Phase and Frequency Correction

Objective

Use the Costas Loop Module to correct the phase and frequency offset of the received signal.

System architecture file: Qpsk_stage5.grc

Steps and Instructions

1. Continuing from the previous unit, add a Costas Loop after the Linear Equalizer to process the received signal.
2. Observe the constellation diagram characteristics of the signal after processing through the Costas Loop.

System Simulation

GNU Radio QPSK Tutorial

GNU Radio QPSK Tutorial

Additional Notes

Costas Loop

• The Costas Loop module is suitable for synchronous BPSK, QPSK and 8PSK signals.
• Using a second-order loop, it can simultaneously track the phase and frequency (derivative of phase) changes over time.
• The use scenario assumes that the frequency is close to the ideal range. If the frequency deviation is too large, the loop will not converge, resulting in continuous phase rotation.

Exercise 6

Simulate different frequency offsets and loop bandwidth settings, and observe the convergence process of the Costas Loop under different conditions.