Question

If bandwidth is of primary concern, which one of the following scheme is generally not considered?
1. PSK
2. ASK
3. DPSK
4. FSK

Answer 1

Correct Answer - Option 4 : FSK

If R_b is the bit rate, then:

For ASK: BWASK = 2Rb

For PSK: BWPSK = 2Rb

For FSK: BW_FSK  = 2 Rb + |f1 - f2|

f1 and f2 are the two lower and upper frequencies.

Observation:

BWASK = BWPSK < BWFSK

Hence compared to ASK and PSK, FSK requires a large bandwidth.

Note: 

The probability of error is maximum in ASK.

Hence PSK is the most widely used.