现以软件无线电的基本知识为基础，分析了单级和多级抽样频率转换，并进行了比较。
On the basis of the soft radio, this paper analyzes the sampling frequency transform for single series and the series, and compares them.
研究了高倍抽取的数字下变频设计，重点分析了基于级联积分梳状滤波器、级联补偿滤波器、级联根升余弦滤波器的多级抽样频率算法。
In this paper, the high decimation ratio of digital down converter is studied and the multi-stage decimation algorithm is especially analyzed based on CIC filter, CFIR filter and RRC filter.
方法通过多级随机抽样抽取济南市4所初中550名初一学生，采用问卷调查。
Methods A total of 550 students in 4 junior schools were sampled with multistage sampling and surveyed.
方法：(1)抽样方法：采用多级随机抽样法。
Methods: (1) sampling method: Apply multilevel and random sampling method.
方法采用多级随机抽样法。
Methods Stratified random group sampling was adopted in survey.
方法采用多级随机抽样法。
Methods Stratified random group sampling was adopted in survey.
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