一种基于CDMA2000 1x EVDO微弱信号的捕获算法

A code acquisition algorithm for weak CDMA2000 1x EVDO signal

针对弱信号条件下的CDMA2000 1x EVDO手机上行信号,提出一种基于短时相关快速傅里叶变换(FFT)运算和差分相干相结合的联合捕获算法。首先采用短时相关和FFT运算精确估计出信号的多普勒频偏值;在此基础上利用差分相干提升信号的相关峰。通过设置自适应判决门限和相干长度获得较好的捕获概率;同时对所提算法和相干累积算法的捕获灵敏度和计算复杂度进行了对比。最后,结合实测数据验证了算法有效性,实验表明本文算法在保证低于相干累积算法复杂度的情况下,提高捕获灵敏度约1.5 d B。

Aiming at acquiring accurately the CDMA20001x EVDO(Evolution-Data Optimized) uplink spread code under weak signal conditions, a joint acquisition algorithm based on short time correlation Fast Fourier Transform(FFT) and differential coherent accumulation is proposed. Firstly, the short time correlation and FFT algorithm is adopted to estimate the Doppler frequency offset accurately; the correlation peak is obtained by differential coherent accumulation of demodulated signal based on the frequency offset estimated value. Then by setting the adaptive decision threshold and accumulation length, the higher probabilities of detection are obtained; the acquisition sensitivity and computation complexity of the proposed algorithm are compared with that of the coherent accumulation algorithm. Finally, based on the measured data, simulation is performed and the results show that the acquisition sensitivity of the proposed algorithm is improved by about 1.5 dB than that of the coherent accumulation algorithm, and the computation complexity is lowered.