# Spectral and Energy Efficiency Trade-Off in UAV-Based Olive Irrigation Systems
### Motivation and Contributions  
Internet of Things technologies have revolutionized agricultural value chains when deployed in advanced data analysis. Conversely, despite the benefits of IoT implementation in precision agriculture, the energy efficiency and spectral efficiency trade-off problem could impact the agricultural and food sectors in the coming decades. Indeed, on the one hand, the large amount of data transmitted by IoT nodes can be overwhelming, requiring new approaches to data management/analysis and raising exigencies concerning spectral efficiency. On the other hand, in an IoT-based environment, most sensors and actuators encounter the limited energy issue. In particular, unmanned aerial vehicles (UAVs) require significant energy to maintain flight and perform various tasks such as remote sensing. If a drone runs out of battery mid-flight, it could crash and cause damage to the crops or other equipment. In practice, to avoid this problem, the drone will automatically return to its launch location when the drone's battery runs out. Then, depending on the drone's model, the battery will be recharged or replaced. However, frequent battery recharging (or replacement) can be costly and time-consuming and reduce UAV applications' efficiency and productivity. Consequently, guaranteeing sustainable energy to these devices represents another critical challenge.  
In this work, we aim to design a smart irrigation system for olive orchards in the Al Jouf region, a province in the northern region of Saudi Arabia. This region is the largest plant-producing region producing olive oil in the Middle East, with an area of about 7700 hectares and more than 30 million olive trees [28]. Therefore, the design of an IoT-based irrigation system in such open-field farming represents a challenging issue, especially regarding the communication network's energy efficiency and spectral efficiency. To solve this problem, we propose a smart irrigation system based on UAVs and M-MIMO (massive multiple input, multiple output) technology [12]. Specifically, UAVs ensure remote sensing (RS), which offers the advantage of collecting vital information on a large temporal and spatial scale (which cannot be achieved with traditional technologies), whereas M-MIMO ensures low delays, a large scale, and high-speed communications among different IoT devices.  
In this work, we aim to accomplish the following contributions:  
* Design a network model with a three-layered architecture for a UAV-based olive irrigation system.
* Analytically compute the achievable spectral efficiency as well as the energy efficiency of the studied system when a swarm of single antenna UAVs simultaneously communicate with a ground base station equipped with a large number of antennas.  
Numerically determine the optimal number of ground base station antennas, as well as the optimal number of IoT devices (UAVs and actuators) that should be used to ensure the maximum energy efficiency while guaranteeing a high spectral efficiency.  
The remainder of the paper is organized as follows: In Section 2, we describe our proposed UAV-based olive irrigation system with the deployment of M-MIMO communication. The evaluation experiments and results are described in Section 3. Section 4 presents the results of the proposed method. Then, the conclusion and future works are given in Section 5.