Getting Started

Overview of the Model

The model shown in the preceding section, Opening the Model, simulates the effect of phase noise on quadrature amplitude modulation (QAM) of a signal. During a simulation, the model generates a random signal and modulates it using QAM. The model then adds noise to the signal to simulate a channel. The model also displays the symbol error rate and a scatter plot of the modulated signal.

Notice that the model looks like a block diagram. The blocks generate and process data during a simulation. For example, the Random Integer Generator block, labeled "Random Integer," generates a signal consisting of a sequence of random integers between zero and 255. This signal then moves in the direction of the arrows to other blocks in the model. The following sequence of blocks processes the signal:

• The Rectangular QAM Modulator Baseband block, to the right of the Random Integer Generator block, modulates the signal using baseband 256-ary QAM.
• The AWGN Channel block simulates a channel with noise, by adding additive white Gaussian noise (AWGN) to the modulated signal.
• The Phase Noise block adds random noise to the angle of the complex signal.
• The Rectangular QAM Demodulator Baseband block, to the right of the Phase Noise block, demodulates the signal.

In addition, the model uses the following blocks to calculate the errors introduced by noise and displays the results:

• The Discrete-Time Scatter Plot Scope block, labeled "AWGN plus Phase Noise," displays a scatter plot of the signal with added noise.
• The Error Rate Calculation block compares the received signal with the transmitted signal and calculates the number of symbols that differ between the two signals.
• The Display block, at the far right of the model window, displays the symbol error rate (SER), the total number of errors, and the total number of symbols processed during the simulation.

All these blocks are included in the Communications Blockset and Simulink. You can find more detailed information about any standard block by right-clicking the block and selecting Help from the context menu.

Opening the Model

Quadrature Amplitude Modulation