the optical fiber. However, due to their relatively simple design, LEDs are very useful for low-cost applications.

Communications LEDs are most commonly made from Indium gallium arsenide phosphide (InGaAsP) or gallium arsenide  (GaAs). Because InGaAsP LEDs operate at a longer wavelength than GaAs LEDs (1.3 micrometers vs. 0.81–0.87 micrometers), their output spectrum, while equivalent in energy is wider in wavelength terms by a factor of about 1.7. The large spectrum width of LEDs is subject to higher fiber dispersion, considerably limiting their bit rate-distance product (a common measure of usefulness). LEDs are suitable primarily for local-area-network applications with bit rates of 10–100 Mbit/s and transmission distances of a few kilometers. LEDs have also been developed that use several quantum wells to emit light at different wavelengths over a broad spectrum and are currently in use for local-area WDM  (Wavelength-Division Multiplexing) networks.

How do work mobile phone

        Mobile phone how work

In the most basic form, a mobile phone is essentially a two-way radio, consisting of a radio transmitter and a radio receiver. When you chat with your friend on your mobile phone, your phone converts your voice into an electrical signal, which is then transmitted via radio waves to the nearest cell tower. The network of cell towers then relays the radio wave to your friend’s mobile phone, which converts it to an electrical signal and then back to sound again. In the basic form, a mobile phone works just like a walkie-talkie.

 In additional to the basic function of voice calls, most modern mobile phone come with additional functions such as web surfing, taking pictures, playing games, sending text messages and playing music. More sophisticated smart phones can perform similar functions of a portable computer.

                  Radio frequency

Mobile phone use radio waves to communicate. Radio waves transport digitized voice or data in the form of oscillating electric and magnetic fields, called the electromagnetic field (EMF). The rate of oscillation is called frequency. Radio waves carry the information and travel in air at the speed of light.

Digital Revolution

                  Digital Revolution

           In the second half of the 20th Century, life was transformed around the world as digital technology rapidly advanced and became more accessible.

     The Digital Revolution Defined

              The Digital Revolution began between the late 1950’s and 1970’s. It is the development of technology from mechanical and analog to digital.
            During this time, digital computers and digital record keeping became the norm.
           The introduction of digital technology also changed the way humans communicate, now via computers, cell phones, and the internet.
         This revolution led way to the Information Age.
Historical Development of Digital Technology

            The 1947 invention of the               revolutionary transistor is     credited with sowing the seed for digital technology to come.
          By the 1950’s and 1960’s, many            governments, military forces, and other organizations were already using computers. Soon after, the computer was introduced for household use and by the 1970’s, many families had computers for personal use.

             This occurred at around the same time that video games became popular, both for home systems and arcade use. The infiltration of digital technology even led to the creation of jobs.
            As businesses moved to digital records keeping, the need for data entry clerks grew. The 1980’s brought computer production to films, robots to industry, and automated teller machines (ATMs) to banks. By 1989, 15% of all households in the US owned a computer.
Ek

             Analog mobile phones made way to digital mobile phones in 1991 and the demand soared. This was the same year that the internet was made available to the public.
               By the end of the decade, the internet was so popular that many businesses had a website and nearly every country on earth had a connection. 
                When the 21st century began, cell phones were a common possession and high-definition television became the most common broadcasting method, replacing analog television.
                 By 2015, around 50% of the world had constant internet connection, and ownership rates of smartphones and commonness of tablet possession have nearly surpassed those of home computers.                     The ability to store information has grown exponentially with terabyte storage now being very accessible

The Digital Revolution Defined

The Digital Revolution began between the late 1950’s and 1970’s. It is the development of technology from mechanical and analog to digital. During this time, digital computers and digital record keeping became the norm. The introduction of digital technology also changed the way humans communicate, now via computers, cell phones, and the internet. This revolution led way to the Information Age.
Historical Development of Digital Technology

The 1947 invention of the revolutionary transistor is credited with sowing the seed for digital technology to come.
           By the 1950’s and 1960’s, many governments, military forces, and other organizations were already using computers. Soon after, the computer was introduced for household use and by the 1970’s, many families had computers for personal use. This occurred at around the same time that video games became popular, both for home systems and arcade use.
          The infiltration of digital technology even led to the creation of jobs. As businesses moved to digital records keeping, the need for data entry clerks grew.
          The 1980’s brought computer production to films, robots to industry, and automated teller machines (ATMs) to banks. By 1989, 15% of all households in the US owned a computer. Analog mobile phones made way to digital mobile phones in 1991 and the demand soared.

           This was the same year that the internet was made available to the public. By the end of the decade, the internet was so popular that many businesses had a website and nearly every country on earth had a connection.
            When the 21st century began, cell phones were a common possession and high-definition television became the most common broadcasting method, replacing analog television.

           By 2015, around 50% of the world had constant internet connection, and ownership rates of smartphones and commonness of tablet possession have nearly surpassed those of home computers.
        The ability to store information has grown exponentially with terabyte storage now being very accessible

Electronic waste

                  Electronic waste or e-waste describes discarded electrical or electronic devices. Used electronics which are destined for reuse, resale, salvage, recycling, or disposal are also considered e-waste.                                                       Informal processing of e-waste in developing countries can lead to adverse human health effects and environmental pollution.
The processes of dismantling and disposing of electronic waste in developing countries led to a number of environmental impacts as illustrated in the graphic. Liquid and atmospheric releases end up in bodies of water, groundwater, soil, and air and therefore in land and sea animals – both domesticated and wild, in crops eaten by both animals and human, and in drinking water.[52]

One study of environmental effects in Guiyu, China found the following:[53]

Airborne dioxins – one type found at 100 times levels previously measured
Levels of carcinogens in duck ponds and rice paddies exceeded international standards for agricultural areas and cadmium, copper, nickel, and lead levels in rice paddies were above international standards
Heavy metals found in road dust – lead over 300 times that of a control village's road dust and copper over 100 timescomponents, such as CPUs, contain potentially harmful components such as lead, cadmium, beryllium, or brominated flame retardants. Recycling and disposal of e-waste may involve significant risk to health of workers and communities in developed countries.
and great care must be taken to avoid unsafe exposure in recycling operations and leaking of materials such as heavy metals from landfills and incinerator ashes.

Rapid changes in technology, changes in media (tapes, software, MP3), falling prices, and planned obsolescence have resulted in a fast-growing surplus of electronic waste around the globe. Technical solutions are available, but in most cases, a legal framework, a collection, logistics, and other services need to be implemented before a technical solution can be applied.

Display units (CRT, LCD, LED monitors), processors (CPU, GPU, or APU chips), memory (DRAM or SRAM), and audio components have different useful lives. Processors are most frequently out-dated (by software no longer being optimized) and are more likely to become "e-waste" while display units are most often replaced while working without repair attempts, due to changes in wealthy nation appetites for new display technology. This problem could potentially be solved with modular smartphones or Phonebloks. These types of phones are more durable and have the technology to change certain parts of the phone making them more environmentally friendly. Being able to simply replace the part of the phone that is broken will reduce e-waste. An estimated 50 million tons of E-waste are produced each year.The USA discards 30 million computers each year and 100 million phones are disposed of in Europe each year. The Environmental Protection Agency estimates that only 15–20% of e-waste is recycled, the rest of these electronics go directly into landfills and incinerators.

In 2006, the United Nations estimated the amount of worldwide electronic waste discarded each year to be 50 million metric tons.According to a report by UNEP titled, "Recycling – from E-Waste to Resources," the amount of e-waste being produced – including mobile phones and computers – could rise by as much as 500 percent over the next decade in some countries, such as India.The United States is the world leader in producing electronic waste, tossing away about 3 million tons each year. China already produces about 2.3 million tons (2010 estimate) domestically, second only to the United States. And, despite having banned e-waste imports, China remains a major e-waste dumping ground for developed countries.

The processes of dismantling and disposing of electronic waste in developing countries led to a number of environmental impacts as illustrated in the graphic. Liquid and atmospheric releases end up in bodies of water, groundwater, soil, and air and therefore in land and sea animals – both domesticated and wild, in crops eaten by both animals and human, and in drinking water.

One study of environmental effects in Guiyu, China found the following:[53]

Airborne dioxins – one type found at 100 times levels previously measured
Levels of carcinogens in duck ponds and rice paddies exceeded international standards for agricultural areas and cadmium, copper, nickel, and lead levels in rice paddies were above international standards
Heavy metals found in road dust – lead over 300 times that of a control village's road dust and copper over 100 times

"Android" what is

                            Android

Android is a mobile operating system  developed by Google, based on a modified version of the Linux kernel and other open source software and designed primarily for touchscreen mobile devices such as smartphones and tablets. In addition, Google has further developed Android TV for televisions, Android Auto for cars, and Wear OS for wrist watches, each with a specialized user interface. Variants of Android are also used on game consoles, digital cameras, PCs  and other electronics.

*Initially developed by Android Inc., which Google bought in 2005, Android was unveiled in 2007, with the first commercial Android device launched in September 2008. The operating system has since gone through multiple major releases, with the current version being 8.1 "Oreo", released in December 2017. The core Android source code is known as Android Open Source Project (AOSP), and is primarily licensed under the Apache License.
Initially developed by Android Inc., which Google bought in 2005, Android was unveiled in 2007, with the first commercial Android device launched in September 2008. The operating system has since gone through multiple major releases, with the current version being 8.1 "Oreo", released in December 2017. The core Android source code is known as Android Open Source Project (AOSP), and is primarily licensed under the Apache License.

Android is also associated with a suite of proprietary software developed by Google, including core apps for services such as Gmail and Google Search, as well as the application store and digital distribution  platform Google Play, and associated development platform. These apps are licensed by manufacturers of Android devices certified under standards imposed by Google, but AOSP has been used as the basis of competing Android ecosystems, such as Amazon.com's Fire OS, which utilize their own equivalents to the Google Mobile Services.

What is mobile application.......?

               Mobile application

**A mobile application, most commonly referred to as an app, is a type of application software designed to run on a mobile device, such as a smartphone or tablet computer.

**Mobile applications frequently serve to provide users with similar services to those accessed on PCs. Apps are generally small, individual software units with limited function.

**This use of app software was originally popularized by Apple Inc. and its App Store, which offers thousands of applications for the iPhone, iPad and iPod Touch.

**A mobile application also may be known as an app, web app, online app, iPhone app or smartphone app.
Mobile applications are a move away from the integrated software systems generally found on PCs. Instead, each app provides limited and isolated functionality such as a game, calculator or mobile web browsing.

**Although applications may have avoided multitasking because of the limited hardware resources of the early mobile devices, their specificity is now part of their desirability because they allow consumers to hand-pick what their devices are able to do.

**The simplest mobile apps take PC-based applications and port them to a mobile device. As mobile apps become more robust, this technique is somewhat lacking.
**A more sophisticated approach involves developing specifically for the mobile environment, taking advantage of both its limitations and advantages. For example, apps that use location-based features are inherently built from the ground up with an eye to mobile given that the user does not have the same concept of location on a PC.

**A mobile app is a computer program  designed to run on a mobile device such as a phone/tablet or watch.

**Mobile applications often stand in contrast to desktop applications which run on desktop computers, and with web applications which run in mobile web browsers rather than directly on the mobile device.

**In 2009, technology columnist David Pogue  said that newer smartphones could be nicknamed "app phones" to distinguish them from earlier less-sophisticated smartphones.[1]The term "app", which is short for "software application", has since become very popular: In 2010, it was listed as "Word of the Year" by the American Dialect Societ

**Most mobile devices are sold with several apps bundled as pre-installed software, such as a web browser, email client, calendar, mapping program, and an app for buying music, other media, or more apps. Some pre-installed apps can be removed by an ordinary uninstall process, thus leaving more storage space for desired ones.

**Where the software does not allow this, some devices can be rooted to eliminate the undesired apps.

**Apps that are not preinstalled are usually available through distribution platforms called app stores. They began appearing in 2008 and are typically operated by the owner of the mobile operating system, such as the Apple App Store, Google Play, Windows Phone Store, and BlackBerry App World.

**However, there are independent app stores, such as Cydia, GetJar  and F-Droid. Some apps are free, while others must be bought. Usually, they are downloaded from the platform to a target device, but sometimes they can be downloaded to laptops or desktop computers. For apps with a price, generally a percentage, 20-30%, goes to the distribution provider (such as iTunes), and the rest goes to the producer of the app.
**The same app can, therefore, cost a different price depending on the mobile platform.

Apps can also be installed manually, for example by running an Android application package on Android devices.

what is mobile operating system

      Mobile operating system

*A mobile operating system (or mobile OS) is an operating system for phones, tablets, smartwatches, or other mobile devices.

*While computers such as typical laptops are 'mobile', the operating systems usually used on them are not considered mobile ones, as they were originally designed for desktop.

*computers that historically did not have or need specific mobile features.

*This distinction is becoming blurred in some newer operating systems that are hybrids made for both uses.

*Mobile operating systems combine features of a personal computer

*operating system with other features useful for mobile or handheld use; usually including, and most of the following considered essential in modern mobile systems; a touchscreen, cellular, Bluetooth, Wi-Fi Protected Access, Wi-Fi, Global .

*Positioning System (GPS) mobile navigation, video- and single-frame picture cameras, speech recognition, voice recorder, music player, near field communication, and infrared blaster. By the end of 2016, over 430 million smartphones were sold with 81.7 percent running Android, 17.9 percent running iOS, 0.3 percent running Windows 10 Mobile  (no longer marketed) and the other OSes cover 0.1 percent.

*Android alone is more popular than the popular desktop operating system Windows, and in general smartphone use (even without tablets) outnumber desktop use (desktop use, web use, overall is down to 44.9% in the first quarter of 2017).

*Mobile devices with mobile communications abilities (e.g., smartphones) contain two mobile

*operating systems – the main user-facing software platform is supplemented by a second low-level proprietary real-time operating system which operates the radio and other hardware.

*Research has shown that these low-level systems may contain a range of security

*vulnerabilities permitting malicious base stations to gain high levels of control over the mobile device.

*Mobile operating systems have majority use as of 2017 (measured by web use); with even only the smartphones running them (excluding tablets) more used than any other kind of device.

* Thus traditional desktop OS is now a minority used kind of OS; see usage share of operating systems.

*Examples of mobile device operating systems include Apple iOS, Google Android, Research in Motion’s BlackBerry OS, Nokia’s Symbian, Hewlett-Packard’s webOS (formerly Palm OS) and Microsoft’s Windows Phone OS. Some, such as Microsoft’s Windows 8, function as both a traditional desktop OS and a mobile operating system.

Most mobile operating systems are tied to specific hardware, with little flexibility. Users can jailbreak or root some devices, however, which allows them to install another mobile OS or unlock restricted applications.

*However, variations occur in popularity by regions, while desktop-minority also applies on some days in regions such as United States and United Kingdom.

What is 5g technology

5G

Fifth-generation wireless, or 5G, is the latest iteration of cellular technology, engineered to greatly increase the speed and responsiveness of wireless networks. With 5G, data transmitted over wireless broadband connections could travel at rates as high as 20 Gbps by some estimates -- exceeding wireline network speeds -- as well as offer latency of 1 ms or lower for uses that require real-time feedback. 5G will also enable a sharp increase in the amount of data transmitted over wireless systems due to more available bandwidth and advanced antenna technology.
In addition to improvements in speed, capacity and latency, 5G offers network management features, among them network slicing, which allows mobile operators to create multiple virtual networks within a single physical 5G network. This capability will enable wireless network connections to support specific uses or business cases and could be sold on an as-a-service basis. A self-driving car, for example, would require a network slice that offers extremely fast, low-latency connections so a vehicle could navigate in real time. A home appliance, however, could be connected via a lower-power, slower connection because high performance isn't crucial. The internet of things (IoT) could use secure, data-only connections.

5G networks and services will be deployed in stages over the next several years to accommodate the increasing reliance on mobile and internet-enabled devices. Overall, 5G is expected to generate a variety of new applications, uses and business cases as the technology is rolled out.

How 5G works

Wireless networks are composed of cell si tes divided into sectors that send data through radio waves. Fourth-generation (4G) Long-Term Evolution (LTE) wireless technology provides the foundation for 5G. Unlike 4G, which requires large, high-power cell towers to radiate signals over longer distances, 5G wireless signals will be transmitted via large numbers of small cell stations located in places like light poles or building roofs. The use of multiple small cells is necessary because the millimeter wave spectrum -- the band of spectrum between 30 GHz and 300 GHz that 5G relies on to generate high speeds -- can only travel over short distances and is subject to interference from weather and physical obstacles, like buildings.

5G NR speed in sub-6 GHz bands can be modestly higher than 4G with a similar amount of spectrum and antennas.[3][4] Adding LAA (Licensed Assisted Access) to a 4G configuration can add hundreds of megabits to the speed.[5]

Until there is substantial field testing, 5G speeds can only be estimated. Qualcomm, the leading chipmaker, presented at Mobile World Congress model that has been cited by many. [6][7][8] The simulation predicts 490 Mbps median speeds for a common configuration of 3.5 GHz 5G Massive MIMO. It predicts a 1.4 Gbps median speed for a configuration using 28 GHz millimeter waves. [9]

Some 3GPP 5G networks will be slower than some advanced 4G networks. T-Mobile's LTE/LAA network is deployed and serving customers at over 500 megabits per second in Manhattan. [10] The 5G specification allows LAA as well but it has not yet been demonstrated

Previous generations of wireless technology have used lower-frequency bands of spectrum. To offset millimeter wave challenges relating to distance and interference, the wireless industry is also considering the use of lower-frequency spectrum for 5G networks so network operators could use spectrum they already own to build out their new networks. Lower-frequency spectrum reaches greater distances but has lower speed and capacity than millimeter wave, however.

5G systems in line with IMT-2020 specifications,[16] are expected to provide enhanced device- and network-level capabilities, tightly coupled with intended applications. The following eight parameters are key capabilities for IMT-2020 5G:

Different between RF and microwave radio frequency

RF or Radio Frequency is a term that is often used to describe the number of times per second or oscillation of an electromagnet radiation. Anything between 3Hz and 300GHz is still refered to as RF waves, but they are subdivided depending on the actual frequency. Microwave is the general term used to describe RF waves that starts from UHF (Ultra High Frequency) to EHF (Extremely High Frequency) which covers all frequencies between 300Mhz to 300GHz, lower frequencies are refered to as radio waves while higher frequencies are called millimeter waves.

People have found a lot of uses for radio frequency waves, most of which are in the field of communications. Radio waves are generally used for AM/FM radio stations due to the relative ease of using these types of waves. Microwaves which occupy the upper spectrum of RF waves have an even wider range of applications. Starting from the common microwave oven that uses microwaves to heat and cook our food, to military weapons that can heat the skin of enemy forces. But the most common use of microwaves are still in communications.
ithout even knowing that they are using microwaves are the WiFi routers and cards that we use to connect to our networks wirelessly. They utilize 2.4 or 5GHz RF waves to transmit data to and from our devices. Aside from that, microwave links are also used by internet service providers to transmit data from one point to another. Despite the introduction and adoption of fiber optic cables for this purpose. Microwave transmitters and receivers are still in use today in some areas. Microwaves are also being studied by some scientists today due to its capability to transmit power over the air. It is now being considered as a viable transmission method for harvesting solar power from space.

*To summarize, microwave is simply a part of the RF spectrum that has become quite popular due to the large number of its possible uses.

*Microwave is just a subset of the RF range

*. RF covers 3 Hz to 300 GHz while Microwaves occupies the higher frequencies at 300MHz to 3GHz

*RF waves have a lot of applications

* RF is more commonly related to

*AM/FM transmission while

*Microwaves are used in wider

*applications like heating and high-

*bandwidth data transmission systems

*Microwaves can also be used to transmit power from one point to another

*Most of the microwave applications range upto 100 GHz. Following are the unique features of the microwaves:
*

* High antenna gain and directivity

*Large Bandwidth
• It travels by LOS(Line Of Sight)
• In 1-10GHz range Microwaves noise level is very low and hence very low signal can also be easily detected at receiver
• Microwaves penetrate ionosphere with less attenuation as well as less distortion. •

What is sim card how it's work

Subscriber Identity Module Card

Sim card use normally mobile phone. A SIM card (short for subscriber identity module card) is a portable memory chip used in GSM phones. It is a crucial component in mobile telecommunications as it identifies and stores the telephone number and connects the cellphone to the mobile carrier's network. Since SIM cards also have a (limited) memory element, they can also be used as portable stores for one's phone contacts.

A SIM card is small and rectangular, about 25mm by 15mm, and notched at one corner. This feature ensures a handy, fail-safe way of inserting the card correctly into the corresponding slot in a mobile phone.type of different storage like 16kb,32kb,64kb,and 128 kb sim card available in market.
There are two competing technologies for mobile phones. The most prevalent one when looking at the worldwide picture is GSM (Global Standard for Mobiles), which is mainly used in Europe, Africa, South America and parts of Asia. Its competitor is CDMA (Code Division Multiple Access), which is more widely used in the USA and parts of China. (Note that most regions do not exclusively use either one or the other, but that the 2 technologies frequently coexist from different mobile providers.)

GSM mobile phones use SIM cards, while CDMA phones use RUIM (Re-Usable Identity Module) cards. The two standards are incompatible with each other, though there are industry efforts to produce devices that can work with both. The concept of SIM cards offers a major portability advantage. If you want to switch from one handset to another, say due to a dead battery or simply upgrading your handset to another model, then all you have to do is transfer the SIM card to the new phone and power it on. The SIM card will automatically connect to the same network and all your phone contacts will still be available. For international travelers, all they have to do is carry their GSM phone handsets to a new country and purchase a new SIM card and airtime in the other country. This is usually far cheaper than using your own SIM card in a foreign country.

SIM cards are usually protected by an embedded 4-to-8 digit PIN (Personal Identity Number) code, which one usually must to enter when the phone is starting up, although this can be disabled on the phone. You can, and should, change the PIN to a number different from the original one that shipped with the SIM card, which is typically a widely-known and easy to guess default such as 0000 or 1234.

What is LTE and VOLTE Network

LTE
LTE is a mobile Internet technology standard. It’s an abbreviation of Long Term Evolution. You may wonder why LTE keeps popping up in context of 4G. Well, 4G (or fourth generation) is just a common name given to LTE technology. In short, 4G and LTE are synonyms.

Theoretically, LTE supports download speed of 100 MBits per second and upload speed of 50 MBits per second. Another variant of LTE, called LTE-Advanced, supports download speed of 1 GBits per second and upload speed of 500 MBits per second.

LTE is considered a technological evolution on both CDMA and GSM standards, that were used several years ago. Nowadays, LTE is fast becoming available across the globe and mobile Internet Service Providers are upgrading their networks from 3G to 4G. LTE is at present the fastest data transfer technology and soon it may become the most dominant among all the mobile Internet technologies being used.

VOLTE
Full form of VoLTE is Voice over LTE.
VoLTE is pronounced as Vee O LTE.
VoLTE is a technology wherein you can simultaneously send voice and data over the network without diminishing quality of voice. In case of LTE, if you make a voice call and you also keep your data connection on, the quality of voice will reduce. So, in order to make a good quality voice call, you will have to switch off data. You may have noticed that in case of 2G and 3G, while you are making phone call, some phones will automatically stop data transfer so as to preserve the voice quality.

But in case of VoLTE, the voice quality will not reduce even if your data connection is on. With VoLTE it is very easy to transmit telephone conversation over the data network.
It is easy to see that VoLTE is superior technology. It has following major benefits over LTE:

*Voice quality is better in VoLTE.

*You can keep data connection on

*while making a voice call.

*VoLTE can connect calls faster

*4G VoLTE works on higher

*frequencies like 800 MHz and thus it can make connections much farther away from the mobile phone tower.

*In previous technologies, it was

*sometimes difficult to find a mobile signal.

*Use of VoLTE may save phone’s battery.

*VoLTE allows to you make video calls without using any third party apps.

What is a GPS SYSTEM

The global positioning system (GPS) is a 24-satellite navigation system that uses multiple satellite signals to find a receiver’s position on earth. GPS was developed by the U.S. Department of Defense (DoD). The technology was originally used for military purposes. Since 1980, when GPS technology was made available to the consumer market, it has become common in cars, boats, cell phones, mobile devices and even personal heads-up display (HUD) glasses.

A GPS navigation device, GPS receiver, or simply GPS is a device that is capable of receiving information from GPS satellites and then to calculate the device's geographical position. Using suitable software, the device may display the position on a map, and it may offer directions. The Global Positioning System (GPS) is a global navigation satellite system (GNSS) made up of a network of a minimum of 24, but currently 30, satellites  placed into orbit by the U.S. Department of Defense.[

The GPS was originally developed for use by the United States military, but in the 1980s, the United States government allowed the system to be used for civilian purposes. Though the GPS satellite data is free and works anywhere in the world, the GPS device and the associated software must be bought or rented.

GPS receivers find their location by coordinating information from three or four satellite signals. That information includes the position of the satellite and the precise time of transmission. With three signals, any 2D position can be found on earth; additional satellite signals make it possible to find altitude.

GPS technology works in almost any condition and is accurate to within 3-15 meters, depending on the number of signals received, the spread of satellites in the sky and the technologies used in the receiver.

HISTORY 

As with many other technological breakthroughs of the latter 20th century, the modern GPS system can reasonably be argued to be a direct outcome of the Cold War  of the latter 20th century. The multibillion-dollar expense of the program was initially justified by military interest.

In 1960, the US Navy put into service its Transit satellite based navigation system to aid in ship navigation. Between 1960 and 1982, as the benefits were been shown, the US military consistently improved and refined its satellite navigation technology and satellite system. In 1973, the US military began to plan for a comprehensive worldwide navigational system which eventually became known as the GPS (global positioning system). In 1983, in the wake of the tragedy of the downing of the Korean Airlines Flight 007, an aircraft which was shot down while in Soviet airspace due to a navigational error, President Reagan made the navigation capabilities of the existing military GPS system available for dual civilian use. However, civilian use was initially only a slightly degraded "Selective Availability" positioning signal. This new availability of the US military GPS system for civilian use required a certain technical collaboration with the private sector for some time, before it could become a commercial reality. In 1989, Magellan Navigation Inc. unveiled its Magellan NAV 1000, the world’s first commercial handheld GPS receiver. These units initially sold for approximately US$2,900 each. In 2000, the Clinton administration removed the military use signal restrictions, thus providing full commercial access to the US GPS satellite system.

What is an IMEI number ?

The International Mobile Equipment Identity (IMEI) number is a unique identification or serial number that all mobile phones and smartphones have. It is normally 15 digits long.

The IMEI number can be found on the silver sticker on the back of your phone, under the battery pack, or on the box your phone came in.

You can also display the IMEI number on the screen of your mobile phone or smartphone by entering *#06# into the keypad.

You have have heard of the term IMEI, or seen it listed on your phone’s original packaging. At first glance, its not really clear what exactly you are meant to do with it, or what the IMEI even is. The common advice is to always note down your IMEI number in case its lost or stolen — and for good reason. Your IMEI number is unique to your  device, and can be used to identify its make, model, and serial number.

As smartphones have become more readily available — and more valuable — they have become a target of thieves around the world. Against this backdrop, having a record of your IMEI number is not to be underestimated. So, what exactly is an IMEI number and how do you find yours?
Since 2004, the IMEI appears in the format AA-BBBBBB-CCCCCC-D. The sections labelled A and B are known as the Type Allocation Code (TAC). The TAC portion of the IMEI identifies the manufacturer and model of the device. For example, the Google Pixel TAC code is 35-161508, while the iPhone 6s Plus is 35-332907. Some models have multiple TACs depending on revision, manufacturing location, and other factors — the iPhone 5C has a total of five different TAC codes.

Parts of a Mobile Cell Phone and Their Function

There are all kinds of parts and electronic components in a mobile cell phone. These parts and components can be divided into Big Parts and Small Parts. This article explains all about big parts and components in a mobile cell phone and their function.
When learning how to repair a mobile cell phone, it is important to identify its parts and understand their function. Here I must also remind you that any PCB of a mobile phone is divided into 2 sections namely: Network Section; and Power Section. Have a look at the image below to understand PCB of a mobile cell phone.

Antenna Switch: It is found in the Network Section of a mobile phone
Cell Phone Antenna Switch
and is made up of metal and non-metal. In GSM sets it is found in white color and in CDMA sets it is found in golden metal.

Work: It searches network and passes forward after tuning.

Faults: If the Antenna Switch is faulty then there will be no network in the mobile phone.

P.F.O: It is found near the Antenna Switch in the Network Section of the
Cell Phone PFO
PCB of Mobile Phone. It is also called P.A (Power Amplifier) and Band Pass Filter.

Work: It filters and amplifies network frequency and selects the home network.



Faults: If the PFO is faulty then there will be no network in the mobile phone. If it gets short then the mobile phone will get dead.

RF IC / Hagar / Network IC: This electronic component found near
Cell Phone Network IC / RF IC
the PFO in the Network Section of a Mobile Phone. It is also called RF signal processor.

Work: It works as transmitter and receiver of audio and radio waves according to the instruction from the CPU.

Faults: If the RF IC is faulty then there will be problem with network in the mobile phone. Sometimes the mobile phone can even get dead.

26 MHz Crystal Oscillator: It is found near the PFO in the Network
Mobile Phone 26 MHz Crystal Oscillator
Section of a Mobile Phone. It is also called Network Crystal. It is made up of metal.

Work: It creates frequency during outgoing calls.

Faults: If this crystal is faulty then there will be no outgoing call and no network in the mobile phone.

VCO: It is found near the Network IC in the Network Section of a Mobile
Mobile Phone VCO
Phone.

Work: It sends time, date and voltage to the RF IC / Hager and the CPU. It also creates frequency after taking command from the CPU.

Faults: If it is faulty then there will be no network in the mobile phone and it will display “Call End” or “Call Failed”.

RX Filter: It is found in the Network Section of a Mobile Phone.
Mobile Phone RX Filter
Work: It filters frequency during incoming calls.

Faults: If it is faulty then there will network problem during incoming calls.

TX Filter: It is found in the Network Section of a Mobile Phone.
Mobile Phone TX Filter
Work: It filters frequency during outgoing calls.

Faults: If it is faulty then there will network problem during outgoing calls.

ROM: It is found in the Power Section of a Mobile Phone.
Mobile Phone ROM
Work: It loads current operating program in a Mobile Phone.

Faults: If ROM is faulty then there will software problem in the mobile phone and the set will get dead.

RAM: It is found in the Power Section of a Mobile Phone.
Mobile Phone RAM
Work: It sends and receives commands of the operating program in a mobile phone.

Faults: If RAM is faulty then there will be software problem in the mobile phone and it will get frequently get hanged and the set can even get dead.

Flash IC: It is found in the Power Section of a Mobile Phone. It is also
Cell Phone Flash IC
called EEPROM IC, Memory IC, RAM IC and ROM IC.

Work: Software of the mobile phone is installed in the Flash IC.

Faults: If Flash IC is faulty then the mobile phone will not work properly and it can even get dead.

Power IC: It is found in the Power Section of a Mobile Phone. There are
Cell Phone Power IC
many small components mainly capacitor around this IC. RTC is near the Power IC.

Work: It takes power from the battery and supplies to all other parts of a mobile phone.



Faults: If Power IC is faulty then the set will get dead.

Charging IC: It is found in the Power Section near R22.
Cell Phone Charging IC
Work: It takes current from the charger and charges the battery.

Faults: If Charging IC is faulty then the set will not get charged. If the Charging IC is short then the set will get dead.

RTC (Simple Silicon Crystal): It is Real Time Clock and is found in
Mobile Phone RTC (Real Time Clock)
the Power Section near Power IC. It is made up of either metal or non-metal. It is of long shape.

Type of mobile

Analog and Digital

*Mobile telephone systems are either analog or digital. In analog systems, voice messages are transmitted as sound waves. When you speak into an analog mobile telephone, your voice wave is linked to a radio wave and transmitted. In digital systems, voice messages are transmitted as a stream of zeroes and ones.
When you speak into a digital mobile telephone, your voice wave is converted into a binary pattern before being transmitted.
Mobile telephone systems are either analog or digital. In analog systems, voice messages are transmitted as sound waves. When you speak into an analog mobile telephone, your voice wave is linked to a radio wave and transmitted. In digital systems, voice messages are transmitted as a stream of zeroes and ones. When you speak into a digital mobile telephone, your voice wave is converted into a binary pattern before being transmitted.

*A mobile device (or handheld computer) is a computing device small enough to hold and operate in the hand. Typically, any handheld computer device will have an LCD flatscreen  interface, providing a touchscreen interface with digital buttons and keyboard or physical buttons along with a physical keyboard. Many such devices can connect to the Internet and interconnect with other devices such as car entertainment systems or headsets via Wi-Fi, Bluetooth, cellular networks or near field communication (NFC).
Integrated cameras, digital media players, the ability to place and receive telephone calls, video games, and Global Positioning System (GPS) capabilities are common. Power is typically provided by a lithium battery. Mobile devices may run mobile operating systems that allow third-party apps specialized for said capabilities to be installed and run.

FDM, TDMA, and CDMA Mobile
*Mobile telephone system all utilize some method to allow multiple users to share the system concurrently. The three methods for doing this are In a FDM system, the available frequency is divided into channels. Each conversation is given a channel. When the system runs out of channels in a given area, no more telephone calls can be connected. In this way, FDM operates much like the channel button on your television set. The AMPS and NAMPS mobile telephone systems utilize FDM.

In a TDMA system, your encoded voice is digitized and then placed on a radio-frequency (RF) channel with other calls. This is accomplished by allocating time slots to each call within the frequency. In the D-AMPS (Digital AMPS) system, each 30kHz carrier frequency is divided into three time slots. In the GSM and PCS systems, each 200kHz carrier is divided into eight time slots. The D-AMPS, D-AMPS 1900, GSM, PCS and iDEN systems all utilize TDMA.

In a CDMA system, your encoded voice is digitized and divided into packets. These packets are tagged with "codes." The packets then mix with all of the other packets of traffic in the local CDMA network as they are routed towards their destination. The receiving system only accepts the packets with the codes destined for it.

Analog systems are FDM. Digital systems can utilize either TDMA or CDMA.

FDM systems typically allow one call per 10Khz or 30Khz of spectrum. Early TDMA systems tripled the capacity of FDM systems. Recent advances in TDMA promise to provide forty times the carrying capacity of FDM systems. CDMA promises to improve on the results of TDMA.

There are many kinds of mobile devices, designed for different applications. This includes:

1.Mobile computers

2.Mobile Internet devices

3.Tablets/Smartphones

4.Laptops

5.Wearable computers

6.Calculator watches

7.Smartwatches

8.Head-mounted displays

9.Personal digital assistants

10.Enterprise digital assistants

11.Graphing calculators

12.Handheld game consoles

13.Portable media players

14.Calculators

15.Ultra-mobile PCs

16Digital media player

17.Digital still cameras (DSC)

18.Digital video cameras (DVC) or
19.digital camcorders

20.Feature phones

21.Pagers

22.Personal navigation devices (PND)

23.Smart cards

ve-Magnetic-Therapy.com Search Magnetic wave Electromagnetic radiation Electromagnetic pollution Electromagnetic field Health effects EMF Exposure EMF Effects Radiation side effects Background radiation Man-made radiation EMF pollution EMF Cover-up EMF military EMF expert Early experiment Recent research Radiation hazard Radiation cancer Cell phone harm Cell phone hazard Tower radiation Cell phone tower Invention Massage injury Massage stroke Health Benefits Media report Health Center Magnetic product Contact us Home › Magnetic wave › Electromagnetic radiation How cell phone towers work

*When you make a call on your mobile phone, it emits electromagnetic radio waves also known as radio frequency, or RF energy. Antenna from the nearest cell phone tower will then receive these radio waves.

*Cell phone tower consists of antennas that both transmit and receive signals from mobile phones.

*After receiving signal from a mobile phone, the cell phone tower then transmits the signals to a "switching center" - a telephone exchange for mobile phones. Here the call is connected either to another mobile phone or to telephone network.

*A mobile phone system requires a number of cell phone towers. Each cell phone tower sits in the middle of a geographical area known as "cell". That is why mobile phones are also known as "cellular" phones.

*The number of calls (or "traffic") that a cell phone tower can handle at any one time is limited by engineering design constraints. In order to operate the mobile phone network as efficiently as possible, cell phone towers are located to maximize the number of calls that can be connected during peak use periods.

*Therefore, geographic size of a cell depends on the traffic during these periods. Cells in populated areas with many mobile phone users will be smaller than cells in less populated areas.

*As you cross the boundary of one cell, the cell next to it will automatically take over. This is called a "hand-over" or "hand-on". It is controlled by a computer in switching center. The switching center knows which cell your mobile is in and switches it to the next cell if you move across a boundary.

*Your call will continue to get "handed-on" to each cell in turn until you reach the edge of the last boundary. Then you will be out of range of any cells and your call won't be transmitted.

*High electromagnetic energy fields
Almost all mobile phones, except for satellite phones, use cellular technology including GSM, CDMA (Code Division Multiple Access) and the old analog mobile phone systems.

*Wireless communication systems operate at several frequencies in electromagnetic spectrum. In the US, mobile phones operate in 2 main electromagnetic frequency ranges. The older systems operate near 850 MHz and the newer personal communications services, or PCS, operate near 1900 MHz.

*European mobile phones use Global System for Mobile Communications (GSM), a different technology that operates at slightly different frequencies, near 900 MHz and 1800 MHz.

*Many other applications transmit energy in nearby frequency bands.

*The next generation of mobile phone technology, expected to result in widespread use of videophones and access to multimedia information, is called Universal Mobile Telecommunication System (UMTS), which operates in the 2 GHz region in the UK.

*With handsets that have an energy saving discontinuous transmission mode (DTX), there is an even lower frequency pulsing at 2Hz, which occurs when the user is listening, but not speaking.

*The above does not include the energy fields from the cell phone tower. A cell phone tower antenna typically radiates 60 W.

*Every communication between handset and cell phone tower is grouped into "frames", which are in turn grouped into "multi frames". This results in an additional low-frequency pulsing of the signal at 8.34 Hz.

*This pulsing, unlike the 217 Hz radiation, is unaffected by call density. Thus it is a permanent feature of the emission.

*It has been reported that the DTX pulse frequency at 2 Hz and the TDMA frequency of 8.34 Hz correspond to frequencies of electrical oscillations found in human brain, specifically the delta and alpha brain waves, respectively.

*It is thus quite possible that living organisms have a 2-fold sensitivity to pulsed GSM signal, both to the microwave carrier and the lower frequency pulsing of TDMA and DTX signals.

what is Cellular network

A cellular network or mobile network is a communication network where the last link is wireless. The network is distributed over land areas called cells, each served by at least one fixed-location transceiver, but more normally three cell sites or base transceiver stations. These base stations provide the cell with the network coverage which can be used for transmission of voice, data, and other types of content. A cell typically uses a different set of frequencies from neighboring cells, to avoid interference and provide guaranteed service quality 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, tablets and laptops equipped with mobile broadband modems, 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 desirable features:

• More capacity than a single large transmitter, since the same frequency can be used for multiple links as long as they are in different cells
• Mobile devices use less power than with a single transmitter or satellite since the cell towers are closer
• Larger coverage area than a single terrestrial transmitter, since additional cell towers can be added indefinitely and are not limited by the horizon

 Major telecommunications providers have deployed voice and data cellular networks over most of the inhabited land area of Earth. This allows mobile phones and mobile computing devices to be connected to the public switched telephone network and public Internet. Private cellular networks can be used for researchor for large organizations and fleets, such as dispatch for local public safety agencies or a taxicab company.

 Cellular network Concept

In a cellular radio system, a land area to be supplied with radio service is divided into cells, in a pattern which depends on terrain and reception characteristics but which can consist of roughly hexagonal, square, circular or some other regular shapes, although hexagonal cells are conventional. Each of these cells is assigned with multiple frequencies (f₁ – f₆) 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 mobile communication switching system developed by Amos Joel of Bell Labs that permitted multiple callers in the same area to use the same frequency by switching calls made using the same frequency to the nearest available cellular tower having that frequency available and 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).
The first commercially cellular network, the 1G generation, was launched in Japan by Nippon Telegraph and Telephone (NTT) in 1979, initially in the metropolitan area of Tokyo. Within five years, the NTT network had been expanded to cover the whole population of Japan and became the first nationwide 1G network.

Network signal encoding

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

With TDMA, the transmitting and receiving time slots used by different users in each cell are different from each other.
With FDMA, the transmitting and receiving frequencies used by different users in each cell are different from each other. 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) 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. TDMA 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.

 Network 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, provided the masts and cellular network users' equipment do not transmit with too much power.

The elements that determine frequency reuse are the reuse distance and the reuse factor. The reuse distance, D is calculated as

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

where R is the cell radius and N is the number of cells per cluster. Cells may vary in radius from 1 to 30 kilometres (0.62 to 18.64 mi). The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells.
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 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.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

 Cell towers frequently use a directional signal to improve reception in higher-traffic areas. In the United States, the FCC limits omnidirectional cell tower signals to 100 watts of power. If the tower has directional antennas, the FCC allows the cell operator to broadcast up to 500 watts of effective radiated power (ERP).

Although the original cell towers created an even, omnidirectional signal, were at the centers of the cells and were omnidirectional, a cellular map can be redrawn with the cellular telephone towers located at the corners of the hexagons where three cells converge.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, and three towers for each cell and greatly increases the chances of receiving a usable signal from at least one direction.
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.
Cell phone companies also use this directional signal to improve reception along highways and inside buildings like stadiums and arenas.

 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 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 handing over
 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
 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 the usually 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 ¹⁄₂ mile (0.80 km), while in rural areas, the range could be as much as 5 miles (8.0 km). It is possible that in clear open areas, a user may receive signals from a cell site 25 miles (40 km) 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). The transition from existing analog to the digital standard followed a very different path in Europe and the US.As a consequence, multiple digital standards surfaced in the US, while Europe and many countries converged towards the GSM standard.

 Structure of the mobile phone cellular network

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

• A network of radio base stations forming the base station subsystem.
• The core circuit switched network for handling voice calls and text
• A packet switched network for handling mobile data
• 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 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 and access schemes: frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and space division multiple access (SDMA).

Small cells

Main article: Small cell

Small cells, which have a smaller coverage area than base stations, are categorised as follows:

• Microcell, less than 2 kilometres
• Picocell, less than 200 metres
• Femtocell, around 10 metres