Welcome Nasir
I am glad that my suggestion helped you.You are working on 20mbps ?Eye diagram you got is seems fine with acceptable range of BER.You can reduce sample per bit to low value for fast calculations.Fo QPSK and OFDM follow the instruction given by Alisthu because i dont have access to latast version.As soon as i get the latest version i will try to help you out.Best of luck