GPS P码捕获中降采样滤波器研究及实现.doc

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GPS P 码捕获中降采样滤波器研究及实现
龚琪1,吴晓非1,邹永忠2,谭敏强1**
(1. 北京邮电大学信息与通信工程学院,北京 100876;
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2. 北京邮电大学计算机学院,北京 100876)
摘要:降采样数字滤波器可广泛应用于通信、声音和图像处理系统中。而当输入信号的带宽
高于需处理的带宽时,对信号进行降采样处理可以大大减少数据量,提高数据率使实时处理
容易实现。同时,为了克服在频域上的混叠,还需要先用低通滤波器过滤非处理带宽的信号
能量,然后再降采样,,本文以 GPS P 码捕获为例,提出利用一种
改进的积分梳状 CIC 滤波器来实现小数倍的降采样,
能有 1dB 以上的提高,而且比 FIR 滤波器方法实现简单,资源消耗少。
关键词:信号与信息处理;CIC 滤波器;降采样;抗混叠;FIR 滤波器
中图分类号:
Down-sampling filter research and implementation in GPS P
code acquisition
Gong Qi1, Wu Xiaofei1, Zou Yongzhong2, Tan Minqiang1
(1. School of Information munication Engineering, Beijing University of Posts and
munications, Beijing 100876;
2. School puter Science, Beijing University of Posts and munications,
Beijing 100876)
Abstract: Down-sampling digital filter can be widely used munications,voice and image
processing the input signal bandwidth is higher than the bandwidth required to
handle ,down-sampling the signal can greatly reduce the amount of data, and real-time processing
can be easily achieved. Meanwhile, in order to e the frequency domain aliasing, the
low-pass filter is used to filter non-processing bandwidth of the signal energy, then
down-sampling is used to avoid aliasing. In view of this situation, GPS P code acquisition use an
improved b CIC filter to achieve a rational down-sample,and having low-pass
effect,than the traditional method of cumulative more than 1dB performance improvement,and
FPGA implementation is simple,less consumption of resources.
Keywords: Signal and Information Processing; CIC filter; down-sampling; anti-aliasing; FIR filter
0 引言
在软件无线电中,数字下变频后的数字滤波器的主要作用是降采样,低通滤波,一般由累
加方法或 FIR ,会引入干扰, FIR 滤波器需要
大量的乘法器,且一般采样速率很高,因为 FIR 滤波器需要工作在很高的频率,使用资源多,功
,由于传统 CIC
降采样,针对这种情况,尝试改进 CIC 实现结构,可以避免产生中间的高频率信号,从而来实现
降采样,并可将乘法器的使用数目降低到零, 这样就大大减少了硬件资源的消耗[1].
1 FIR 滤波器的设计
利用 matlab 工具箱中自带的 FDAtool 可以确定滤波器的系数。首先根据系统要求