محاضرة 14

• Carrier Recovery


  Module that helps extract or derive the carrier signal's frequency/phase, used in demodulator to retrieve the transmitted baseband information
• Clock Recovery


  Module that helps recover synchronized clock which is needed as sampling clock for ADC and also used as DEMUX clock pulses
• Clock Recovery Types


  • Times-two clock recovery
  • Early late clock recovery
  • Zero crossing clock recovery
  • Synchronizer clock recovery
• Times-two Clock Recovery


  1. Incoming signal is multiplied by two, effectively doubling its frequency

  2. Can be achieved by XORing the signal with its delayed version
• Early Late Clock Recovery

  1. Receiver generates multiple clock signals that are slightly offset in phase

  2. Compares the quality of data sampled at early and late times

  3. Adjusts clock phase to find optimal sampling point
• Zero Crossing Clock Recovery


  1. Detects the zero crossings of the input signal and uses them as reference points to generate the clock

  2. Compares time between zero crossings with expected interval to adjust clock phase
• Synchronizer Clock Recovery


  1. Uses phase-locked loops (PLLs) or delay-locked loops (DLLs) to track phase and frequency of received signal

  2. Adjusts phase and frequency of local clock to match incoming signal
• Edge Detection Logic is used in PAM Clock Recovery Circuit

  
• PAM Clock Recovery Circuit derives clock for demux from the received PAM signal
• Carrier Recovery Types


  • Times-n carrier recovery
  • Decision directed carrier recovery
• Times-n Carrier Recovery


  1. Multiplies incoming signal by local oscillator signal that is n times the frequency of the carrier

  2. Shifts spectrum to baseband or lower IF

  3. Carrier frequency can then be extracted using low-pass filter
• Decision Directed Carrier Recovery

  1. Utilizes decisions made by demodulator to estimate and track carrier phase and frequency

  2. Compares received symbols with expected symbols based on estimated carrier phase and frequency

  3. Iteratively adjusts carrier phase and frequency estimation
• PSK Carrier Recovery Block Diagram is provided
• BPSK Carrier Recovery Description

  1. BPSK signal is band pass filtered

  2. Squared or multiplied by itself to remove 180 degree phase shifts

  3. Resulting 2x frequency signal is band pass filtered and applied to phase detector

  4. X2 frequency multiplier used between VCO and phase detector to ensure VCO frequency matches carrier frequency

  
• منظومة البليط تستخدم في إقامة اتصالات بين المحليين والخارجين والمحليين بين أنحاء العالم
• منظومة البليط تستخدم في إقامة اتصالات بين المحلين والخارجين والمحليين بين أنحاء العالم
• Sampling


  The process of converting a continuous-time signal into a discrete-time signal
• Pulse Amplitude Modulation (PAM)


  • A type of analog modulation where the message signal modulates the amplitude of a series of signal pulses
• Pulse Width Modulation (PWM)


  • A type of modulation where the message signal modulates the width of a series of signal pulses
• Pulse Position Modulation (PPM)


  • A type of modulation where the message signal modulates the position of a series of signal pulses
• Date of lab session

  20/12/2023
• Sampling Model in Simulink


  Set Sine Wave to 1 Hz (2 * π * 1) and Pulse Generators to: 0.01 Sec, 0.1 Sec, 1 Sec
• Scope 3: unsuccessful Sampling as the sampling frequency equals to the signal frequency
• Scope 2: Good Sampling as fs=10 times the signal frequency. (more than Nyquist Rate)
• Scope 1: Better Sampling as fs=100 times the signal Frequency
• PWM & PPM


  1. PWM is produced by comparing Sawtooth Generator with the signal

  2. PPM is produced by using PWM output to a Monostable block (Falling edge detection). Pulse duration 0.015 sec.
• Scope 1 is for PWM
• Scope 2 is for PPM
• محاضره تجريبيه