How Do Cell Phones Work?
For most of us, a mobile phone is a part of our lives. But I'm sure you're curious minds have always been struck by such questions as how a mobile phone makes a call, and why there are different generations of mobile communications? (upbeat music) Let's explore the technology behind mobile communications. When you speak on your phone, your voice is picked up by your phone's microphone. The microphone turns your voice into a digital signal with the help of MEMS sensor and IC. The digital signal contains your voice in the form of zeros and ones. An antenna inside the phone receives these zeros and ones and transmits them in the form of electromagnetic waves. Electromagnetic waves transmit the zeros and ones by altering the wave characteristics, such as the amplitude, frequency, phase, or combinations of these. For example, in the case of frequency, zero and one are transmitted by using low and high frequencies respectively. So, if you could find a way to transmit these electromagnetic waves to your friend's phone, you would be able to establish a call. However, electromagnetic waves are incapable of traveling long distances. They lose their strength due to the presence of physical objects, electrical equipment, and some environmental factors. In fact, if there were no such issues, even then, electromagnetic waves would not carry on forever, due to the Earth's curved structure. To overcome these issues, cell towers were introduced, using the concept of cellular technology. In cellular technology, a geographic area is divided into hexagonal cells with each cell having its own tower and frequency slot.
Generally, these cell towers are connected through wires, or more specifically ,optical fiber cables. These optical fiber cables are laid under the ground or the ocean, to provide national orinter national connectivity. The electromagnetic waves produced by your phone are picked up by the tower in your cell and convert them into high frequency light pulses. These light pulses are carried to the base transceiver box, located at the base of the tower for further signal processing, After processing, your voice signal is routed towards the destination tower. Upon receiving the pulses, the destination tower radiates it outwards in the form of electromagnetic waves, and your friend's phone then receives the signal. This signal undergoes a reverse process, and your friend hears your voice. So, it's true that mobile communications are not entirely wireless, they do use a wired medium too. This is how mobile communications are carried out. However, there was a big issue that we intentionally left unanswered. Mobile communication is only successful when your tower transfers the signal to your friends tower. But how does your tower know in which cell tower area your friend is located? Well, for this process, the cell tower gets help from something called a mobile switching center. The MSC is the central point of a group of cell towers. Before moving further, let's explain more information about the MSC. When you purchase a SIM card, all the subscription information is registered in a specified MSC. This MSC will be your home MSC.
The home MSC stores information such as service plans, your current location, and your activity status. If you move outside the range of your home MSC, the new MSC, which serves you instead, is known as a foreign MSC. As you enter a foreign MSC region, it communicates with your home MSC. In short, your home MSC always knows which MSC area you are in. To understand in which cell location the subscriber is within the MSE area, the MSC uses a few techniques. One way is to update the subscriber location after a certain period. When the phone crosses apre defined number of towers, the location update is again done. The last one of these is when the phone is turned on. Let's try to under stand all of these procedures with an example. Suppose, Emma wants to call John. When Emma dials John's number, the call request arrivesat Emma's home MSC. Upon receiving John's number, the request will beforwarded to John's home MSC. Now, John's MSC checksfor his current MSC. If John is in his home MSC, the call requests will be immediately sent to his current cell location, and it checks whether John is engaged on another call, or if his mobile is switched off. If everything is positive, John's phone rings, and the call will be connected. However, if John is not in his home MSC, John's home MSC simply forwards the call request to the foreign MSC. The foreign MSC will follow the previously explained procedure to locate John's phone, and will then establish the call. Now, let's discuss why the frequency spectrum is quite important in mobile phone communications.
To transfer zeros and ones in digital communication, each subscriber is allocated a frequency range. However, the frequency spectrum available for cellular communications is quite limited, and there are billions of subscribers. This issue is solved with the help of two technologies, one frequency slot distribution, and two, multiple access technique. In the first technique, different frequency slots are carefully allocated to different cell towers. In the multiple access technique, this frequency slot is efficiently distributed amongst all the active users in the cell area. Now, the big question. Why are there different generations of mobile phone technologies? 1G originally allowed users, for the first time, to carry a phone without a cable attached to it. But 1G suffered from two major problems. The first problem was that the wireless transmission was in an analog format. Analog signals that are easily altered by external sources. So, it provided poor voice quality and poor security. The second problem was that it used the frequency division multiple access technique, which used the available spectrum in an inefficient way. These factors paved the way for the second generation of mobile communications, 2G used digital multiple access technologies, namely TDMA, or CDMA technology.
The second generation also introduced a revolutionary data service, SMS, and internet browsing. 3G technology was focused on giving a higher data transfer speed. It used a WCD multiple access technique, along with an increase in bandwidth. To achieve this, the 3G speed of two Mbps allowed the transfer of data for uses such as GPS, videos ,voice calls, et cetera. 3G was a huge step in the transformation of the basic phone to a smartphone. Next came 4G, which achieved speeds of 20 to 100 Mbps. This was suitable for high resolution movies and television. This higher speed was made possible due to the OFD multiple access technology, and MIMO technology. MIMO uses multiple transmitter receiver antennas inside both the mobile phone and the towers. The next generation of mobile communication, 5G, to be rolled out soon, will use enhanced MIMO technology and millimeter waves. It will provide seamless connectivity to support the internet of things, such as driverless cars and smart homes.
With worldwide mobile subscriptions estimated to be around 7 billion in 2014, cell phones have become a universal and indispensable tool for modern life. With a cell phone, you can talk to anybody on the planet from almost anywhere. But do you really know how your cell phone works?
In the most basic form, a cell phone is essentially a two-way radio, consisting of a radio transmitter and a radio receiver. When you chat with your friend on your cell 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 cell phone, which converts it to an electrical signal and then back to sound again. In the basic form, a cell phone works just like a walkie-talkie.
In additional to the basic function of voice calls, most modern cell phones 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 Waves
Cell phones transmit radio waves in all directions. The waves can be absorbed and reflected by surrounding objects before they reach the nearest cell tower. For example, when the phone is placed next to your head during a call, a significant portion (over half in many cases) of the emitted energy is absorbed into your head and body. In this event, much of the cell phone’s EMF energy is wasted and no longer available for communication.
Antenna
An antenna is a metallic element (such as copper) engineered to be a specific size and shape for transmitting and receiving specific frequencies of radio waves. While older generation cell phones have external or extractable antennas, modern cell phones contain more compact antennas inside the device thanks to advanced antenna technologies. It’s important to understand that any metallic components in the device (such as the circuit board and the metal frame for the iPhone) can interact with the transmission antenna(s) and contribute to the pattern of the transmitted signal.
Many modern smart phones also contain more than one type of antenna. In addition to the cellular antenna, they may also have Wi-Fi, Bluetooth and/or GPS antennas.
Connectivity
In order to conserve battery life, a cell phone will vary the strength of its transmitted signal and use only the minimum necessary to communicate with the nearest cell tower. When your cell phone has poor connectivity, it transmits a stronger signal in order to connect to the tower, and as a result your battery drains faster. That’s why good connectivity not only reduces dropped calls, but also saves battery life.
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