1. Introduction to LoRa wireless technology
LoRa is a long-distance wireless transmission technology based on spread spectrum technology. It is actually one of many LPWAN communication technologies. It was first adopted and promoted by the American Semtech company. This solution provides users with a simple means of achieving long-distance, low-power wireless communication. Currently, LoRa wireless technology mainly operates in the ISM frequency band, mainly including 433, 868, 915 MHz, etc.
LoRa is a physical layer or wireless modulation used to establish long-distance communication links. Many legacy wireless systems use frequency shift keying (FSK) modulation as the physical layer because it is a very efficient modulation that achieves low power consumption. LoRa is based on linear frequency modulation spread spectrum modulation, which maintains the same low power consumption characteristics as FSK modulation, but significantly increases the communication distance. Linear spread spectrum has been used in military and space communications for decades due to its ability to achieve long communication ranges and robustness to interference, but LoRa is the first low-cost implementation for commercial use.
The advantage of LoRa modules is the long-distance capability of the technology. A single gateway or base station can cover an entire city or hundreds of square kilometers. In a given location, distance depends largely on the environment or obstacles, but LoRa and LoRaWAN have a link budget that is superior to any other standardized communications technology. Link budget, usually expressed in decibels (dB), is the primary factor determining distance in a given environment.
2. LoRa wireless technology network composition
The LoRa network is mainly composed of four parts: terminal (can have built-in LoRa module), gateway (or base station), server and cloud. Application data can be transferred in both directions.
LoRa Alliance The LoRa Alliance is an open, non-profit organization led by Semtech in March 2015. Its founding members include French Actility, Chinese AUGTEK and Royal Dutch Telecom kpn. In less than a year, the alliance has developed more than 150 member companies, including many heavyweight manufacturers such as IBM, Cisco, and Orange of France. There are a large number of companies in each link of the industrial chain (terminal hardware manufacturers, chip manufacturers, module gateway manufacturers, software manufacturers, system integrators, network operators). The openness of this technology makes competition and cooperation more difficult. The adequacy has promoted the rapid development and ecological prosperity of LoRa.
3. Lora network architecture and principles
In a mesh network, individual terminal nodes forward information from other nodes to increase the communication distance of the network and the size of the network area. While this increases range, it also increases complexity, reduces network capacity, and reduces battery life as nodes accept and forward information from other nodes that may not be relevant to them. When implementing long-distance connections, the long-distance star architecture makes the most sense to protect battery life.
In a LoRaWAN network, nodes are not associated with dedicated gateways. In contrast, data transmitted by one node is usually received by multiple gateways. Each gateway forwards packets received from the end node through some backhaul (cellular, Ethernet, etc.) to a cloud-based network server. The intelligence and complexity are placed on the server, which manages the network and filters incoming data for redundancy, performs security checks, performs scheduling validation through optimal gateways, and performs adaptive data rates, etc.
4. Introduction to LoRaWAN protocol
LoRaWAN is a low-power wide area network communication protocol based on the open source MAC layer protocol released by the LoRa Alliance. It mainly provides local, national or global network communication protocols for battery-powered wireless devices.
LoRaWAN defines the communication protocol and system architecture of the network, and the LoRa physical layer enables long-distance communication links. Designed from the bottom up, LoRaWAN optimizes LPWAN (Low Power Wide Area Network) for battery life, capacity, distance and cost. An overview of the LoRaWAN specifications for different regions is given, as well as a high-level comparison of the different technologies competing in the LPWAN space.
5. LoRaWAN network topology
The LoRaWAN network is a typical Mesh network topology. In this network architecture, the LoRa gateway is responsible for data aggregation and connecting terminal devices and back-end cloud data servers. The gateway and server are connected via TCP/IP network. There is two-way communication between all nodes and the gateway. Considering the battery-powered situation, the terminal node usually sleeps. When there is data to be sent, it wakes up and then sends the data.
Therefore, using LoRa technology, we are able to obtain longer transmission distances with low transmit power. This low-power wide-area technology is necessary for large-scale deployment of wireless sensor networks.
6. Advantages and Disadvantages of LoRa Technology
Generally speaking, transmission rate, operating frequency band and network topology are the three main parameters that affect the characteristics of sensor networks. The choice of transmission rate will affect the transmission distance and battery life of the system; the choice of operating frequency band must compromise the frequency band and system design goals; and in the FSK system, the choice of network topology is determined by the transmission distance requirements and the nodes needed by the system. Determined by number. LoRa combines digital spread spectrum, digital signal processing and forward error correction coding technology to achieve unprecedented performance. Previously, only high-level industrial radio communications would incorporate these technologies, but with the introduction of LoRa, the situation in the field of embedded wireless communications has completely changed.
Forward error correction coding technology adds some redundant information to the data sequence to be transmitted, so that the error symbols injected during the data transmission process will be corrected in time at the receiving end. This technique reduces the need to create "self-healing" packets for retransmission and works well in resolving burst errors caused by multipath fading. Once packet groups are built and forward error correction coding is injected for reliability, the packets are fed to a digital spread spectrum modulator. This modulator feeds each bit in the packet into a "spreader," which divides the time of each bit into a number of chips.
Even if it is noisy, the LoRa module can handle it calmly. The LoRa modem is configured to be divided into a range of 64-4096 chips/bit, and the highest spreading factor (12) of 4096 chips/bit can be used. Relatively speaking, ZigBee can only divide the range into 10-12 chips/bit.
By using a high spreading factor, LoRa technology can transmit small-capacity data over a wide range of radio spectrum. In fact, when you measure it through a spectrum analyzer, the data looks like noise, but the difference is that the noise is uncorrelated, and the data is correlated, and based on this, the data can actually be extracted from the noise. The higher the spreading factor, the more data can be extracted from the noise. In a well-functioning GFSK receiver, a minimum signal-to-noise ratio (SNR) of 8dB is required to reliably demodulate the signal. By configuring AngelBlocks, LoRa can demodulate a signal with a signal-to-noise ratio of -20dB. The GFSK method is consistent with this The resulting difference is 28dB, which equates to a much greater range and distance. In an outdoor environment, a 6dB gap can achieve twice the original transmission distance.
Super strong link budget allows signals to fly farther. In order to effectively compare the transmission range performance between different technologies, we use a quantitative indicator called "link budget". The link budget includes every variable that affects the signal strength at the receiving end, which in its simplified form includes transmit power plus receiver sensitivity. The transmit power of AngelBlocks is 100mW (20dBm), the receiver sensitivity is -129dBm, and the total link budget is 149dB. In comparison, GFSK wireless technology, which has a sensitivity of -110dBm (an excellent figure), requires 5W of power (37dBm) to achieve the same link budget value. In practice, the receiver sensitivity of most GFSK wireless technologies can reach -103dBm. In this case, the transmitter transmission frequency must be 46dBm or approximately 36W to achieve a link budget value similar to LoRa. Therefore, using LoRa technology we can obtain wider transmission range and distance with low transmission power. This low-power wide-area technology is exactly what we need.
7. About LPWAN technology
Low Power Wide Area Network (LPWAN) is an indispensable part of the Internet of Things. It has the characteristics of low power consumption, wide coverage and strong penetration. It is suitable for sending and receiving a small amount of data every few minutes. Data applications, such as water transportation positioning, street light monitoring, parking space monitoring, etc. The LPWAN-related organization LoRa Alliance currently has 145 members around the world, and its lush ecosystem allows devices that follow the LoRaWAN protocol to have strong interoperability. A communication gateway that fully complies with the LoRaWAN standard can access tens of thousands of wireless sensor nodes within 5 to 10 kilometers. Its efficiency is much higher than the traditional point-to-point polling communication mode, and it can also significantly reduce node communication power consumption.