Jake Robinson ET3220 Unit 4 Assignment 1: Unit Review Questions
6.2
The function of a modem is modulation and demodulation. A modem takes a signal and modulates it so that the data can be sent via an audio link such as a phone. Then at the other end of the line another modem demodulates the signal back into the original data that was to be sent.
6.3
Three major advantages of digital transmission over analog transmission are: 1. Digital transmissions cannot get corrupted by noise. 2. Digital signals typically use less bandwidth. 3. Digital transmissions can be encrypted so that only the intended recipient can decode it.
6.4
In ASK or amplitude-shift keying the two binary values are represented by two different amplitudes of the carrier frequency. The limitations of ASK are that it is linear and sensitive to atmospheric noise, distortion, propagation condition on different routes in PSTN. It requires extensive bandwidth and is therefore a waste of power.
6.7
QAM is a popular analog signaling technique that is known as quadrature amplitude modulation. This modulation technique is a combination of ASK and PSK. QAM can also be considered a logical extension of QPSK. QAM takes advantage of the fact that it is possible to send two different signals simultaneously on the same carrier frequency, by using two copies of the carrier frequency, one shifted by 90 degrees with respect to the other.
6.8
The sampling theorem tells us that the sampling rate must be two times that of the analog frequency.