132
E. Fraccaroli and D. Quaglia
band is a 25 mW area, but the duty cycle is 0.1%; this zone can be interesting to
communicate when an object is emitting once a day: the risk of collision is really
lower and the number of time you will have to re-emit is, as a consequence, lower, so
in this sub-band, you can expect to preserve your energy. The 869.4 to 869.65 zone
is particularly interesting because you can communicate at 500 mW with a 10%
duty cycle. An end device would not be able to exploit such resource when running
on battery but a gateway can use it: the higher power allows to communicate far
away and be heard over the local noise; the larger duty cycle allows the gateway
to communicate with many devices or send a larger amount of data. The last zone
869.7 to 870 is the last 25 mW/1% zone where you can deploy extra LoRaWAN
channels. It is worth noting that this regulation on 868 MHz band applies in Europe,
but similar regulations exist for all other countries.
LoRaWAN has three different classes of operations to address the different
application needs:
• Class A. It is the default operation mode which must be supported by all
LoRaWAN end devices; class A communication is always initiated by the end
device and is fully asynchronous. Each uplink transmission can be sent at any
time and is followed by two short downlink windows, giving the opportunity for
bi-directional communication, or network control commands if needed. This is a
CSMA-type protocol. The end device can enter low-power sleep mode for as long
as defined by its own application: there is no network requirement for periodic
wake-ups. This makes class A the lowest power operating mode while still
allowing uplink communication at any time. Because downlink communication
must always follow an uplink transmission with a schedule defined by the end
device application, downlink communication must be buffered at the network
server until the next uplink event.
• Class B. Devices are synchronized to the network using periodic beacons and
open downlink “ping slots” at scheduled times. This provides the network the
ability to send downlink communications with a deterministic latency, but at the
expense of some additional power consumption in the end device. The latency is
programmable up to 128 s to suit different applications, and the additional power
consumption is low enough to still be valid for battery powered applications.
• Class C. It further reduces latency on the downlink by keeping the receiver of
the end device open at all times that the device is not transmitting (half duplex).
Based on this, the network server can initiate a downlink transmission at any
time on the assumption that the end device receiver is open, so no latency. The
compromise is the power drain of the receiver (up to 50 mW) and so class C
is suitable for applications where continuous power is available. For batterypowered devices, temporary mode switching between classes A and C is possible
and is useful for intermittent tasks such as firmware over-the-air updates.
LoRaWAN defines two layers of cryptography, i.e., a unique AES 128-bit Network Session Key (NwkSKey) shared between the end device and network server
and a unique AES 128-bit Application Session Key (AppSKey) shared end-to-end
at the application level (lower part of Fig. 3.18). As depicted in Fig. 3.21, NwkSKey
E. Fraccaroli and D. Quaglia
band is a 25 mW area, but the duty cycle is 0.1%; this zone can be interesting to
communicate when an object is emitting once a day: the risk of collision is really
lower and the number of time you will have to re-emit is, as a consequence, lower, so
in this sub-band, you can expect to preserve your energy. The 869.4 to 869.65 zone
is particularly interesting because you can communicate at 500 mW with a 10%
duty cycle. An end device would not be able to exploit such resource when running
on battery but a gateway can use it: the higher power allows to communicate far
away and be heard over the local noise; the larger duty cycle allows the gateway
to communicate with many devices or send a larger amount of data. The last zone
869.7 to 870 is the last 25 mW/1% zone where you can deploy extra LoRaWAN
channels. It is worth noting that this regulation on 868 MHz band applies in Europe,
but similar regulations exist for all other countries.
LoRaWAN has three different classes of operations to address the different
application needs:
• Class A. It is the default operation mode which must be supported by all
LoRaWAN end devices; class A communication is always initiated by the end
device and is fully asynchronous. Each uplink transmission can be sent at any
time and is followed by two short downlink windows, giving the opportunity for
bi-directional communication, or network control commands if needed. This is a
CSMA-type protocol. The end device can enter low-power sleep mode for as long
as defined by its own application: there is no network requirement for periodic
wake-ups. This makes class A the lowest power operating mode while still
allowing uplink communication at any time. Because downlink communication
must always follow an uplink transmission with a schedule defined by the end
device application, downlink communication must be buffered at the network
server until the next uplink event.
• Class B. Devices are synchronized to the network using periodic beacons and
open downlink “ping slots” at scheduled times. This provides the network the
ability to send downlink communications with a deterministic latency, but at the
expense of some additional power consumption in the end device. The latency is
programmable up to 128 s to suit different applications, and the additional power
consumption is low enough to still be valid for battery powered applications.
• Class C. It further reduces latency on the downlink by keeping the receiver of
the end device open at all times that the device is not transmitting (half duplex).
Based on this, the network server can initiate a downlink transmission at any
time on the assumption that the end device receiver is open, so no latency. The
compromise is the power drain of the receiver (up to 50 mW) and so class C
is suitable for applications where continuous power is available. For batterypowered devices, temporary mode switching between classes A and C is possible
and is useful for intermittent tasks such as firmware over-the-air updates.
LoRaWAN defines two layers of cryptography, i.e., a unique AES 128-bit Network Session Key (NwkSKey) shared between the end device and network server
and a unique AES 128-bit Application Session Key (AppSKey) shared end-to-end
at the application level (lower part of Fig. 3.18). As depicted in Fig. 3.21, NwkSKey