- What happens if zeros are added instead of cyclic prefix in OFDM system?
- How does it affect performance of system?
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2 Answers
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The main idea of using Cyclic prefix in OFDM systems is because of 2 reasons,
1) To eliminate ISI from previous symbol.
2) To model linear convolution as circular convolution
If an OFDM symbol is Zero padded instead of cyclic prefix, ISI due to adjacent symbol still gets eliminated, but it cannot be modeled using circular convolution. Circular convolution converts frequency selective multipath channel into flat fading channel. Circular convolution simplifies channel estimation and equalization which can be done easily in Frequency domain.
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$\begingroup$ if you are familiar with Simulink, have a look to this model behindthesciences.com/useful-links/ltesimulinkmodel where you can modify the CP with the zero padding and check the effect that @spectre commented. $\endgroup$ Commented Mar 29, 2016 at 6:20
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CP avoids ISI and converts linear convolution to a circular convolution which simplifies frequency domain equalization.
You can achieve something similar with ZP with some post processing. At the end of the received symbol if the leakage on the zero part is copied and added to the beginning of the symbol it will still be converting linear convolution to a circular convolution. However with this operation, you are also adding some noise as the zero padding part will not be noise free at RX.
Using ZP instead of CP has power advantages, but CP on the other side can be useful for synchronization type of receiver operations, which is not possible with ZP.
Hope this helps
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$\begingroup$ I assume ZP means zero padding? While CP means Cyclic prefix? $\endgroup$– BenCommented Mar 27 at 22:24