Dear Chai,
you are missing some modulation parameters for the third cell, please change to the following:
scStr.modulation.mcs = [15, 15, 15];
scStr.modulation.nStreams = [1, 1, 1];
scStr.modulation.precodingMatrix{1} = 1;
scStr.modulation.precodingMatrix{2} = 1;
scStr.modulation.precodingMatrix{3} = 1;Let me know if you encounter further problems.
best
Stefan