# A Communication Framework for Image Transmission through LPWAN Technology
## 1 Introduction  
Communication and information technologies are becoming increasingly vital in our daily lives. Smart cities, agricultural monitoring, sensors service control, telemetry, smart grids, smart homes, smart health services, and human-body signal monitoring are just a few of the applications that have emerged since the advent of the Internet of Things (IoT) concept. Because the nature of the sensed data includes simple environmental variables, most IoT applications rely on the transmission of a small amount of data over a long distance. However, when data information increases in long-distance transmissions, IoT communication networks are limited, especially when looking for cost-effective and scalable solutions. Because of their high operational costs and limited coverage, particularly in remote areas, cellular networks are rarely used for agricultural applications. Unlicensed Low-Power Wide-Area Network (LPWAN) technologies have gained popularity due to their appealing characteristics, which include long range, scalability, low operational cost, and low energy consumption. Nonetheless, due to their limited capacity, unlicensed LPWAN-based solutions are still limited when it comes to transporting a large amount of data [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11]. As previously stated, LPWAN technologies can be classified based on the frequency bands in which they operate: licensed bands such as LTE-M, Extended coverage 2G, andNB-IoT. Additionally, they operate in unlicensed bands such as 1 SigFox, On-Ramp, and LoRaWAN. In terms of design goals, both types of LPWAN networks have advantages and disadvantages [12; 13]. LoRaWAN was used in this work, and its modulation in particular was investigated due to its flexibility in terms of adaptive data rate and noise robustness. LoRaWAN is one of the most prominent LPWAN technologies, with a network deployed in over 77 countries and over a billion end-device connections. LoRaWAN operates at 868 MHz in Europe and 915 MHz in North America in the sub-GHz Industrial, Scientific, and Medical (ISM) frequency bands [12]. The LoRaWAN modulation scheme, also known as LoRa, employs a spread spectrum technique with a payload of 222 bytes per message [7; 10; 11]. Under these conditions, the number of messages to send for an IoT application where regular images must be transmitted is prohibitively large, and the transmission time is a couple of hours given the spectrum access restrictions of ISM bands. For example, in the best scenario with 500 kHz of bandwidth (BW) and a Spreading Factor (SF) of 7, the time over the air (ToA) for transmitting an image larger than 15 kbytes is around 100 ms per message. Furthermore, taking into account the ISM frequency band policies, which require a duty cycle of 1% for every single transmission (ETSI EN 300 220-1) [14], the total time exceeds 5 h, which is prohibitively long for any IoT application. With the same SF and BW conditions, but frequency hopping between 915 and 928 MHz (implemented between channels with no contiguity [14]), the time is around 3 min, not including saturation, collisions, and other problems associated with the use of shared spectrum. Image transmission is a challenging issue in both cases, and it is a general problem addressed in the literature for LPWAN networks, particularly when high data rates with low power consumption and long communication range are required [15; 16; 17; 18]. As a result, a framework for transporting images using LoRa modulation without affecting features such as duty cycling, frequency hopping, or the use of multiple nodes to transmit different information packets simultaneously has been developed [13; 19; 20; 21; 22; 23]. The communication system was developed on Software-Defined Radios (SDR) for LoRa information packet transmission and reception in order to have complete control over the LoRa modulation features.