 Hello, everyone. Welcome to a video lecture on frequency reuse. I am K. R. Biradhar, assistant professor, department of electronics and telecommunication engineering, Vulture Engineering Stop Technology, Saulapur. Let us start with the learning outcomes first. At the end of this video, you will be able to design cellular system with minimum signal to interference ratio. Cellular systems, some of the basic concepts. Before discussing the frequency reuse, let us see some of the basic concepts of cellular system. To begin with, high capacity is achieved by limiting the coverage of each base station to a small geographical area called a cell. Same frequencies or time slots or codes are reused by specially separated base stations. This factor of being reuse allows you high capacity so that large number of customers more revenue from the system. A switching technique called handoff is used here to enable the call to proceed uninterrupted when one user moves from one cell to another. Neighboring base stations are assigned different group of channels so as to minimize the interference. What do you mean by channels? We have seen earlier certain frequencies or time slots or codes and they form the channel. Therefore, neighboring cells must not use same frequencies but we have to use it after some definite distance so as to minimize interference. By systematically spacing base stations, the available channels are reused as many times as necessary. As demand increases, the number of base stations may be increased thereby providing additional capacity. So, there are ways and means today to expand your services. If your number of customer increases, you can scale up your system. So, this reuse factor and certain other advanced techniques will allow to continue providing services to a more and more number of stations. Even though you are not asking for extra bandwidth, cellular system design fundamentals to solve problems of spectral congestion and user capacity, replacing a single high power transmitter with many low power transmitters. Neighboring base stations are assigned different groups of channels so that the interference between base stations is minimized. Fixed number of channels to support a large number of subscribers. High network capacity is achieved by keeping same cell reuse distance high so that the interference caused is kept sufficiently low. Frequency reuse, the procedure of allocating the channels is called frequency reuse. In other words, the design procedure of allocating channel groups for all of the cellular base station within a system is called frequency reuse or frequency planning. Large distance to keep co-channel interference within limit. By design of antennas, the same area is limited within the cell and the same group of frequencies is reused to cover another cell separated by a large enough distance to keep co-channel interference within the limits. Why a large enough distance because you want to keep a co-channel interference which is generated by cells using the same frequency under control. Intelligent allocation and reuse of channels, cellular radio systems rely on intelligent allocation and reuse of channels throughout the coverage area. Each base station is allocated a group of radio channels to be used within the small geographical area of its cell. Concept of frequency reuse, the figure shows the concept of frequency reuse. There are seven cells which are represented by different letters A, B, C, D, E, F and G forms the one cluster. These are also called adjacent cells use different frequency band to avoid interference. This cluster is replicated all over the geographical area. In the diagram, same cluster replicated after some distance forms cluster 2. Note that the cell A present in the first cluster is repeated in cluster 2 with same letter as cell A. The distance between these two cells is called reuse distance. It is interesting to know you cannot have any random number of cells in a cluster. You cannot have a cluster size of 5 cells. One more thing is if the cluster size is small say for example 4, reuse distance will go down, capacity will increase but at the same time interference increases. Capacity of cellular system here S denotes number of duplex channels available for use or total number of duplex channels. Small key represents number of channels assigned for a cell. Capital N represents number of cells sharing S channels that is also called the cluster size. Therefore, S is equal to small k into n. C represents total number of duplex channels with frequency reuse. M is a number of replica of cluster. Therefore, C is equal to m into k into n. k in already you know that is equal to S. Therefore, C is equal to m S. Let us see one example. Given total available bandwidth is 30 megahertz, channel bandwidth is 50 kilohertz for duplex channels. Each cell has how many channels for 7 cell reuse? First the video and write your solution. First the video and write your solution. First the video and write your solution. I think you might have written the solution. Let us see here. The total available channels for given spectrum is 30 megahertz divided by 50 kilohertz is equal to 600 channels are available. k is equal to 600 divided by 7 that is 85 channels are available in each cell for n is equal to 7. Here k is the number of channels in each cell and n is the cluster size. Identify number of cells in a cluster. In order to identify the number of cells in a cluster we use the formula capital n is equal to i square plus i j plus j square. Take for example, i equal to n j equal to 1. Therefore, n is equal to 2 square plus 2 into 1 plus 1 square this is equal to 7 cells. In a cluster as shown in the diagram identifying the core channel cells. In order to identify core channel neighboring cells consider this figure having n is equal to 19 cells reuse and having i is equal to 3 and j equal to 2. Move i cells along any chain of hexagons in this example it is 3 turn 60 degrees counter clockwise and move j cells that is 2 in this diagram. In this way you can identify the core channel cells. These are the reference I referred to prepare the above presentation. Thank you. Thank you.