Ddc ( digital down - conversion ) high - efficiency structure is studied to realize the variable carrier frequency band - pass signal acquisition on wideband condition 参考软件无线电设计的概念和国内外相关文献，提出了多项滤波下变频结构的fpga实现。
Therefore , a method in design and fpga implementation of wideband digital if receivers based on polyphase filters to fulfill decimation and filtering is proposed 本文正是基于这种目的，研究并设计了基于软件无线电技术的中频数字接收机的数字下变频。
Frequency estimation technology and bandpass filtering , which are named as wideband digital downconversion technology , are the key technologies to realize data rate conversion system 测频技术以及带通滤波,即宽带数字下变频技术,是实现数据率转换系统的关键技术。
Digital down / up converter ( ddc / duc ) , modulation and demodulation are discussed in the dissertation as some essencial parts of sdr platform 本文以软件无线电的理论为基础，研究了软件无线电中的部分关键技术：包括数字上下变频的实际处理模型以及调制解调部分的实现。
This paper presents a method of realization of numeric transducer using tms320c542 dsp . the program of numeric down - transducer and multi - rate sampling is given 摘要在tms320c542数字信号处理器上，用查表方法实现了dsp数字变频器，并给出相关的数字下变频和多抽样率信号处理程序。
Conventional ddc down - converts digitally by digital mixing , filtering , and decimating ; on condition of high - speed a / d converters , the commercial ddc is no longer applicable 传统的ddc通过数字混频、滤波、抽取实现数字下变频，在高速a d和电子侦察环境条件下商用ddc不能使用。
Unlike the monostatic sar , two independent local oscillators are used for up / down conversion in bistatic case , so low frequency components of phase noise cannot be cancelled 双基地sar用两个独立的本振分别实现上变频和下变频,相噪低频分量不能相互抵消,形成与单基地sar不同的低频相噪。
As a result , some key technologies of sdr such as modulation , demodulation , ddc and dug have been hot topics . in this paper , some key technologies of sdr are researched deeply 于是，软件无线电中的一些关键技术，例如：调制解调技术，数字上变频，数字下变频等成为该领域的研究热点。
At last , this thesis realizes digital down converter based on fpga , and the whole designing process includes algorithm simulation , vhdl description , fpga simulation and real system test 最后,基于fpga对数字下变频进行了设计及实现,具体包括:算法仿真、 vhdl描述、 fpga仿真和实际系统测试。
Downconvertion and error control system based on concatenated code are the critical part of the leo spread spectrum communication system , and are widely used in the communication system 下变频和基于级联码的差错控制系统是该特种小卫星扩频通信系统的关键部分，并且在通信系统中有着广泛地应用。
