# A Communication Framework for Image Transmission through LPWAN Technology
## 2 Related Work  
Many works have presented LPWAN design goals, requirements, and features [24; 25; 26; 27; 28]. All of them concluded LPWANs are the most suitable network solution for massive IoT system deployments over large areas with energy-efficient working schemes, low-cost and low-complexity end-devices, low data rates, and high latency. With a wide variety of LPWAN technologies, there has been a growing interest in the evaluation and comparison of the network performances, in particular the ones working in unlicensed frequency bands. LoRaWAN is one of the most representative LPWAN technologies which operate in sub-GHz Industrial, Scientific, and Medical (ISM) frequency bands at 868 MHz in Europe and 915 MHz in North America. This technology has been widely deployed in more than 77 countries worldwide, reaching billions of end-device connections [29]. LoRAWAN is a proprietary technology based on LoRa physical (PHY) layer which brings large coverage, low energy consumption, and low data rates. LoRaWAN was developed in North America by Semtech, IBM, Actility, and Microchip. The LoRaWAN network is single-hop where end-devices or motes are connected directly to a LoRAWAN base station acting as the gateway to the information server. LoRa PHY is based on a Chip Spread Spectrum (CSS) modulation. CSS is a subcategory of direct-sequence spread spectrum (DSSS) that takes advantage of the controlled frequency diversity to recover data from weak signals, even near the noise level. CSS modulation was used in military communications due to the relatively low transmission power requirements, robustness to channel degradation, multipath, fading, Doppler effect, and jamming interference [30]. Recently, a growing interest in LPWAN technologies has appeared and several works have reported different contributions in the comparison, evaluation, and application of LPWAN. In this regard, LoRaWAN has taken particular relevance due to its flexible and configurable characteristics, for instance, in the work of [31; 32], a realistic testbed for LoRaWAN network is presented; other works have explored energy consumption schemes for LoRAWAN networks [33; 34; 35; 36], the extension of network coverage in urban areas [37; 38], improvements for the Adaptative Data Rate (ADR) of LoRa modulation technique [39; 40; 41], and wireless systems solutions combined with the use of 5G systems [42; 43]. Among the different LoRaWAN network implementations, platforms such as DPP2-CC430, DPP-SX1262, and SX1276 are mainly used [5; 31; 37; 44; 45; 46; 47; 48]. Other works have produced analytic and simulation cases, where LoRaWAN network performance features such as Bit Error Rate (BER) and Signal-to-Noise Ratio (SNR) are obtained [49; 50]. In addition, there has been an increasing interest to investigate optimal modulation parameters in LoRaWAN, such as the Spreading Factor (SF), modulation bandwidth, and transmission power for improving data rate, collision avoidance, resource allocation, and latency. In this regard, multiple techniques and evaluation scenarios have been recently proposed, some of them include fair ADR algorithms [51], time-slotted spreading factor hopping schemes for mitigating blind spots [52], performance evaluation in building environments [53], collision avoidance resource allocation techniques [54], experimental evaluation of LoRa packet reception [55], radio channel evaluation of massive node deployment [56], traffic evaluation studies [57], enhanced data transmission techniques [58], integration with cognitive radio schemes [59], secure firmware updates with adaptive data rate techniques [60], and the study of the wireless propagation of LoRa chirp radio signals over the water of rivers in tropical regions [61]. From the application point of view, LoRaWAN has encountered a relevant place as the network solution for IoT services. Thus, in [62] a LoRa sensor network for monitoring pastured livestock location is presented.