Multiple binary signal transmission

The figure below illustrates how frequency multiplexing is used to transmit three binary signals.  A carrier wave (shown at the bottom of the figure) consists of seven pulses containing different frequencies.  The time-frequency portrait (the top of the figure) is a spectrogram which reveals the binary messages: 1001100 (top), 1100111 (middle), and 0101001 (bottom).  In Math 313 we will discuss this example in detail.