由MATLAB程序产生2Gbi/s的基带OFDM信号先将2^15-1个伪随机序列映射到256个进行4QAM编码调制的子载波上，编码后的OFDM符号再经过IFFT变换将其转换为时域波形，接着添加6.4ns的循环前缀（CP），产生的数据波形再装载到Tektronix任意波形发生器（AWG）中，产生2Gbit/s的基带OFDM信号。基带OFDM信号频谱示意图如图3所示。其中包括256个OFDM子载波256个子载波中200个子信道用来传送数据信号，27个高频和28个低频子信道为了过采样的需要置0，OFD

In OFDM transmission, all the available subcarriers from the DFT is not used for data transmission. Typically some subcarriers at the edge are left unused to ensure spectrum roll off. For the example scenario, out of the available bandwidth from -10M

本文介绍了OFDM技术及其功率谱的，并通过仿真研究了OFDM的功率谱密度特点。在同样条件下，增大子载波数目，会使信号带宽增加，带外衰减加快，功率谱密度图形更加接近于矩形。另外，添加循环前缀将使离散峰值谱线的值略微增大。-This article describes the OFDM technology and its power spectrum, and to study the characteristics of the power spectral density of the OFD

Spectrum efficiency and channel robustness are the main key features of orthogonal division multiplexing which one is used in broadband communication. OFDM belongs to multicarrier modulation which carries the data information over many subcarriers. O