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随着无线信道容量的增加和服务面的扩大,愈来愈需要适用于无线模拟音频信道的话音保密通信系统。现用于无线通信系统的模拟频谱倒置,对防止窃听和保证安全是适用的,但由于它的音质下降不可避免,使应用受到了限制。已经证明,用只改变取样数据的符号来完成数字谱的倒置,还避免了失真。数字倒置理论上是由离散的付氏变换推演而来,并已为实验证明。从频谱倒置的观点来讨论孔径效应。用异或门和一个二进制计数器来实现数字频谱倒置。这些电路可以很容易集成在一个大规模集成电路(LSI)蕊片上,以避免元件值的差异。在0.3-3.7kHz的频带内,用8kHz取样速率的数字处理得到的信噪比大于50db,失真小于-50db。
With the increase of wireless channel capacity and the expansion of service area, there is an increasing need for a voice secured communication system suitable for wireless analog audio channels. Analog spectrum inversion, now used in wireless communication systems, is suitable for preventing eavesdropping and ensuring safety, but applications are limited due to its unacceptable reduction in sound quality. It has also been shown that by inverting the sign of the sampled data to complete the inversion of the digital spectrum, distortion is also avoided. Digital inversion is theoretically derived from the discrete Fourier transform and has been experimentally demonstrated. Aperture effects are discussed from the viewpoint of spectral inversion. Digital spectrum inversion is implemented with XOR gates and a binary counter. These circuits can be easily integrated into a large integrated circuit (LSI) chip to avoid component value differences. In the 0.3-3.7kHz band, with 8kHz sampling rate of the digital processing of the signal to noise ratio is greater than 50db, the distortion is less than -50db.