### Related Works  
Sub-pixel OCC scenarios have not been extensively studied yet in the literature. Nevertheless, they have been indirectly addressed on several works. For instance, in [11], two equations which facilitate the determination of the 2D pixel projection \((x,y)\) occupied by  
Figure 1: Concept on the use of OCC in Smart Cities. a transmitter on an image sensor, (1) and (2), are formulated and experimentally validated. These equations facilitate the determination (\(x\), \(y\)) occupied by a transmitter on an image sensor. These values are determined based on the separation (\(D\)) between the object and the camera as well as the distances (\(dx\), \(dy\)) and the camera's field of view (\(FOVx\), \(FOVy\)) relative to the transmitter along with the camera's pixel resolution (\(Nx\), \(Ny\)). \[x =\frac{2\cdot Nx\cdot\arctan\Bigl{(}\frac{dx}{2D}\Bigr{)}}{FOVx} \tag{1}\] \[y =\frac{2\cdot Ny\cdot\arctan\Bigl{(}\frac{dy}{2D}\Bigr{)}}{FOVy} \tag{2}\]  
There have also been several studies that have explored long-distance OCC links. However, these studies involved modifications to the camera to increase the transmitter's projections onto the image sensor, spanning multiple pixels. For instance, in [12], a novel technique was developed to extend the reach of RS-based OCC, achieving a link distance of 400 m through the use of telephoto lenses. In [6], another RS link spanning 328 m was implemented, where the LED array was detected using a magnifying lens with a sufficiently narrow horizontal field of view (28.1 degrees) to ensure the transmitter's projection always exceeded 2 \(\times\) 2 pixels. In [13], sensor image parameters were adjusted to blur the transmitter's projection on the image sensor, thereby increasing the RS link distance. Being able to work with transmitter projections at or below a single pixel on the receiver without the need for modifications is of significant interest. The use of telephoto or magnifying lenses eliminates the need for cameras primarily used for recording purposes and confines the spatial separation of transmitters to a small region. Consequently, working with sub-pixel projections enables both the extension of link distances and an increase in the quantity of such links within the same environment. However, the number of studies that have genuinely addressed these conditions is rather limited, often focusing on verifying the feasibility of such communications. For instance, in [14], the feasibility of a GS link is demonstrated, wherein the transmitter's projection onto the receiver is sub-pixel, which is facilitated by the fact that the emitted light energy from the LED affects multiple pixels. In [4], this concept is further tested, this time under adverse weather conditions, using an RS link. Several studies have addressed both transmitter detection and tracking tasks in OCC systems. However, none of them specifically tackle sub-pixel scenarios, making it the sole algorithm capable of universally addressing this aspect. Other approaches focus on transmitters with a predefined size and shape or cater to specific applications, rendering them challenging to extrapolate. For instance, in [15], segmentation and edge detection techniques are employed to detect LED arrays at close distances. In [13], a method for transmitter detection and tracking in mines is defined with the sole distinguishing parameter being the transmitter's luminosity. In [9], a method for tag detection based on OCC technology is proposed and tested for object identification. In this case, it does not involve communication frames but rather the constant transmission of identifiers to locate objects. The detection process involves resizing images to VGA format and applying space-time correlation based on defined tags. Furthermore, these algorithms are hardly suitable for use in sensor networks beyond the sub-pixel context. For example, in [16], if the transmitter projections are not sufficiently high, there is a high likelihood of losing their information when converting the image to VGA format.