## 3 Overview of Multihop CA-IoT Architectures and Testbeds
#### Theoretical Analysis of Multihop CA-IoT Design and Operation  
In MCA-IoT testbeds, the communication technology, event routing architecture, and sensor node (SN) power supply are key factors influencing operational stability, cost, and deployment management complexity [4; 8]. Due to the high cost and limited availability of Wi-Fi and cellular communication technologies, low-power wireless technologies such as LoRa, BLE, ZigBee, IEEE 802.15.4, Z-Wave, and SigFox are preferable. These technologies, grounded in suitable routing topologies and theoretical frameworks [4; 8; 17], offer a combination of affordability [16; 31], robustness, and simplicity [4; 31], making them ideal for widespread adoption. For example, ZigBee and Z-Wave, with ranges from 10 to 100 m, are designed for low-power applications and are most effective when deployed in low-density, mesh-like, or centralized topologies [19]. They are typically used in home automation and operate under line-of-sight conditions depending on environmental factors. However, they are characterized by high latency, unreliable Medium Access Control (MAC) protocols (CSMA/CA), low data rates, and high susceptibility to interference and multipath fading. ZigBee IP incorporates a 6 LoWPAN adaptation layer, an IPv6 network layer, and  
Figure 6: WSN-based Agri-IoT architecture for precision irrigation application [10]. the resource-intensive RPL routing protocol [9]. Conversely, Wi-Fi, GPRS, and cellular technologies (e.g., LTE-M and NB-IoT) are associated with high power consumption and require specific location or architectural access. Near-field communication (NFC) and Radio Frequency Identification (RFID) protocols, used for very short-range communication (up to 4 cm), are primarily employed in check-in and inventory systems. LoRa and SigFox, while supporting long-range communication, are limited by fixed network sizes, low data rates, and message capacities [19]. BLE, being a short-range protocol, supports clustering architectures with significant energy-saving potential. However, the critical issues related to these architectures, especially environmental constraints, have led to network management challenges and abrupt SN failures due to rapid battery depletion in previous benchmark testbeds [3, 5, 14, 15]. To optimize the performance of an MCA-IoT network, it is essential to integrate mechanisms that reduce power depletion during sensing, processing, and communication tasks. Given the susceptibility of centralized CA-IoT networks to signal attenuation and retransmissions in dense and obstructive environments, this study recommends using an energy-efficient multihop routing framework, as proposed by the authors of [8], to guide outdoor deployment. Specifically, an optimal approach involves utilizing BLE technology for all intra- and inter-cluster multihop communications while leveraging LoRa for the final relay CH-to-BS communication to achieve comprehensive farm coverage. Therefore, the proposed multihop route-actuating framework is derived based on the comparative energy efficiency analysis using the \(E_{TER,min}\) metric [8]. This metric incorporates the total energy \(E_{i,j}\) expended per \(L\) bits of each \(i-j\) route in the single-hop and multihop paradigms. According to Equation (1), \(E_{ij}\) encompasses the distance-dependent transmit power \(P_{Tx}\), the power consumed by the transmitter circuit \(P_{Tx-{\it{dec}}}\), and the power consumed in the receiver circuit \(P_{Rx-{\it{dec}}}\):  
\[E_{ij}=\frac{(P_{Tx}+P_{Tx-{\it{dec}}}+P_{Rx-{\it{dec}}})}{L-bits} \tag{1}\]  
\(P_{Tx-{\it{dec}}}\) includes the sum of the power consumed by the digital-to-analog converter \(P_{DAC}\), mixer \(P_{mix}\), transmit filters \(P_{fil}\), and frequency synthesizer \(P_{syn}\). Similarly, \(P_{Rx-{\it{dec}}}\) comprises the sum of the power expended by the frequency synthesizer \(P_{syn}\), low-noise amplifier \(P_{LNA}\), mixer \(P_{mix}\), intermediate frequency amplifier \(P_{IFA}\), receive filter \(P_{fil}\), and analog-to-digital converter \(P_{ADC}\).