Communications Blockset

Running an Equivalent Baseband Simulation

To open a baseband simulation that computes the same error rates as in the passband model of the previous section, type bbmoddoc in the MATLAB Command Window. Then you can run the simulation by choosing Start from the model window's Simulation menu.

Complex Baseband Modulated Signal

Notice that the signal lines from the M-PSK Modulator Baseband block to the AWGN Channel block, and from the AWGN Channel block to the M-PSK Demodulator Baseband block have an annotation that says double (c). The (c) portion indicates that the baseband modulated signal is a complex signal, not a real signal. By contrast, the unmodulated signal is a real signal. The meaning of the complex modulated signal appears in Baseband Modulated Signals Defined.

Differences Between the Passband and Baseband Examples

The differences in construction between this model and the passband model, pbmoddoc, of the previous section are

• This model uses baseband modulation blocks (M-PSK Modulator Baseband, M-PSK Demodulator Baseband) instead of passband modulation blocks.
• The two To Workspace blocks in this model use variable names that differ from those in the passband model, so that the data sets from the two models do not conflict with each other.
• The Error Rate Calculation block in this model uses a Receive delay parameter of 0 instead of 1, because baseband demodulation causes no delay, while passband demodulation causes a one-sample delay.

Performance differences between the two models are discussed in Speed of Baseband Versus Passband Models.

Running a Passband Simulation

Generating Error Curves