# A Long-Distance Communication Architecture for Medical Devices Based on LoRaWAN Protocol
## 2 Related Works  
From research in the field, LoRa was first developed by the start-up Cycleo in 2009, in Grenoble, France, and was acquired three years later by Semtech (USA). In 2015, LoRaWAN was standardized by the LoRa-Alliance, and it is implemented in 42 countries and is still ongoing in other countries, due to various mobile operators (e.g., Bouygues and Orange in France, KPN in the Netherlands, and Fastnet in South Africa) [11]. Since the LoRaWAN protocol is promoted by LoRa Alliance, which consists of more than 5800 member companies, the physical layer of LoRa belongs to and is maintained by Semtech and has announced an extension of the LoRa physical layer called Long Range-Frequency Hopping Spread Spectrum (LR-FHSS). The LR-FHSS is a fast FHSS (Frequency Hopping Spread Spectrum) modulation with bit rates ranging from 162 bits/s to 7.8 bits/s used for uplink only and was designed to introduce higher levels of network flexibility,targeting applications that require differentiated service levels [11; 12]. There exist both private and public LoRa networks and everyone can set up their own LoRa gateway. LoRa represents a wireless communication modulation technique, which uses a variation of Chirp Spread Spectrum (CSS--is a spread spectrum technique, where information is spread out by encoding the information onto a chirped signal which is a linear frequency sweep) to transmit messages. Many older wireless systems use Frequency Shift Keying (FSK) because it is effective for low power but LoRa offers the possibility of communicating using Gaussian Frequency Shift Keying (GFSK). Thus, we work with frequencies under the order of GHz in the unlicensed Industrial, Scientific, and Medical (ISM) band, such as 868 MHz in Europe, 915 MHz in North America, and 433 MHz in Asia [13]. LoRa as well as other wireless technologies using unlicensed ISM bands are limited by duty cycle (1% of communication time in Europe). LoRa is also based on Chirp Spread Spectrum (CSS) technique, which maintains the same low power characteristics as FSK modulation but significantly increases the communication range. As I say, the transfer rate of the technology is between 300 bps and 50 kbps and it depends on the spread factor and the bandwidth of the channel. Moreover, messages transmitted using different spreading factors can be received simultaneously by LoRa base stations. The maximum payload length for each message is 243 bytes [14]. The Long Low-Power Wide-Area (LPWA) systems operating in the Industrial, Scientific, and Medical (ISM) band have a limited transmission power of 14 dBm whereas the transmission power in the cellular bands is from 20 to 23 dBm. The CSS technique has been used in military and space communications for decades, due to the long communication distances that can be obtained and robustness to interference, but LoRa is the first low-cost implementation for commercial use. In conclusion, the advantage of the LoRa technology is the ability to cover long distances; thus, a single gateway or base station can cover entire cities or hundreds of square kilometers. The range of coverage depends largely on the environment or obstacles in a given area, but LoRa technology and open LoRaWAN protocol have greater coverage than any other standardized communication technology [15]. The network protocol and architecture have the greatest influence in determining the battery life of a node, the network capacity, the quality of service, the security and the variety of applications served by the network. The environmental access control mechanism offered by LoRaWAN protocol allows several end devices to communicate with a gateway using LoRa modulation [13]. For any Low-Power Wide-Area communication network, it is extremely important to incorporate security. LoRaWAN uses two levels of security: one for the network and one for the application. Network security ensures the authenticity of the network node, while the security level of the application ensures that the network operator does not have access to the end-user application data [11].