# An IoT-Based Solution for Intelligent Farming +
## 2 Related Work
### IoT/M2M Protocols and Communication Technologies
#### Low-Power Wide-Area Network Technologies  
An emergent area on low power communications respects the LPWAN technologies. They operate in the license-free bands of the spectrum and can be positioned between the cellular networks and the short-range communications, taking the best of each one. They potentially cover communication ranges similar to a cellular cell, keeping a low power consumption like some of the short-range communications technologies. The data rates are also similar to the short-range communication solutions and, despite being smaller than WLANs and cellular networks data rates, are adequate for many IoT solutions. Some examples are Sigfox, Long Range (LoRa) WAN, NarrowBand-IoT (NB-IoT) and LTE-M.  
Sigfox [16] is a centralized, cellular-like, low-throughput wireless communication system. Energy-wise, it is very efficient, but it provides a limited capacity (a few messages per day with up to 12 bytes each). It requires cellular coverage which, at least in Portugal, is based on the deployment of gateways on existing public telecommunications base-stations. Its actual coverage is still relatively small, particularly in rural areas. It does not allow to perform localization and the bandwidth is insufficient for reporting the amount of data required by the SheepIT project.  
LoRa [19] is a Wireless Wide Area Network (WWAN) specification designed to allow long range communications for IoT-like applications. It was designed to minimize energy consumption and provides modest bit-rates (300 bps to 50 kbps per channel). It may be used as a private network, but it may also be used to deploy a shared service infrastructure. LoRa provides a reasonable bandwidth and is energy-efficient. It also permits RSSI-based localization, but its performance in this regard is poor. For example, a practical evaluation in a limited area (110 \(\times\) 64 m) and with an infrastructure based on six anchor nodes, impracticable for farming applications, generates errors of several meters [38]. LoRa also has a Time-of-Flight based localization scheme that is proprietary, closed source and can only be used in a black-box manner. Results on its accuracy are scarce, but indicate a poor performance, at least for wide ranges (e.g., 100 m for stationary nodes using a public location service [39]). Moreover, LoRa prescribes a star topology and constrains the kind of synchronization and communication between nodes and the gateways (e.g., for battery-powered devices--class A uses an ALOHA-like protocol, without synchronization, and with dedicated receiving slots that may not be needed). Finally, LoRa nodes were considered too expensive to be implemented in each of the animal sensors.  
NB-IOT [17] and LTE-M [18], part of 3 GPP Long-Term Evolution (LTE), have been developed for M2M and IoT applications. Despite providing relatively high bandwidth and potentially low consumption, these protocols depend on a public communication infrastructure, which is often unavailable in rural areas, so it is unsuited for the objectives of SheepIT. Moreover, the need for paying a fee to the telecom operator by each animal eventually may lead to unbearable exploration costs.