# Integrated Photonics for IoT, RoF, and Distributed Fog-Cloud Computing: A Comprehensive Review
## 3 Radio-over-Fiber (RoF) for IoT and Fog Computing  
Radio-over-Fiber (RoF), shown in Figure 2, is a technology that enables the transmission of radio frequency (RF) signals over optical fiber links, combining the low-loss, high-bandwidth characteristics of fiber optics with the flexibility and ubiquity of wireless \begin{table}
\begin{tabular}{l l l} \hline
**Requirement** & **Fog Computing** & **Cloud Computing** \\ \hline Speed & Moderate to high, with a focus on real-time or near-real-time processing at the edge. & Very high, optimized for large-scale centralized processing and analytics. \\ \hline Energy-Efficiency & Critical due to power-constrained edge environments. & Higher energy tolerance due to centralized infrastructure and advanced cooling. \\ \hline Latency & Very low latency (within a few milliseconds) is required for real-time applications. & Higher latency is acceptable (10-100 ms) for non-time-sensitive workloads. \\ \hline Scalability & Distributed and modular; must scale across multiple geographic locations. & Centralized scalability via vertical (compute/storage) and horizontal (more nodes) expansion. \\ \hline Wireless Communication & Highly dependent, especially for mobile/IoT applications. & Less dependent; typically wired, high-speed links within data centers. \\ \hline Fiber Optic Communication & Used to connect Fog nodes to the Cloud or among themselves. & Fundamental for long-distance, high-capacity data center interconnects. \\ \hline Capacity & Moderate, supports localized data-processing and short-term storage. & Very high, designed for massive data aggregation, analytics, and long-term storage. \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison of Fog and Cloud computing across key requirements. Figure 1: Hierarchical Fog/Cloud computing architecture. communication [9; 10; 16]. Unlike traditional coaxial cables or free-space transmission, RoF allows RF signals to be centrally generated, modulated, and distributed over long distances with minimal signal degradation. This capability makes RoF particularly attractive for emerging applications in IoT and Fog computing architectures. In IoT systems, RoF provides an efficient backhaul and fronthaul infrastructure for dense deployments of wireless sensors and devices. It supports low-latency data transport from distributed IoT nodes--such as sensors, meters, and cameras--to Fog gateways and Cloud processing units, enabling real-time monitoring and control [12; 16]. RoF also facilitates the aggregation of RF signals from heterogeneous low-power protocols (e.g., Bluetooth, LoRa, WiFi, 5G, and emerging 6G) and carries them via high-capacity optical fibers to centralized processing centers [13]. Moreover, RoF supports scalable deployment models such as centralized radio access networks, which reduce infrastructure complexity and maintenance overhead in smart city and industrial IoT environments [11]. Its ability to transport millimeter-wave and 5G signals over fiber with minimal loss further strengthens its relevance for next-generation wireless systems. For example, [PERSON] et al. [17] proposed a hybrid RoF transport system to support heterogeneous indoor mobile networks, including 5G and 6G. Their approach enables the seamless integration of multiple wireless technologies over a unified optical infrastructure. NEC researchers also demonstrated a 1-bit outphasing modulation RoF system that delivers high bandwidth efficiency and complies with 3 GPP standards, offering a cost-effective solution for indoor 5G/6G deployments [18]. These developments highlight RoF's strong potential for unifying diverse wireless signals on a shared optical platform. For Fog computing, which brings data storage, processing, and decision-making closer to the network edge, RoF offers several advantages. It enables high-speed, low-latency connections between edge devices and Fog nodes through fiber links, supporting real-time analytics and local actuation.