## 6 Results
### Equalization by Median Filtering  
The third algorithm is adaptive median filtering (AMF), as described in Section 3.3. We also performed offline signal processing on the distorted data of the QPSK and 16 QAM OFDM subcarriers, and the implementation of the proposed MF algorithm was examined with different fiber lengths in the presence of dispersion. It was observed that for QPSK modulation in OFDM subcarriers and a maximum fiber length of 100 km, we obtained an EVM of 16.4% after equalization, while for 16 QAM modulation in OFDM subcarriers and a maximum fiber length of 50 km we obtained an EVM of 12.2% after equalization, both of which were below the 3 GPP [44] threshold limit. We obtained an EVM improvement of 2.3% for QPSK and 2.9% for 16 QAM after MF equalization for the same fiber length.  
The constellation diagrams obtained after MF equalization are shown by Figures 15 and 16, for the QPSK and 16 QAM modulation scheme applied in each OFDM subcarrier, respectively.  
Figures 17 and 18 present the different EVM results tested with different fiber lengths both for QPSK and 16 QAM, revealing that the proposed method of MF equalization technique can be applied effectively in order to eliminate dispersion in a converged mm-wave A-RoF system at 60 GHz.  
Figures 19 and 20 present the different EVM results for varying input powers with a fixed fiber length both for QPSK and 16 QAM, along with the 3 GPP threshold for the two cases. Figure 19 shows that for the fixed fiber length of 70 km and QPSK modulation, when the power is very low the EVM values are high; however, as the power increases  
Figure 14: EVM results obtained before and after Constant Modulus Algorithm (CMA) equalization vs the fiber lengths for the QPSK constellation.  
Figure 13: EVM measurements for QPSK modulation using CMA equalization (100 km SMF link). (**a**) Constellation diagram for QPSK before equalization with EVM 18.7%. (**b**) Constellation diagram for QPSK after CMA equalization with EVM 15%.  
from 3 dBm to 13 dBm the EVM values decrease, and after 7 dBm of power the values are below the 3 GPP threshold limit. Thus, in the cases where the power is below 7 dBm or the length of the fiber is increased, there is also in this modulation format a need for equalization in the proposed setup.  
Figure 16: EVM measurements for 16 QAM modulation using MF equalization (50 km SMF link). (**a**) Constellation diagram for 16 QAM before equalization with EVM 15.1%. (**b**) Constellation diagram for 16 QAM after LMS equalization with EVM 12.2%.  
Figure 15: EVM measurements for QPSK modulation using MF equalization (100 km SMF link). (**a**) Constellation diagram for QPSK before equalization with EVM 18.7%. (**b**) Constellation diagram for QPSK after MF equalization with EVM 16.4%.  
Figure 19: EVM results obtained for varying RF input power levels for a fixed fiber length of 70 km using QPSK as a modulation format.  
Figure 17: EVM results obtained before and after median filter equalization vs. the fiber lengths for the QPSK constellation.  
Figure 18: EVM results obtained before and after median filter equalization vs. the fiber lengths for the 16 QAM Constellation.  
Similarly, Figure 20 presents the EVM performance for the fixed fiber length of 50 km, and for 16 QAM. When the power is low the EVM values are high, and as soon as the power increases the EVM decreases. Thus, there is a need for equalization in order for the EVM values to be below the 3 GPP threshold limit for 16 QAM.