数码率低于10KbPS的双环自适应增量调制系统的研制

本文叙述一种双环自适应增量调制(TLADM)系统。它由一个内环和一个外环组成。内环是线性增量调制(LDM);外环是数字压扩增量调制(DCDM),具有量化阶自适应的功能。这种TLADM是专为移动通信研制的,具有数码率低、电路简单、单一电源、功耗低等特点。对所研制的系统进行了性能测试,在数码率为9.6KbPS时,对于400HZ正弦信号,最大的信号量化噪声比(SNR)_m是18.5dB,SNR>16dB的动态范围>25dB,800HZ正弦信号时的(SNR)_m是17.8dB,SNR>15dB的动态范围>20dB,平均单词可懂度为90％。数码率为8KbPS,400HZ正弦信号时的(SNR)_m为17.7dB,SNR>16dB的动态范围大于22dB,话音可懂。文中进行了理论分析,介绍了测试结果。

Development of Two Loop Adaptive Delta Modulation System at Bit Rates Lower Than 10KBPS

This paper describes a two loop adaptive delta modulation system (TLADM) consisting of an inner loop and outer loop. The inner loop is of linear delta modulation (LDM) and the outer loop is of digital companding delta modulation (DCDM) which functions as an adaptive quantize step size control. The system developed here has many advantages such as low bit rates, simple circuits, single voltage source and low pewer dissipation. At the bit rate of 9.6KBPS for a sinusoidal signal input of 400Hz, the system has a SNR_(max) of 18.5dB, with dynamic range>25dB for SNR>16dB. At the input frequency of 800Hz, the SNR_(max) is 17.5dB, with the SNR<15dB over an input range>22dB. At 9.6 KBPS, a mean intelligibility of words is 90%. In this paper, the noise performance and experimental resulta are also given.