一个OFDM符号128个有效符号，插入128个虚拟子载波

符号率（即有效数据率）fsymbol，而发送速率（需要包括虚拟子载波）2fsymbol

输入的数据需要2倍的发送数据率，以便进行内插，实现位定时跟踪，即4倍fsymbol采样率的调制信号

OFDM symbol Nfft=128 points

一个OFDM符号数据点 Nfft*2 = 256 ， Guard Interval点 ＝Ng*2=64

-　a OFDM symbol 128 effective symbols, insert 128 virtual sub-carrier

　symbol rate (i.e. valid data rate), and fsymbol sending rate (need to include virtual sub-carrier) 2fsymbol

　input data need 2 times the sending data rate for interpolation, realize a timing tracking, namely fsymbol sampling rates four times the modulation signal

　OFDM symbol Nfft = 128 points

　a OFDM symbol of data points Nfft* 2 = 256, Guard Interval point = Ng* 2 = 64