A Review of the Internet of Things (IoT) Landscape: Technologies, Applications, and Open Challenges

The Internet of Things (IoT) has emerged as a large-scale ecosystem that integrates sensing, communication, and computation across diverse application domains. Its deployment spans smart homes, wearable devices, industrial automation, and smart cities, where heterogeneous devices are required to operate under strict performance, reliability, and resource constraints. This paper presents a comprehensive review of IoT systems, with a particular focus on architectural models, application domains, communication technologies, signal processing techniques, and deployment challenges. Rather than providing a high-level overview, the paper examines how architectural design choices, communication mechanisms, and signal processing strategies jointly influence overall system performance. Key challenges—including availability, reliability, mobility support, scalability, interoperability, energy efficiency, security, and privacy—are analyzed from a system-level perspective. Unlike existing surveys that address isolated aspects of IoT, this work emphasizes cross-layer interdependencies, highlighting how constraints at one layer propagate to others. The objective is not to propose new solutions but to consolidate existing research, clarify persistent limitations in current IoT deployments, and identify future research directions toward more robust and efficient IoT systems.