Signal Encoding Techniques Digital Signals Digital Data, Analog - PowerPoint PPT Presentation

ITS323/CSS331 Signal Encoding Introduction Digital Data, Signal Encoding Techniques Digital Signals Digital Data, Analog Signals Analog Data, Digital Signals ITS323: Introduction to Data Communications Analog Data, CSS331: Fundamentals of Data Communications Analog Signals Sirindhorn International Institute of Technology Thammasat University Prepared by Steven Gordon on 3 August 2015 ITS323Y15S1L04, Steve/Courses/2015/s1/its323/lectures/signal-encoding-techniques.tex, r3920

ITS323/CSS331 Contents Signal Encoding Introduction Introduction Digital Data, Digital Signals Digital Data, Analog Signals Digital Data, Digital Signals Analog Data, Digital Signals Analog Data, Analog Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Signal Encoding Techniques Signal Encoding ◮ Signals transmitted chosen to optimize use of Introduction transmission medium Digital Data, ◮ E.g. conserve bandwidth, minimize errors Digital Signals ◮ Digital signaling: digital or analog data encoded into Digital Data, Analog Signals digital signal Analog Data, Digital Signals ◮ Analog signaling: digital or analog data transmitted by Analog Data, analog carrier signal using modulation Analog Signals ◮ Baseband signal is the input data signal ◮ Carrier signal has frequency f carrier ◮ Modulated signal is output

ITS323/CSS331 Encoding and Modulation Techniques Signal Encoding Introduction Digital Data, Digital Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Reasons for Using Different Techniques Signal Encoding Digital data, digital signal: Equipment less Introduction complex/expensive than digital-to-analog modulation Digital Data, equipment Digital Signals Digital Data, Analog data, digital signal: Permits use of digital Analog Signals transmission equipment Analog Data, Digital Signals Digital data, analog signal: Some media only propagate Analog Data, Analog Signals analog signals, e.g. optical fibre, wireless Analog data, analog signal: Some analog data can easily be transmitted as baseband signals, e.g. voice; enables multiple signals at different positions in spectrum to share transmission media

ITS323/CSS331 Contents Signal Encoding Introduction Introduction Digital Data, Digital Signals Digital Data, Analog Signals Digital Data, Digital Signals Analog Data, Digital Signals Analog Data, Analog Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Digital Data, Digital Signals Signal Encoding ◮ Digital signal: sequence of discrete voltage pulses Introduction ◮ Each pulse is a signal element Digital Data, Digital Signals ◮ Binary data transmitted by encoding each bit (data Digital Data, element) into signal elements Analog Signals ◮ E.g. binary 1 represented by lower voltage level, binary 0 Analog Data, Digital Signals for higher level Analog Data, ◮ Data rate = data elements or bits per second Analog Signals ◮ Signaling or modulation rate = signal elements per second (baud)

ITS323/CSS331 Receiver Interpreting Incoming Signal Signal Encoding Introduction Digital Data, Digital Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals ◮ Important factors for successful reception: SNR, data rate, bandwidth ◮ Increase in data rate increases bit error rate (BER) ◮ Increase in SNR decreases BER ◮ Increase in bandwidth allows increase in data rate ◮ Also encoding scheme . . .

ITS323/CSS331 Definition of Digital Signal Encoding Formats Signal Encoding Introduction Digital Data, Digital Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Digital Signal Encoding Formats Signal Encoding Introduction Digital Data, Digital Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Comparing Different Encoding Schemes Signal Encoding Signal Spectrum Introduction Digital Data, ◮ Desire no high frequency components so less bandwidth Digital Signals is required Digital Data, Analog Signals ◮ Desire no dc component so ac coupling can be used Analog Data, Digital Signals (reduces bit error rate) Analog Data, ◮ Concentrate trasmitted power in middle of bandwidth Analog Signals Clocking and Synchronization ◮ Transmitted signal can be used by receiver to synchronise bit timing

ITS323/CSS331 Comparing Different Encoding Schemes Signal Encoding Error Detection Introduction Digital Data, ◮ Receiver can detect some bit errors from the received Digital Signals signal Digital Data, Analog Signals Analog Data, Digital Signals Signal Interference Analog Data, Analog Signals ◮ Provide good performance (few bit errors) in presence of noise Cost and Complexity ◮ Desire smaller signaling rate to achieve a given data rate

ITS323/CSS331 Spectral Density of Various Signal Encoding Signal Encoding Schemes Introduction Digital Data, Narrower is better Digital Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Improving on NRZ Signal Encoding Multilevel Binary Schemes Introduction Digital Data, ◮ Bipolar AMI, Pseudoternary Digital Signals Digital Data, ◮ Use more than two signal levels Analog Signals ◮ No dc component, simple error detection, no loss of Analog Data, Digital Signals synchronization (in some cases), small bandwidth Analog Data, Analog Signals needed ◮ Requires more transmit power for same level of BER as two-level schemes Biphase Schemes ◮ Manchester, differential Manchester ◮ More than 1 transition per bit ◮ Similar features to multilevel schemes, but larger bandwidth required

ITS323/CSS331 Improving Synchronization Signal Encoding ◮ In Bipolar AMI a long sequence of 0’s makes it difficult Introduction for the receiver to synchronize Digital Data, Digital Signals ◮ Solution: if long sequence of same bit, replace with Digital Data, special sequence of bits Analog Signals ◮ B8ZS (Bipolar with 8-zeros substitution) Analog Data, Digital Signals ◮ If 8 0’s and last pulse was positive, replace 8 0’s with Analog Data, 000 + − 0 − + Analog Signals ◮ If 8 0’s and last pulse was negative, replace 8 0’s with 000 − +0 + − ◮ HDB3 (High density bipolar 3-zeros)

ITS323/CSS331 Encoding Rules for B8ZS and HDB3 Signal Encoding Introduction Digital Data, Digital Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Example Technologies using Encoding Schemes Signal Encoding ◮ NRZ/NRZI: RS-232, HDLC, USB, . . . Introduction ◮ Manchester: Ethernet, Token Ring, . . . Digital Data, Digital Signals ◮ Multilevel Binary: US T-carrier and European E-carrier Digital Data, telecommunication systems Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Contents Signal Encoding Introduction Introduction Digital Data, Digital Signals Digital Data, Analog Signals Digital Data, Digital Signals Analog Data, Digital Signals Analog Data, Analog Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Digital Data, Analog Signals Signal Encoding ◮ Transmit digital data over media that only support Introduction analog signals, e.g. telephone network, microwave Digital Data, systems Digital Signals ◮ Telephone network designed to transmit signals in Digital Data, Analog Signals voice-frequency (300 to 3400 Hz) ◮ Modems (modulator-demodulator) convert digital data Analog Data, Digital Signals to signals in this frequency range Analog Data, ◮ 3 basic modulation techniques: Analog Signals 1. Amplitude Shift Keying (ASK) 2. Phase Shift Keying (PSK) 3. Frequency Shift Keying (FSK) ◮ Resulting signal occupies bandwidth centred on carrier frequency

ITS323/CSS331 Modulation of Analog Signals for Digital Data Signal Encoding Introduction Digital Data, Digital Signals Digital Data, Analog Signals Analog Data, Digital Signals Analog Data, Analog Signals

ITS323/CSS331 Comparing the Shift Keying Schemes Signal Encoding Amplitude Shift Keying Introduction Digital Data, ◮ Inefficient modulation technique Digital Signals ◮ Used on voice lines < 1200 bps and optical fibre Digital Data, Analog Signals Analog Data, Digital Signals Frequency Shift Keying Analog Data, Analog Signals ◮ Used on voice lines, coaxial cable, HF radio systems ◮ Extended with M frequencies: improve efficiency, higher error rate Phase Shift Keying ◮ Used in wireless transmission systems ◮ Extended with M phases, e.g. QPSK ( M = 4), ◮ Combined with ASK: Quadrature Amplitude Modulation (QAM); used in ADSL and wireless systems

ITS323/CSS331 Example Technologies using Shift Keying Signal Encoding ◮ ASK: Optical fibre, RFID Introduction ◮ FSK: HF/shortwave radio, UHF/VHF radio comms, Digital Data, Digital Signals RFID Digital Data, ◮ PSK and QAM: mobile phones, Wi-Fi, cable modems, Analog Signals Analog Data, xDSL, DVB, . . . Digital Signals Analog Data, Analog Signals