Can anyone please help me in simulating a simple BPSK transceiver system that correctly receives a signal through a DUC and DDC? I have attached the screenshot of my Simulink system along with constellation diagrams, spectrums and DUC and DDC filter responses. Below are the specs used in the system:

Binary Generator Specs 

Probability of zero - 0.5 

Initial seed - 61 

Sample Time - 1/10e3 (10 KHz Sampling Frequency) 

Samples per frame - 44

Digital Up-Converter Specs

Interpolation Factor - [1 16 2] (Total Interpolation factor - 32)

Here, 3x1 Matrix elements indicate the interpolation factor of the three individual stages of interpolation. Simulink DUC block uses a FIR interpolation filter, followed by a CIC filter and a CIC compensator.

Minimum order filter design - Yes

Two-sided Bandwidth of the input signal - 2e3 (2 KHz)

Source of stopband frequency - Auto

Passband ripple of cascaded response - 0.1 dB

Stopband attenuation of cascaded response - 80 dB

Type of oscillator - Sine wave

Center Frequency of output signal - 100e3 (100 KHz)

Input sample rate - 10e3 (10 KHz).

Digital Down Converter Specs

Decimation factor - [2 16 1] (Total decimation factor - 32)

Minimum order filter design - Yes

Two sided Bandwidth of the input signal - 2e3 (2KHz)

Soure of stopband frequency - Auto

Type of Oscillator - Sine wave

Center Frequency - 100e3 (100 KHz)

Input Sample Rate - 10e3*32=320 KHz

As you can see, I do not get correct BER, which means my signal is getting aliased as I receive through the DDC. As seen from the spectrums, I receive correct frequency translation and correct output sampling rates, which means the signal is getting correctly up-converted.

Please help me in debugging where the problem lies. I presume the problem is with the filtered response. The simulink block allows to modify the filter orders of the FIR interpolator, CIC interpolator and CIC compensator. If anyone could help me in correctly design the system, I would be beholden to you. Thank you