See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/339938413 Wireless technologies for smart agricultural monitoring using internet of things devices with energy harvesting capabilities Article in Computers and Electronics in Agriculture · May 2020 DOI: 10.1016/j.compag.2020.105338 CITATIONS READS 6 173 2 authors, including: P. Spachos University of Guelph 114 PUBLICATIONS 847 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: B. Debowski - MEng Project View project LeftBrain-RightBrain Deep Hierarchical Model for NLP/NLU View project All content following this page was uploaded by P. Spachos on 17 March 2020. The user has requested enhancement of the downloaded file. Wireless Technologies for Smart Agricultural Monitoring using Internet of Things Devices with Energy Harvesting Capabilities Sebastian Sadowskia , Petros Spachosa,∗ a School of Engineering, University of Guelph, Guelph, Ontario, N1G 2W1, Canada Abstract Technological advances in the Internet of Things (IoT) have paved the way for wireless technologies to be used in new areas. Agricultural monitoring is an example where IoT can help to increase productivity, efficiency, and output yield. However, powering these devices is a concern as batteries are often required due to devices being located where electricity is not readily available. In this paper, an experimental comparison is performed between IoT devices with energy harvesting capabilities that use three wireless technologies: IEEE 802.11g (WiFi 2.4 GHz), IEEE 802.15.4 (Zigbee), and Long Range Wireless Area Network (LoRaWAN), for agricultural monitoring. Four experiments were conducted to examine the performance of each technology under different environmental conditions. According to the results, LoRaWAN is the optimal wireless technology to be used in an agricultural monitoring system, when the power consumption and the network lifetime are a priority. Keywords: Wireless Technologies, ZigBee, LoRa, WiFi, Internet of Things, Energy Harvesting, Smart Agriculture, Monitoring, Solar power 1 1. Introduction 22 23 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 In the era of the Internet of Things (IoT), everyday objects are equipped with microcontrollers and communication devices that can work together to help us transform our world for the better [1, 2]. A promising area where IoT devices can alleviate many issues and provide promising solutions is in agriculture. When IoT devices and Wireless Sensor Networks (WSN) are used in agriculture, advanced farming techniques can be applied which is known as Precision Agriculture (PA) [3]. PA allows for a greater amount of control in the growing of crops and the raising of livestock. By using technology to monitor crops, the efficiency can be increased and costs can be reduced since more precise remedies can be applied to crops [4]. IoT devices can be used in monitoring systems consisting of nodes that interact with the environment using sensors to gather real-time information and transmit it to a control room for further processing. However, in every monitoring system [5], power consumption is often a top concern in order for the system 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 ∗ Corresponding author Email address: petros@uoguelph.ca (Petros Spachos) Preprint submitted to Computers and Electronics in Agriculture 45 46 to function properly. If a sensor node stops transmitting, data regarding its monitoring area would be missing and the system would no longer have accurate information. In PA applications with WSN, batteries are used to power the sensor nodes while outside. This is a major issue, since at some point either the battery needs to be replaced or if possible, recharged. Due to the node being outdoors, rechargeable batteries and energy harvesting devices can be used. Solar power is a promising approach since it is readily available and it can be easily harvested to allow for the sensor node to function for a longer period of time. At the same time, to optimize power consumption, the power requirements of each component of the node should be carefully examined. While IoT devices have been of great value to society in the automation of tasks, they often consume a large amount of energy [6, 7]. Energy consumption comes from various processes such as sensing systems, application operating systems, and the communication radio [8]. In order to improve energy efficiency, each of the individual processes needs to be optimized [9]. When it comes to IoT devices, processes such as the operating and sensing systems are often based on the application requirements, making it difficult to reduce their energy requirements. March 4, 2020 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 Optimization to the device power consumption can be achieved through an efficient communication radio. Reducing the energy requirements of wireless communication can help to optimize the battery life of nodes. In agricultural applications, IEEE 802.11 (WiFi) [10], IEEE 802.15.4 (Zigbee) [11], and Long Range Wireless Area Network (LoRaWAN) [12], are among the commonly used wireless technologies. Each technology has unique characteristics. The proper selection of the wireless technology, can extend the lifetime of the nodes and eventually extend the lifetime of the network. At the same time, PA can be greatly benefitted from the use of proper wireless technology with rechargeable batteries and IoT devices with energy harvesting capabilities. New technologies and IoT devices have revolutionized the way farmers are able to interact and monitor their growth. By combining traditional approaches, such as energy harvesting techniques, with low cost, low power and inch scale IoT devices, PA can be performed. A promising solution toward achieving PA is the use of an IoT system with energy harvesting capabilities. The IoT uses small, low power embedded electronics that transmit data across a network. Often, when sensor nodes are configured and placed outdoors in a field, a power source is required. When electricity is not available, batteries must be used. Due to the need to replace batteries once depleted, rechargeable batteries are an optimal alternative. Towards such a system, there is a need for detailed reports on the energy requirements. Real experimental results on the energy requirements of different technologies are needed for the proper selection of the different components and technologies. This work tries to fill this gap. In this paper, through extensive experimentation, a comparison between the power consumption of three wireless technologies: IEEE 802.11g (WiFi 2.4 GHz), Zigbee, and LoRaWAN is performed. Narrowband-IoT (NB-IoT) is another popular technology for IoT application however, its associated cost makes it less popular than the previous three technologies, while SigFox, although it is similar to LoRaWAN is not widely available. The technologies were selected based on the prevalence and popularity in agricultural applications [13]. Their energy requirements are compared when they are used at an agricultural monitoring system using IoT devices with solar energy harvesting capabilities. Three systems were created each performing similar tasks while using different wireless technologies. Non-line-of-sight exists between the sensor and the base station. Four experiments were conducted and the energy requirement of the system was modeled, while an accurate estimation of the lifetime is also provided. The 108 experimental results can be used for the selection of the proper wireless technology and IoT devices for agricultural monitoring following application requirements. The rest of this paper is organized as follows: Section 2 reviews the related work on wireless technologies in agricultural applications. In Section 3, the system architecture is presented, followed by Section 4, with a description of the experimental procedure. The experimental results and a discussion are presented in Section 5. Finally, Section 6 concludes this work. 109 2. Related Work 99 100 101 102 103 104 105 106 107 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 2 Over the years, applications using IoT devices and WSN in PA have increased in popularity [14, 15, 16, 17]. By using battery-powered sensor nodes combined with traditional farming practices, an increase in output efficiency and a reduction in costs can be achieved. While some researchers have focused on implementing energy harvesting to extend sensor node lifetime, others have modified the sensor nodes to use less energy through its standard operating procedure [18]. In [19], a survey was performed studying the lifetime of WSN and the energy saved with different types of network topologies. According to the results, there are many problems and issues when selecting a topology for extending the network lifetime. In order for the network lifetime to be extended trade-offs must occur and other parameters are required to be sacrificed. It was suggested that energy-efficient articles be developed to optimize energy supply. In [20] and [21], systems were proposed for agricultural monitoring. In [20], the designed system used WiFi-based IoT devices to monitor nitrate concentrations in groundwater. In the design of the system, WiFi was selected for communicating the information due to its low cost, high throughput, and ease of integrating with web-based services. In [21], a WSN for irrigation control was developed using Zigbee for wireless communication. Zigbee was selected due to its low cost and off-the-shelf components to reduce the hardware complexity. In order to reduce the power consumption the transmit power was configured to be 0 dBm. In both of the systems presented, the power consumption was not a major concern, with a greater focus being placed on the total cost and ease of integrating with the system. In [22], a study was performed on sensor nodes with solar energy harvesting capabilities. An energy management policy is used in order to produce the optimal throughput and minimizes the mean delay in the network. Another method of optimizing power consumption can be seen in [23]. A circuit was created 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 for wireless sensor nodes where energy from a solar panel could be transferred to a rechargeable battery even in poor weather conditions. The sampling rate of the nodes can also affect the energy consumed and the supplied power. In [24], a method is presented to decide the sampling rate of sensor nodes to manage its energy efficiently. Simulations demonstrated the efficiency of the proposed algorithm compared to other algorithms. The system presented in [25] used a WSN in a cotton field to monitor soil moisture with automatic drip irrigation. Sensor nodes were developed to function using battery power while relay nodes functioned using solar power. A routing protocol was used in order to route data and increase power savings. Experimental results were conducted over a six month period and demonstrated that the system could function for a long period of time while collecting sensor information. There have been many works that have used renewable energy sources for agricultural applications to extend network lifetime. In [26], due to the unpredictability associated with weather conditions, solar energy harvesting was combined with wireless charging in order to allow for nodes to function for longer periods of time. By combining the advantages of both solar energy harvesting and wireless charging it was found that a significant increase in network performance could be achieved. In this work, we expand on the papers described above and our previous work [27] and design a wireless IoT system for agricultural monitoring with energy harvesting capabilities. There is a lack of research performed on using different types of wireless technologies for agricultural applications. In search of a system design, a comparison is performed between three wireless technologies: WiFi, Zigbee, and LoRaWAN to determine which technology consumes the lowest amount of power and provides the longest network lifetime. Three systems, each using one of the wireless technologies to communicate, are developed and tested. The experimental results can fill the gap and provide real experimental values on the energy requirements of each technology. 215 they just forward the data towards the destination. The third type of node, the destination node, has only a communication unit that receives all the data and stores them in a server for further processing. In this work, we focus on measuring the energy requirements of three wireless technologies to be used as the communication unit of each node. Each monitoring node has a number of hardware components. It contains an Arduino Uno, a power converter, one rechargeable battery, a solar panel, a soil moisture sensor, and a communication unit. The monitoring nodes forward the sensor data to the destination node using the wireless technology that we measure every time. For WiFi, a CC3000 WiFi Shield was used, for Zigbee, a Series 2 XBees with a 2 mW Wire Antennas was used, and for LoRaWAN, a Dragino LoRa Shield, was used. 216 3.1. Components 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 191 3. System Architecture 239 240 192 193 194 195 196 197 198 The proposed system has three types of nodes. The monitoring nodes have sensors to collect information, they form the packets and then forward them to the relay nodes. The monitoring node architecture is shown in Fig. 1. The relay nodes receive and transmit the data packets. They have a similar architecture with the monitoring nodes, however, they do not have any sensors and 241 242 243 244 245 246 247 3 • Solar Panel: To provide energy harvesting capabilities to the node, a Star Solar D165X165 monocrystalline solar panel was used [28]. Being only 170 × 170 × 2 mm, the solar panel is capable of providing a 6.0 V output at a peak of 3.65 W when full sunlight is present. The small size makes it suitable for placement in a field where it would have minimal interference to any of the growing plants surrounding it while still providing a significant energy output. The solar panel is shown in Fig. 2a. • Grand-Pro Lithium Polymer Battery: A Grand-Pro 3.7 V 6600 mAh Lithium Polymer (LiPo) battery was used [29]. The battery is shown in Fig. 2b. • Power Converter: A developed power converter was used to supply power to the wireless node [30]. When connected to the battery, the power converter was designed to provide a constant 5 V power output while the charge on the battery was above 3.4 V. If the charge dropped below 3.4 V, the power converter would cease to function and would wait until the battery was sufficiently charged before supplying power again. This safety feature allowed the battery to maintain a voltage level preventing it from over-discharging and damaging the battery cells. In addition to recharge the battery, the converter was also capable of interfacing with an energy harvesting device. The energy harvesting device could then be used to supply power to the node and recharge the battery. If it was no longer providing power to the battery, it could then supply power Figure 1: Monitoring node architecture used for experimentation. 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 to the system. The power converter is shown in Fig. 2c. • Microcontroller: In order to connect all the hardware components together, an Arduino Uno Rev3 microcontroller was chosen [31]. It was selected based on its low power consumption and ease of development in configuring all the components together. It is based on the ATmega328P, which contains six analog-to-digital converts that can be used to easily connect and read data from analog sensors. The Arduino Uno is shown in Fig. 2d. Other microcontrollers, such as the Arduino MKR series can also be used. The energy requirements of each component were measured separately, hence, if the microcontroller is changed, the overall energy requirements can be easily estimated. At the same time, it worths to mention that, during the measurement of the energy requirements of each wireless technology, the microcontroller energy requirements were subtracted from the total energy consumption of the system. 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 269 270 271 272 273 274 275 • Grove Soil Moisture Sensor: To measure the moisture levels in the soil a Grove Soil Moisture Sensor was used [32]. Soil moisture is a commonly measured parameter in agricultural monitoring allowing for a system design similar to what would be used in a real-life application. The selected sensor draws a significant amount of current and reduc- 297 298 299 300 301 302 303 4 ing the device lifetime when environmental conditions are being measured. This was not an issue for our design since we focused on the energy consumption of the wireless technologies, however, it is something that can be optimized in future implementations. The soil moisture sensor is shown in Fig. 2e. • CC3000 WiFi Shield: To connect the Arduino using WiFi a Sparkfun CC3000 WiFi Shield was used [33]. WiFi is one of the most commonly used wireless technologies, available in most devices, used to connect to a Wireless Local Area Network (WLAN) and the Internet. WiFi has a short transmission range in Line-of-Sight (LoS) only capable of reaching up to 50 m distance. In addition, WiFi has a very large power consumption which often makes it a poor choice to use in wireless devices outdoors that require a power supply. The CC3000 communicates using the IEEE 802.11g standard. The WiFi shield is shown in Fig. 2f. • Series 2 XBee with 2 mW Wire Antenna: To create a Zigbee network between the devices the Series 2 XBees with a 2 mW Wire Antennas were used [34]. The Series 2 XBees are low power radios which communicate on the Zigbee mesh network. These devices are capable of creating point-to-point or multi-point networks connecting together hundreds of nodes. Devices using Zig- (a) Solar Panel. (e) Soil moisture sensor. (b) LiPo Battery. (c) Power Converter. (f) WiFi (2.4Ghz). (g) Series 2 XBee. (d) Arduino Uno. (h) Dragino Lora. Figure 2: Hardware components used for experimentation. 304 305 306 307 308 309 bee have a transmission range up to 120 m in LoS, which can provide many benefits when it is used in an agricultural monitoring system such as reducing the system costs and allowing for easy configuration of the devices. The Series 2 XBee is shown in Fig. 2g. 325 326 327 328 329 330 331 332 333 334 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 • Dragino LoRa Shield: To communicate devices using LoRaWAN the LoRa Shields for Arduino developed by Dragino were used [35]. LoRaWAN is known for being a long-range technology communicating at a low frequency of 915 MHz (in North America), and the signals produced have large wavelengths, hence, they can travel further distances. In LoS, LoRaWAN is capable of transmitting up to 15000 m, which makes it one of the best technologies for agricultural monitoring. Its large transmission range can greatly reduce the number of nodes required and its low power consumption can keep nodes functioning for a longer period of time compared to more commonly used technologies. The LoRa Shield is shown in Fig. 2h. 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 5 3.2. System Characteristics When comparing different types of wireless technologies, parameters such as the power consumption and the transmission range are important in determining the optimal technology for agricultural monitoring. While the power consumption of a wireless technology is important in determining the longevity of a node’s power supply, other parameters should be considered as well, in the selection of the proper communication technology. The transmission range is among the crucial parameters. By using devices that transmit further, a smaller number of relay nodes are required in order for a transmission to reach the intended destination. Another common parameter is the throughput. When there is a need for a large amount of data to be transmitted, a technology with a high throughput should be used. Other parameters often used are the cost and ease of implementation. Having a low cost per-device can allow for a large number of nodes to be implemented in the network while having a simple and easy implementation can allow for the network to have a low set up time and make it easier to debug if a problem occurs. A summary of the parameters of the wireless technologies being compared in this paper can be seen in Table 1. For transmission range, LoRaWAN is the optimal Table 1: Summary of wireless technologies and their characteristics. Wireless Technology WiFi (2.4GHz) Zigbee LoRaWAN Throughput Transmission Power ConRange sumption 50 m Moderate Wide availability High energy consumption 250 kbit/s 120 m Easy to set up Requires extra hardware 50 kbit/s 15000 m Low Extremely Low Wide range Requires extra hardware Parameter Battery Current Supply Arduino Uno (Max. Current Consumption) Grove Soil Moisture Sensor (Max. Current Consumption) Series 2 XBee (Max. Current Consumption) Dragino LoRa Shield (Max. Current Consumption) CC3000 WiFi Shield (Max. Current Consumption) 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 Disadvantages 54 Mbit/s Table 3: Estimated max. current consumption and min. lifetime of monitoring node for each wireless technology. Table 2: System parameters corresponding to components used in monitoring nodes. 350 Advantages Value Wireless Technology 6600 mAh WiFi-based node Zigbee-based node LoRaWANbased node 45 mA 35 mA 40 mA 10 mA 1 Hz Tranmission Interval 1s Transmission Power -10 dBm capable of reaching up to 15000 m in LoS. Zigbee was the second furthest in LoS with 120 m, while WiFi has the lowest transmission range only capable of reaching 50 m in LoS. In terms of throughput, WiFi can transmit the most amount of data reaching speeds of 54 Mbit/s. Zigbee is the next highest with 250 kbit/s, followed by LoRaWAN with 50 kbit/s. At the same time, parameters such as the current consumption, the sampling frequency, transmission interval, and transmission power are important in measuring the power consumption of a device. Table 2, summarizes the current supplied by the battery, maximum current utilized by the various components, and parameters such as the sampling frequency, the transmission interval, and the transmission power that affect the power consumption. The power values were measured with the Monsoon power monitor. In addition to the current draw of the components, while greatly affecting the power consumption, the 270 24 120 55 90 73 Table 4: Estimated relay node current consumption and lifetime for each wireless technology. 190 mA Sampling Frequency Estimated Max. Estimated Current Min. Consumption (mA) Lifetime (h) Wireless Technology WiFi-based node Zigbee-based node LoRaWANbased node 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 6 Estimated Current Estimated Consumption (mA) Lifetime (h) 190 35 40 165 10 660 transmission ranges of the wireless technologies are important when designing a system for agricultural monitoring. When the devices have a large monitoring range, a smaller number of nodes can be used in the monitoring of a field. A monitoring node would require an Arduino Uno, a sensor, a battery, and a communication unit. Table 3 shows the expected lifetime of each monitoring node when each wireless technology is used with maximum current consumption. Again, the Monsoon power monitor was used for the energy measurements. At the same time, when the nodes act as relay nodes to forward the data, the larger the transmission range the smaller the number of the required units to reach the destination. To achieve the maximum transmission range, the maximum current consumption is required. Table 4 shows the estimated lifetime, when each of the 423 transmit the information every 1 s. Note that these times were used in order for the systems to consume a larger amount of power and therefore cease functioning sooner. If the systems were to be placed in an actual environment for agricultural monitoring the times could be greatly reduced since actual conditions do not rapidly vary in a short period of time. Before starting the experiments, the batteries were fully charged. 424 4.2. Outdoor Experiments 416 417 418 419 420 421 422 425 426 Figure 3: Green roof lab at University of Guelph. 427 428 385 386 387 communication units is used as a relay node, and forwards the sensor data from the monitoring node towards the destination. 429 430 431 432 399 3.3. Cost Analysis In the design of a system using prototypes, the cost is an important factor. For an analysis of the cost for each of the nodes, the unit price for a single component is considered. The total cost for the design of the monitoring nodes was found to be $155.59 USD, the most expensive out of all the three nodes. For the relay node, the total cost was found to be $142.70 USD, and the cheapest was found to be the destination costing $87.85 USD. While the cheapest, the price does not include the cost of a computer or server that would be needed in order to store and process the data. 400 4. Experimental Procedure 388 389 390 391 392 393 394 395 396 397 398 433 434 435 436 437 438 439 440 441 402 403 404 405 406 407 408 409 410 411 412 413 414 415 4.1. Experimental Setup For testing purposes, nodes were configured to sample the charge left on the battery every 1 Hz and • Experiment 2 - With energy harvesting. The solar panel was connected to each node. This experiment took place during August 2018. • Experiment 3 - With energy harvesting. The solar panel was connected to each node. This experiment took place during December 2018. • Experiment 4 - With energy harvesting. The solar panel was connected to each node. This experiment took place during May 2019. 454 455 5. Results and Discussion 443 444 To evaluate the proposed system, extensive experimentation was conducted. For each wireless technology, identical nodes were configured. The experiments were conducted at an outdoor environment where the solar panels for each of the nodes would obtain a similar amount of solar energy throughout the day. The testing area was a roof research lab at the University of Guelph Engineering Building, shown in Fig. 3. To measure the charge left on the battery, probes from the power converter were connected and measured on the Arduino and transmitted to a computer that was functioning as the destination. • Experiment 1 - No energy harvesting capabilities. In this experiment, the solar panel was not connected to the node, to examine and characterize the performance of the battery alone, without the solar panel. Due to uncontrollable weather conditions performing three experiments would guarantee results that demonstrate the system performing with varying amounts of sunlight. The current consumed by the nodes was also measured. In order to measure the current consumption of the devices, the Monsoon power monitor was used. Monsoon is a monitoring tool that is capable of supplying an input voltage, measuring the current drawn by the device, and can display the average measurements. To measure the current consumption of the devices, nodes were first powered and warmed up until the system was fully operational. The current was then measured for two minutes and the values were recorded. 442 401 Four experiments were performed, and each experiment lasted until the power supply in one of the monitoring nodes was drained. 445 446 447 448 449 450 451 452 453 456 457 7 In this section, the experimental results are presented followed by a discussion. 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 5.1. Results According to the experimental results obtained, the system functioned as required with each wireless technology, capable of transmitting information until the battery of a monitoring node was depleted. Due to the large amount of data that was gathered throughout the experiments, only a fraction is shown in the following figures. The voltage charge remaining on the battery over time for the first experiment, with no energy harvesting capabilities, can be seen in Fig. 4, while Fig. 5, Fig. 6, and Fig. 7 shows the remaining battery levels over time for experiments 2, 3, and 4, respectively. An overall summary of the results and a comparison of the technologies can be seen in Table 5. The average current consumption of the different devices along with the estimated lifetime was also measured. In terms of current consumption, WiFi consumed the most requiring 171.17 mA, followed by Zigbee which required 69.36 mA and lastly, LoRaWAN which uses the lowest amount of current by consuming only 29.33 mA, on average. Using these values along with the battery size of 6600 mAh, the expected lifetime of the devices could be calculated. A LoRaWAN based system would be expected to run for 225.00 h, a Zigbeebased system should function for 95.15 h, while a WiFibased system has an expected lifetime of 38.56 h. According to the experimental results, as seen in Fig. 4, the LoRaWAN system lasted for 166.23 h before failing, the Zigbee system functioned for 80.28 h, and WiFi stopped after 29.06 h. During the second experiment, shown in Fig. 5, again the device using LoRaWAN technology was the most optimal capable of lasting 228.20 h on a single battery charge. The Zigbee-based device was the second to cease operating stopping after 95.15 h. WiFi was determined to be the worst operating technology in terms of energy consumption, only functioning for 38.56 h. In the third experiment, shown in Fig. 6, the results are similar to the previous experiments with fewer sunlight hours, forcing the nodes to use their batteries for power. This experiment took place during December 2018. The LoRaWAN-based system saw a large reduction in lifetime only functioning for 174.64 h, the Zigbee-based system was able to last 92.19 h, while the WiFi system experienced a similar runtime of 30.67 h. Results from the fourth experiment can be seen in Fig. 7. This experiment took place during May 2019 and the solar panels manage to collect a greater amount of energy than the third experiment, but less than the amount gathered from the second experiment. Using LoRaWAN the system was capable of running 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 8 for 189.22 h, the Zigbee system only functioned for 88.25 h, and the WiFi-based system stopped after 28.85 h. 5.2. Discussion Through the experiments performed, it can be seen that LoRaWAN is the optimal technology in terms of energy consumption for communicating information between nodes in a wireless IoT system with energy harvesting capabilities. After measuring the current consumption of the different devices, it could be seen that LoRaWAN nodes consumed over a fifth the amount of current of WiFi nodes and over half the current of Zigbee nodes. Hence, this allows for LoRaWAN to last a much longer duration using batteries with similar capacities. The benefits LoRaWAN provides can be easily observed when a battery is selected to compare the lifetimes of the nodes. With a 6600 mAh battery, LoRaWAN system is expected to last approximately 225.00 h, which is much greater than the 95.15 h Zigbee system can provide, or the 38.56 h obtained from WiFi system. When compared with the first experimental results, it can be determined that the estimated time is not always accurate. For instance, LoRaWAN system functioned for only 166.23 h, Zigbee system was only capable of achieving a runtime of 80.28 h, and WiFi system runs for 29.06 h. Based on the real-world results, a great difference can be noticed between the estimated and the actual lifetime. One reason for the difference can be attributed to the nonlinear discharge rate of the LiPo batteries. With all batteries not being ideal drops in the charge can occur reducing the lifetime of the device [36, 37, 38]. Another factor is the power converter. The power converter used to supply power to the device from the battery was designed to prevent the battery from over-discharging. Therefore, the power converter would stop the supplying power once the charge on the battery reached 3.4 V. To improve the battery life of the devices, the next set of experiments saw the addition of a solar panel to provide energy harvesting capabilities to the devices. According to the experimental results, adding energy harvesting to a system can greatly increase the lifetime of the nodes in the network. At the same time, the amount of sunlight obtained will greatly affect the additional lifetime that the device will be able to function. The second experiment saw a large amount of sunlight supplying energy to the devices, with the third experiment supplying a very little amount of energy, and the fourth experiment providing energy to be between the previous two experiments. (a) WiFi. (b) Zigbee. (c) LoRaWAN. Figure 4: Experiment 1 - No energy harvesting capabilities. (a) WiFi. (b) Zigbee. (c) LoRaWAN. Figure 5: Experiment 2 - August 2018 with solar energy harvesting. (a) WiFi. (b) Zigbee. (c) LoRaWAN. Figure 6: Experiment 3 - December 2018 with solar energy harvesting. (a) WiFi. (b) Zigbee. Figure 7: Experiment 4 - May 2019 with solar energy harvesting. 9 (c) LoRaWAN. Table 5: Summary of results. Wireless Average Current Estimated Technology Consumption (mA) Lifetime (h) Experiment 1 WiFi 171.17 38.56 29.06 Zigbee 69.36 95.15 80.28 LoraWAN 29.33 225 166.23 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 At the LoRaWAN-based system, a larger amount of variance between the runtimes could be observed. The second experiment saw the node run for 228.20 h, the third for 174.64 h, and the fourth for 189.22 h. Due to the long base runtime of the device, it can be noticed that a larger amount of solar harvesting could occur further increasing the runtime of the device. At its peak, the second experiment saw the device last for an additional 50 h before run out of energy, while in the third experiment the solar panel provided very little benefits to the system. At the Zigbee-based system, solar harvesting was able to greatly increase the lifetime of the node during the experiment. The second experiment saw Zigbee system run for 104.80 h, 92.19 h during the third experiment, and 88.25 h in the fourth experiment. When compared to the first experiment, with energy harvesting a Zigbee node could last for an additional 25 h with a large amount of sunlight, while for a low amount lasted for 88.25 h. This is a great improvement for the Zigbee system as being able to function for a greater period would allow for more data to be gathered before the battery in the node would need to be recharged or replaced. Lastly, the WiFi-based system using energy harvest has very little impact on the runtime of the device. During the second experiment, the node runs for 28.3 h, while in the third experiment for 30.67 h, and for 28.85 h in the fourth experiment. Overall, the largest impact gained from energy harvest was approximately 1 h. A system using WiFi consumed too much power draining the battery charge that using energy harvesting will have almost no impact on the system. In the WiFi experiments, it can be seen that the solar panel provided little benefits. There was a very little amount of battery charge recovered over the period that the node functioned. For the Zigbee and LoRaWAN systems, the solar panel provided more benefits and made a bigger difference in the system lifetime. Several other parameters such as the sampling frequency, transmission interval, and transmission power could also affect the estimated and actual lifetime of the systems. To decide how much each of the parameters affects the power consumption additional experimenta- Experimental Node Lifetime (h) Experiment 2 Experiment 3 28.3 30.67 104.8 92.19 228.2 174.64 Experiment 4 28.85 88.25 189.22 618 tion would be necessary. According to the experimental results in Table 5 and the previous discussion on the characteristics of each technology as shown in Table 1, WiFi is ideal if a large amount of information is required to be transmitted between short distances. However, at the cost of such a high speed, a greater amount of power consumed. On the other hand, LoRaWAN has a much lower throughput but it is able to transmit far distances with the minimal amount of power being consumed. In the middle there is Zigbee. It has a slightly higher throughput than LoRaWAN, but a greatly reduced transmission range. The power consumed by Zigbee is still low and a network can be easily set up with nodes capable of being easily configurable and meshed together in the network. 619 5.3. Open issues 604 605 606 607 608 609 610 611 612 613 614 615 616 617 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 10 In this work, we discussed experimental results on the energy requirements of three popular wireless technologies for PA with IoT devices. The results can be used as an indicator for the selection of the proper wireless technology. However, there are still open issues that should be addressed in order to improve the performance of an IoT-based system for agriculture. The proper selection of the sensor is an important parameter that can affect the overall energy consumption of the system as well as the cost of the system. Sensors with high accuracy can be helpful while they can also increase the total cost and the energy requirements. On the other hand, less expensive sensors, with lower power requirements but less accurate might affect the accuracy of the system. Moreover, factors such as the deployment environment and the environmental conditions should always be considered. In a harsh environment, the performance of the solar panel might not be as expected, while the cost of the protective case for each node should also be considered. At the same time, the cost of the microcontrollers keeps decreasing. Hence, advance filtering techniques can be applied without extra energy requirements, to clean the data locally at each node and minimize the need for wireless data transmission. 644 6. Conclusions 699 700 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 In this paper, we provide an experimental analysis between three wireless technologies: Zigbee, LoRaWAN, and WiFi when they are used in an agricultural monitoring system with energy harvesting capabilities. Three identical systems were created each using one wireless technology. The systems were placed outdoors and the batteries could be recharged through solar panels. The systems were compared on the lifetime of the nodes, where the node that functioned for the longest time would be the most optimal for an agricultural application. Experimental results demonstrated that a LoRaWAN system would be ideal as it was capable of functioning for the longest period before the first monitoring node stops transmitting due to lack of energy. Zigbee system was the next ideal, followed by WiFi system. However, power consumption and device lifetime are usually not the only parameters that are considered when designing a system. While WiFi has a poor power consumption, the throughput is much higher allowing for a larger amount of information that can be transmitted between devices. The results produced in the paper can be used as an indicator for the selection of a wireless technology to be used in an agricultural monitor system with energy harvesting capabilities. 701 [9] 702 703 704 [10] 705 706 707 [11] 708 709 710 711 [12] 712 713 714 715 [13] 716 717 718 719 [14] 720 721 722 723 [15] 724 725 726 727 [16] 728 729 730 731 732 [17] 733 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 References [1] A. Al-Fuqaha, M. Guizani, M. Mohammadi, M. Aledhari, M. Ayyash, Internet of things: A survey on enabling technologies, protocols, and applications, IEEE Communications Surveys Tutorials 17 (4) (2015) 2347–2376. doi:10.1109/ COMST.2015.2444095. [2] A. Zanella, N. Bui, A. Castellani, L. Vangelista, M. Zorzi, Internet of things for smart cities, IEEE Internet of Things Journal 1 (1) (2014) 22–32. doi:10.1109/JIOT.2014.2306328. [3] S. Ivanov, K. Bhargava, W. Donnelly, Precision farming: Sensor analytics, IEEE Intelligent Systems 30 (4) (2015) 76–80. doi: 10.1109/MIS.2015.67. [4] C. Brewster, I. Roussaki, N. Kalatzis, K. Doolin, K. Ellis, Iot in agriculture: Designing a europe-wide large-scale pilot, IEEE Communications Magazine 55 (9) (2017) 26–33. doi: 10.1109/MCOM.2017.1600528. [5] R. Khan, I. Ali, M. Zakarya, M. Ahmad, M. Imran, M. Shoaib, Technology-assisted decision support system for efficient water utilization: A real-time testbed for irrigation using wireless sensor networks, IEEE Access 6 (2018) 25686–25697. doi: 10.1109/ACCESS.2018.2836185. [6] K. Wang, Y. Wang, Y. Sun, S. Guo, J. Wu, Green industrial internet of things architecture: An energy-efficient perspective, IEEE Communications Magazine 54 (12) (2016) 48–54. doi:10.1109/MCOM.2016.1600399CM. [7] F. TongKe, Smart agriculture based on cloud computing and iot, Journal of Convergence Information Technology 8 (2). [8] B. Martinez, M. Montón, I. Vilajosana, J. D. Prades, The power of models: Modeling power consumption for iot devices, IEEE 734 735 [18] 736 737 738 739 [19] 740 741 742 743 744 [20] 745 746 747 748 [21] 749 750 751 752 [22] 753 754 755 756 [23] 757 758 759 760 761 762 763 11 [24] Sensors Journal 15 (10) (2015) 5777–5789. doi:10.1109/ JSEN.2015.2445094. J. Burrell, T. Brooke, R. Beckwith, Vineyard computing: sensor networks in agricultural production, IEEE Pervasive Computing 3 (1) (2004) 38–45. doi:10.1109/MPRV.2004.1269130. N. Wang, N. Zhang, M. Wang, Wireless sensors in agriculture and food industry—recent development and future perspective, Computers and electronics in agriculture 50 (1) (2006) 1–14. D. Han, J. Lim, Design and implementation of smart home energy management systems based on zigbee, IEEE Transactions on Consumer Electronics 56 (3) (2010) 1417–1425. doi: 10.1109/TCE.2010.5606278. F. Adelantado, X. Vilajosana, P. Tuset-Peiro, B. Martinez, J. Melia-Segui, T. Watteyne, Understanding the limits of lorawan, IEEE Communications Magazine 55 (9) (2017) 34–40. doi:10.1109/MCOM.2017.1600613. M. Ayaz, M. Ammad-Uddin, Z. Sharif, A. Mansour, E. M. Aggoune, Internet-of-things (iot)-based smart agriculture: Toward making the fields talk, IEEE Access 7 (2019) 129551–129583. doi:10.1109/ACCESS.2019.2932609. N. Ahmed, D. De, I. Hussain, Internet of things (iot) for smart precision agriculture and farming in rural areas, IEEE Internet of Things Journal 5 (6) (2018) 4890–4899. doi:10.1109/JIOT. 2018.2879579. W. Chen, Y. Lin, Y. Lin, R. Chen, J. Liao, F. Ng, Y. Chan, Y. Liu, C. Wang, C. Chiu, T. Yen, Agritalk: Iot for precision soil farming of turmeric cultivation, IEEE Internet of Things Journal 6 (3) (2019) 5209–5223. doi:10.1109/JIOT.2019.2899128. S. N. Daskalakis, G. Goussetis, S. D. Assimonis, M. M. Tentzeris, A. Georgiadis, A uw backscatter-morse-leaf sensor for low-power agricultural wireless sensor networks, IEEE Sensors Journal 18 (19) (2018) 7889–7898. doi:10.1109/JSEN. 2018.2861431. P. Spachos, S. Gregori, Integration of wireless sensor networks and smart uavs for precision viticulture, IEEE Internet Computing 23 (3) (2019) 8–16. doi:10.1109/MIC.2018.2890234. F. Viani, M. Bertolli, M. Salucci, A. Polo, Low-cost wireless monitoring and decision support for water saving in agriculture, IEEE Sensors Journal 17 (13) (2017) 4299–4309. doi: 10.1109/JSEN.2017.2705043. A. A. Aziz, Y. A. Sekercioglu, P. Fitzpatrick, M. Ivanovich, A survey on distributed topology control techniques for extending the lifetime of battery powered wireless sensor networks, IEEE Communications Surveys Tutorials 15 (1) (2013) 121– 144. doi:10.1109/SURV.2012.031612.00124. M. E. E. Alahi, L. Xie, S. Mukhopadhyay, L. Burkitt, A temperature compensated smart nitrate-sensor for agricultural industry, IEEE Transactions on Industrial Electronics 64 (9) (2017) 7333– 7341. doi:10.1109/TIE.2017.2696508. F. Viani, M. Bertolli, M. Salucci, A. Polo, Low-cost wireless monitoring and decision support for water saving in agriculture, IEEE Sensors Journal 17 (13) (2017) 4299–4309. doi: 10.1109/JSEN.2017.2705043. V. Sharma, U. Mukherji, V. Joseph, S. Gupta, Optimal energy management policies for energy harvesting sensor nodes, IEEE Transactions on Wireless Communications 9 (4) (2010) 1326– 1336. doi:10.1109/TWC.2010.04.080749. C. Alippi, C. Galperti, An adaptive system for optimal solar energy harvesting in wireless sensor network nodes, IEEE Transactions on Circuits and Systems I: Regular Papers 55 (6) (2008) 1742–1750. doi:10.1109/TCSI.2008.922023. Y. Zhang, S. He, J. Chen, Y. Sun, X. S. Shen, Distributed sampling rate control for rechargeable sensor nodes with limited battery capacity, IEEE Transactions on Wireless Communications 12 (6) (2013) 3096–3106. doi:10.1109/TCOMM.2013. 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 050613.121698. [25] Z. Ruirui, C. Liping, G. Jianhua, M. Zhijun, X. Gang, An energy-efficient wireless sensor network used for farmland soil moisture monitoring, in: IET International Conference on Wireless Sensor Network 2010 (IET-WSN 2010), 2010, pp. 2–6. doi:10.1049/cp.2010.1017. [26] C. Wang, J. Li, Y. Yang, F. Ye, Combining solar energy harvesting with wireless charging for hybrid wireless sensor networks, IEEE Transactions on Mobile Computing 17 (3) (2018) 560– 576. doi:10.1109/TMC.2017.2732979. [27] S. Sadowski, P. Spachos, Solar-powered smart agricultural monitoring system using internet of things devices, in: 2018 IEEE 9th Annual Information Technology, Electronics and Mobile Communication Conference (IEMCON), 2018, pp. 18–23. doi:10.1109/IEMCON.2018.8614981. [28] Large 6v 3.7w solar panel. URL https://www.adafruit.com/product/417 [29] Polymer lithium ion battery - 6600mah 3.7v. URL https://www.seeedstudio.com/ Polymer-Lithium-Ion-Battery-6600mAh-3. 7V-p-1711.html [30] P. Spachos, D. Hatzinakos, Self-powered wireless sensor network for environmental monitoring, in: 2015 IEEE Globecom Workshops (GC Wkshps), 2015, pp. 1–6. doi:10.1109/ GLOCOMW.2015.7414207. [31] Arduino uno rev3. URL https://store.arduino.cc/usa/ arduino-uno-rev3 [32] Grove - moisture sensor. URL http://wiki.seeedstudio.com/Grove-Moisture_ Sensor/ [33] Sparkfun wifi shield - cc3000. URL https://www.sparkfun.com/products/retired/ 12071 [34] Xbee 2mw wire antenna - series 2. URL https://www.sparkfun.com/products/retired/ 10414 [35] Lora shield for arduino. URL http://www.dragino.com/products/module/ item/102-lora-shield.html [36] M. Chen, G. A. Rincon-Mora, Accurate electrical battery model capable of predicting runtime and i-v performance, IEEE Transactions on Energy Conversion 21 (2) (2006) 504–511. doi: 10.1109/TEC.2006.874229. [37] L. Gao, S. Liu, R. A. Dougal, Dynamic lithium-ion battery model for system simulation, IEEE Transactions on Components and Packaging Technologies 25 (3) (2002) 495–505. doi: 10.1109/TCAPT.2002.803653. [38] B. S. Bhangu, P. Bentley, D. A. Stone, C. M. Bingham, Nonlinear observers for predicting state-of-charge and state-of-health of lead-acid batteries for hybrid-electric vehicles, IEEE Transactions on Vehicular Technology 54 (3) (2005) 783–794. doi: 10.1109/TVT.2004.842461. 12 View publication stats