Analysis of the system architecture composition of LoRa technology

At present, the network layer protocol based on LoRa technology is mainly LoRaWAN, and there are a small number of non-LoRaWAN protocols, but the communication system network is all star network architecture, and the simplification and improvement on this basis. Mainly include the following 3 kinds.
　　(1) Point-to-point communication.
　　Point-to-point communication is mostly seen in the early LoRa technology. Point A initiates, point B receives, and can reply or not reply to confirm. It is recommended to separate the frequency points between multiple groups and simply use the high sensitivity of LoRa modulation. Specific applications and experimental projects. The advantage lies in the simplest, the disadvantage lies in the absence of networking.
　　(2) Star network polling.
　　Point-to-multipoint communication, N slave nodes communicate with the central point in turn, upload from the node, wait for the central point to receive it and return confirmation, and then the next node will start uploading again, until all N nodes are completed, and a cycle ends. This structure is essentially point-to-point communication, but time-sharing processing is added, and the frequency points between N slave nodes can be separated or reused. The advantage lies in the low cost of a single project, but the disadvantage is that it is only suitable for applications with a small number of slave nodes and low network real-time requirements.
　　(3) Star network concurrency.
　　Point-to-multipoint communication. Multiple slave nodes can communicate with the central point at the same time. The slave nodes can report data randomly. The nodes can automatically adopt frequency hopping and rate adaptive technology according to the external environment and channel blockage. Logically, the gateway can receive different rates and With the combination of signals at different frequencies, the gateway can physically receive 8, 16, 32 or even more channels of data at the same time, reducing the probability of collisions when a large number of nodes are uplinking. The system has great scalability, can build a network separately, and can be cross-connected. The LoRa field currently mainly refers to LoRaWAN technology.
　　2. System composition
　　The system composition of point-to-point communication and star network polling is relatively simple. Both ends are nodes, which are divided into master and slave. After the master node receives the uplink data from the slave node, it will send a downlink confirmation frame to the slave node, and then the slave node enters sleep, the working mode is relatively simple. Here we mainly explain the concurrency structure of the LoRaWAN star network. The LoRaWAN system is mainly divided into three parts: node/terminal, gateway/base station, and server.
　　Node/Terminal (Node): LoRa node, representing a large number of various sensing applications, is divided into three different working modes of Class A, Class B and Class C in the LoRaWAN protocol. In Class A working mode, the node actively reports, sleeps normally, and can receive gateway downlink data only in a fixed window period. The advantage of Class A is that it has extremely low power consumption, which is lower than that of non-LoRaWAN LoRa nodes. For example, the working life of more than 10 years for water meter applications is usually based on Class A. ClassB mode is a fixed period of time synchronization. In a fixed period, the window period can be randomly determined to receive gateway downlink data, taking into account real-time performance and low power consumption, and is characterized by high requirements for time synchronization. Class C mode is a constant sending and receiving mode. The node does not consider power consumption and can receive gateway downlink data at any time. The real-time performance is the best. It is suitable for applications that do not consider power consumption or require a large amount of downstream data control, such as smart meters or smart street light control.
　　Gateway/base station (Gateway): The gateway is a key device for building a LoRaWAN network, and its purpose is to alleviate the concurrency conflicts caused by massive node data reporting. The main features are as follows: 1) Strong compatibility, all applications conforming to the LoRaWAN protocol can be accessed; 2) Flexible access, a single gateway can access dozens to tens of thousands of nodes, the nodes are randomly connected to the network, and the number can be extended; 3 ) Strong concurrency, the gateway can support at least 8 frequency points, and at the same time random 8 channels of data concurrent, the frequency points can be expanded; 4) Full duplex communication can be realized, uplink and downlink concurrency does not conflict, and the effectiveness is strong; 5) High sensitivity, the same The speed is higher than that of non-LoRaWAN devices; 6) the network topology is simple, the star network is more reliable, and the power consumption is lower; 7) the network construction cost and operating cost are very low.
　　Server: Responsible for the management and data analysis of the LoRaWAN system, and the main control commands are issued by the server. According to different functions, it is divided into: network server (Network Server) communicates with gateway to realize LoRaWAN data packet analysis and downstream data packaging, communicates with application server to generate keys such as network address and ID; application server (Application Server) is responsible for loading data Encryption and decryption, and the generation of some keys; Client Server is a server based on B/S or C/S architecture developed by users, mainly dealing with specific application services and data presentation.
　　The advantages of the LoRaWAN system include: wide coverage, saving network optimization and construction costs, and reducing on-site construction complexity; server-side authentication can achieve cross coverage, reducing coverage blind spots; server-side overall management, improving channel utilization, and increasing system capacity; Gateway multi-channel concurrency reduces conflicts, supports node frequency hopping, and increases system capacity; node rate adaptation (Adaptive Data Rate) reduces power consumption and concurrent conflicts, and increases capacity; high security, two-level AES-128 (Advanced Encryption Standard-128) ) Data encryption; star network structure to improve robustness; LoRaWAN protocol standardization.