Design and experiment of wireless image sensor node with real-time adjustable resolution

In order to overcome the problems of low and non-adjustable resolution existing in wireless images sensor nodes applied in agricultural images acquisition at present, a wireless image sensor node with real-time adjustable resolution was designed and realized in this paper. The node was composed of an image acquisition module, a processor module, a wireless communication module and a power module. The node needed to not only capture, compress, and transmit image data, but also perform multiple task schedules and network protocols, so a powerful ARM (advanced RISC machines) processor S3C6410 was chosen as the processor module of the node. Considering the cost and power consumption, a CMOS (complementary metal oxide semiconductor) type image sensor chip was chosen to design the image acquisition module of the node. The design of image acquisition module included image sensor PCB (printed circuit board) design, chip pin interface design, appropriate lens selection, and development of the sensor chip driver. In order to monitor a larger area of the crop and remotely transmit crop images, the node integrated a WiFi (wireless fidelity) or 4G (the 4th generation) module. A solar power supply system was designed to make the node work stably in the field for a long time. To ensure the stability and reliability of the node, the powerful embedded Linux operating system was employed as the software development platform, and a modular designing method was adopted to program the software system of the node in C/C++ language based on this platform. In order to realize real-time adjustment of the resolution, an algorithm of resolution real-time adjustment based on driver layer and application layer collaboration and multi-thread concurrence was proposed, and all the functions of resolution real-time adjustment of image acquisition, image compression and image transmission were realized in the application layer of software system. In order to verify the performance of the node designed, a series of tests were conducted in Cencun experimental base of South China Agricultural University and Guangdong Dongsheng Farm (Panyu) from April to September in 2016. In the tests, 7 nodes were deployed in the farmland to form an acquisition and transmission network based on WiFi and 4G technologies. To ensure the nodes work stably in the field, where the climate was changeable and the infrastructure was absent, the nodes were encapsulated in a waterproof spherical shield, and a solar panel plus rechargeable batteries was used to supply power for them. The nodes were tested from the aspects of multi-resolution capability, real-time adjustment capability, image acquisition and transmission performance (transmission time and packet loss rate), and the availability of node energy. The test results indicated that the node had 7 different resolutions and its highest resolution was up to a pixel of 5 M, and more importantly, it could adjust its resolution in real time under the control of a remote user, then capture images with different resolution, and finally transmit them to the remote server. The time consumed to capture, compress and transmit 4 images with different resolution of 640×480, 1280×1024, 2048×1536, and 2592×1944 was 4.67, 8.77, 15.38 and 22.74 s respectively, and the average transmission packet loss ratio of 4 images was less than 1%. The tests validate the node designed in this work can capture crop images with different resolution in real time and transmit them remotely, and satisfy the requirement of different users for different crop image precision. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.