EETE 4220 Digital Communication and Switching Lecture Notes PDF

EETE 4220 Digital Communication and Switching Semester I AY 2024-25 Class Lecture -8 Outcome #8 & 9-Multiplexing Course Lecturer :Lenin Joseph (LJ) E&E Sect...

EETE 4220 Digital Communication and Switching Semester I AY 2024-25 Class Lecture -8 Outcome #8 & 9-Multiplexing Course Lecturer :Lenin Joseph (LJ) E&E Section. Dept. of Engineering. ACT Dec 25, 2024 1 OUTCOME #8 & #9 8. Explain about electronic space division switching 9. Explain about the time division switching EETE 4220 Digital Communication & Switching -E&E Section. Dept. of Engine Dec 25, 2 ering. ACT 2024 MULTIPLEXING Multiplexing – set of techniques that allow the simultaneous transmission of multiple signals across a single data link. Multiplexing vs. No Multiplexing 4 Path – physical link 4 Channel – portion of a path Frequency Division Multiplexing (FDM) A technique by which the total bandwidth available in a communication system is divided into a series of non-overlapping frequency sub-bands, each of which is used to carry a separate signal.  A technique that can be applied when the BW of a link is greater than the combined BWs of the signals to be transmitted. Applications of FDM Frequency Division Multiplexing is used in the following communication systems:  Telemetry Systems  FM and TV Broadcasting Systems  Telephone systems transmitting multiple telephone calls through high capacity trunk lines  Communication satellites transmitting multiple channels of data on uplink and downlink radio beams  Broadband DSL modems transmitting large amounts of computer data through twisted pair telephone lines. Time Division Multiplexing (TDM) A method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern. Multiple signals are transmitted over a single channel in different time slots. A digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices. Synchronous TDM Synchronous means that the multiplexer allocates exactly the same time slot to each device at all times whether or not a device has anything to transmit TIME DIVISION MULTIPLEXING Interleaving – switching from device to device at a constant rate and in a fixed order In a system with n input lines, each frame has at least n slots Time-slot length is fixed Demultiplexing TDM signals  Quarter of the capacity of the link is being wasted Advantage of Synchronous TDM: no addressing is necessary Disadvantage of Synchronous TDM: o Does not guarantee that the full capacity of a link is used Asynchronous TDM Asynchronous means flexible or not fixed Frames and Addresses in Asynchronous TDM  Only three lines sending data Frames and Addresses in Asynchronous TDM  Only four lines sending data Frames and Addresses in Asynchronous TDM  All five lines sending data Applications of TDM  Telegraphy  Digital Telephony Wave-division multiplexing (WDM)  conceptually the same as FDM, except that the multiplexing and demultiplexing involve light signals transmitted through fiber optic channel.  The frequencies are very high compared to FDM. Space Division multiplexing (SDM)  Space Division Multiplexing is a method of transmitting multiple wireless signals on a common frequency in such a way that they do not interfere with one another.  Space Division Multiplexing is achieved by multiple antenna elements forming a phased array antenna. MULTIPLE ACCESS TECHNIQUES  In telecommunications and computer networks, a channel access method or multiple access method allows several terminals connected to the same multi-point transmission medium to transmit over it and to share its capacity.  Examples of shared physical media are wireless networks, bus networks, ring networks, star networks and half-duplex point-to-point links.  A multiple access scheme is based on a multiplexing method that allows several data streams or signals to share the same communication channel or physical medium. TIME DIVISION MULTIPLE ACCESS (TDMA) A special form of TDM that provides multiple voice channels per satellite or telephone spectrum.  It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot.  TDMA is used in the digital 2G cellular systems such as GSM. Each frequency channel is divided into eight timeslots, of which seven are used for seven phone calls, and one for signaling data. FREQUENCY DIVISION MULTIPLE ACCESS (FDMA)  A channel-access scheme is based on the frequency- division multiplexing (FDM) scheme, which provides different frequency bands to different data-streams.  In FDMA, the data streams are allocated to different nodes or devices.  An example of FDMA systems were the first- generation (1G) cell-phone systems, where each phone call was assigned to a specific uplink frequency channel, and another downlink frequency channel.  Each message signal (each phone call) is modulated on a specific carrier frequency.  SPACE DIVISION MULTIPLE ACCESS (SDMA)  Spatial division multiple access (SDMA) is a channel access method used in mobile communication systems which reuses the same set of cell phone frequencies in a given service area.  Two cells or two small regions can make use of the same set of frequencies if they are separated by an allowable distance (called the reuse distance). CODE DIVISION MULTIPLE ACCESS (CDMA)  A multiple access scheme is based on Spread Spectrum, meaning that a wider radio spectrum in Hertz is used than the data rate of each of the transferred bit streams, and several message signals are transferred simultaneously over the same carrier frequency, utilizing different spreading codes. Application of CDMA  CDMA is used in satellite systems so that many signals can use the same transponder.  CDMA is widely used in cellular telephone systems, for it permits more user to occupy a given band than other methods. REFERENCES Text Book Frenzel, L., Principles of Electronic Communication Systems, 3rd Ed. McGrawHill, 2008 Book References Sklar, Benard, “Digital Communications: Fundamentals and Application”, Prentice Hall, USA, 2001 Glover, Ian A / Grant, Peter M, “ Digital Communications”, Prentice Hall, UK, 2004 Proakis,John G,“ Digital Communications”, McGraw Hill Inc, USA, 2000 Wesolowski,Krzysztof, “Introduction to Digital Communication Systems”,2009 Web References\ e-library(s) https://ebookcentral.proquest.com/lib/momp/detail.action?docID=3011330 571, CD/DVD, Electronic Communication Systems: A complete Course, ACT Store THANK YOU