Architecture Design

4.1 Three-Layer System Architecture

The smart campus environmental monitoring system is organized into three functional layers: the Field Sensor Layer, the Edge Computing Layer, and the Cloud Platform Layer. This separation of concerns ensures that each layer can be designed, deployed, and maintained independently, while the standardized interfaces between layers enable integration of diverse sensor technologies and cloud platforms.

The Field Sensor Layer encompasses all physical measurement devices — noise monitors, particulate sensors, gas analyzers, meteorological instruments, water quality probes, and energy meters. These devices communicate with the Edge Computing Layer using wired protocols (RS485 Modbus RTU, 4–20 mA) or wireless protocols (LoRaWAN, NB-IoT, Wi-Fi). The Edge Computing Layer hosts one or more edge gateways per zone, providing local data buffering, protocol translation, alarm processing, and secure uplink to the cloud. The Cloud Platform Layer provides long-term storage, analytics, visualization, reporting, and API integration with third-party systems.

Figure 4.1: Smart Campus Environmental Monitoring System Topology — Three-Layer Architecture with Zone Gateways

4.2 Edge Gateway Zone Design

Each edge gateway serves a defined geographic zone of the campus, typically covering 5–20 sensor nodes depending on the sensor density and communication range. Zone boundaries are drawn to minimize cross-zone cable runs, respect physical barriers (buildings, roads, fences), and align with operational responsibility boundaries (e.g., one zone per building, one zone per boundary section).

The edge gateway must be sized for the number of sensor channels in its zone, with at least 20% spare capacity for future expansion. RS485 bus length must not exceed 1200 m per segment without repeaters, and the maximum number of devices per RS485 bus is 32 (with standard transceivers) or 256 (with enhanced transceivers). LoRaWAN gateway coverage radius is typically 300–1000 m in urban environments depending on building density and interference.

4.3 Cabinet Wiring Design

The field equipment cabinet is the integration point between the sensor field wiring and the edge gateway. Proper cabinet design ensures safe, reliable, and maintainable operation over the system lifetime. The cabinet must be organized with clear separation between power circuits and signal circuits, proper grounding of all metallic components, and labeled terminal blocks for every connection.

Surge protection devices (SPDs) must be installed on all external connections — power input, RS485 lines, and Ethernet ports — to protect against lightning-induced surges. The SPD must be coordinated with the upstream circuit breaker to ensure that the SPD fails safely without creating a fire hazard. All outdoor cable entries must use waterproof cable glands with appropriate IP rating to prevent water ingress.

Figure 4.2: Field Equipment Cabinet Wiring Diagram — DIN Rail Layout with RS485, PoE, and 4G Connections

4.4 Network Planning and Redundancy

Network planning for environmental monitoring systems must address the specific reliability requirements of the application. Safety-critical alarm paths require redundant network paths, while general monitoring data can tolerate brief outages if edge buffering is in place. The network plan must document the primary and backup connectivity for each edge gateway, the expected latency for each path, and the failover behavior when the primary path fails.

For outdoor deployments, cellular (4G LTE or NB-IoT) is the most common primary uplink due to its wide coverage and independence from campus network infrastructure. Fiber Ethernet provides higher bandwidth and lower latency for high-density indoor deployments. Wi-Fi is suitable for indoor sensors in areas with existing Wi-Fi infrastructure but requires careful channel planning to avoid interference.

4.5 Typical System Configurations

Three standard system configurations are defined to cover the range of park sizes and complexity levels. Each configuration specifies the number of edge gateways, sensor nodes, connectivity approach, and cloud platform tier. These configurations serve as starting points for project scoping and can be customized based on the specific requirements of each deployment.