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The work is devoted to digital communication systems. The formation of signals manipulated by minimum shift keying (MSK) is considered. Signals with frequency manipulation and continuous phase are widely used in modern data transmission systems. Especially popular are the MSK signals, which has not only a continuous phase, but also a small modulation index of 0.5, which makes it possible to use them in radio data channels with filters of lumped selection, the bandwidth of which can be close to the clock frequency of the digital signal. Signals of this type are used in modern satellite navigation systems Compass, Galileo, GPS and GLONAS. The advantage of these signals is a slight parasitic amplitude modulation, even when the bandwidth of said narrowband filters is 5–10 % smaller than the clock frequency of the digital stream. The peculiarity of MSK signals is that for a single clock cycle the phase is linearly (without discontinuity) changed by anamount exactly equal to 90 , which ensures its spectral efficiency. The system of encoding and decoding of a digital message has been defined, which makes it possible to greatly simplify the output stages of a demodulator of a quadrature signal with a shift. The demodulation of a signal manipulated by a minimum shift has been simulated. The study of the effect on the demodulator of "white" noise showed that for the error probability per message element equal to 10-4 , the difference between the theoretical analysis and the simulation results is approximately 1.3 dB relative to the signal-to-noise ratio, which is explained by the effect of noise on the devices carrier recovery and clock synchronization. |
