Communications Blockset

Rayleigh Fading Channel Demo

The Rayleigh Fading model, rayleighfading, illustrates the effect of multipath Rayleigh fading on a signal modulated by quadrature phase shift keying (QPSK). The following aspects of the demo are described:

• Structure of the Demo
• Visible Results

Structure of the Demo

This demo uses various Communications and DSP Blockset blocks to model multi-path Rayleigh fading. The demo includes the following blocks:

• Random Integer block, which provides source of uniformly distributed random integers in the range [0, M-1], where M is the M-ary number
• QPSK Modulator Baseband
• Multipath Rayleigh Fading Channel
• FIR Interpolation block, which implements raised cosine filtering
• Discrete-Time Scatter Plot Scope

Visible Results

The scatter plot illustrates the effect of fading on the signal constellation. The channel is presently set to contain two paths. However, you can change this by varying the number of elements and their values in the delay and gain vectors. In addition, the Maximum Doppler shift (Hz) parameter in the Multipath Rayleigh Fading Channel block changes the fading pattern. The amplitude values for each path are drawn from the Rayleigh distribution while the Doppler values are drawn from the Doppler spectrum from the Jakes channel model.

Filtered QPSK vs. MSK Demo

Gray Coded 8-PSK Demo