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Multiplexing

Explore multiplexing in CSE 3213 - Frequency, Time, and Space Division Multiplexing. Learn about modulation techniques like ASK, FSK, PSK, and more. Discover the performance and efficiency of digital-to-analog encoding schemes.

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Multiplexing

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  1. Multiplexing CSE 3213

  2. Frequency Division Multiplexing

  3. Time Division Multiplexing

  4. Space Division Multiplexing

  5. Digital Data, Analog Signals (5.2) CSE 3213

  6. Digital Data, Analog Signal • main use is public telephone system • has frequency range of 300Hz to 3400Hz • uses modem (modulator-demodulator)

  7. Modulation Techniques

  8. Amplitude Shift Keying • Values represented by different amplitudes of carrier • Usually, one amplitude is zero • i.e. presence and absence of carrier is used • Susceptible to sudden gain changes • Inefficient • Used for voice grade lines (up to 1,200 bps) • Used over optical fiber (e.g., 1 = light pulse; 0 = no light)

  9. Binary Frequency Shift Keying • Most common form is binary FSK (BFSK) • Two binary values represented by two different frequencies (near carrier) • Less susceptible to error than ASK • Used for • Up to 1,200 bps on voice grade lines • High frequency radio (3-30 MHz) • Even higher frequency on LANs using coaxial cable

  10. Multiple FSK • each signalling element represents more than one bit • more than two frequencies used • more bandwidth efficient • more prone to error

  11. FSK on Voice-Grade Line

  12. Phase Shift Keying • Phase of carrier signal is shifted to represent data • Binary PSK • Two phases represent two binary digits • Differential PSK • Phase shifted relative to previous transmission rather than some reference signal • Binary 0: same phase as previous signal burst • Binary 1: opposite phase to previous signal burst

  13. Differential PSK

  14. Quadrature PSK • More efficient: each signal element representing more than one bit • QPSK: each element represents two bits

  15. PSK Combined with ASK • 9600 bps modem use 12 angles, four of which have two amplitudes

  16. Performance of Digital to Analog Modulation Schemes

  17. Performance of Digital to Analog Modulation Schemes Transmission bandwidth: ASK and PSK bandwidth directly related to bit rate FSK bandwidth related to data rate for lower frequencies, but to offset of modulated frequency from carrier at high frequencies Roll-off factor r depends on technique for filtering signal to establish B 17

  18. Bandwidth Efficiency for Digital-to-Analog Encoding Schemes R/BT

  19. Analog Data, Analog Signals (5.4) CSE 3213

  20. Analog Data, Analog Signals • Why modulate analog signals? • Higher frequency can give more efficient transmission • Permits frequency division multiplexing (Chapter 8) • Combining an input signal m(t) and a carrier of frequency fc to produce a signal s(t) whose bandwidth is centered at fc • m(t): modulating signal • s(t): modulated signal • Types of modulation:

  21. Analog Modulation

  22. Transmission Bandwidth of Analog Modulation Schemes • FM and PM require greater bandwidth than AM. • B is the bandwidth of the original signal.

  23. Summary • Signal encoding techniques • digital data, digital signal • NRZ, multilevel binary, biphase • modulation rate, scrambling techniques • analog data, digital signal • PCM, DM • digital data, analog signal • ASK, FSK, BFSK, PSK • analog data, analog signal • AM, FM, PM

  24. Reading • Chapter 5, Stallings’ book

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