LoRa is one of the LPWAN communication technologies. It is an ultra-long-distance wireless transmission solution based on spread spectrum technology adopted and promoted by the American Semtech Company. This solution changes the previous trade-off between transmission distance and power consumption, providing users with a simple system that can achieve long distance, long battery life, and large capacity, thereby expanding the sensor network. Currently, LoRa mainly operates in free frequency bands around the world, including 433, 868, 915MHz, etc.
The following is a list of questions and answers about LoRa to help you further understand the knowledge behind LoRa:
1. What is LoRa modulation?
LoRa (Long Range) is a modulation technology that provides longer communication distances than similar technologies. The modulation is based on spread spectrum technology, a variant of linear modulation spread spectrum (CSS), with forward error correction (FEC).
LoRa significantly improves reception sensitivity and, like other spread spectrum technologies, uses the entire channel bandwidth to broadcast a signal, making it more robust to channel noise and insensitivity to frequency offsets due to the use of low-cost crystal oscillators.
LoRa can modulate the signal 19.5dB below the noise floor, while most frequency shift keying (FSK) requires a signal power of 8-10dB above the noise floor to modulate correctly. LoRa modulation is the physical layer (PHY) and can be used by different protocols and different network architectures – Mesh, Star, Point-to-Point, etc.
2. What is the difference between LoRa technology, SIGFOX and NWave?
In general, LoRa technology uses a spread spectrum technology; SIGFOX uses narrowband BPSK modulation technology; NWave uses the Weightless standard, which is similar to the technology used by SIGFOX.
Companies currently using ultra-narrowband technology have many transceiver chips to choose from, while LoRa can only use chips provided by Semtech.
3. How does LoRa handle interference?
The LoRa modem can suppress co-channel GMSK interference up to 19.5dB, or in other words, it can accept signals 19.5dB lower than the interfering signal or noise floor. Because it has such strong anti-interference, the LoRaTM modulation system can not only be used in frequency bands with high spectrum usage, but can also be used in hybrid communication networks to expand coverage when the original modulation scheme in the network fails.
4. What is the data rate of LoRa?
LoRaWAN defines a specific set of data rates, but the end chip or PHY can have a variety of options.
5. What is LoRa gateway?
LoRa gateway is designed for long-distance star architecture and is used in LoRaWAN systems. They are multi-channel, multi-modulation transceiver, and can demodulate multiple channels simultaneously. Due to the characteristics of LoRa, they can even demodulate multiple signals simultaneously on the same channel. The gateway uses RF devices different from those of the end nodes, has higher capacity, and acts as a transparent bridge to relay messages between the end device and the central network server.
The gateway connects to the network server through a standard IP connection, and the end device uses single-hop wireless communication to one or more gateways. Communication between all terminal nodes is generally two-way, but also supports operations such as multicast functions, software upgrades, wireless transmission or other bulk publishing of messages, thus reducing wireless communication time. There are different gateway versions depending on the required capacity and installation location (home or tower).
6. What is a LoRa concentrator?
The terms gateway and concentrator are both used, but they are equivalent components in the LoRa system. In other industries, the definitions of gateway and concentrator mean different components.
7. What is LoRaWAN?
LoRa modulation is PHY, LoRaWAN is MAC protocol, used for large-capacity, long-distance, low-power star networks, and the LoRa Alliance is standardizing low-power wide area networks (LPWAN).
The LoRaWAN protocol is optimized for low-power, battery-powered sensors and includes different levels of end nodes to optimize the balance between network latency and battery life. It’s fully bi-directional and built by security experts ensuring reliability and security.
The LoRaWAN architecture can also easily locate moving targets for asset tracking, which is the fastest growing application of the Internet of Things. Major telecom operators are deploying LoRaWAN as a nationwide network, and the LoRa Alliance is standardizing LoRaWAN to ensure that different national networks are interoperable.
8. What is the data rate of LoRaWAN?
For LoRa, the LoRaWAN data rate ranges from 0.3kbps to 11kbps, and the GFSK data rate in Europe is 50kbps. In North America, the minimum data rate is 0.9kbps due to FCC restrictions. To maximize end device battery life and overall network capacity, the LoRaWAN network server manages each end device data rate and RF output individually through the Adaptive Data Rate (ADR) algorithm.
ADR is crucial for high-performance networks and is scalable. In terms of infrastructure, a network is deployed with minimal investment. When capacity needs to be increased, more gateways are deployed. ADR will increase the data rate and expand network capacity by 6 to 8 times.
9. What is the capacity of LoRa gateway? How many nodes can be connected to a gateway?
First and foremost, capacity is a result of the number of packets accepted within a certain period of time. A gateway has 8 channels and can receive nearly 1.5 million packets of data per day using the LoRaWAN protocol. So if your application sends one packet per hour, a single gateway can handle approximately 62,500 end devices.
10. What is a LoRa end node or point?
LoRa end nodes are parts of the LoRa network that perform sensing or control. These end nodes establish communication with a LoRa gateway (concentrator or base station) using the LoRaWAN network protocol.
11. What is Adaptive Data Rate (ADR)?
ADR is a method that changes the actual data rate to ensure reliable packet delivery, optimal network performance, and capacity scaling. For example, nodes closer to the gateway use higher data rates (shorter transmission times) and lower output power. Only nodes at the very edge of the link budget use the lowest data rate and maximum output power.
The ADR method can adapt to changes in network infrastructure and support changing path losses. To maximize the battery life of end devices and overall network capacity, the LoRa network infrastructure manages the data rate and RF output of each end device separately by implementing ADR.
12. What is the process of LoRa Channel Activity Detection (CAD) mode?
CAD is used to detect the presence of LoRa signals, rather than using a received signal strength (RSSI) method to identify whether a signal is present. It can distinguish noise from the desired LoRa signal. The CAD process requires both symbols. If detected by CAD, the CAD_Detected interrupt becomes active and the device is in RX mode to accept the data payload.
13. What is the relationship between signal bandwidth (BW), symbol rate (Rs) and data rate (DR)?
Theoretically, Rs=BW/(2^SF), DR= SF*(BW/2^SF)*CR, but we recommend that you use the Semtech LoRa Modem Calculator to evaluate the data rate and transmission time according to different configuration selections.
14. How to choose LoRa signal bandwidth (BW), spreading factor (SF) and coding rate (CR)?
LoRaWAN primarily uses the 125kHz signal bandwidth setting, but other specialized protocols can utilize other signal bandwidth (BW) settings.
Changing BW, SF and CR also changes the link budget and transmission time, which requires a trade-off between battery life and distance. Please use the LoRa Modem Calculator to evaluate the trade-offs.
15. Is LoRa a mesh network, point-to-point transmission, or a network?
LoRa itself is a PHY and can be used in all network topologies. Mesh networks extend the range of the network, but at the expense of reduced network capacity, synchronization overhead, and reduced battery life due to synchronization and hop count. LoRa gateways and modules are networked in a star network, while LoRa modules can theoretically be networked in point-to-point polling. Of course, the efficiency of point-to-point polling is much lower than that of a star network.
As LoRa’s link budget and distance range increase, there is no need to use mesh network architecture to extend the distance, so LoRaWAN chooses a star architecture to optimize network capacity, battery life, and ease of installation.
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