Communications Blockset

Transmitting Along a Noisy Channel

After modulation, the data is ready for transmission. The AWGN Channel block, in the Channels library, simulates a noisy channel by adding white Gaussian noise to the data stream. The AWGN Channel block uses a Gaussian distribution whose variance is determined using these mask parameters:

• Es/No, which is - 1 decibel in this example
• Input signal power, which is 1 watt because BPSK modulation produces values of -1 and 1
• Symbol period, which is .5 second

The AWGN Channel block can compute the variance in other ways as well, but this example chooses this mode by setting the Mode parameter to Signal to noise ratio (Es/No).

Like the Bernoulli Random Binary Generator block, the AWGN Channel block requires an Initial seed parameter that initializes the random number generator. If you change the Initial seed parameter, then the block generates a different random sequence. The Initial seed parameters of the AWGN Channel block and the Bernoulli Random Binary Generator block do not need to match.

Note    The input to the AWGN Channel block is a complex Simulink signal, not a real one (See Digression: Exploring Data Types.). This causes the AWGN Channel block to add complex noise, dividing the calculated variance equally between the real and imaginary components.

Modulating the Encoded Messages

Mapping the Received Data