Mobile communication, Frequency reuse-Basic Electronics for KTU Students(EST130)

In this video lecture, we will learn about mobile communication, therein we will study about cellular concept, mobile phone system, features of cellular concept, frequency reuse. First of all, what is the difference between normal telephone communication system and mobile communication system? What is mobile communication? Mobile communication is the provision of telephone services to phones which may move around freely, rather than stay fixed in one location. Mobile phones connect to a network of base stations. This network is interconnected to public switching telephone network to allow any phone in the world to be dialed. So mobile communication is communication using mobile phones and portable computing devices, such as smartphones, tablets, computers, etc. So communication using mobile devices is called mobile communication. The term mobile means able to move or to be moved freely or easily. Wireless is also associated with this mobile communication. The wireless is defined as no wires, we already studied in radio communication, we are using wireless communication technique. So mobile communication is an example of wireless communication method. So hope you, next we will discuss basic principle of cellular communication. Here we will discussing about the network components and cellular concept. What are the network components used for mobile communication? First one cell site, then mobile telephone switching office, public switching telephone network. These are the network components used for mobile communication system. First what is cell site? Cell site consists of a transmitter and receiver for phone connection. Then mobile telephone switching office, MDSO, it is used for the control and operation purpose of mobile communication. Third one public switching telephone network, it provides connection to phones located in individual homes. These are the network components used for mobile communication. Figure shows the network components used for mobile communication. We discussed cell site used for transmitter and receiver. Mobile telephone switching office is used for the operation purpose. So PSTN network, it provides connection to phones located in individual homes. What are cells? A cell is the basic geographical unit of a cellular system. The term cellular means the areas into which a covered region is divided. Cells are base stations transmitting over small geographical areas that are represented as hexagons. So in a mobile communication, a cell means the coverage area of that base station. The coverage area of that base station is represented by a cell and it has a shape of hexagon. So in a mobile system, a given region or a country is divided into several cells of hexagonal shape. Depending on the location and population, the diameter of the cell varies. In heavily populated cities, cells diameter is 1 to 2 km and in less populated regions like villages, it is 1 to 16 km. Subscribers in a cell will be given a frequency and adjacent cells will have different frequency. Figure shows the cellular concept. The entire country is divided into particular cells. The coverage area of each base station is represented by a cell and its structure is hexagonal shape. Subscribers in a cell will be given a frequency and adjacent will have different frequencies. represented by f1, f2, f3, f4 that are the frequencies and each cell have different frequencies. So the same frequency f1 will not come to that adjacent. Same frequency will not come to adjacent cells. This is the cellular concept of mobile communication. So we discussed that in a cellular system, the entire country is divided into cells. So when showing a cellular system, we want to show an area totally covered by the radio and without any gaps, we need to have signal strength as large as possible for all points within a cell. So hexagon is closest to a circle and this is an idealized representation. Each cell size varies depending on the landscape. The true shape of cells is not perfect hexagon, it may vary but look like a hexagon shape. The power level of a transmitter within a single cell must be limited to reduce the interference with the neighboring cell. Figure shows a single base station and its coverage area. That coverage area is represented by a hexagonal shape. That coverage area is called a cell and it is up to 35 kilometers. Here in this case of base station, the coverage area is 35 kilometers from that base station. Next is cluster. What is cluster? A cluster is a group of cells. In a cluster, no frequencies are used. This given figure illustrates a cluster. Here there are seven cells and each cell have different frequencies. Seven different frequencies we are using in this cluster and frequencies is not reused in a cluster. So like this thing, cluster is a group of cells. A group of cells is called a cluster. So frequency reuse, why frequency reuse? For the efficient spectrum usage for radio communication system, we are using frequency reuse purpose. Example, suppose each user is allocated a channel and each channel have a bandwidth of 25 kilohertz to enable sufficient audio quality to be carried as well as enabling there to be a good band between adjacent channels to ensure there is no interference. Using this concept, only possible to accommodate 40 users in a frequency band of 1 megahertz and 4000 users in a frequency band of 100 megahertz wide. Today cellular systems have millions of subscribers and therefore a far more efficient method of using the available spectrum is needed. The method that is employed is to enable frequencies to be reused. So here each cellular base station is allocated a group of radio channels with a small geographical area called a cell. The neighboring cells are assigned with different channel groups. By limiting the coverage area to within the boundary of a cell, the channel groups may be reused to cover different cells. Limit interference level with tolerable limits. Because of only a small number of radio channel frequencies are available for mobile system, engineers had to find a way to reuse the radio channels to carry more than one conversation at a time. The solution adopted by the industry that was the frequency planning or frequency reuse concept. In this concept is based on assigning to each channel a group of radio channels within a same geographical area. Cells are assigned a group of channels that is completely different from neighboring cells. The coverage area of a cell is called the footprint. The same group of channels can be used in different cells that are far enough away from each other so that the frequencies do not interfere. This is called frequency reuse and the reuse distance is rc root of root n where rc is the range that covered by the base station and n is the number of cells in a cluster.