# MIMO Self-Heterodyne OFDM Using Band Selection Technique
## 4 Simulation Results and Discussion  
To evaluate the performance of the two proposed system models with band selection technique, a set of experiments has been conducted. These experiments examine Bit Error Rate (BER) performance of the proposed systems. Assume that a perfect and imperfect channel estimation (with 10% error over each symbol in each path delay for each channel). Moreover, the antenna channels are assumed to be uncorrelated. The simulation parameters of the experiments are summarized in Table 1, where OFDM with QPSK modulation is used. Figure 5: FSTBC MIMO self-het OFDM transmitter when the data is transmitted in the lower band for 1 st and 2 nd transmitting antennas and in the upper band for 3 rd and 4 th transmitting antennas. Figure 6 shows the BER performance of the FSTBC MIMO self-het OFDM system and STBC MIMO self-het OFDM system without the use of the band section technique, assuming perfect channel estimation. As shown in Figure 6, the BER of \(10^{-3}\) is achieved at SNR equal to 14.7 dB for FSTBC MIMO self-het OFDM system and 17.9 dB for STBC MIMO self-het OFDM system. Thus, the proposed system improves the BER performance by approximately 3 dB. Figure 7 compares the BER performance of STBC MIMO self-het OFDM system with and without using BS proposed technique, assuming perfect channel estimation. The simulation results in Figure 7 shows that, the STBC MIMO self-het OFDM system with BS technique improves the BER performance by 1.9 dB at BER of \(10^{-3}\) when compared to the STBC MIMO self-het OFDM system without the BS technique [12]. The BER performance is improved due to the use of the BS approach in the proposed systems to select the optimum sub band for the transmission of each symbol over the different transmitted antenna. The used of optimum sub band with higher gain for transmission reduces the probability of error and consequently improve the BER performance. Thus, the capacity of the communication system will be increased by using the BS technique. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Simulation Method** & \multicolumn{2}{c}{**Monte Carlo**} \\ \hline Number of subcarriers (K) & \multicolumn{2}{c}{512} \\ \hline \multirow{2}{*}{Number of transmitting antenna (\(\text{A}_{\text{t}}\))} & STBC & FSTBC \\ \cline{2-3}  & 2 & 4 \\ \hline Number of receiving antennas (Ar) & \multicolumn{2}{c}{2} \\ \hline Sampling frequency (\(\text{f}_{\text{s}}\)) & 1 MHZ \\ \hline Sampling time (\(\text{T}_{\text{s}}\)) & 10-6 s \\ \hline Modulation type & QPSK \\ \hline channel type & Rayleigh channel with four taps multipath components \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters [22]. Figure 6: BER of FSTBC MIMO self-het OFDM and STBC MIMO self-het OFDM systems with perfect channel estimation. Figure 8 shows the BER performance of the FSTBC MIMO self-het OFDM system with and without [22] using BS technique, assuming perfect channel estimation. The simulation results in Figure 8 shows that the use of the BS technique with the FSTBC MIMO self-het OFDM system improves the BER performance by 2.1 dB at a BER of \(10^{-3}\). Figure 8: BER of FSTBC MIMO self-het OFDM system with and without [22] using BS technique assuming perfect channel estimation. Figure 7: BER of STBC MIMO self-het OFDM system with and without [12] using BS technique, assuming perfect channel estimation. Figure 9 illustrates the BER performance of the FSTBC MIMO self-het OFDM system with BS technique compared to STBC MIMO self-het OFDM system with BS technique, assuming perfect channel estimation. As shown in Figure 9, the FSTBC MIMO self-het OFDM system with BS technique obtains BER = \(10^{-3}\) at SNR equal to 12.8 dB while the STBC MIMO self-het OFDM system with BS technique introduces the same BER at SNR equal to 16 dB. Therefore, FSTBC MIMO self-het OFDM system with BS technique outperform the STBC MIMO self-het OFDM system with BS technique by 3.2 dB.