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Hi Rice,
I have a question about the interpolator and decimator used in the OFDM design.
I have read http://warp.rice.edu/forums/viewtopic.php?id=290 and got pretty confused about the role of upsampling and downsampling.
1) What is the sampling rate before interpolator in the transmitter part? I can only see input sample period as 4, how to convert it into actual period in hardware?
2) If the current sample rate is 10MHz and the over-the-air bandwidth is 10MHz, should it be upsampled by a factor of 4?
3) Could you explain the role of the low-pass filter after upsampling and before downsampling?
Thanks a lot.
Tan
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The OFDM PHY is clocked at 40MHz, which corresponds to a sample period of 1 in the Sysgen model. So a sample period of 4 in Simulink corresponds to a 10MHz rate in hardware. Low-pass filters are used to avoid aliasing when changing sample rates.
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Ok, I undertand that. But after the 10MHz signal pass the interpolator, the sample rate becomes 40MHz, right? In that case, the signal actually transmitted over the air is 40MHz. Is that correct?
Also, the OFDM reference design is a baseband OFDM system, right? I have not seen any high frequency carrier after the DAC.
Thanks again.
Tan
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The OFDM transceiver operates at baseband, sending/receiving digital I/Q samples at 40MHz (with 10MHz occupied bandwidth). The radio board translates the baseband I/Q to/from RF.
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Thank you very much. I understand that now.
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