Teaching materials used as a reference for the communication experiment.

Objective

In this stage, we will explore the impact of the channel on signals and compare the distortion of the signals at the receiving end and the sending end. The main focus will be on the effects of noise, frequency offset, and time offset in the channel model on the signal.

System architecture file: Qpsk_stage2.grc

Objective

In this stage of the experiment, we will use the Polyphase Clock Sync module to implement three functions: clock recovery, inter-symbol interference (ISI) elimination, and downsampling (reducing the number of samples per symbol).

System architecture file: Qpsk_stage3.grc

Objective

Using a differential decoder to eliminate phase ambiguity, decode the signal after the Costas loop and restore the original transmitted data stream.

System architecture file: Qpsk_stage6.grc

Objective

In this experiment, we will investigate the impact of multipath effects on signals and how to use equalizers to eliminate these effects. The main principle used in the equalizer here is the Constant Modulus Algorithm (CMA) in adaptive algorithms.

System architecture file: Qpsk_stage4.grc

Objective

In this experiment, we will observe the effects of up-sampling and filtering through a QPSK constellation diagram, and explore how to use matched filters to eliminate intersymbol interference (ISI).

System architecture file: Qpsk_stage1.grc

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

Introduction to QPSK

Quadrature Phase-Shift Keying (QPSK) is a widely used modulation technique in modern digital communication systems, known for its efficient spectral utilization and interference resistance. QPSK transmits data by changing the phase of the carrier signal, where each symbol represents two bits, corresponding to four possible phase states (0, 90, 180, 270 degrees).

Objective

This step is mainly to generate QPSK signals randomly and observe the effect of different Excess BW parameters on the signal bandwidth.

System architecture file: Qpsk_rrc_rolloff.grc

Processing Baseband Signals

Feed the modulated signal from the previous section to a Virtual Sink, id=ooksignal. Next, we add some modules, as shown in the figure below:

The parameters of the added modules are as follows: