LoRa and LoRaWAN

KPN uses LoRa modulation and LoRaWAN as LPWAN technology. The radio and modulation part is specified and patented by the company Semtech . The LoRa Alliance is in charge of standardizing the LoRaWAN part of the stack. Figure 2 gives a graphical representation of the complete stack.

Figure 2 Overview of the complete LPWAN technology stack (Image credit IOP Institute of Physics)

Communication between communication devices and gateways is spread out over different frequency channels and data rates. The selection of the data rate is a trade-off between communication range and message duration. Within the selected channel the LoRa protocol, which is a chirp spread spectrum modulation technique, determines how many bits are required to code the data (coding rate) which results in a maximum data rate. The basic principle of spread spectrum is that each bit of information is encoded as multiple chirps. Within the given bandwidth the relationship between the bit and chirp rate for LoRa modulation may differ between spreading factor (SF) 7 to 12. The communication device may transmit on any channel available at any time, using any available data rate, as long as the following rules are respected:

• The communication device changes channel in a pseudo-random fashion for every transmission. The resulting frequency diversity makes the system more robust to interferences.

• The communication device respects the maximum transmit duty cycle relative to the sub-band used and local regulations.

• The communication device respects the maximum transmit duration (or dwell time) relative to the sub-band used and local regulations.

LoRa data rates range from 0.3 kbps to 50 kbps. Depending on the environmental conditions between the communication device and the gateway the network will determine the best spreading factor (SF) to work on. To maximize ba ttery life, range and overall network capacity, the LoRa network infrastructure can manage the data rate and output power used for the communication for each device individually by means of an adaptive data rate (ADR) scheme. This means that the better the coverage is, the lower the SF will be (Figure 3). KPN requires all users to turn on the ADR functionality to prevent unnecessary congestion in the network. ADR is switched on in the device itself, not by the network. In cases where ADR cannot continuously be used, the device needs to know when to temporarily turn off ADR and must switch it on again as soon as the use case allows it.

Figure 3 Energy consumption and bitrate in relation to the LoRa spreading factor