## 6 Results and Discussion
### Discussion
This is observed clearly by comparing each 3 PD subgraph from Figure 9 with their corresponding 5 PD counterparts from Figures 6-8, where there was minimal improvement even at short range (referring to turbid profiles) where the geometric spread is less. This shows that the behavior of a fixed-geometry array tends to resemble a point receiver, with FOV equivalent to the sum of FOVs of the individual PDs as the range from Tx increases. This simplifies the power distribution analysis in a 3D space for an array populated along 3D axes, as applying rotations to only the roll, pitch, and yaw on the planes of the PDs (ignoring their displacement vectors) about the array's center coordinate would yield a near-accurate response, while the intensity distribution remains governed by the parameter \(\alpha\). Ripples of received power were observed in the regions beyond the viewing angle of the LED (\(\alpha\geq 50^{\circ}\)), where the combined effects of the PDs emerging into the light field and the irregularities in intensity distribution produce waves of high and low power along the horizontal distance at a given height, until it reaches a peak, before declining thereafter. This is visible in Figure 11. The horizontal distance at which this peak occurs increases with increasing vertical height from Tx. Figures 6-8 further show a considerable connectivity distance is possible in this region, which is beyond the beam-spread angle \(\theta\), although the intensity is less than 50% of \(I_{0}\) in this region and the AOI to the PDs is small. One of the more interesting observations is that in clearer waters (Figures 6 and 9a-c), for any given \(\alpha\), the consecutive separations between the white lines increase. In the turbid profiles (Figures 7, 8 and 9d-i), this separation is more consistent, except when \(\alpha\) is almost 90\({}^{\circ}\) or the location is very close to the Tx. This could be due to the very low influence of attenuation in Jerlov I compared to the effect of geometric loss. As seen in Figure 6, the separation between the Tx and 0 dB boundary spans almost twice the distance as the distance from the Tx to the 10 dB line. This signifies that for clear water UOWCs, although NRZ-OOK may be effective, a more bandwidth-efficient scheme such as higher-order PPM schemes may offer longer connectivity. This is corroborated by the BER results in Figure 10. As turbidity increases, the boundary for NRZ-OOK reaches much closer to the 0 dB line, and therefore using more complex modulation schemes may not be so beneficial. Considering BER, Figure 10 shows that with greater vertical distance, as the horizontal distance increases, the BER curve drops from a high value to a minimum, before increasing again to pass the FEC threshold. This is due to the lower light intensity experienced at these locations as well as some PDs of the arrays that have yet to come into view of the light rays. In the F-array, this complete blind spot causes the \"flat\" lines in Figure 10a,d,g for \(\beta=60^{\circ}\). The minima are where all contributing factors have reached an optimal level. In Figure 10a, the locations of the minima in the F-array are distributed across the space. C55 (Figure 10c), on the other hand, shows shallower minima across all \(\beta\), but their locations are more predictable and the BER response was also more consistent. The F-type arrays produce two loci with a significant distance in between, where the received power is at the same level due to a form of creating about the viewing angle of the LED, which could be due to the combined effect of the variation of relative intensity distribution and the PD's angular sensitivity distribution both reaching optimums for output power. If 3D intensity distribution is visualized, two circular loci of the same power level would have been seen around the center axis of the Tx.