Resources » Articles/Knowledge Sharing » How things work
How mobile telephony works
Mobile telephony is the word which is familiar to all the people around the world. It is familiar to even children. Such an impact is made by the mobile phones to the common people. Even though everyone is familiar with the mobile phone, no one knows how the Mobile Telephony Works. In this article, I tried to explain each and every terminology of the Mobile Telephony and also its working. I think this will be useful.
Cellular network- An important technology
We all know that one of the fastest growing technologies in the world is the Cellular telephony. The first and second generation of the cellular phones is over and now we will soon witness the third generation cellular phones. The main concept of the traditional cellular phone is to hold the phone conversations in the pocket. Now the technology has changed a lot. The third generation cell phones have much more to do.
The new generation cell phones have a lot more job to do. Some of them are as follows;
- Make task/to-do lists
- Send/receive pictures
- Get information from the internet
- Integrate with other devices
- Store contact information
- Keep track of appointments
- Send/receive email
- Send/receive video clips
- Play games
The cellular concept
The basic concept of the cellular phone is to access telephone in each and every corner of the world at any time. Mobile telephony is the basic need of a cell phone. The person named St. Louis developed mobile telephony. He is from USA. The technology developed by St. Louis is being used today with a bit of modification.
Fig: Firstmobile telephone system
The System Architecture of the cell phone consists of a base station. This base station is held responsible for the cellular network or coverage area. Only the users within the range of base station can only receive/transmit signals. These signals are received/transmitted from the base station. A wired connection of network is being used between the base stations.
There are a lot of faults for the traditional cellular technology. They are not capable of accommodating too many users under a base station. The traditional base station is of high power. So the phones should transmit at high power. This is practically impossible. So the walkie-talkies are much preferred earlier. So an improved design is implemented. These ideas were implemented in 60’s, but the main problem was about the unavailability of the electronic equipments. Because of this, they waited until the mid 80’s to implement the first generation of cellular systems.
The cellular concept is the drive behind modern phones. The tessellation is the technology used here. There are several low power base stations. A handoff occurs when a user moves from one base station to another.
Fig: Tessellation of base stations
In this process, the base stations are split up into several small cells. Each cell consists of a base station. The mobiles under this cell communicate with the base station.
The 3 Core Principles of mobile network are;
- Users handoff
- Frequency reuse.
Tessellation can be termed as a cluster of small areas which constitutes a larger region. The tessellated area will not be having any sort of overlapping or gaps. The given region can be tessellated using given three regular polygons.
The polygons which tessellates in all given situations are:
- Equilateral triangle
- Regular Hexagon
Fig: Regular polygons that always tessellate
The coverage area under the base station is always in a circular region. The users located outside this circular coverage area will receive only weak signal. But the main problem is that the circles are not tessellated. In order to rectify this defect, hexagon is used. It is the only polygon which is similar to a circle. So the hexagon is used to represent the coverage area of a base station.
Fig: Hexagonal coverage area
The coverage area constructed of the regular polygon resembles a honeycomb. So it can also be mentioned as a honeycomb structure. The name ‘cellular’ is thus obtained. So the mobile telephony is sometimes referred as cellular network.
The handoff is the most important concept in the cellular network. As the term ‘mobile’ indicates, mobile phone users roam within a network or moves to another network. If they are not given a continuous access to the network while they are roaming, then this technology will become a huge flop. This occurs only when the user moves out of a specified network. A handoff is required when they moves from one cell to another.
Now let us deal with the concept of handoff in detail. Assume a base station B1. The signals are received and transmitted by the user from this cell. Assume that the user now reaches the base station B2. Now he is under the coverage area of base station B2. As a result, the user experiences only a little signal from B1 and the signal from B2 keep on increasing. At a specified stage, the signal from the base station dominates the signal from B2. At this point, the handoff occurs. As a result, the entire signal will now be reaching the user from the base station B2.
Fig: Handoff process
The Frequency Reuse is another factor allowing the cellular communication. Now days, the mobile phone users are kept on increasing. But the frequency spectrum is limited. So the frequency reuse technique is used to effectively utilize the given limited frequency spectrum. The main concept behind this is to split up the total frequency spectrum into smaller ones. A cell or a base station is provided with a specific frequency band. Only through this specified spectrum, the communication in the given cell takes place. No neighboring cells will be having the same frequency band. As a result there will not be any chances of distortion due to interference. But this same frequency spectrum can be used by the cells placed far away from the specified cell and thus the name ‘frequency reuse’ is used.
Fig: Example of Frequency Reuse
Multiple access in cellular networks
In many mobile systems, there is a chance for a receiver to receive signals from different transmitters. This is the case when different users under the same tower communicate with each other. There arises a difficulty to share the limited frequency spectrum. A multiple access technique is used in these situations.
The three main techniques used her are as follows:
- Frequency division multiple access (FDMA)
- Time division multiple access (TDMA)
- Code division multiple access (CDMA)
Frequency division multiple access
In Frequency Division Multiple Access method, the base station receives a band of frequencies of the radio signals. This frequency spectrum is splitted up into numerous sub bands. Each user under the same base station is provided with a specific sub band frequency to communicate with the base station.
Fig: Frequency Division Multiple Access
A sub band consists of frequencies of continuous manner. The sub band will be having a width of 100 kilohertz. The center frequency of the sub band is transmitted during this process. When the base station is set to that specified frequency, no one can decode the signal, except the desired user. So the chance of interference is reduced.
Time division multiple access
The Time Division Multiple Access unlike FDMA, the frequency is not splitted up into sub bands. In this technology, the ‘round robin’ access method is used. In this method, the base station communicates with one user at a time. In Time Division Multiple Access method, the time is split up into the intervals of equal length. These are grouped and this group is called as a frame. One slot per frame is given to each user. During the length of the phone conversation, the slot is kept fixed.
Code division multiple access
The Code Division Multiple Access scheme is more complicated than others. In this method, all the users are allowed to communicate with the receiver in the same set of time. This is done using the same frequencies too. This may result in the interference of the signals. In order to avoid it, the signal of the required user is encrypted using a specified code given to the user.
There are mainly two methods used in the Code Division Multiple Access technique. They are as follows:
- Frequency hopping
- Direct Sequence
Fig: Complete Cellular Network
In Frequency Hopping technique, the frequency values of fixed values is assigned to each user. A slot is assigned here. In first slot, the signal is transmitted using the first frequency of the hopping sequence. In the next interval, second frequency is transmitted and so on. In Direct Sequence method, the same frequency is used by the different users at the same time. This may sometime results in interference. But a special code is used by the user to distinguish required message from others. This is the most difficult form of CDMA technology to implement.
GSM v/s CDMA
The main advantage of GSM is that it is being used worldwide. They can support the international roaming. They can be operated from anywhere the world. The GSM technology was established much earlier than the CDMA technology. So it has a slighter advantage. An additional m-commerce is available in the GSM technology as it uses the subscriber identity modules, simply called as SIM cards. But it is not being used in the American market. But, the simultaneous conversation is possible in the CDMA technology. It is more efficient and it significantly reduces the size of the cell phones. Only less power is needed for the phones incorporated with the CDMA technology.
The cellular technology is one of the versatile technologies used now a day. The cellular technology is now in its third generation. The cell phones are now the integral part of our life. Now, the mobile phones have a wide range of uses. It can now even replace the personal computers.
Read related articles: Working of mobile telephony
Did you like this resource? Share it with your friends and show your love!
Active MembersTodayLast 7 Daysmore...