What is the secret of upsampling by 4???

Started by ytac...@ou.edu April 27, 2008

During my readings in DSP for SDR applications using FPGA, I found an interesting note which is the upsampling ratio of 4. I found this in two different locations, one at digitizing the IF signal and one at upsampling before pulse shaping. My question is about the reasons of choosing the ratio of 4 for these two cases. I am elaborating on them in the text below:

1- For IF sampling at the receiver. Some designs choose to oversample the IF signal by 4 which means the fs=4IF. Is the main reeason behind this ratio is to allow for efficient downconverting stage since the DDS will be replaced by simple Mux?

2- At pulse shaping at the transmission stage, many designs choose to upsample by 4 (and some choose even 2 but I feel the majority is 4). Is the reason behind the ratio of 4 is to allow phase and frequency tracking since if we upsample by 2 then we can only track the phase but not the frequency shifts of the signal at the receiver? Is this true?

I raise this question to DSP and FPGA group experts and I am looking forward for their opinions.