基于复合调制的数字AM广播系统中的码元判决方法

Symbol Judgment in Digital AM Broadcasting System Based on Hybrid Modulation

摘要: 调幅波段数字广播系统采用AM-MPPSK复合调制有众多优势。本文在阐述MPPSK调制原理和基本码元判决方法的基础上，针对码元判决提出了改进。动态门限法弥补了固定门限的不足，使系统能获得最佳的解调性能，但解调时要先进行信道估计，算法较复杂，进而引入改进的MPPSK调制，阐述了改进的原理和改进的码元判决方法。改进后的MPPSK调制在任何码元周期内都有幅度冲击，避免了原解调过程中需要进行幅度判决来区分0码元和非0码元的情况，理论和实验都表明改进后可取得更好的解调性能。针对系统误码率性能随信噪比提升总会进入平台期的问题，引入了部分双码元联合判决方法，仿真结果表明可有效利用前一码元的判决结果，对下一码元的判决更加可靠，系统的抗干扰性能更好。

Abstract: 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.