# A Communication Framework for Image Transmission through LPWAN Technology
## 2 Related Work
In [63], an air quality monitoring and improvement system based on wireless sensor and actuator networks using LoRa communication is proposed. In [64], a development for air quality monitoring and gas leakage events with the LoRa sensor network is presented. The work in [65] presents several low-cost solutions using novel user interfaces and wireless communication technologies for monitoring irrigation systems. In [66], a new LoRa-like receiver is proposed to improve the robustness of symbol decoding to synchronization errors for satellite communications. In [67], a rural healthcare IoT architecture with the use of LoRa is shown. In [68], the development of a smart irrigation system is presented with enhanced coverage in urban areas thanks to the use of LPWAN sensor nodes based on LoRa and LoRaWAN. In [69], a farm monitoring system which incorporates unmanned aerial vehicles (UAVs), and LoRa technology for farm management and operation is presented. In [70], a smart campus proposal is presented with the use of LoRa. Ref. [71] presents the results of a study promoted by the Lisbon city council for trialing LPWAN technology for waste management. The work in [72] presents a traffic flow detection system based on LoRa, mainly focused on traffic conditions monitoring for accidental risk reduction in highways. Image transmission on LoRaWAN has already been tackled by many authors in the literature. In [15], a monitoring method with image sensors communicating over the LoRa physical layer was presented. The authors proposed a scheme for overcoming the bandwidth limitation on LoRa. The transmitter and receiver node consists of a LoRa Arduino shield that comprises an RN2903 transceiver stacked on an Arduino Mega microprocessor. The experimental setup is composed of an Adafruit TTL serial camera that captures a JPEGimage, then images are encrypted as hexadecimal data and split into packets to transfer via LoRa. Image postprocessing consists on the evaluation of the Peak Signal-to-Noise Ratio (PSNR) of the received image. Results use different SF values with different coverage ranges. Results with a typical SF value of 7 show a total transmission packets of 314 with a transmission time of 67 s. In addition, the number of transmitted images were 21, where only 12 were successfully received. Some important features such as image size, medium-access duty cycle, shipping time, and LoRa symbol forms are not presented. The work in [73] presents a low-cost, low-power, long-range image sensor. The proposed system uses a Teensy 3.2 board as the host microcontroller to drive the CMOS uCamII camera capable of providing JPEG bitstream. First, the authors retrieve raw 128 \(\times\) 128 (8 bits per pixel) greyscale images, then image compression on the board is carried out on the embedded system. The authors use an encoding scheme proposed in [74] where image compression is carried out by independent coding blocks to ensure that data packets are decodable and correctly received at the sink, and the de-correlation of neighboring blocks must be performed before packet transmission by appropriate interleaving methods to ensure that error concealment algorithms can be efficiently processed on the received data. The proposal presented in [74] uses a discrete cosine transformation for image compression. The result of this compression scheme is a JPEG-like coder and operates on 8 \(\times\) 8 pixel blocks with advanced optimizations on data computation to keep the computational overhead low. In addition, an optimized pixel interleaving scheme based on Torus Automorphisms is used [75]. Data are transmitted in different packets, with an interleaving scheme for retrieving enough information to obtain an approximation of the original value without affecting the energy consumption and time of use, or complexity of the image reconstruction process. The reconstructed image quality is acceptable until 80%. The LoRa module in Air9 from Modtronix with the reference SX1276 chip is used in the implementation.