Modulation & Multiplexing - week 7

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  • Modulation
    • Pulse position modulation (PPM)
      • Larger amplitudes create wider gaps from reference pulse
        • High bandwidth to transmit and store which creates more errors
    • Pulse width modulation (PWM)
      • Larger amplitudes create wider pulses
        • High bandwidth to transmit and store which creates more errors
    • Pulse number modulation (PNM)
      • Larger amplitudes creates more pulses
      • Pulse code modulation (PCM)
        • Samples audio, quantizes these and codes it as a binary number in pulses
        • Encoder and decoder clock needs to be exactly synchronized
          • Can be fixed by ...
            • Encoding a separate clock signal
            • Adding a signal to reset clocks regularly
            • Using bit stuffing to break up long runs of 1's or 0's
      • Pulse amplitude modulation (PAM)
        • Larger amplitudes create higher pulse amplitudes
        • A method of encoding information for transmission
        • Channel coding
          • Return to zero (RZ)
            • Pulse for 1 and no pulse for 0 (pulse starts at period and ends half way)
          • Non return to zero (NRZ)
            • Pulse for 1 and no pulse for 0 (pulse starts and ends at period start and end)
            • Does not independently facilitate clock synchronization
          • Non return to zero inverted (NRZI)
            • Pulse changes state for 1 (pulse starts and ends half way through period)
            • Immune to polarity reversal
              • Binary frequency modulation (digital FM)
                • Pulse changes state twice for 1 and once for 0 (pulse starts at period and ends half way for 1 and at end of period for 0)
                • Fully self clock
                  • Phase modulation (PE) / Manchester coding
                    • Pulse for 1 (low-high), pulse for 0 (high-low)
            • Partially self clock
              • Return to zero (RZ)
                • Pulse for 1 and no pulse for 0 (pulse starts at period and ends half way)
          • Binary frequency modulation (digital FM)
            • Pulse changes state twice for 1 and once for 0 (pulse starts at period and ends half way for 1 and at end of period for 0)
            • Fully self clock
              • Phase modulation (PE) / Manchester coding
                • Pulse for 1 (low-high), pulse for 0 (high-low)
      • De-multiplexer
        • Used in DAC to separate a single line into separate channels

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