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Lecture Wireless and mobile computing – Chapter 20: Signal encodin techniques

The following will be discussed in this chapter: Differential encoding, modem functions, digital vs analog (advantages of digital over analog), binary amplitude shift keying (limitations), NRZ-L, QPSK Vs.OQPSK, QAM. | SIGNAL ENCODIN TECHNIQUES Review/Recap Lecture 20 Overview Differential Encoding Modem Functions Digital Vs Analog (Advantages of Digital Over Analog) Binary Amplitude Shift Keying (Limitations) NRZ-L QPSK Vs.OQPSK QAM Differential Encoding Q:- What is differential encoding? Way of looking at techniques Data Medium Digital Analog Digital Analog NRZ Manchester Differential Manchester Pulse Coded Modulation (digitized voice) ASK FSK PSK modems AM/FM radio Television Encoding Techniques Encoding schemes deal with how to transport bits over the physical media We must deal and manage many issues to well represent and interpret the bits: Timing of bits (start and end, duration, Signal levels) Clocking ( Synchronizing transmitter and receive, External clock, Sync mechanism based on signal) Error detection, Signal interference and Noise immunity Cost and complexity Encoding Techniques Encoding techniques depend on the type of data to transmit and the medium being used: Digital data on digital signal (our focus in this brief description.) Analog data on digital signal Digital data on analog signal Analog data on analog signal Digital Data, Digital Signal Digital signal: Discrete, discontinuous voltage pulses Each pulse is a signal element Binary data encoded into signal elements A Simple Encoding Scheme 0 is Vo (some voltage) 1 is V1 Example : let us encode 10011101 Clock Vo V1 Problem? Let us now try to encode two bytes that come one 2 seconds after the other: 10011101 and 00001101 What is the problem with this encoding scheme? What is the solution? Bipolar Encoding (RZ Signal) 1 is 0 is Example : let us encode 01100010 0 0 Clock +0.85V -0.85V HightV + NoV –» 1bit LowV + NoV –» 0bit Problem? The problem with this encoding scheme is that we have to return to 0 each time the transmission is done which generates some complexity and cost in implementing and managing this technique We should look for a better technique We have 2 alternatives: | SIGNAL ENCODIN TECHNIQUES Review/Recap Lecture 20 Overview Differential Encoding Modem Functions Digital Vs Analog (Advantages of Digital Over Analog) Binary Amplitude Shift Keying (Limitations) NRZ-L QPSK Vs.OQPSK QAM Differential Encoding Q:- What is differential encoding? Way of looking at techniques Data Medium Digital Analog Digital Analog NRZ Manchester Differential Manchester Pulse Coded Modulation (digitized voice) ASK FSK PSK modems AM/FM radio Television Encoding Techniques Encoding schemes deal with how to transport bits over the physical media We must deal and manage many issues to well represent and interpret the bits: Timing of bits (start and end, duration, Signal levels) Clocking ( Synchronizing transmitter and receive, External clock, Sync mechanism based on signal) Error detection, Signal interference and Noise immunity Cost and complexity Encoding Techniques Encoding techniques depend on the type of data to transmit and the medium being used: Digital .