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Two ELEC 241 students disagree about a homework problem. The issue concerns the discrete-time signal , where the signal has no special characteristics and the modulation frequency is known. Sammy says that he can recover from its amplitude-modulated version by the same approach used in analog communications. Samanthasays that approach won't work.
One way for someone to keep people from receiving an AM transmission is to transmit noise at the same carrierfrequency. Thus, if the carrier frequency is so that the transmitted signal is the jammer would transmit . The noise has a constant power density spectrum over the bandwidth of the message . The channel adds white noise of spectral height .
A system for hiding AM transmissions has the transmitter randomly switching between two carrier frequencies and . "Random switching" means that one carrier frequency is used for some period of time, switches tothe other for some other period of time, back to the first, etc. The receiver knows what the carrierfrequencies are but not when carrier frequency switches occur. Consequently, the receiver must be designed toreceive the transmissions regardless of which carrier frequency is used. Assume the message signal hasbandwidth . The channel adds white noise of spectral height .
Stereophonic radio transmits two signals simultaneously that correspond to what comes out of the left and rightspeakers of the receiving radio. While FM stereo is commonplace, AM stereo is not, but is much simpler tounderstand and analyze. An amazing aspect of AM stereo is that both signals are transmitted within the samebandwidth as used to transmit just one. Assume the left and right signals are bandlimited to Hz.
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