QPSK System Design and Simulation: Laboratory Manual Hours: 4 SCIE, UESTC

Outline Objectives Theories Experiments Carrier synchronization Symbol synchronization Experiments

Objectives Generating QPSK modulated signals, including generation of information source, matched filter design and modulation operations; Retrieving signals transmitted over wireless propagation channels, i.e., modulated signals at receiver. Note that the transmitter and receiver are mutual independent. Further, frequency offset may occur in received signals, therefore, carrier and symbol synchronization are required.

Objectives (Con’t) Understanding the theories on optimal receiver structure, correlated detection and matched filtering; Designing an optimal receiver for QPSK modulated signals.

Theories QPSK Receiver Diagram

Carrier Synchronization Theories Carrier Synchronization Enormous algorithms for carrier synchronization, PLL, narrowband filtering, etc. We utilize a digital signal processing method to directly estimate the frequency offset used latter to compensate the carrier frequency offset. Assuming in this experiment, the frequency offset between transmitter and receiver is within 50k Hz, or less than 1/1000 of the symbol rate.

Symbol Synchronization Theories Symbol Synchronization

Symbol Synchronization (Con’t) Theories Symbol Synchronization (Con’t) Different symbol synchronization techniques only differ in the timing recovery algorithms and the loop filter design. The function of loop filter, so termed as smoothing filter, is to eliminate noise. Various methods, such as, Godner algorithm, maximal output power algorithm, etc. The maximal output power algorithm, which is a refinement of gradient descent, is utilized in this experiment.

Experiments Write matlab program to Simulate QPSK signal modulation, and generate QPSK modulated signals Demodulate QPSK signals Directly demodulate QPSK signals without carrier or symbol synchronization, and observe the output signal constellation. Add carrier synchronization and symbol synchronization at the receiver, and observe the corresponding output signal constellation. Select different algorithms for carrier synchronization and symbol synchronization, and observe the constellation Analysis and reports

Experiments (Con’t) You are expected to complete individually and independently. Your work must be original and the lab report shall be written independently. The reports should include theory, simulation results and its corresponding analysis. MATLAB codes will be attached in the appendix.

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