LoRa architecture for air quality monitoring

Long Range technology (LoRa) is a technology used in the current Internet of Things (IoT) applications. The frequency supported by this network is around 433Mhz, 868MHz or 956Mhz. This type of network uses the Frequency Shifting Keying and has a small error rate. Moreover, LoRa has the advantage that it is a platform for long-distance communication and another factor is that it has a long-term battery performance. We will present an architecture based on LoRa Gateway which will be connected to PyCom. We will use as well specific gas sensors which will measure the quality of the air. This architecture will be connected to a breadboard with different types of gas sensors to collect data about the air pollutants.

Daily, a lot of cars are being used in large cities, which result in a high concentration of CO 2 and the effect of a greenhouse is created as well. In order to have a better understanding of the effects of such gases, we have to measure the quantity of gas emission in the air. In Table 1 [4] After analyzing the current the table, we can see that the numbers are exceeding in Figure 1.: Figure 1. Pollutants parameters in Bucharest [5]

LoRa MODULATION
LoRa emerges as a novelty nowadays, and one important factor is that it is a proprietary spread spectrum modulation scheme and it is a derivative of CSS modulation. The sensitivity is exchanged with the data rate in a fixed channel bandwidth. It also induces a variable data rate, whereas we use an orthogonal spreading factor allowing the system designer to trade the data rate for range or power allowing optimization of the network performance in a bandwidth which is constant. This type of modulation has the possibility to function at the same time with another existing network architecture. [6]

Chirp Spread Spectrum
Chirp Spread Spectrum was invented in 1940's and it was used in military and secure applications, because this type of modulation doesn't require a high transmission power but a low one; it is now widely used in a lot of applications which don't need much power. The principle of this spectrum enables the increase of the bandwidth of a signal to compensate for the degradation of the signal-to-noise ratio of a radio channel [6]

LoRa Spread Spectrum and Key Properties
In a LoRa system the modulation is done by making a chirp signal which continuously varies in frequency, therefore the spreading factor being created. The timing and frequency offsets are equal and so the receiver design is simplified. It is generally known that the spectral bandwidth is almost equal to the frequency bandwidth of the chirp. Afterwards the data signal is fragmented at a higher data rate and modulated to the signal that is a spectral bandwidth.
The key properties for LoRa modulation are:

EXPERIMENTS
We chose the PyCom LoPy4 for our experiments as it has the best coverage, around 22km taken from Table 2 representing a comparison between frequency, range and topology of different interconnectivity technologies. Figure 3 presents the implemented LoRa architecture.  Firstly, the gas sensors transmit the data to the PyCom LoPy4 board, afterwards to the Gateway and lastly to the Cloud Platform developed during the SWITCH project [8] for time critical applications. The transmitted data is shown on a web dashboard.

CONCLUSIONS AND FUTURE WORK
In this paper we presented how a LoRa architecture using a PyCom as a module will transmit data to a gateway and then to a LoRa gateway. We tried as well the LoRa GPS hat and noticed that by using a PyCom the whole operation is simpler. The PyCom transmits the data received from the gas sensors to the gateway and then to the cloud platform. If we used a LoRa GPS hat, then it would have been more complicated because we would require a Raspberry Pi3 which uses more power than a PyCom and more computation power, whereas what we need is just to transmit the data from the taken measurements to the gateway.
In conclusion, a LoRa architecture for air pollution is using low power and has a longer range then other types of network. As future work we will program the PyCom and connect it to the LoRa gateway to transmit the received data from the gas sensors.