Comparison of Analog-Modulation Systems
The comparison of analog modulation systems (conventional AM, DSB SC, SSB SC, VSB, FM, and PM) can be based on three practical criteria:
1. Bandwidth efficiency of the system.
2. Power efficiency of the system, as reflected in its performance in the presence of noise.
The output SNR at a given received signal power is used as a criterion for comparing the power efficiencies of various systems.
3. Ease of implementation of the system (transmitter and receiver).
The most bandwidth-efficient analog communication system is the SSB SC system with a transmission bandwidth equal to the signal bandwidth. In bandwidth-critical applications, such as voice transmission over microwave and satellite links and some point-to-point communication systems in congested areas, this system is used widely. When transmission signals have a significant dc component, such as image signals, SSB SC cannot be used because it cannot effectively transmit direct current. A good compromise is the VSB system (with its bandwidth slightly larger than SSB and a capability for transmitting dc values), which is widely used in television broadcasting and some data-communication systems. When bandwidth is the major concern, PM and particularly FM systems are least favorable. Only in terms of their high level of noise immunity, their usage may sometimes be justified.