英语翻译
英语翻译
频谱变换过程如图3所示,其中F表示模拟频率,即信号的实际频率,f表示数字频率,即经采样频率归一化的频率.对中心频率为70MHz、带宽为10MHz的模拟信号(如图3(a)所示)以80MHz频率采样,得到幅频特性如图3(b)所示的信号,该信号由采样前信号以80MHz为周期延拓得到,图中只画出了信号频谱的主周期.图3(c)绘出了数字下变频后的信号,信号频谱左移10MHz.经低通滤波后只保留零频附近的信号,如图3(d)所示.为保证信号经4倍抽取后频谱无混叠,必须设置低通滤波的数字带宽为1/16.4倍抽取后的信号如图3(e)所示,可以看到信号的数字频谱展宽了4倍.注意到在对信号采样时信号的正频域频谱发生反转,因此将抽取后的频谱再反转一次,恢复出OFDM基带频谱,如图3(f)所示.
接收机中的核心处理部分DSP和FPGA接收到速率降为20M Baud的基带信号后,对信号进行同步、信道估计、均衡及解调,从而完成了接收机功能.
数字下变频技术是构建可编程数字无线电结构的接收机的一项关键技术.它使得宽带信号在中频上的带通采样得到实际应用,系统关心的信号的频谱可以精确地从采样信号中分离并下变频至基带.
Spectrum transform the process shown in Figure 3,F said that analogue frequency,the actual frequency signal,digital frequency f said that the sampling frequency of the normalized frequency.The center frequency of 70 MHz,10 MHz bandwidth of the analog signal (Figure 3 (a) below) sampling frequency of 80 MHz,amplitude and frequency characteristics are Figure 3 (b) shows the signal,the signal from the sampling signal prior to 80 MHz be a cycle extension,the map was drawn spectrum of the signal cycle.Figure 3 (c) of the digital downconversion charted after the signal,the left 10 MHz frequency spectrum.The low-pass filter after only reservation near zero-frequency signals in Figure 3 (d) shows.To ensure the signal from four times after Aliasing-Free,Low-pass filter must be installed digital bandwidth of 1 / 16.4 times the signal from Figure 3 (e) shown,we can see that the figures signal a wide spectrum four times.Noting the sampling of the signal,the signal is frequency-domain spectrum in reverse,the spectrum will be taken after a further reversal and restore the OFDM baseband spectrum,in Figure 3 (f) as shown.
Receiver address some of the core DSP and FPGA receive M Baud rate reduced to 20 of the base band signal,the signal synchronization,channel estimation,balanced and demodulation,thus completing the receiver functions.
Digital Downconversion technology is the construction of programmable digital radio receiver structure of a key technology.It allows broadband signals in the IF bandpass sampling of the practical applications,systems concern of the spectrum signal can be accurately sampled signals from the isolated and under to the baseband frequency.