you need to read more about the topic, the world is moving from SISO to MIMO looking for higher data rates. Converting MIMO to SISO is kind of meaninless unless you have a very good reason.
Iam doing project on Performance anlaysis of MIMO Receivers algorithms in BLAST system and SISO frequency selective channel system. my question is that how to convert system model x = Hs +n to SISO frequency selective channel model and thier advantages for that.