Carrier Phase Recovery. EE3723 : Digital Communications. Synchronization. Carrier Phase Recovery. Carrier Phase Synchronization Techniques.

Size: px

Start display at page:

Download "Carrier Phase Recovery. EE3723 : Digital Communications. Synchronization. Carrier Phase Recovery. Carrier Phase Synchronization Techniques."

Alaina Fields
5 years ago
Views:

1 EE3723 : Digital Communications Carrier Phase Recovery Week 10: Synchronization (Frequency, Phase, Symbol and Frame Synchronization) Carrier and Phase Recovery Phase-Locked Loop 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications EE May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 2 Carrier Phase Recovery Carrier Phase Synchronization Techniques Reference methods out of band pilot tone transparent tone-in-band (TTIB) Extraction methods feed-forward (with or without timing synchronization) data aided and non-data aided Phase-Locked Loop feed-back (with or without timing synchronization) data aided and non-data aided 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 3 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 4

2 Pilot Tone: Transmitter Pilot Tone: Detector 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 5 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 6 TTIB: Transmitter TTIB: Detector 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 7 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 8

3 Extraction Methods Extraction Method: Feed-Forward Phase Estimator 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 9 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 10 Extraction Method: Feedback Phase Estimator Decision-Directed Feedback Estimator 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 12

4 Extraction Method: Removing Modulation Carrier Recovery Carrier Recovery is the process of extracting a phase-coherent reference carrier form the received signal.this is sometimes called phase referencing In phase modulation techniques, the binary data is encoded as a precise phase of the transmitted carrier (referred to as absolute phase encoding) Depending upon the encoding method,the angular separation between adjacent phasors may vary between 30 and 180. To correctly demodulate the data, a phase-coherent carrier is recovered and compared with the receiver carrier in a product detector 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 13 Carrier Recovery To determine the absolute phase of the received carrier, it is necessary to produce a carrier at the receiver that is phase coherent with the transmit reference oscillator. This is the main function of a carrier recovery circuit. With PSK and QAM, the carrier is suppressed in the balanced modulator and therefore, not transmitted specifically. Consequently, at the receiver, the carrier cannot simply be tracked with a standard Phase Locked Loop (PLL). With suppressed carrier systems, such as PSK and QAM, sophisticated methods of carrier recovery are required, such as Squaring loop, a Costas loop, or a Remodulator _ Invented in 1932 Phase Locked Loop _ Based on feedback control theory _ Has many applications in communications: _ Carrier synchronization: Costas receiver _ Demodulation: e.g., DSB, FM _ Frequency multiplication and division 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 16

Phase Locked Loop Phase Locked Loop Three main components: _ Phase detector (Multiplier) _ Loop filter _ Voltage controlled oscillator (VCO) 20-May-15 Muhammad Ali Jinnah University, Islamabad

carrier recovery for BPSK The received BPSK waveform is filtered and then squared.

5 Phase Locked Loop Phase Locked Loop Three main components: _ Phase detector (Multiplier) _ Loop filter _ Voltage controlled oscillator (VCO) 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 18 Squaring Loop Squaring Loop Squaring loop is a common method of achieving carrier recovery for BPSK The received BPSK waveform is filtered and then squared. Filtering reduces the spectral width of the received noise The squaring circuit removes the modulation and generates the second harmonic of the carrier frequency. This harmonic is phase-tracked by the PLL. BPSK Input Bandpass Filter Squarer PLL VCO out Frequency Divider Recovered Carrier Output frequency from the VCO of the PLL is then divided by 2 and used as the phase reference for the product detectors. Squaring Loop Carrier recovery circuit for a BPSK receiver

6 Costas Loop Received Signal 20-May-15 Muhammad Ali Jinnah University, Islamabad Digital Communications (EE3723) 21

Synchronization. EE442 Lecture 17. All digital receivers must be synchronized to the incoming signal s(t).

Synchronization. EE442 Lecture 17. All digital receivers must be synchronized to the incoming signal s(t). Synchronization EE442 Lecture 17 All digital receivers must be synchronized to the incoming signal s(t). This means we must have a way to perform (1) Bit or symbol synchronization (2) Frame synchronization