USRP N210在OAI平台上应用需要考虑的问题

USRP N210在OAI平台上应用需要考虑的问题

先看看N210的Spec吧，

• Two 100 MS/s 14-bit analog to digital converters
• Two 400 MS/s 16-bit digital to analog converters
• Digital down-converters with programmable decimation rates
• Digital up-converters with programmable interpolation rates

而我们知道，LTE的采样频率一般为7.68,15.36,30.72 Ms/s在不同的带宽下。

因此，需要在发送端通过FFT变换，把采样点转换成适用于N210的采样点。

举个例子，在5MHz带宽的信道下，每帧有7680个采样点，为了适用N210，可以通过7680FFT+5000FFT的混合基进行变换。

下面是OAI maillist里的一段话。

          For example, in a 5 MHz channel we generate 7680 samples per subframe.  On the N210, this could be compressed to 5000 using a 7680-point FFT followed by a 5000 point IFFT with input compression (zero-removal).  Today we don't have these mixed-radix FFTs, but it can be done, say with FFTW (initially) or later by adding them to the fixed-point tools in OAI.  For the other sampling multiply the DFT sizes by 2 and 4.