中文摘要：

脉冲位置调制式声表面波（SAW）标签利用较少的反射脉冲实现高效编码，正逐渐取代开关键控编码成为声表面波射频标签的主流编码方式。反射回波之间的时延估计精度成为该方式编码容量和解码的核心。该文提出了一种利用计算回波包络二次相关的高精度估计回波脉冲时延的方法。研究了插值算法对相关峰值估计的影响。通过实际声表面波标签回波信号的实际测试和对照实验，证实了该方法的有效性。

英文摘要：

The pulse position modulation （PPM） is a high efficiency encoding method for surface acoustic wave （SAW） radio frequency identification （RFID）. It uses fewer reflectors than on-off keying （OOK） in condition of the same code capacity. And it is becoming a mainstream encoding method in SAW RFID and is gradually taking place of OOK. For PPM, the accuracy of time delays estimation becomes the key problem of the coding capapcity and demodulation. In this paper, a method by calculating the correlation twice of the envelopes is proposed to estimate the time delays of reflected echoes. The effect of interpolation on the location of the peak of the correlation function is investigated. The feasibility and efficiency of this algorithm have been verified by the comparison test of the appli- cable SAW ID tag.