1. (CPS)²: Integration of Center Pivot Systems with Wireless Underground Sensor Networks for Autonomous Precision Agriculture Author: Agnelo R. Silva and Mehmet C. Vuran From: University of Nebraska-Lincoln Cyber-physical Networking Lab Department Computer Science and Engineering Presenter:Xiangyi Gu

2. Contents Removable media Abstract and Introduction 1 Background and related work 2 Experiment set up 3 Experiment results 4 Research Challenges 5 Conclusion 6

3. 1. Abstract and Introduction Correctly evaluate farming needs PA (Precision Agriculture) A high density of soil sensors (wired sensors must be installed and removed frequently) a series of practices and tools. In this paper, a novel cyber-physical system is developed though the integration of center pivot systems with wireless underground sensor networks (WUSNs)

4. Problem: wireless communication channel for the soil-air path is significantly affected by many spatio-temporal aspects Location and burial depth of the sensor The soil texture and moisture The vegetation canopy CPS must be developed The speed of the center pivot engine

5. According to this paper, the results show the concept is feasible and can be made highly reliable using commodity wireless sensor motes, and the realization requires non-trivial management due to stochastic real-time communication constraints

6. The rest of paper is organized as follows: 2 The center pivot system and irrigation methods are explained WUSN: Characteristics; Classification; Related work 3 The methodology used in the experiments are described 4 The empirical results for the integration of CP system with WUSNs are discussed 5 The main challenges for the development are discussed 6 The paper is concluded

7. 2.1 Center-Pivot System Cost is high large area Testbed for experiments Apply chemicals Provide emergence irrigation The amount of water is determined by the travel speed of the pivot: the higher travel speed means a smaller amount of water applied to the field A sprinkler pipeline is used and one end of the pipeline is connected to a pivot element at the center of the irrigated Area. Usually, the irrigated area has a circular shape that is clearly visible from the air.

8. Motivation Simplicity Good accuracy Low cost The soil monitoring is an essential part of the solution. If the accuracy of the soil measurements is high enough, the irrigation process can entirely automated to realize a cyber- physical system for PA Problem: Current CP solutions is the delay to detect problems with the system: cause emergence problem We must employ an efficient solution for the communication with the underground sensors WUSN is used in this work to provide the communication infrastructure

9. 2.2 Classification of Wireless Underground Communication Networks Aboveground sender node sends messages to underground nodes The sender is buried and the receiver is above the ground The sender is buried and the receiver is above the ground Both the sender and the receiver are buried underground and communicate through soil UG2UG UG2AG AG2UG WUSN require the buried sensor be deployed at two specific regions: topsoil (first 30cm) and subsoil (blow the topsoil:30cm-100cm)

10. Problem: Topsoil is preferable because the smaller length, the smaller signal attenuation. However, PA applications are mainly related to subsoil WUSNs.

11. 3.Experiment Setup The experiments with 433MHz sensor nodes are from South Central Agricultural Lab of University of Nebraska-Lincolin. The analysis of the soil texture, particle density and bulk density of the site are shown as tale1:

13. 3.1 Hardware Architecture

14. 3.2 Communication Module 1. UG node continuously sends HELLO message to find AG node 2. If the AG node responds, a transaction is initiated and AG node sends 100 packets to UG node PER( packet error rate) the UG node evaluates the quality of the communication RSS(received signal strength) for each packet. A summary containing The PER, Max RSS, Min RSS The Average RSS for that transaction is sent to AG node(state 4 and 14) 3. The UG node sends the sequence of 100 packets to the AG node(state 6 and 15), similar repeat

15. 3.3 Experiment Procedure A B. C. Realized on December 7, 2009. This experiment is related to the UG node located at the position 0. The corn crop had been harvested and the effects of the vegetation canopy can be neglected. The soil moisture is measured and the volumetric water content is found to be 16:6%. Realized on September 9, 2009. The experiment is realized at an area of the crop field where no vegetation canopy is present. Therefore, the canopy effect can be neglected. The soil moisture is measured and the VWC is found to be 22:7% The same scenario as the Experiment B, but it is realized inside the corn crop where reached its maximum height, 285cm. Therefore, the wireless communication is performed subject to the effects of the canopy.

16. 3.3 Experiment Procedure Three different experiments are realized with different conditions of soil moisture and vegetation canopy To avoid the effects of additional factors, the same nodes are used. For these experiments, the horizontal inter node distance between the AG and UG nodes is 3m. the AG node is installed on the structure of the center pivot, the UG node is buried (35-cm burial depth) at the position 0 degree

17. 4. Experiment Results Illustrate the effects of the horizontal inter node distance between the AG and UG nodes on the real-time communication performance

18. The gray area are observed at the beginning and at the end of the communication window and represent in complete transactions (node 315 is non directional all the time for AG2UG link)

19. Figure 8: Effects of the horizontal inter-node distance on RSS:a AG2UG link, b UG2AG link 1, two links present similar performance and AG2UG perform silightly better for positive values of distance; 2, the distance-1m is the point where both AG2UG and UG2AG present the max and very soimilar RSS (received signal strength) value 3. On average, the communication range is 39.2% longer before the UG node than after the UG node; ( expected)

20. Figure9: RSS and PER (packet error rate) for different UG node location 1. The UG2AG links have similar mean and variance in RSS compared to the AG2UG links; 2. Different inter-node distances are considered together and it agree with their experiment; 3. The range of the RSS (received signal strength) values also varies as a function of the UG node’s location

21. Based on these results They observe that besides the high variance of the RSS(received signal strength), the communication channel presents high quality; When UG2AG and AG2UG links are both operational, a high quality communication is observed; Error control scheme are necessary because for the small portion of communication ranges( gray area) a significant increase in errors occur. There results are important for the design of communication protocols for WUSNs

22. 4.2 Effects of Canopy and Soil Moisture In this part, the result of experiments related to the growth of the crop and the soil Moisture are discussed.

23. No canopy effect and a smaller soil a smaller soil moisture effect moisture effect Soil moisture effect only Canopy and soil moisture effect soil moisture effect ExperimentAExperimentBExperimentC 4.2 Effects of Canopy and Soil Moisture

24. 5.Research Challenges Soil IrregulartiyReal-time Operation Soil Moisture Error Control Energy-efficient Operation Challenges Due to the movement of the CP system, the communication availability is significantly limited the soil irregularity is an extremely complex parameter to be controlled if the channel is unidirectional, error detection/correction schemes are highly recommended The soil moisture strongly affects the communication performance. The environment can potentially change the characteristics of the communication channel, for instance, due to the rainfall or after an artificial irrigation. To provide a lifetime of more than 3 years for the UG nodes

25. 6.Conclusion In this work, we propose a novel cyber-physical system through the integration of center pivot systems with wireless underground sensor networks, The two main components is the center-pivot (CP) system, a popular and efficient irrigation solution, and the WUSNs, a recent extension of the WSNs to the underground environment. Through empirical analysis, we show that an efficient PA solution is feasible using commodity wireless sensor nodes, Due to the criticality of real- time communication constraints, the realization depends on several research challenges as discussed in the paper.

26. 7.Future work In my opinion, the result this paper achieved is just initial part(which is not quite believable). From here, the first step is finding the better quality and stable hardware. Because we need to face a number of unstable natural factors, such as soil moisture, real time changing conditions.