*Amplitude shift keying (ASK)—the amplitude of the carrier signal varies.
*Frequency shift keying (FSK)—the frequency of the carrier signal varies.
*Phase shift keying (PSK)—the phase of the carrier signal varies.
*Quadrature amplitude modulation (QAM)—both the phase and amplitude of the carrier signal vary. * QAM enables a higher data transmission rate than other digital-to-analog methods. * Baud rate and bit rate are not synonymous. Bit rate is the number of bits transmit-ted per second. Baud rate is the number of signal units transmitted per second. One signal unit can represent one or more bits. * The minimum required bandwidth for ASK and PSK is the baud rate. * The minimum required bandwidth (BW) for FSK modulation is BW =f c1 .f c0 + N baud , where f c1 is the frequency representing a 1 bit, f c0 is the frequency representing a 0 bit, and N baud is the baud rate. * A regular telephone line uses frequencies between 600 and 3000 Hz for data communication. * ASK modulation is especially susceptible to noise. * Because it uses two carrier frequencies, FSK modulation requires more bandwidth than ASK and PSK. * PSK and QAM modulation have two advantages over ASK:
*They are not as susceptible to noise.
*Each signal change can represent more than one bit. * Trellis coding is a technique that uses redundancy to provide a lower error rate. * The 56K modems are asymmetric; they download at a rate of 56 Kbps and upload at 33.6 Kbps. * Analog-to-analog modulation can be implemented by using the following:
* Amplitude modulation (AM)
* Frequency modulation (FM)
* Phase modulation (PM) * In AM radio, the bandwidth of the modulated signal must be twice the bandwith of the modulating signal. * In FM radio, the bandwith of the modulated signal must be 10 times the bandwidth of the modulating signal.