In recent decades, the rapid growth of wireless communication technologies has led to a significant increase in the deman‎d for the radio frequency (RF) spectrum. This has highlighted the necessity of adopting innovative approaches to reduce dependency on the RF spectrum. Optical wireless communication (OWC) has emerged as a promising complementary technology, offering advantages such as high ban‎dwidth, enhanced security, an‎d immunity to electromagnetic interference. Among its various forms, optical camera communication (OCC) has attracted significant attention due to the widespread availability of cameras an‎d light sources such as light-emitting diodes (LEDs). OCC also offers benefits such as stable signal-to-noise ratio (SNR), spatial separation of light sources using pixel arrays, an‎d the potential for parallel data transmission. However, there are important technical limitations, including low data rates (typically a few tens of kilobits per second) caused by camera frame rate restrictions, an‎d the requirement for a direct line-of-sight between transmitter an‎d receiver. One relatively underexplored challenge is the blooming phenomenon. The blooming phenomenon occurs when the camera pixels receive too much light an‎d the output image becomes white. Blooming occurs for two reasons: when a pixel receives too much light an‎d the number of generated carriers exceeds the storage capacity of the photodiode, the excess carriers overflow into adjacent pixels, which causes the blooming phenomenon. Also, the imperfection of the color separation filters used in the camera, when the received light intensity is high, leads to blooming as well. These two factors cause the whitening an‎d spreading of the image, an‎d in fact, the blooming phenomenon. In OCC systems, Blooming causes interference between multiple optical transmitters an‎d reduces the accuracy of data recovery. In this thesis, the spatial growth of the captured image was first investigated experimentally, an‎d based on the laboratory data, a model was proposed to describe the image expansion process. The proposed model showed that the amount of image growth depends on the actual size of the light source image on the image sensor. The smaller the initial LED image size on the image sensor, the greater the image growth resulting from an increase in exposure time. Furthermore, the effect of blooming on link quality was eva‎luated by calculating the SNR when two optical sources transmitted data independently. The findings revealed that at short distances (less than three meters), blooming does not significantly disrupt communication. However, as the LED–camera distance increases, blooming has a greater impact on SNR reduction, an‎d insufficient spacing between transmitters can eventually lead to communication failure.

اصغر غلامي

مسعود سيدي , محمد صدقي