Manipulation (digital modulation) - in the theory of discrete message transmission, the process of converting a sequence of code symbols into a sequence of signals (a special case of modulation at discrete levels of the modulating signal).
Content
Types of Manipulation
The following types of manipulations are available:
- Frequency manipulation
- Phase manipulation
- Amplitude manipulation
- Quadrature Amplitude Manipulation
Frequency Shift
Frequency Shift Keying (FSK) is a type of manipulation in which the frequency of the carrier signal changes stepwise depending on the values of the symbols of the information sequence. Frequency manipulation is very noise-resistant, since the interference mainly distorts the amplitude, not the frequency of the signal.
Amplitude Manipulation
Amplitude Manipulation (AMN; Eng. Amplitude shift keying (ASK) - change in the signal at which the amplitude of the carrier oscillation changes abruptly. For digital data transmission, channel coding is used, in accordance with the code of which the signal is manipulated in accordance with the type of coding. manipulations include RZ code, NRZ code , Manchester II , MLT-3 , PAM-5 .
Phase Manipulation
Phase shift keying (PSK) is one of the types of phase modulation in which the phase of the carrier wave changes stepwise depending on the information message.
Binary Phase Shift Keying (BPSK)
Quadrature Phase Shift Keying (QPSK)
Octal Phase Shift Keying (8-PSK)
Quadrature Amplitude Manipulation
Quadrature amplitude manipulation ( QAM) Quadrature amplitude modulation (QAM) is a manipulation in which both the phase and amplitude of the signal change, which allows you to increase the amount of information transmitted by one state (reference) of the signal. In the English language literature this type of manipulation is often called QAM, the designation QASK is rarely used.
Trellised coded modulation
When using block or convolutional coding, the noise immunity of radio communications is increased by expanding the frequency band and complicating the radio equipment without increasing the signal-to-noise ratio (SNR). To maintain noise immunity at the same SNR value, it is possible to reduce the used frequency band and simplify the radio equipment by using trellised coded modulation (TCM), which was first developed in 1982 by Ungerbock . TCM is based on a collaborative coding and manipulation process.
As an example, consider a combined encoder / modulator, the overall structure of which is shown in the figure. Bit b0 allows you to select one of the two constellations that happened during the first separation. Further, the selection is determined depending on bits b1 and b2.
Literature
- Prokis, J. Digital Communications = Digital Communications / D. Klovsky. - M .: Radio and Communications, 2000. - 800 p. - ISBN 5-256-01434-X .
- Sklyar B. Digital Communication. Theoretical Foundations and Practical Applications = Digital communications: Fundamentals and Applications. - 2nd ed. - M .: Williams Publishing House, 2003. - 1104 p. - ISBN 5-8459-0386-6 .
- Feer K. Wireless Digital Communications: Modulation Techniques. - Per. from English // Under. ed. V.I. Zhuravleva. - M .: Radio and communications, 2000 .-- 520 p. - ISBN 5-256-01444-7 .