A novel modulation technique to transmit bandlimited and intersymbol interference (ISI)-free multilevel digital signals is proposed for the use in digital radio-microwave, mobile and satellite radio systems. Emphasis is on the design of a 9.6 kb/s 4-level digital FM modem for satellite communications, especially for VSAT application. Experimental measured-eye diagrams and the power spectrum of this modem are reported. Optimization between the required signal power and bandwidth of the transmission channels could be done by selecting the number of signal levels and modulation index of the modem. A preliminary study shows that the modem technique may give better performance than coherent PSK systems, especially for low-speed data transmission where phase noise and lock-up speed of carrier recovery loop limit the system performance.
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机译：提出了一种用于传输带状和智能干扰（ISI） - 免费多级数字信号的新型调制技术，用于数字无线电微波，移动和卫星无线电系统。重点是为卫星通信的9.6 kB / s 4级数字FM调制解调器设计，特别是对于VSAT应用。报道了该调制解调器的实验测量视眼图和该调制解调器的功率谱。可以通过选择调制解调器的信号电平和调制索引来完成所需信号功率和传输信道带宽之间的优化。初步研究表明，调制解调器技术可以提供比相干PSK系统更好的性能，特别是对于载波恢复环路的相位噪声和锁定速度限制了系统性能的低速数据传输。
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