Mobile Communications

in this easy add video lecture we will learn about mobile communications variant we will study about cellular concept mobile phone system features of cellular concept such as frequency reuse and cell splitting handoff procedure and global system for mobile or GSM when we have to call someone we just take out a mobile phone and dial the required number but has anyone ever wondered how these mobile phones work what exactly happens when we make a call from our mobiles let's start with the cellular concept we can make a call from one part of the country to another part of the country practically every city is divided into small areas each area is called as a cell thus a cell is defined as a basic geographical unit of a cellular communication system seriously pay attention this is important as the city is geographically divided into small cells it is mandatory that all cells must be symmetrical in shape based on this we have four geometrical shapes such as Circle Square equilateral triangle and hexagon if we select the shape of a cell as a circle then the area between the two circles will not get covered by the base station and any attempt of communication from that area will fail thus we eliminate the circular shape hexagon has the highest area as compared to the other two shapes thus we divide the geographical area into hexagonal cells the next concept is a cluster a group of cells is called as a cluster the cluster size is not fixed it depends on the requirements of the area let's study the mobile phone system now the basic structure of the mobile phone system is as shown where ms means mobile station BTS is base transceiver station BSC is base station controller and MSC is mobile switching center in this diagram MSE is nothing but the mobile phone of a user every cell has its own base transceiver station at its center whenever a call is set up the first signal is sent to the base transceiver station of the cell from this base transceiver station it goes to the central base station controller which controls the working of all the base stations from BSC it then goes to MSC or mobile switching center which is the master controller of the entire system these MSC s are different for different areas from MSC of area one the signal is transmitted to MSC of area 2 where it follows the reverse sequence as MSC to BSC BSC to BTS and from BTS - MS whenever a user makes an attempt to call someone a separate channel is assigned to the user by the MSC if all the channels are already occupied by other users then this user has to wait for a channel to become free in such a case the user gets the notification such as call cannot be completed or network error etc hey it's time to concentrate now now let's see the features of the cellular concept its first feature is frequency reuse in frequency reuse same set of frequencies are used for radio channels located in different areas as shown in the diagram below every cell named as a uses the same set of frequencies the advantages of frequency reuse are many transmitters of small output power operating at the same frequency can be used it reduces the minimum height of the transmitting antenna as each antenna has to cover a small distance but the disadvantage is that if the system is not properly designed then it may lead to co-channel interference co-channel interference is a phenomenon in which two frequency signals of adjacent channels interfere with each other the second feature of the cellular concept is cell splitting in cell splitting technique each cell is divided into smaller cells known as micro cells the radius of these small cells is half of the original radius cell splitting technique proves advantages when the traffic of cell phone users increases beyond the limit of a regular cell let's see what do we mean by a handoff procedure consider a situation where we are traveling from place a to place B via a car sometimes it happens that for a short period of 2 or 3 seconds the signal strength on mobiles becomes very low and again it increases and reaches its normal level have you ever thought why this happens the answer to this question is the handoff procedure when someone user X travels in area a he receives the signal from base station that is antenna a has a stronghold on out devices signal but as he moves away from antenna a the signal strength gradually decreases at a boundary of cell a the whole of antenna a on the device is minimum at the same time when the device is about to enter into cell B base station B starts to take hold on the device thus at the border of cell a and cell B both the antennas have equal amount of hold on the device of user X as user X crosses the border and enters into cell be area B strength of base station a very rapidly decreases and strength of base station B rapidly increases in short the device receives the signal network from base station B but during this procedure the call is still on hence base station a handovers this call to base station B without any effect on a call this procedure is known as the handoff procedure this process happens so rapidly that the user never notices it we all know that there are two types of systems available as gsm and cdma we will only study the basics of GSM system GSM stands for global system for mobile GSM is nothing but a big system made up of few small systems such as mobile stations ms base station subsystem BSS network and switching subsystem NSS operating subsystems OSS the architecture of this GSM network is as shown mobile station ms/ms is nothing but the device used for communication such as cell phone fax machine etc base station subsystem BSS BSS gets connected to ms wire radio interface it has two different blocks as BTS base transceiver system and BSC base station controller practically every MS gets connected to BTS of that area this beauty s sends the signal to BSC many BTS are connected to one BSC and at the end of this BSC is connected to MSC hence BSS system consists of BTS and BSC network and switching subsystem NSS this system mainly contains MSC MSC is the backbone of the entire network it controls all the operations from setting up a call till the handoff procedure other blocks of NSS are h l our home location register which keeps the database of all the users who reside in the same geographical area VL our visitor location register keeps the track of all the users who are visitors for that particular geographical area mainly roaming customers auc authentication center mainly controls the authentication of the users by checking their sim numbers etc and sends the required information to the MSC let's take a quick review of what we have learned we started with the cellular concept where we learned that every geographical area is divided into hexagonal shaped small areas called a cell a group of such cells is called as a cluster after that we studied the basic structure of the mobile phone system where M s means mobile station BTS is base transceiver station BSC is base station controller and MSC is mobile switching Center whenever a call is initialized a signal follows the sequence as M s to BTS BTS to BSC BSC to MSC of area one from MSC one to MSC of area two from MSC to BSC from BSC to BTS and from BTS to receiving m/s or user next we studied two features of the cellular concept such as frequency reuse in which the same set of frequencies are used for radio channels located in different areas and sales splitting where each cell is divided into smaller cells known as micro cells next we studied the handoff procedure where we learnt how a control over a call is transferred from one base station to another base station when a user travels from one area to another lastly we saw a GSM system consisting of different subsystems as mobile station ms base station subsystem BSS network and switching subsystem NSS operating subsystem OSS

Channel: EzEd Channel

Views: 475,773

Keywords: EzEd, Mobile Communications, Cellular Concept, Mobile Phone System, Features of Cellular Concepts, Frequency Reuse, Cell Splitting, Handoff Procedure, Global System for Mobile, GSM, GSM Technology, GSM Module, Mobile Communication Technology, Engineering Lecture, Engineering, Basic Electrical Engineering, Basic Electronic Engineering, BEE, Mumbai University, Pune University, F.E., Frequency Reuse in Cellular Network, Frequency Reuse Factor, cell splittig in mobile communication

Id: tt1-Ohe9QQU

Length: 11min 28sec (688 seconds)

Published: Sat Sep 30 2017