# MAC Layer Protocols for Internet of Things: A Survey
## 3 Long Range MAC Layer Protocols
### LoRa--Long Range Protocol  
LoRa defines a physical layer technology developed by Cycleo in 2010, a company that was acquired by Semtech from Camarillo, United States of America.The LoRa module manufacturer offers the user a programmed library that allows communication between LoRa nodes, providing a simple link protocol [109]. Libelium, a company based in Zaragoza, Spain provides the tools and libraries needed to operate with LoRa [110]. The LoRa protocol is an open standard defining physical layer to use direct sequence spread spectrum (DSSS) with multiple spreading factors that range from 7 to 12. This combination allows the establishment of a relationship between distance coverage and the desired data rate. This technique in sub-GHz ISM band enables robust communication with a low power consumption for long distances. By using Frequency Shift Key (FSK) modulation with the optional use of forward error correction (FEC), LoRa allows demodulation of the signal even when the signal level is below the noise level. LoRa also counts on use of a frequency modulated (FM) chirp, based on a spread spectrum modulation with a chirp spread spectrum (CSS) variation. Thus, LoRa modulates data in different channels and speeds them, with a forward integrated error correction (FEC). Thus, it is possible to increase the coverage range while maintaining the low energy consumption characteristics offered by the FSK modulation. The usage of coding gain significantly improves receiver sensitivity and uses the full bandwidth spectra to transmit a signal. Then, it is more robust to channel noise and independent from the frequency compensations caused by low cost crystals. LoRa techniques assure signal demodulation lower than \(-50\) dB SNR against 8 to 10 dB necessary for FSK demodulation of signals in different ISM bands. The frequency band used in Europe is the ISM band of 863-870 MHz regulated by European Telecommunications Standards Institute (ETSI). It uses 8 arbitrarily chosen channels, according to the current UN-111 in Spanish BOE-A-2013-4845 [111], with a bandwidth of 0.3 MHz per channel. For the ISM 902-928 MHz FCC regulation, LoRa works with 2.16 MHz per each one of the 13 channels. To address the low-cost, low-power and robustness issues, LoRa Modulation counts on some key properties. Easy scalability of the LoRa modulation involves frequency and bandwidth domains, thus  
Figure 21: LTE eMTC uplink channels. allowing its use in wide band direct sequence and narrow-band frequency hopping systems. This adaption can be done by programming the device to work according to its needs. The low-cost and low-power high efficiency can be achieved with a constant modulation scheme and the great link budget obtained using the processing gain, thus reducing the transmitted power. The asynchronous nature and high bandwidth used makes the LoRa signal more resistant to interference mechanisms, whether they are in-band or out-of-band inferences. LoRa modulation presents better immunity, mainly to pulsed AM (Amplitude Modulated) interference, compared with FSK modulation systems. This is due to the period duration of the LoRa modulation is longer than the short duration typical bursts of FHSS systems. The effects of fading and multipath, common in urban and suburban areas, are faced with wide spreading of the chirps in the spectrum. The usage of Chirp Spread Spectrum (CSS) modulation, allows the system to be more resistant to these effects. The Doppler effect, when present, influences the quality of demodulated signals in applications. However, the CSS modulation shows small sensitivity to the Doppler effect due to the low frequency variation generated by it. This characteristic can be suitable for applications where the monitored targets have mobility support. With robustness against spectrum interference and unaware of fading and multipath effects, LoRa exceeds the link budget of conventional FSK systems and can increase up to four times the range, when compared to FSK systems. This is considering fixed transmission power and throughput.