摘要:用传统方法产生正交频分复用(OFDM)信号的主要问题是难以保证同相和正交模拟通道之间精确的幅度和相位匹配。文中首先对OFDM信号的同相和正交基带分量的数字产生进行了分析,在此基础上给出两种产生OFDM信号的新方法,这两种方法克服了传统方法的缺点,而且易于实现。
关键词:OFDM ; 上变频 ; DDS ; 插值滤波
分类号:TN911.3
Study on the Generation of OFDM Signals
( School of Electronic Science and Engineering , NUDT, Changsha 410073 )
Abstract: The main drawback of classical analogue generation of OFDM signals is the difficulty in ensuring accurate amplitude and phase matching between the in-phase (I) and the quadrature (Q) channels. In the paper, the digital generation of the I and Q baseband components is analysed, and then two new approaches to the generation of OFDM signals are introduced which overcome the drawback of the classical method and can be more easily implemented.
Key words: OFDM ; upconversion ; DDS ; interpolation filtering
引言
OFDM技术是利用多个相互正交的载波对信号进行并行传输的复用技术,OFDM传输系统具有频带利用率高、抗频率选择性衰落等突出优点;目前,OFDM技术被欧洲广播联盟用于陆地数字广播,此外,它在码分多址(CDMA)系统、非对称数字用户环路(ADSL)等无线及有线通信系统中正得到越来越多的应用。 用传统方法产生OFDM信号时,很难保证同相与正交通道之间精确的幅度和相位匹配,因而所产生信号的质量难以得到提高;文中给出两种产生OFDM信号的新方法,这两种方法各有所长,并且都避免了因在两个通道上分别进行低通滤波和模拟上变频而引起的幅度和相位偏差。
OFDM信号数字基带的产生原理及传统产生方法
OFDM信号是正交多载波调制信号,当各载波对应的子信号为线性调制信号时,它可表示为:
参考文献:
J.-F.Hélard and D.Castelain.Digital I and Q Generation for OFDM. ELECTRONICS LETTERS, 25th November 1999:2081~2082
Shinsuke Hara, Ramjee Prasead. Overview of Multicarrier CDMA. IEEE Communications Magazine, December 1997:126~133
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