The rapid development of the Internet of Things puts higher demands on wireless communication technologies, and LPWAN, which is designed for low-bandwidth, low-power, long-distance, and large-scale connected Internet of Things applications, is also rapidly emerging. LoRa is a typical representative of LoRa, which is based on ultra-long-range low-power data transmission technology below 1GHz. Its acceptance sensitivity is astonishing -148dbm, which is the highest compared with other advanced sub-GHz chips in the industry. The receiving sensitivity is improved by more than 20db, which ensures the reliability of the network connection.
Due to its low power consumption, ease of construction and deployment, it is widely used in wide-area Internet of Things. LoRa operates primarily in free global bands (ie, unlicensed bands), including 433, 868, and 915 MHz. The LoRa network is mainly composed of a terminal (built-in LoRa module), a gateway (or base station), a server, and a control system. The data can be transmitted in both directions.
It uses linear frequency modulation spread spectrum modulation technology, which maintains the same low power consumption characteristics as FSK (Frequency Shift Keying) modulation, and significantly increases the communication distance, while improving network efficiency and eliminating interference, that is, different spread spectrum The terminals of the sequence do not interfere with each other even if they are transmitted at the same frequency. Therefore, the concentrator/gateway developed on this basis can receive and process data of multiple nodes in parallel, greatly expanding the system capacity.
The advantages of LoRa are mainly reflected in the following aspects:
1. Greatly improved reception sensitivity and reduced power consumption
The link budget of up to 157db allows communication distances of up to 15 kilometers (related to the environment). Its receiving current is only 10mA, and the sleep current is 200nA, which greatly delays the battery life.
2. The gateway/concentrator based on this technology supports parallel processing of multiple channels and multiple data rates, and the system capacity is large.
As shown in Figure 2, the gateway is the bridge between the node and the IP network (through 2G/3G/4G or Ethernet). Each gateway can process 5 million communications per node per day (assuming 10 bytes per transmission, 10% network occupancy). If the gateway is installed at the location of the existing mobile communication base station and the transmission power is 20 dBm (100 mW), it can cover about 2 km in a densely constructed urban environment, and up to 10 km in a suburb with a lower density.
3. The system based on terminal and concentrator/gateway can support ranging and positioning.
LoRa's measurement of distance is based on the signal's airborne transmission time rather than the traditional RSSI (Received Signal Sterngth Ind-icaTIon), while positioning is based on the multipoint (gateway) measurement of the airborne time difference of one point (node). Its positioning accuracy can reach 5m (assuming a range of 10km).