Vol.5 No.1 (February 2015)
Symbol Judgment in Digital AM Broadcasting System Based on Hybrid Modulation
Many advantages can be achieved by using AM-MPPSK hybrid modulation in digital AM broad-casting system. This paper describes the MPPSK scheme principle and basic judgment method in hybrid modulation, on which some improvements are made. Dynamic threshold method is pro-posed to make up for lack of the fixed threshold discrimination, to insure the best demodulation performance. Dynamic threshold method requiring the demodulator to perform channel estimation is more complicated. Thus, an improved MPPSK modulation is introduced, and its principle and symbol decision are described. By this improvement, the impact magnitude appears in any symbol period, which avoids the need for amplitude judge to distinguish zero and non-zero symbols. Theory and experiments have proven that better demodulation performance can be obtained. Partial dual symbol joint discrimination is introduced to solve the platform of bit error ratio at high signal to noise ratio. The simulation results show that the partial dual symbol joint discrimination makes a more reliable judgment by effectively utilizing the previous symbol judge results.
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