## 3 Standards for Cyber-Physical Energy Systems (CPES) Wireless Networking
### LoRaWAN  
The only LPWAN technology currently available on the market for setting up own radio infrastructures in the free ISM band is long range wide area (LoRa) [32]. LoRa is a wireless infrastructure for LPWAN developed by Semtech Corporation. The system architecture consists of three components: the end devices, gateways, and a network server (Figure 1). The end devices are integrated into the LoRaWAN by a LoRa radio chip. A gateway forms the radio base station for all nodes and forwards their data packets to the network server (NS) connected via IP. As the gateways are transparent for the connected nodes, the NS filters receive duplicate messages of a node via more than one gateway and decide which gateway is responsible for the downlink. The NS also provides the API for one or more application servers [32].  
Figure 1: Long Range (LoRa) system components.  
LoRa defines a modulation technique [44] for radio data transmission on the license-free ISM band 169 MHz, 433 MHz, 868 MHz (Europe), and 915 MHz (North America); the radio module is also referred to as \"concentrator\". LoRa meets the above requirement for adaptivity in LPWANs with the patented chirp spread spectrum [45; 46] modulation. This enables control of the data rate and signal level for each connected device via an individually selectable spreading factor (SF) in a value range from 7 to 12. This allows the energy consumption to be controlled specifically according to the usage profile and the distance of the node from the base station. More intensive use of the radio network with a modulation frequency (BW) and an improved error correction can be obtained with LoRa by setting a lower data rate. In Europe, typical BW values are 125 kHz, 250 kHz, and 500 kHz. The error correction is controlled by a code rate (CR, value range 1-4). The relationship of these influencing factors to the data rate (R\({}_{\text{b}}\)) is calculated as follows:  
\[R_{b}=\frac{SF\times BW\times 4}{2^{SF}\times(4+CR)}\ Bit/s \tag{1}\]  
Without taking CR into account, a raw data rate of 22 Bit/s to 27 kbit/s is, therefore, possible in Europe. As another limitation, the regulation of shared access for the frequency band used must also be taken into account. In the European ISM band, the duty cycle transmission may not exceed 1% of the time [47].  
The LoRa specification distinguishes three device classes--A, B, and C--for end devices [32] in order to meet different requirements for power consumption. The most economical class A devices use the ALOHA method in the uplink, where a downlink is only possible in a short time window immediately after the uplink. This class is suitable for sensors that transmit regularly and only need to receive an acknowledgment of receipt. Class B devices can also receive data independently of uplink. For this purpose, fixed time windows are defined with the network server, in which the nodes are woken up and supplied via a beacon packet broadcasted by the gateway. This device class is required when actuators have to be switched or other information has to be supplied to the node. Class C devices are permanently in receiving mode. Therefore, battery operation is not possible. This allows fast feedback to the node. All three classes can be mixed within a LoRa network.  
There are numerous case studies that investigate the reliability, range, and achievable data rate of LoRa. Owing to the different conditions and parameters, these results vary significantly. In a suburban area, coverage of 3 km could be achieved [48]. Another study [41] inside buildings confirms an achievable range of more than 300 m through several walls, but none of the SF could achieve a 100% loss-free transmission. TTN [43] reports a LoRa packet transmission that was achieved over a distance of 702 km with a transmission power of 25 mW (measured in August 2017), transmitted by a helium-filled balloon from an altitude of 38,772 km under perfect weather conditions.