The optimization of QAM signals demodulator
Keywords:quadrature amplitude modulation, demodulation, clock synchronization, coherent accumulation data
AbstractIntroduction. The processes of signal processing in the quadrature demodulator and the problem of clock synchronization and reference oscillations of quadrature basis providing are considered for a relatively high speed modulation conditions.
Main part. The analysis is performed and the basic concepts of the implementation of PLL clock oscillation for optimum decoding of phase of signal elements in the QAM signal are formulated. The approach to unify features a reliable determination of character with no synchronization reference quadrature basis is proposed. The rationale for coherent accumulation of current signal elements for statistical support of clock synchronization process is done. Time values of the signal elements of QAM signal are considered, some rules for operation with circular data buffers while it’s coherent accumulate are formulated. The results of the implementation of coherent clock synchronization in demodulation QAM signals on the example of recommendation ITU-T V.29 is presented.
Conclusions. It is shown that the described algorithm of coherent clock synchronization implementation and concepts that formed the basis of its providing reliable clock synchronization during demodulation of QAM signals with high modulation speed.
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Recommendation V.29: 9600 bits per second modem standardized for use on point-to-point 4-wire leased telephone-type circuits [Електронний ресурс]. – Режим доступу: http://www.itu.int/rec/T-REC-V.29/. – Назва з екрану.
Data communication over the telephone network. Available at: http://www.itu.int/rec/T-REC-V/en
Phase-shift keying. Available at: http://en.wikipedia.org/wiki/QPSK#Quadrature_phase-shift_keying_.28QPSK.29.
Digital Video Broadcasting. Available at: http://en.wikipedia.org/wiki/Digital_Video_Broadcasting.
Recommendation V.29: 9600 bits per second modem standardized for use on point-to-point 4-wire leased telephone-type circuits. Available at : http://www.itu.int/rec/T-REC-V.29/
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