Answers to Lora-related questions

LoRa (Long Range) is a modulation technology that provides a longer communication distance than comparable technologies. Modulation is a variant of Linear Modulated Spread Spectrum (CSS) based on spread spectrum technology, with Forward Error Correction (FEC)

1.) What is LoRa Modulation?

LoRa (Long Range) is a modulation technology that provides a longer communication distance than comparable technologies. Modulation is a variant of Linear Modulated Spread Spectrum (CSS) based on spread spectrum technology, with Forward Error Correction (FEC). LoRa significantly improves reception sensitivity, using the entire channel bandwidth to broadcast a single signal, as with other spread spectrum technologies, resulting in more robust channel noise and insensitivity to frequency shifts 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 on the noise floor to modulate properly. LoRa modulation is the physical layer (PHY) that can be used by different protocols and different network architectures – Mesh, Star, point-to-point, and so on.

2.) What is LoRaWAN?

LoRa modulation is a PHY and LoRaWAN is a MAC protocol for high-capacity, long-range, low-power star networks, and the LoRa Alliance is standardizing low-power wide-area networks (LPWANs). The LoRaWAN protocol is optimized for low-power, battery-powered sensors, including different levels of end nodes to optimize the balance between network latency and battery life. It's completely bi-directional, built by security experts to ensure reliability and security. The LoRaWAN architecture also makes it easy to 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 national network, and the LoRa Alliance is standardizing LoRaWAN to ensure that different national networks are interoperable.

3.) What is a LoRa gateway?

LoRa gateways are designed for long-distance star architectures and are used in LoRaWAN systems. They are multi-channel, multi-modulation transceiver and receiver, multi-channel simultaneous demodulation, and can even be multi-signal demodulation on the same channel at the same time due to the characteristics of LoRa. The gateway uses a different RF device than the end node, with a 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 via a standard IP connection, and the end device communicates wirelessly to one or more gateways using a single hop. Communication between all end nodes is generally bidirectional, but it also supports operations such as multicast functions, software upgrades, wireless transmissions, or other high-volume publishing of messages, which reduces wireless communication time. Depending on the required capacity and installation location (home or tower), there are different gateway versions.

4) What is the LoRaWAN data rate?

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 FCC limits the minimum data rate to 0.9kbps. To maximize the battery life and overall network capacity of the end device, the LoRaWAN network server manages the data rate and RF output of each end device separately through the Adaptive Data Rate (ADR) algorithm. ADR is critical for high-performance networks and is scalable. In terms of infrastructure, deploying a network with minimal investment and deploying more gateways when additional capacity is needed, ADR will result in higher data rates, which can extend network capacity by a factor of 6 to 8.

5.) What is a LoRa Concentrator?

The terms gateway and concentrator are both used, but they are equivalent components in LoRa systems. In other industries, the definition of gateway and concentrator means different parts.

6.) How does LoRa deal with interference?

The LoRa modem can suppress co-channel GMSK interference up to 19.5dB, or in other words, it can accept a signal that is 19.5dB lower than the interfering signal or floor noise. Because of its strong immunity to interference, the LoRaTM modulation system can be used not only in the frequency bands with high spectrum utilization, but also in hybrid communication networks to extend coverage when the original modulation scheme in the network fails.

7.) What is the LoRa data rate rate?

LoRaWAN defines a specific set of data rates, but the terminal chip or PHY is available in a variety of options. The SX1272 supports data rates from 0.3 to 37.5kbps, and the SX1276 supports 0.018 to 37.5kbps.

8.) What is a LoRa endpoint or point?

The LoRa end node is the part of the LoRa network that senses or controls. They are remotely battery-powered. These end nodes use the LoRaWAN network protocol to establish communication with the LoRa gateway (concentrator or base station).

9.) What is Adaptive Data Rate (ADR)?

ADR is a method that varies the actual data rate to ensure reliable packet delivery, optimal network performance, and capacity scale. For example, nodes close to the gateway use higher data rates (shorter transmission times) and lower output power. Only nodes at very marginal link budgets use the lowest data rate and maximum output power. The ADR method can adapt to changes in network infrastructure and support varying path losses. To maximize the battery life and overall network capacity of the end devices, the LoRa network infrastructure manages the data rate and RF output of each end device separately through the implementation of ADR.

10.) What is the actual Tx power that can be reached on the antenna of a LoRa device?

The output power at the chip pins is +20dBm, and after matching/filtering losses, the power behind the antenna is +19dBm +/-0.5dB. The maximum output power is specified differently in different regions, and the LoRaWAN specification defines different output power in different regions to maximize the link budget.

11.) What is the price of the LoRa solution?

LoRa devices, such as the SX1272 or SX1276, use a lower-cost crystal oscillator. In narrowband technology, an expensive temperature-controlled crystal oscillator is required during RX/TX transceiver to reduce frequency drift. Depending on the volume and functionality, the typical BOM cost of a full endpoint is 2 2 5 dollars. The long transmission distance means that the network infrastructure is simplified, as no trunks are required and the deployment is less expensive. Lower power consumption means lower cost batteries and network maintenance.

12.) What is the process of LoRa Channel Activity Detection (CAD) mode?

CAD is used to detect the presence of a LoRa signal, rather than using a method of accepted signal strength (RSSI) to identify if a signal is present. It is able to distinguish the noise from the LoRa signal that is needed. The CAD process requires two symbols, and if detected by CAD, CAD_Detected interrupt becomes valid and the device is in RX mode to accept the data payload.

13.) Why can't my LoRa device or module output power reach 20dBm?

The +20dBm specification is for the pinout power of the chip. In any RF system, bandpass filters and RF switches have insertion loss characteristics, typically achieving +19dBm on the antenna after matched filtering.

14.) Can the mode be changed frequently between FSK and LoRa modulation?

Yes, no problem. LoRa devices can switch from FSK to LoRa (and vice versa) via a simple SPI register write. There is no impact on the performance and reliability of the equipment. LoRa devices can be configured or reconfigured to any parameters as specified in the data sheet.

15.) If I can't reach +20dBm, how can I solve the output power problem?

1. Please make sure you are connected to the correct pin (PA_Boost) settings for the 20dBm output pin. There are two output ports per band. One is a high-power port called PA_boost, and the other is a high-efficiency port called RFO.

2. Then, detect the software configuration. There are three registers that should be configured correctly: RegPaConfig, RegOcp, and RegPaDac. This means that you should select the correct pins in the software for the appropriate output, and then set the correct values for the power level you need.

3. Confirm that they are consistent with the Semtech reference design in order to design a good PCB layout. This is important for the maximum output power possible.

16.) How does the LoRa system achieve mass production testing?

There are three important parameters to be tested in series production: frequency tolerance, output power, and sensitivity. Frequency and output power are easy to test using a spectrum analyzer. If your signal generator does not produce a single LoRa signal, it is highly recommended to test the sensitivity using FSK mode. There is only one RF link in the chip, and both FSK and LoRa are modulated in the digital domain. RF paths can be misassembled, such as virtual soldering, so verification is important. The digital part of the chip LoRa and FSK modulation is not affected by the assembly, so it is sufficient to test the FSK sensitivity for verification of production test performance.

17.) How to choose the right crystal oscillator for LoRa devices?

Normally, for most designs with a bandwidth of 62.5kHz or higher, a +/- 10ppm XTAL is sufficient. With a bandwidth of less than 62.5kHz, TCXO is highly recommended. For more detailed information on crystal specifications, please refer to the data sheet as well as the LoRa Modem Calculator Tool and Application Note - AN1200.14_XO_Gidance_LoRa_Modulation_STD".

18.) For LoRa bandwidth signals, how do you measure frequency accuracy in LoRa mode?

If you are just for measurements, you can use the Synthesizer TX (FSTX) mode, as listed in the LoRa register table, to generate a CW tone based on the LoRa configuration.

19.) 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 configurations.

20.) How to choose LoRa signal bandwidth (BW), spread spectrum factor (SF) and coding rate (CR)?

LoRaWAN primarily uses a 125kHz signal bandwidth setting, but other proprietary protocols can utilize other signal bandwidth (BW) settings. Changing the BW, SF, and CR also changes the link budget and transmission time, and there is a trade-off between battery life and distance. Use the LoRa modem calculator to evaluate the trade-offs.

21.) What are the steps for fault detection when two SX127x modules from different manufacturers cannot communicate with each other?

First, check the frequency shift caused by the crystal oscillator between the two devices. Bandwidth (BW), center frequency, and data rate are all derived from the crystal frequency. Second, check the software/firmware settings on both sides to ensure that the frequency, bandwidth, spread factor, coding rate, and packet structure are consistent.

22.) In LoRa mode, how is it possible to receive an incorrect packet when cyclic redundancy check (CRC) is enabled?

In LoRa mode, the payload is added to the FIFO even if the CRC is wrong. Before getting a payload, the bit PayloadCrcError must be checked to know that it is complete. In Explicit Header mode, there is a small possibility that a false detection will result in a "clone" packet.

Either the wrong header opens the CrcOn bit, then the payload will be wrong, and the modem will mark it as a PayloadCrcError condition, so the packet will be easily filtered out; Either the wrong header disables the CrcOn bit, in which case the pattern thinks the packet is good. These occasional bad packets will have a random length (extracted from the error header message) and can be easily filtered out by the host, e.g. by seeing the size of the anomaly.

23.) Can I send or receive a payload packet of unlimited length with a LoRa device?

No, the maximum size packet length in LoRa mode is 256 bytes.

24.) How do I use DIOx pins in LoRa mode? Do all DIOx pins have to be connected to the MCU?

When you start designing, check the DIO mapping in both LoRa and FSK modes. You can find DIO mapping information in the SX127x LoRa data sheet. DIO doesn't have the same functionality as the usual (typical) MCU GPIOs. There are special interrupt messages (or clock outputs) that indicate events or chip status, which makes your firmware design easier to implement. Theoretically, you might not connect the DIO pin, so you poll the relevant registers to know the status result. Of course, we recommend connecting DIO as much as possible for the external interrupt function, saving the resource load of the MCU, and can operate in a very low-power mode (when packing, sending or receiving packets, the MCU sleeps).

25.) Why are there two RSSI registers in LoRa mode? What's the difference?

In LoRa mode, both registers, RegPktRssiValue and RegRssiValue, are useful. RegPktRssiValue refers to the packet RSSI level, which is similar to the RSSI in FSK mode (non-LoRa mode).

As you know, LoRa can demodulate packets below the noise floor (PktRssi result), then CurrentRssi is equal to or greater than the noise floor. For more information on how to calculate the values of these two RSSIs, please refer to the Semtech API or the latest LoRa data sheet.

26.) How to calculate the actual bit rate and transmission time of the LoRa system?

Steps (i-V) are listed below:

Calculations are easy by using the LoRa calculator and can be downloaded from the Semtech website

27.) The payload length in LoRa mode can be configured to 256 bytes at any data rate

The SX127x LoRa device has a 256-byte FIFO in LoRa mode. Theoretically, all 256 bytes could be used for TX or RX. However, with a low data rate configuration, the 256-byte payload will have a long transmission time (a few seconds or more), which is not good for fading and high-interference environments. This is not a robust configuration in most environments, so it is recommended that if you want a long payload that uses a low data rate, then the packet can be split into several short packets.

28.) Is LoRa a mesh network, peer-to-peer, or a network?

LoRa itself is a PHY that can be used for all network topologies. Mesh networks extend the range of the network, but at the cost of reduced network capacity, synchronization overhead, and reduced battery life due to synchronization and hop counts. As LoRa's link budget and distance range increase, there is no need to extend the distance with mesh network architecture, so LoRaWAN chooses a star architecture to optimize network capacity, battery life, and easy installation.

29.) Can LoRa use IPv6 and 6LoWPAN?

Yes, LoRa is IPv6 and 6LoWPAN compatible. Actility (LoRa partner) and other partners have implemented 6LoWPAN on top of LoRaWAN.

30.) What is the capacity of a LoRa gateway? How many nodes can be connected to a gateway?

First and foremost, capacity is a consequence of the number of packets received in a given period of time. One SX1301 has 8 channels and can accept close to 1.5 million packets of data per day using the LoRaWAN protocol. So, if your application sends one packet per hour, a single SX1301 gateway can handle about 62,500 end devices.