long range wide area network (LPWAN) (LoRaWAN)
Low Power WANs(LPWAN) are network concepts for the Internet of Things( IoT) and machine-to-machine( M2M) communication. LPWANs are characterized by the fact that they can bridge distances of up to 50 km and require very little energy. There are several technical approaches to implementing LPWANs. One from ETSI: ETSI GSLTN, others are called LoRaWAN, Weightless and RPMA, which stands for Random Phase Multiple Access.
To ensure that the bridgeable distance is not too much affected by free- space attenuation, some of the LPWAN concepts mentioned use frequencies in ISM bands at 433 MHz and 868 MHz. A few also operate in the ISM band at 2.4 GHz.
As for SigFox as a LoRaWAN (Long Range Wide Area Network), for example, it uses the ISM band at 868 MHz in Europe (USA 915 MHz). The bridgeable distance range is over 5 km in urban areas and over 15 km in non-urban areas. There are also already radio transceivers in the 2.4 GHz frequency range that can bridge a range of 10 km. LoRa transmission is a combination of Chirp Spread Spectrum( CSS) and Software Defined Radio( SDR). A key advantage of this modulation technique is its extremely high sensitivity, which can be as low as -135 dBm, up to 20 dB below the noise floor. Corresponding signal levels are still detectable. The LoRaWAN concept supports bidirectional communication, mobility and location-based services.
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The network structure and data rates of LoRaWANs
In terms of network structure, LoRa WAN networks are built in star-in- star topology, with LoRa gateways acting as transparent bridges, switching messages between end points and a central network server. The end points are where the sampling of the measured values or the control takes place. They are connected to a base station, which in turn receives encrypted information from a backbone via TCP/ IP and the SSL protocol. The communication between the end points and the LoRa gateways is done by radio on different frequency channels and with different data rates or wired via Ethernet. The data rates depend on the message duration and range between 300 bit/s and 5 kbit/s.
To maximize battery life from the end components, all data rates and RF output signals are managed by the LoRaWAN network and the end components are controlled by an Adaptive Data Rate( ADR). There are three classes of end devices, all of which can communicate bidirectionally. Class A devices have a scheduled transmission window in the uplink. The wireless sensor uses a controller to determine when and how often to transmit and how much data to transmit. Class B devices are for time-critical applications. They work with a transmission window in the downlink. In this time window the class B device can transmit and is reachable for the LoRaWAN server. And for class C devices, the transmission window is continuously open. The wireless sensor can always receive.
LoRaWAN technology is standardized by the LoRa Alliance. Alternatives to LoRaWAN are SigFox, Weightless, Dash7, 802.11ah and Ingenu.