199dca54-2ccd-4901-90d5-8d2647376715Module3
.pdf
School
Thompson Rivers University**We aren't endorsed by this school
Course
COMP 3271
Subject
Electrical Engineering
Date
Dec 19, 2024
Pages
9
Uploaded by BaronAlbatrossPerson1239
Module 31Module 3Digital TransmissionComputer network is designed to send info. from one point to the other. Info. needs to be converted to digital or analog signalDigital-to-digital conversionif our data is already digital and we are using digital transmission we need digital-to-digital transmission, 3 techniques: line coding, block coding, and scramblingLine coding always needed. block coding and scrambling sometimes neededLine codingProcess of converting digital data to digital signalsassume that data (text, numbers, images, audio, video) are stored in computer memory in the form of a sequence of bitsLine coding converts the sequence of bits into a digital signalAt sender: digital data is encoded to digital signals
Module 32At receiver: digital data is recreated by decoding the digital signalsBlock codingneed redundancy to ensure synchronization and to provide inherent error detectingBlock coding changes a block of m bits into a block of nbits, where nis larger then m. referred to as mB/nB encoding techniqueInvolves 3 steps: division, substitution, and combinationDivision: sequence of bits is divided into groups of mbitsSubstitution: substitute m-bits group for a n-bits groupCombination: Finally the n-bit groups are combined from a streamAnalog-to-Digital ConversionPulse Code Modulation (PCM)most common technique used to change analog signal to digital data (digitization)
Module 33Has 3 processes:The analog signal is sampled every TsThe sampled signal is quantized, which means every sample is considered as a pulseThe quantized values (pulses) are encoded as streams of bitsPCM Bandwidth: Bmin = nb x BanalogDelta Modulation (DM)PCM very complexDM simpleDM finds the change from the previous sampleAnalog Transmissiononly choice if we have a bandpass channel (channel that doesnʼt start from 0Converting digital data to bandpass analog signal is called digital-to-analog conversionConverting low-pass analog signal to a bandpass analog signal is called analog-to-analog conversion
Module 34Digital-to-Analog conversionprocess of changing one of the characteristics of an analog signal based on info. in digital dataSine wave is defined by 3 characteristics: amplitude, frequency, and phaseAny one of those characteristics can be modified in this way, giving us at least 3 mechanisms for modulating digital data into analog signal:Amplitude shift keying ASKFrequency shift keying FSKPhase shift keying PSKIn addition there is a fourth mechanism that combines changing amplitude and phase called: quadrature amplitude modulation QAMmost efficient of these options (most commonly used today)Amplitude Shift Keyingamplitude of the carrier signal is varied to create signal elements. Frequency and phase remain constant while amplitude changesBinary ASK BASKNormally implemented using only 2 levelsReferred to as binary amplitude shift keying or on-off keying OOKPeak amplitude of one signal level is 0; the other is the same as the amplitude of the carrier frequency
Module 35Multilevel ASKMore than 2 levelsCan use 4, 8, 16Frequency Shift Keying (FSK)Frequency of carrier signal is varied to represent data.frequency of modulated signal is constant for the duration of one signal elementchanges for next signal element if the data element changes. Both the peak amplitude and phase remain constant for all signal elementsBinary FSK BFSK
Module 36Phase Shift KeyingPhase of the carrier is varied to represent 2 or more different signal elementsBoth peak amplitude and frequency remain constant as the phase changestoday, PSK is more common than ASK or FSKBinary PSK BPSK
Module 37Analog-to-Analog ConversionRepresentation of analog information by an analog signalModulation is needed if the medium is bandpass in nature or if only a bandpass channel is availableCan be accomplished in 3 ways: amplitude modulation AM, frequency modulation FM, and phase modulation PMAmplitude ModulationCarrier signal is modulated so that its amplitude varies with the changing amplitudes of the modulating signalFrequency and phase of the carrier remain the sameFrequency ModulationFrequency of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signalpeak amplitude and phase of carrier signal remain the constant
Module 38Phase ModulationPhase of the carrier signal is modulate to follow the changing voltage level (amplitude) of modulating signalpeak amplitude and frequency of the carrier signal remain constant, but as the amplitude of the information signal changes, the phase of the carrier changes correspondinglyPM is the same as FM with one differencein FM, the instantaneous change in the carrier frequency is proportional to the amplitude of the modulating signal; in PM the instantaneous change in the carrier frequency is proportional to the derivative of the amplitude of the modulating signal
Module 39