Frequency Modulation
Chapter 9
MODULATION AND
DEMODULATION
D
ata modulators, especially those intended to produce constantenvelope output signals, are “high-leverage” components in that even very small deviations from ideal in their behavior can lead to large degradations in overall system performance. Therefore, successful simulation of wireless communication systems depends upon the use of modulator models that capture all of the significant deviations from ideal behavior.
In the “usual” development of data modulation techniques as presented in most communications texts, the various techniques are presented in order of complexity, starting with the simplest. Thus BPSK would be presented first, then QPSK followed by m-PSK, and so on. Because of its relationship to complex-envelope representations of signals, quadrature modulation plays a central role in simulation of wireless communication systems and models for quadrature modulators, and demodulators serve as building blocks for most other types of data modulators and demodulators.
Therefore, this chapter begins with a discussion of quadrature phase shift keying
(QPSK) and uses this discussion as a vehicle for development of generic models for quadrature modulation and demodulation. The discussion then moves to binary phase shift keying (BPSK) and shows how this simpler format is modeled using the generic quadrature modulation models. A similar approach is then taken for developing models for multiple phase shift keying (m-PSK), minimum shift keying
(MSK), and frequency shift keying (FSK).
9.1
Simulation Issues
The tasks of carrier recovery and symbol-clock regeneration, which are usually considered part of the demodulation process, are an essential part of any data communication system. There are a number of different techniques for accomplishing these
262
Section 9.1
Simulation Issues
263
tasks, and these techniques can be used across a wide range of modulation formats and demodulation
MODULATION AND
DEMODULATION
D
ata modulators, especially those intended to produce constantenvelope output signals, are “high-leverage” components in that even very small deviations from ideal in their behavior can lead to large degradations in overall system performance. Therefore, successful simulation of wireless communication systems depends upon the use of modulator models that capture all of the significant deviations from ideal behavior.
In the “usual” development of data modulation techniques as presented in most communications texts, the various techniques are presented in order of complexity, starting with the simplest. Thus BPSK would be presented first, then QPSK followed by m-PSK, and so on. Because of its relationship to complex-envelope representations of signals, quadrature modulation plays a central role in simulation of wireless communication systems and models for quadrature modulators, and demodulators serve as building blocks for most other types of data modulators and demodulators.
Therefore, this chapter begins with a discussion of quadrature phase shift keying
(QPSK) and uses this discussion as a vehicle for development of generic models for quadrature modulation and demodulation. The discussion then moves to binary phase shift keying (BPSK) and shows how this simpler format is modeled using the generic quadrature modulation models. A similar approach is then taken for developing models for multiple phase shift keying (m-PSK), minimum shift keying
(MSK), and frequency shift keying (FSK).
9.1
Simulation Issues
The tasks of carrier recovery and symbol-clock regeneration, which are usually considered part of the demodulation process, are an essential part of any data communication system. There are a number of different techniques for accomplishing these
262
Section 9.1
Simulation Issues
263
tasks, and these techniques can be used across a wide range of modulation formats and demodulation