# Performance of Adaptive Bit-Interleaved Polar Coded Modulation in FSOC System
## 3 Performance Simulation Results and Discussion of A-Bipcm under Different Turbulence Conditions
(c) Under further different conditions, where the temperature of the upper and lower plates is set to 160 \({}^{\circ}\)C and the corresponding atmospheric coherence length is r\({}_{0}\) = 0.955 considered, a greater fluctuation in the time-domain waveform of the optical signal in the weak turbulence channel and a wider dispersion of its energy is indicated. The optical output power jitter curve is shown in Figure 5.  
Figure 4: Schematic diagram of the transmitter and receiver of the experimental system using adaptive bit-interleaving coding and modulation scheme: (**a**) schematic diagram of the transmitter, (**b**) schematic diagram of the receiver. Figure 3: Principle block diagram of free space wireless laser communication performance verification experimental system based on IM/DD. Figure 6 presents a statistical analysis of the BER under weak turbulence conditions. The comparison chart depicts the BER performance between the conventional polar code encoding and decoding scheme (represented by the dashed line) and the proposed A-BIPCM scheme (represented by the solid line). In Figure 6a, when the atmospheric coherence length \(r_{0}\) = 0.955, T = 160, the optical power of the detector is \(-\)16 dBm. The traditional polar code encoding and decoding performance at BER = 9.13 \(\times\) 10\({}^{-4}\), whereas the A-BIPCM scheme exhibits a significantly higher performance at BER = 7.02 \(\times\) 10\({}^{-5}\). The BER has been improved by representing an order of magnitude. Furthermore, considering the desired BER = 3.8 \(\times\) 10\({}^{-3}\) of the system, the conventional polar coding and decoding scheme requires a received optical power greater than \(-\)16.98 dBm, and the A-BIPCM scheme achieves an improvement of approximately 0.73 dBm in terms of the required received optical power. In Figure 6b, when the atmospheric coherence length \(r_{0}\) = 1.384, T = 120, the optical power of the detector is \(-\)16 dBm. The traditional polar code encoding and decoding performance at BER = 6.36 \(\times\) 10\({}^{-4}\), whereas the A-BIPCM scheme exhibits a significantly higher performance at BER = 6.82 \(\times\) 10\({}^{-5}\). The BER has been improved by representing an order of magnitude. Furthermore, considering the desired BER = 3.8 \(\times\) 10\({}^{-3}\) of the system, the conventional polar coding and decoding scheme requires a received optical power greater than \(-\)17.03 dBm, and the A-BIPCM scheme requires a received optical power greater than \(-\)18.08 dBm. Thus, the A-BIPCM scheme achieves an improvement of approximately 1.05 dBm in terms of the required received optical power. Figure 5: Optical output power jitter curve: (**a**) atmospheric coherence length \(r_{0}\) = 1.839, (**b**) atmospheric coherence length \(r_{0}\) = 1.384, (**c**) atmospheric coherence length \(r_{0}\) = 0.955. In Figure 6c, when the atmospheric coherence length \(r_{0}\) = 1.839, T = 80, the optical power of the detector is \(-\)16 dBm. The traditional polar code encoding and decoding performance at BER = 7.36 \(\times\) 10\({}^{-5}\), whereas the A-BIPCM scheme exhibits a significantly higher performance at BER = 7.13 \(\times\) 10\({}^{-6}\). The BER has been improved by representing an order of magnitude. Furthermore, considering the desired BER = 3.8 \(\times\) 10\({}^{-3}\) of the system, the conventional polar coding and decoding scheme requires a received optical power greater than \(-\)17.69 dBm, and the A-BIPCM scheme achieves an improvement of approximately 0.69 dBm in terms of the required received optical power. In Figure 6d, when the atmospheric coherence length \(r_{0}\) = 3.282, T = 50, the optical power of the detector is \(-\)16 dBm. The traditional polar code encoding and decoding performance at BER = 2.36 \(\times\) 10\({}^{-5}\), whereas the A-BIPCM scheme exhibits a significantly higher performance at BER = 2.11 \(\times\) 10\({}^{-6}\). The BER has been improved by representing an order of magnitude.