A Practical Method for Correcting Phase Errors in a Transceiver System Comprising of OFDM + DUC and DDC I am back with a question related to my OFDM Transceiver System that I am designing where I use DUC and DDC. I could get rid of the high BER problem. I realized that the problem was due to the phase error occuring between the transmitter and the receiver side as I saw the constellation diagram at the receiver rotating constantly. So to get rid of this, I obtained the phase difference between the transmitter and the receiver and I rotated the complex signal with the obtained phase error. However, I feel this is only an ideal method to get rid of the phase error. I read about the phase error compensation techniques but those are mostly when there is a noise in the channel. But in my case, I still haven't added any noise in the channel. I suspect the phase error is either because of the DUC and the DDC, or because of the pulse shaping filters that I used after OFDM modulator. 

So I was wondering if anyone could tell me why is this phase error occuring even without a noisy channel, and what can I do to mitigate the phase error with some estimation.

I have attached the screenshot of my system along with the waveforms obtained. Below are the specs - 

Random Integer Generator Specs

Set Size - 2

Initial Seed - 37

Sample Time - 1/1e6

Samples per frame - 20

OFDM Modulator Specs

FFT length - 32

Number of guard bands - [6;5]

Insert DC Null - Checked

Cyclic Prefix Length - 16

Number of OFDM symbols - 1

Number of transmitted antennas - 1

Raised Cosine Transmit Filter Specs

Rolloff factor - 0.2

Filter span in symbols - 8

Output samplers per symbol - 4

Linear amplitude filter gain - 1

DIgital Up- Converter Specs 

Interpolation factor - [2 8]

Minimum order filter design - Yes

Two-sided bandwitdth - 2.4 e6

Passband ripple - 0.05 dB

Stopband ripple - 90 dB

Center Frequency  - 30e6

Input sample rate - 9.6e6

Digital Down-Converter Specs

Decimation factor - [8 2]

Minimum order filter design - Yes

Two-sided bandwitdth - 2.4 e6

Passband ripple - 0.05 dB

Stopband ripple - 90 dB

Center Frequency  - 30e6

Input sample rate - 153.6e6

Thank you in advance!
I don't think it would be reasonable to expect the phase to be exactly the same. The raised cosine filter for example has a linear phase response. Also don't forget that the auto-correlation for the cyclic prefix detection might find the frame starting at any of the 16 samples of the cyclic prefix, inducing an undetermined phase shift.

Do you have pilot sub-carriers? One simple way is to analyse their phase (which you know a-priori were transmitted with 0 (or some other known) phase) and rotate the sub-carriers in between the pilots (linearly interpolating between the phase of the pilots).