# Indoor Wavelet OFDM VLC-MIMO System: Performance Evaluation
## 3 Simulation Results and Discussion
### Simulation Parameters
SNR is flattened over the 50 MHz bandwidth due to the Pre-SDE performing. For N = 4, SNR is displayed for the four channels with four geometric setups of the LED transmitters. SNR decreases in channels 1, 2, 3, and 4 whenever Pre-FDE is not employed for ImR as well as ImADR (pink and green marks). When Pre-FDE individually is performed (blue marks), SNR of channel 1 is greater than others. Again, this is because channel 1 is the closest one to the detector (at corner). SNR of channels 2 and 4 are almost the same, because both have the same distance from the detector (at corner). When Pre-FDE is performed with Pre-SDE (red marks), SNR is \(\sim\)17 dB as shown in Figure 6(d). SNR is flattened over the 50 MHz bandwidth. Definitely, the SNR comparison should be carried out between the FFT-OFDM system and our suggested one. For the two systems, the SNR is improved when ImADR Pre-SDE is applied after Pre-FDE. For N = 1, the DWT-OFDM applying is almost the same as the FFT-OFDM. The SNR decreases with the increase of frequency when a Pre-FDE is not performed individually or with a Pre-SDE for two techniques. For DWT-OFDM, when N = 2, 3, and 4, the SNR is improved and more identical for all channels than FFT-OFDM. That occurs when both Pre-SDE and Pre-FDE ImADR are performed together. This near similarity can drive the overall channel to more BER improvement. The BER performance of the N-channel imaging wavelet VLC-MIMO is investigated in Figure 8, which shows the BER performance along with the width-direction X and at length Y = 1.5 m for N = 1, 2, 3, and 4, respectively. If the Pre-FDE is not performed, the BER remains above \(10^{-3}\), and it is gradually reduced if Pre-FDE is used. The BER is substantially decreased when Pre-FDE and Pre-SDE are used in either ImR or ImADR. We notice that, in the ImADR case, the efficiency of BER is preferable to that of ImR. This is because of the ImADR's high optical performance. For N = 1, with performing the Pre-SDE after Pre-FDE, the BER is decreased from \(10^{-2}\) to \(10^{-4}\), which is when the ImADR is used instead of ImR. When N = 2, 3, and 4, as noticed in Figure 7(a)-c, the BER is improved for the overall channel according to SNR improvement. The slight difference between the channels in SNR leads to large BER improvement. This improvement has occurred when the space-frequency pre-equalization domain is used. It is also noticed that the BER is reduced with the increasing numbers of LED modules. This is due to the increasing number of LED modules which leads to high capacity. In the same way, the BER in the system proposed in [22] has been improved by performing the Pre-SDE with Pre-FDE. It remains above \(10^{-3}\) when Pre-FDE is not used. In addition, when the Pre-FDE is utilized, the BER progressively starts to reduce. Similarly, by using the Pre-SDE after Pre-FDE for FFT-OFDM, BER has reached \(2\times 10^{-2}\) for N = 4 while it is reached 4 \(\times\)\(10^{-2}\) for WT-OFDM. By using either ImR or ImADR, the system has to meet improvement. Though, the system is more improved by using ImADR than by using ImR. The BER is reduced to less than \(10^{-5}\) for FFT-OFDM and is reduced to less than \(5\times 10^{-6}\) for DWT-OFDM for ImADR along the X-direction. As noticed, the BER is improved by using DWT-OFDM than FFT-OFDM. Figure 8 shows the BER performance with several numbers of LED modules individually (N = 1, 2, 3, 4). The BER is indicated along X-direction (from 0 to 5 m), with Y-direction = 1.5, and Z-axis is 0.85 m. From Figure 8a, at N = 1, when the pre-FDE and pre-SDE are not performed, (green marks), BER for ImADR is less than that for ImR. When the pre-FDE is performed, (blue marks), BER for ImADR is less than that for ImR. This is due to the high optical gain of ImADR. When the pre-SDE is performed after pre-FDE, (red marks), BER for ImADR is less than the BER for ImR, because of the high optical gain of ImADR. Similarly, for N = 2, 3, and 4, BER is decreased when Pre-SDE is performed after Pre-FDE for ImADR than for ImR.