OFDM多载波系统中子载波调制识别新方法

针对OFDM （Orthogonal Frequency Division Multiplexing）信号在非合作通信系统中，具有多种子载波调制类型且有些子载波调制类型难以被调制识别的问题，提出了一种对其子载波分类识别的新方法.此方法结合并改进了星座图聚类投影法和对数似然函数（Logarithmic Likelihood Function，LLF）算法，先对不同子载波调制信号进行星座图聚类投影从而识别出常规子载波调制类型，再进一步通过对数似然函数对常规子载波调制类型和偏移正交（Offset QAM，OQAM）调制类型进行分类识别，并在此基础上推导出子载波组的对数似然函数使其计算结果值更容易被判决门限分类.理论推导和计算机仿真结果表明这种方法能在信噪比高于15 dB的情况下完全识别子载波的调制方式.

OFDM Signal Subcarrier Recognition in OFDM Multi-Carrier System

A new method of classifying and identifying sub-carriers is proposed for Orthogonal Frequency Division Multiplexing (OFDM) signals in non-cooperative communication systems, because there are many sub-carrier modulation types and some sub-carrier modulation types are difficult to be identified in OFDM signals. This method combined and improved the constellation cluster projection method and Logarithmic Likelihood Function (LLF) algorithm. The method first performed constellation clustering projection on different subcarrier modulation signals to recognize the common subcarrier modulation, then calculated the LLF to recognize Offset QAM (OQAM) subcarrier signal and common subcarrier signals. On the basis of the previous step, the LLF of subcarrier group was derived to make the LLF calculation easier to be classified by the decision threshold. Theoretical deduction and computer simulation results showed that the method could recognize the subcarrier modulation when the SNR is 15 dB.