LoRa and LoRaWAN Technology Overview

The purpose of this article is to provide an introductory technical overview of LoRa and LoRaWAN. Low-power wide area networks (LPWANs) are expected to support a major part of the billions of devices predicted by the Internet of Things. LoRaWAN's bottom-up design optimizes LPWAN for battery life, capacity, distance and cost. A summary of the LoRaWAN specification is given for different regions, as well as advanced comparisons of different technologies competing in the LPWAN space. (The content has been deleted and changed compared with the original text)

What is LoRa?

LoRa is a physical layer or wireless modulation used to establish long-distance communication links. Many conventional 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 chirp 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, and because it can achieve long communication distance and interference robustness, LoRa is the first low-cost implementation for commercial use.

Long distance (LoRa)

The advantage of LoRa lies in its long-range capabilities in terms of technology. A single gateway or base station can cover the entire city or hundreds of square kilometers. At a given location, the distance is highly dependent on the environment or obstacles, but LoRa and LoRaWAN have a link budget that is superior to any other standardized communication technology. The link budget, usually expressed in decibels (in dB), is the primary factor in determining distance in a given environment. Below is a network coverage map of Proximus deployed in Belgium. With the implementation of a small amount of infrastructure, it can be easily covered throughout the country.

Where is LPWAN suitable?

One technology cannot meet the application and quantity of all projects in the Internet of Things. WiFi and BTLE are widely adopted standards that are well suited for applications related to personal device communication. Cellular technology is ideal for applications that require high data throughput and are powered. LPWAN offers years of battery life and is designed for sensors and applications that need to send small amounts of data, sent several times per hour over long distances from different environments.

The most critical factors in LPWAN are:

Network Architecture

Communication distance

Battery life or low power consumption

Robustness of interference

Network capacity (maximum number of nodes in the network)

cyber security

One-way and two-way communication

Various service applications

What is LoRaWAN?

LoRaWAN defines the communication protocol and system architecture of the network, while the LoRa physical layer enables long-distance communication links. The protocol and network architecture have the greatest impact on the battery life, network capacity, quality of service, security, and network application service quality of the node.

Network Architecture

Many existing deployed networks use a mesh network architecture. In a mesh network, individual terminal nodes forward information of other nodes to increase the communication distance of the network and the size of the network area. While this increases the range, it also adds 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 a dedicated gateway. Conversely, data transmitted by one node is usually received by multiple gateways. Each gateway forwards the received packets from the endpoint to the cloud-based network server over some backhaul (cellular, Ethernet, satellite or Wi-Fi). Intelligence and complexity are placed on the server, the server manages the network and filters the redundant received data, performs security checks, schedules confirmations through the gateway, and performs adaptive data rates. If a node is mobile or moving, there is no need to switch from gateway to gateway. This is an important feature that can be applied to asset tracking - a major target vertical application for the Internet of Things.

Battery Life

The nodes in the LoRaWAN network are asynchronously communicating, communicating when the data to be sent is ready, whether it is event driven or time scheduled. This type of protocol is often referred to as the Aloha method. In a mesh network or a synchronous network, such as a cellular, nodes must wake up frequently to synchronize the network and check for messages. This synchronization consumes a significant amount of energy and is the first push to reduce battery life. In a recent study, the GSMA compared different technologies for solving LPWAN space, and LoRaWAN has a three to five times advantage over other technology options.

Network capacity

In order to enable a long-range star network, the gateway must have very high capacity or performance to receive messages from a large number of nodes. High network capacity is achieved with adaptive data rates and multi-channel multi-modulation transceivers in the gateway, so messages can be accepted simultaneously on multiple channels. The key factors affecting capacity are the number of concurrent channels, data rate (air time), load length, and how often nodes send data. Since LoRa is based on spread spectrum modulation, when different spreading factors are used, the signals are actually orthogonal to each other. When the spreading factor changes, the effective data rate also changes. The gateway takes advantage of this feature and is capable of accepting multiple different data rates on the same channel at the same time. If a node has a good connection and is close to the gateway, there is no reason to always use the lowest data rate, filling up the available spectrum longer than it takes. The higher the data transfer rate, the shorter the time in the air, which can open up more potential space for other nodes that want to transmit data. The adaptive data rate also optimizes the battery life of the node. For adaptive data rate operation, symmetric uplink and downlink requirements have sufficient downlink capacity. These features make LoRaWAN very high capacity and the network more scalable. The network can be deployed with a minimum amount of infrastructure. When capacity is needed, more gateways can be added, the data rate can be changed, the number of crosstalks can be reduced, and the network capacity can be expanded by 6-8 times. Other LPWAN technologies do not have the scalability of LoRaWAN due to technical trade-offs that limit the capacity of the downlink and make the downlink distance and the uplink distance asymmetrical.

Device class – not all nodes are the same

Terminal devices serve different applications and have different requirements. To optimize various end application specifications, LoRaWAN uses different device categories. The device category weighs the network downstream communication delay and battery life. In communication or actuator type applications, downlink communication delay is an important factor.

Two-way terminal equipment (Class A): Class A terminal equipment allows two-way communication, so the uplink transmission of each terminal equipment follows two short downlink acceptance windows. The transmission time slot is scheduled by the terminal device, based on its own communication requirements and has a small change based on a random time base (ALOHA type protocol). For applications that only need to communicate briefly from the server downlink after the terminal device has sent an uplink transmission, this Class A operation is the lowest power end system. The downlink communication from the server at any other time must wait for the next scheduled uplink.

A two-way terminal device (class B) with scheduling acceptance time slots: In addition to the class A random acceptance window, the class B device opens an additional acceptance window at the scheduling time. In order for the terminal device to open its acceptance window at the scheduled time, the gateway synchronization beacon is accepted once. This allows the server to know when the terminal device is listening.

Two-way terminal devices with the largest accepted time slot (Class C): Class C terminal devices open the node acceptance window almost continuously, and only close when transmitting.

Safety

Joining security is extremely important for any LPWAN. LoRaWAN uses two layers of security: one is network layer security; the other is application layer security. Network security guarantees the reliability of network nodes, while the security of the application layer ensures that network operators cannot access application data of end users. Key exchange uses the IEEE EUI64 identifier for AES encryption. Each technology choice has a trade-off, but LoRaWAN's network architecture features, device class, security, capacity scalability, and mobility optimization meet a wide range of potential IoT applications.

5, LoRaWAN area overview

The LoRaWAN specification is slightly different depending on the spectrum allocation and regulatory requirements of different regions. The LoRaWAN specification has been developed in Europe and North America, but other regions are still being developed by technical committees. Joining the LoRa Alliance as a contributor and participating in technical committees has clear advantages for companies targeting Asian market solutions.

Introduction to LoRa WAN Protocol

Wireless technology in IoT applications, in addition to the 2G/3G/4G of the metropolitan area network, there are also various communication technologies such as LAN and short-distance communication, such as 2.4G band WiFi, Bluetooth, Zigbee and Sub-Ghz. The advantages and disadvantages of these short-range wireless technologies are also very obvious. And from the perspective of wireless application development and engineering operations personnel, there has always been a dilemma: designers can only choose between longer distances and lower power consumption. With LoRa technology, designers can now do both, maximizing communication over longer distances and lower power consumption while saving additional repeater costs.

In general, the transmission rate, operating frequency band, and network topology are the three main parameters that affect the characteristics of the sensing network. The choice of transmission rate will determine the system's transmission distance and battery life. The choice of operating frequency bands is to compromise the design goals of the frequency bands and systems. The choice of network topology in the FSK system is determined by the transmission distance requirements and the number of nodes required by the system. Semtech's cost-effective transceiver solution with new spread-spectrum technology will change the previous trade-offs, providing users with a simple system that can achieve long distances, long battery life and increased system capacity. To expand your sensor network, LoRa technology came into being.

LoRa combines digital spread spectrum, digital signal processing and forward error correction coding with unprecedented performance. Previously, only those high-level industrial radio communications would incorporate these technologies, and with the introduction of LoRa, the situation in embedded wireless communications has changed radically.

The forward error correction coding technique adds some redundant information to the data sequence to be transmitted, so that the error symbols injected in the data transmission process are corrected in time at the receiving end. This technology reduces the need to create "self-healing" packets for retransmission in the past and performs well in solving sudden errors caused by multipath fading.

Once the packet packets are established and forward error correction coding is injected to ensure reliability, these packets are sent to the digital spread spectrum modulator. This modulator feeds each bit in the packet data packet into a "spreader" that divides each bit time into a number of chips. The LoRa modem is configured to be divided into 64-4096 chips/bit. The AngelBlocks configuration modem can use the highest spreading factor (12) of 4096 chips/bit. In contrast, ZigBee can only be divided 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 through a spectrum analyzer, the data looks like noise, but the difference is that the noise is irrelevant, and the data is correlated, based on which the data can actually be extracted from the noise. In fact, the higher the spreading factor, the more data can be extracted from the noise.

At a well-functioning GFSK receiver, the 8dB minimum signal-to-noise ratio (SNR) requires reliable demodulation of the signal. With the configuration of AngelBlocks, LoRa demodulates a signal with a SNR of -20dB, GFSK mode with The result gap is 28dB, which is equivalent to a much larger range and distance. In an outdoor environment, a 6dB difference can achieve twice the original transmission distance.

In order to effectively compare the performance of the transmission range between different technologies, we use a quantitative indicator called "link budget". The link budget includes each variable that affects the signal strength at the receiving end, including transmit power plus receiver sensitivity in its simplified architecture.

AngelBlocks has a transmit power of 100mW (20dBm), a receiver sensitivity of -129dBm, and a total link budget of 149dB. In comparison, GFSK wireless technology with a sensitivity of -110dBm (which is already excellent data) requires 5W of power (37dBm) to achieve the same link budget. In practice, most GFSK wireless technology receivers can achieve a sensitivity of -103dBm. In this case, the transmitter must have a transmit frequency of 46dBm or about 36W to achieve a link budget similar to LoRa.

Therefore, using LoRa technology, we can achieve a wider transmission range and distance with low transmission power. This low-power wide-area technology is exactly what we need.

Transmission rate and distance

The transfer rate is a key variable in system design and will determine many attributes of the overall system performance. The wireless transmission distance is determined by the receiver sensitivity and the transmitter output power. The difference between the two is called the link budget. The output power is limited by the standard specification, so the distance is increased only by increasing the sensitivity, which is also very important due to the data rate. For all modulation methods, the lower the rate, the narrower the bandwidth of the receiver, and the higher the receiving sensitivity. The most widely used modulation method in today's cost-effective wireless transceivers is FSK or GFSK. To further reduce the receiver bandwidth of the FSK system, the only feasible way is to improve the accuracy of the reference crystal. Under the equivalent data rate conditions, the commercial low-cost spread spectrum modulation method can obtain 8-10 dB higher sensitivity than the conventional FSK modulation method. Semtech will introduce a new transceiver that integrates a spread-spectrum modulation called LoRa and traditional GFSK modulation. The graph shows the sensitivity vs. data rate for both GFSK modulation and LoRa spread spectrum modulation systems.

Compared to the FSK system, this new spread spectrum method improves the sensitivity by 30 dB when using the same low-cost crystal, which is theoretically equivalent to an increase of 5 times the transmission distance.

Network architecture and protocol

Choosing a star network or a mesh network is a key factor affecting the performance of the entire wireless network system. The star network is the simplest network structure with the lowest latency. Long-distance, co-channel synchronous transmission, improved co-channel rejection, and high selectivity. These spread-spectrum methods offer an alternative high-performance system solution for sensing networks, which is the traditional FSK modulation method. Unable to reach.

The advantages of the spread spectrum modulation method at the same rate can be easily used to improve the performance of the existing mesh network, and the star network can also achieve excellent system performance. With a star network that can reach a distance of 8-16 km in a suburban environment, we no longer need a very large mesh structure to cover such a wide range.

A multi-channel, multi-modulation concentrator can adapt to different rates and different powers of different nodes, so that the maximum network capacity and the longest battery life can be obtained. The transmission rate of the spread spectrum system can be changed using different spreading factors. The variable spreading factor increases the system capacity of the entire network because signals with different spreading factors can coexist in one channel. With the help of network simulation tools, we can easily observe that compared with the traditional fixed-rate FSK system, the star network using the above technology can easily obtain many advantages, such as 95% of nodes occupy only 10% of total energy consumption. At the same time, the capacity of the entire system will also increase by 5-6 times.

In general, LoRa technology has several advantages over other wireless systems. It uses spread-spectrum modulation to demodulate noise below 20 dB. This ensures a highly sensitive, reliable network connection while increasing network efficiency and eliminating interference. Compared to mesh networks, the LoRaWAN protocol's star topology eliminates synchronization overhead and hop count, thereby reducing power consumption and allowing multiple concurrent applications to run on the network. At the same time, LoRa technology achieves a much longer communication distance than other wireless protocols, which allows the LoRa system to work without a repeater, reducing overall cost of ownership. In addition, compared to 3G and 4G cellular networks, LoRa technology is more scalable and cost-effective for embedded applications.

LoRaWAN is a low-power WAN specification introduced by the LoRa Alliance that provides regional, national or global networks for battery-powered wireless devices. LoRaWAN is aimed at some of the core needs of the Internet of Things, such as secure two-way communication, mobility and local services. This technology eliminates the need for local complex configuration, which enables smart devices to achieve seamless interoperability and free access to users, developers and enterprises in the IoT space.

The LoRaWAN network architecture is a typical star topology in which the LoRa gateway is a transparent relay that connects the front-end terminal equipment to the back-end central server. The gateway and the server are connected by standard IP, and the terminal device communicates with one or more gateways in a single hop, and all nodes are two-way communication.

The communication between the terminal and the gateway is done on the basis of different frequencies and data transmission rates, and the data rate selection needs to be traded off between the transmission distance and the message delay. Due to the spread spectrum technology, different data transmission rate communication will not interfere with each other, and a set of "virtualized" frequency bands will be created to increase the gateway capacity. The LoRaWAN network data transmission rate ranges from 0.3 kbps to 50 kbps. To maximize terminal battery life and overall network capacity, the LoRaWAN network server controls the data transmission rate and the RF of each terminal device through a rate adaptation (ADR) scheme. Output. A nationwide network for the Internet of Things needs to address issues such as critical infrastructure, confidential personal data, or social public services, which are typically addressed in a multi-layered manner:

Unique network key (EU164) and secure network layer;

Unique application key (EU164) and guarantee end-to-end security at the application layer.