The software implementation of quasicoherent minimum shift keying demodulator

Аuthors

Martirosov V. E.^*, Alekseev G. A.^**

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: marti@mai.ru
**e-mail: alexeevg@yandex.ru

Abstract

The aim of this work is to investigate the methods of quasi-coherent demodulation of minimum shift keying (MSK) signals and the creation of a software implementation of MSK demodulator.
Minimum shift keying (MSK) due to its spectral and power efficiency has been widely used in systems with limited frequency and energy resources. MSK signal has a constant envelope and this is an important and sometimes crucial aspect for communication systems operating at low power, with thresholds values of signal/ noise ratio (SNR). In such conditions also often require the use of quasi-coherent demodulation algorithms, as they are compared with incoherent demodulation algorithms provide less error probability. The refore the development of efficient implementation of quasi- coherent MSK signal demodulator is an actual task.
The article considered in detail procedure of quasi- coherent MSK signal demodulation including method of symbol synchronization establishing and algorithm of carrier frequency synchronization. Shows the structural schemes, spectral and times diagrams of signals at different points of the demodulation tract. Based on the considered algorithms is carried out to develop a software implementation of quasi-coherent demodulator of MSK signal for rapid satellites communication channel. Testing of the demodulator using the software stand has been performed. In modeling taking into account the actual conditions of reception, when the frequency of the input signal is shifted and in the transmission channel there exists an additive white Gaussian noise (AWGN).
The simulation results indicate that the implementation of the demodulator is successful. The establishment of a high-frequency synchronization and symbol timing is within the required time, the flow of extracted information symbols corresponds to the transmitted message. To determine efficiency of the resulting implementation has been assessed probability of symbol error of demodulator in a specified range of values the signal/noise ratio. According to the research results the energy loss of the developed quasi-coherent demodulator does not exceed 0.5 dB with respect to the potential noise immunity. This demonstrates the high efficiency of the provided software implementation of quasi-coherent MSK demodulator.
The obtained results argue the possibility of using the developed software model as a research prototype or stand for hardware and/or software implementation of the MSK demodulator in the satellites digital telecommunication system.

Keywords:

telecommunication, quasicoherent demodulation, software implementation, MSK signal, synchronization system

References

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