# BDCOA: Wavefront Aberration Compensation Using Improved Swarm Intelligence for FSO Communication
###### Abstract  
Free Space Optical (FSO) communication is extensively utilized in the telecommunication industry for both ground and space wireless links, as well as last-mile applications, as a result of its lesser Bit Error Rate (BER), free spectrum, and easy relocation. However, atmospheric turbulence, also known as Wavefront Aberration (WA), is considered a serious issue because it causes higher BER and affects coupling efficiency. In order to address this issue, a Sensor-Less Adaptive Optics (SLAO) system is developed for FSO to enhance performance. In this research, the compensation of WA in SLAO is obtained by proposing the Brownian motion and Directional mutation scheme-based Coati Optimization Algorithm, BDCOA. Here, the BDCOA is developed to search for an optimum control signal value of actuators in Deformable Mirror (DM). The incorporated Brownian motion and directional mutation are used to avoid the local optimum issue and enhance search space efficiency while searching for the control signal. Therefore, the dynamic control signal optimization for DM using BDCOA helps to enhance the coupling efficiency. Thus, the WAs are compensated for and optical signal concentration is enhanced in FSO. The metrics used for analyzing the BDCOA are Root Mean Square (RMS), BER, coupling efficiency, and Strehl Ratio (SR). The existing methods, such as Simulated Annealing (SA) and Stochastic Parallel Gradient Descent (SFGD), Advanced Multi-Feedback SFGD (AMSFGD), and Oppositional-Breeding Artificial Fish Swarm (OBAFS), are used for evaluating the performance of BDCOA. The RMS of BDCOA for iterations 500 is 0.12, which is less than that of the SA-SFGD and OBAFS. B 2024 2  
resistance against electromagnetic interference, higher channel capacity (terahertz bandwidth), and ease of installation in challenging places [3; 4; 5]. FSO is applicable in numerous fields, such as those of airborne, space, inter-satellite, and terrestrial links [6]. The typical wireless communication technology utilizing the Radio Frequency (RF) spectrum is applied for general purposes [7]. However, FSO is appropriate when there is a requirement for license free broadcasting, extensive bandwidth, and noise immunity with enhanced capacity [8; 9; 10]. In FSO, the data are initially converted to a modulated light signal and broadcasted through the air to the receiver, which then discovers the light signal and converts it back into data. If the requirement of data rate is to be several gigabits per second, FSO utilizes lasers or light-emitting diodes to generate the light signals and transmit information at rapid speeds over huge distances [11; 12]. Additionally, FSO is utilized in blockage and last-mile applications, and is effective in the back-haul network of upcoming communication networks [13]. The propagation of a laser signal via an atmosphere channel is affected by atmospheric turbulence [14]. This atmospheric turbulence creates phase distortion, broadening laser signal amplitude scintillation, power, deep fade, and beam wandering in the receiver. The closed loop Adaptive Optics (AO) is utilized to minimize the impact of atmospheric turbulence by altering the Wavefront Aberrations (WAs) [15; 16; 17]. Accordingly, the control of wavefront correctors in the AO is handled by using the control algorithm by employing an optimization algorithm [18]. Moreover, the AO is helpful in overcoming the impact of random optical disturbance [19; 20; 21]. This section discusses the existing studies related to optical communication along with their advantages and limitations. [PERSON] et al. [22] presented the uplink and downlink communication system based on AO correction in the transmitter and Maximum Ratio Combining (MRC) diversity approach in the receiver. The AO correction in transmitter and MRC in receiver were used to enhance the BER performance in downlink communication rather than the uplink communication. The receiver diversity with MRC was effective in AO correction.