Performance of BER vs SNR with increased NB of antennas

I have done the MIMO simulations to see the performances of BER vs SNR with increased NB of antennas with different receivers(matched filter, decorrelator, MIMO and MIMO-SIC), I have submitted the plots below, whether anyone can check whether they look like normal or not. If not, what I should still improve. The below figures are done in high SNR regime, I have also done the low SNR regime part, but here it seems unnecessary to summit them.

First figure, with receiver MMSE, from below to top, 2by2, 3by3,......, 8by8
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Second figure, with receiver Decorrelator,
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Third figure, with receiver Matched filter,
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Last figure, with receiver MMSE-SIC,
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It looks like the BER are a little bit high, anyone has any idea to improve the BER performance.
Thanks.

I like to know Simulation parameters of MMSE -SIC receivers.

What type of channel and modulation technique used?

I use Rayleigh fading channel,
for modulation, for 2by2 I use 4QAM, 3by3 I use 8QAM,
......, 8by8 I use 2^8QAM.