Basic FAQs about LoRa's 30 Frequently Asked Questions

1) What is LoRa modulation?

LoRa (Long Range) is a modulation technique that provides longer communication distances than comparable technologies. Modulation is based on spread spectrum technology, a variant of Linear Modulation Spread Spectrum (CSS) with Forward Error Correction (FEC). LoRa significantly improves the acceptance sensitivity, and like other spread spectrum techniques, broadcasts a signal using the entire channel bandwidth, making channel noise and insensitivity due to the use of low-cost crystals more frequency offset. LoRa can modulate the signal 19.5dB below the bottom noise, while most frequency shift keying (FSK) requires an 8-10dB signal power on the bottom noise to properly modulate. LoRa modulation is the physical layer (PHY) that can be used for different protocols and different network architectures - Mesh, Star, peer-to-peer, and more.

2) What is LoRaWAN?

LoRa modulation is a PHY, LoRaWAN is a MAC protocol for large-capacity long-distance low-power star networks, and the LoRa Alliance is standardizing on 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 is completely two-way and built by security experts to ensure reliability and security. The LoRaWAN architecture also makes it easy to target mobile targets for asset tracking, the fastest growing application for 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?

The LoRa Gateway is designed for long-haul star architecture and is used in the LoRaWAN system. They are multi-channel, multi-modulation transceiving, multi-channel simultaneous demodulation, and even multi-signal demodulation on the same channel due to the characteristics of LoRa. The gateway uses a different RF device than the terminal node, has a higher capacity, and relays messages between the terminal device and the central network server as a transparent bridge. The gateway connects to the network server through a standard IP connection, and the terminal device uses one-hop wireless communication to one or more gateways. The communication of all terminal nodes is generally two-way, but also supports such as multicast function operation, software upgrade, wireless transmission or other large-scale release of messages, thus reducing the wireless communication time. There are different gateway versions depending on the required capacity and installation location (home or tower).

4) What is the data rate of LoRaWAN?

For LoRa, the LoRaWAN data rate ranges from 0.3 kbps to 11 kbps, and the European GFSK data rate is 50 kbps. In North America, the minimum data rate due to FCC is 0.9 kbps. To maximize the battery life and overall network capacity of the terminal device, the LoRaWAN network server manages each terminal device data rate and RF output separately through an adaptive data rate (ADR) algorithm. ADR is critical to high-performance networks and is scalable. In terms of infrastructure, deploying a network with minimal investment, deploying more gateways when capacity is needed, ADR will enable higher data rates and expand network capacity by a factor of six to eight.

5) What is the LoRa concentrator?

Both the gateway and concentrator terms are used, but they are equivalent components in the LoRa system. In other industries, the definition of gateways and concentrators means different components.

6) How is LoRa processing interference?

The LoRa modem can suppress the co-channel GMSK interference by up to 19.5 dB, or in other words, it can accept 19.5 dB of the signal below the interference signal or the bottom noise. Because of its strong anti-interference, the LoRaTM modulation system can be used not only in the frequency band with high spectrum usage, but also in the hybrid communication network to expand the coverage when the original modulation scheme fails in the network.

7) What is the rate of LoRa data?

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

8) What is a LoRa terminal node or point?

The LoRa endpoint is part of the LoRa network that is sensed or controlled. They are powered by a remote battery. These endpoints establish communication with the LoRa gateway (concentrator or base station) using the LoRaWAN network protocol.

9) What is Adaptive Data Rate (ADR)?

ADR is a way to change 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 (shortening transmission time) and lower output power. Only the nodes that are very marginal on the link budget use the lowest data rate and maximum output power. The ADR approach can accommodate changes in network infrastructure and support changing path losses. To maximize the battery life and overall network capacity of the terminal equipment, the LoRa network infrastructure manages the data rate and RF output of each terminal device separately by implementing ADR.

10) What is the actual Tx power that can be achieved on the LoRa device antenna?

The power output at the pin of the chip is +20dBm. After the matching/filtering loss, the power on the antenna is +19dBm +/-0.5dB. The maximum output power has different regulations in different regions. The LoRaWAN specification defines different output powers 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. In narrowband technology, an expensive temperature-controlled crystal oscillator is required during RX/TX transceiving to reduce frequency drift. Depending on volume and functionality, a typical bill of materials cost for a complete endpoint is $25. Long transmission distances mean that the network infrastructure is simplified because there is no need for relay deployment costs. Lower power consumption means lower cost battery 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 Received Signal Strength (RSSI) method to identify if a signal is present. It distinguishes between noise and the LoRa signal that is needed. The CAD process requires two symbols. If detected by CAD, the CAD_Detected interrupt becomes active and the device is in RX mode to accept the data payload.

13) Why does my LoRa device or module output less than 20dBm?

The +20dBm specification is for the chip pin output power. In any RF system, the bandpass filter and the RF switch have insertion loss characteristics, and the typical performance of the matched filter can reach +19 dBm.

14) Can I change the mode frequently between FSK and LoRa modulation?

Yes, no problem. The LoRa device can be switched from FSK to LoRa (and vice versa) with a simple SPI register write. There is no impact on the performance and reliability of the device. The LoRa device can be configured or reconfigured to any parameter as specified in the data sheet.

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

1.) Make sure that you are connected to the correct pin (PA_Boost) setting, 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, check the software configuration. Three registers should be properly configured: RegPaConfig, RegOcp, and RegPaDac. This means that you should select the correct pin in the software to make the appropriate output, and then set the correct value according to the power level you need.

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

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

There are three important parameters to be tested in mass production: frequency tolerance, output power, and sensitivity. The frequency and output power are easily tested using a spectrum analyzer. If your signal generator cannot generate a LoRa signal, it is highly recommended to use the FSK mode to test sensitivity. There is only one RF link in the chip, and both FSK and LoRa are modulated in the digital domain. The RF path may be assembled incorrectly (such as a virtual solder), so verification is important. The digital portion of the chip LoRa and FSK modulation is not affected by the assembly, so it is sufficient to verify the FSK sensitivity for verifying the production test performance.

17) How do I choose the right crystal for my LoRa device?

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

18) For the LoRa bandwidth signal, how do you measure the frequency accuracy in LoRa mode?

If only for measurement, you can use the frequency 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)?

In theory, 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 options.

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

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

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

First, check the frequency offset caused by the crystal 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, spreading factor, coding rate, and packet structure are consistent.

22) In LoRa mode, how can I receive a wrong packet when the Cyclic Redundancy Check (CRC) is enabled?

In LoRa mode, the payload is added to the FIFO even if the CRC is wrong. The PayloadCrcError must be checked for its integrity before the payload is taken. In the Explicit Header mode, there is a small possibility that a false detection produces a "clone" packet.

Either the wrong header opens the CrcOn bit, then the payload will be wrong, the modem will mark it as a PayloadCrcError condition, so the packet is easily filtered out; or the wrong header disables the CrcOn bit, in which case the pattern considers The packet is good. These occasional bad packets will have a random length (extracted from the error header information) and are easily filtered out by the host, for example to see the size of the exception.

23) Can I send or accept an unlimited length payload packet with a LoRa device?

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

24) How do I use the DIOx pin in LoRa mode? Are all DIOx pins 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 does not have the same functionality as the usual (typical) MCU GPIO. There are some special interrupt messages (or clock outputs) that indicate event or chip status, which makes your firmware design easier to implement. In theory, you may not be connected to the DIO pin, then poll the relevant registers to know the status result. Of course, we recommend connecting DIO as much as possible as an external interrupt function, saving the MCU's resource load and allowing for a very low-power mode of operation (the MCU sleeps when packaged to send or receive packets).

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

Both RegPktRssiValue and RegRssiValue registers are useful in LoRa mode. RegPktRssiValue refers to the packet RSSI level, and RegRssiValue 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 bottom noise. 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 do you calculate the actual bit rate and transmission time of the LoRa system?

The steps (iV) are listed below:

It is easy to calculate by using the LoRa calculator, which can be downloaded from the Semtech website (link below).

Http://?file=SX1272LoRaCalculatorSetup1%271.zip

27) Can the payload length of LoRa mode be configured to 256 bytes at any data rate?

The SX127x LoRa device has a 256-byte FIFO in LoRa mode. In theory, all 256 bytes can be used for TX or RX. However, with a low data rate configuration, the transmission time of a 256-byte payload will be very long (several seconds or longer), which is not good for anti-fading and high-interference environments. This is not a robust configuration in most environments, so it is recommended that if you want to use a payload with a low data rate, the packet can be broken 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 reach of the network, but at the expense of reduced network capacity, synchronization overhead, and battery life, due to synchronization and hop count. As LoRa's link budget and distance range increase, there is no need to extend the distance with the mesh network architecture, so LoRaWAN chooses a star architecture to optimize network capacity, battery life, and ease of installation.

29) Can LoRa use IPv6 and 6LoWPAN?

Yes, LoRa is compatible with IPv6 and 6LoWPAN. Actility (LoRa Partner) and other partners implemented 6LoWPAN on LoRaWAN.

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

First and foremost, capacity is a result of the number of packets accepted in a given period of time. An SX1301 has eight channels and can accept nearly 1.5 million packets of data per day using the LoRaWAN protocol. Therefore, if your application sends a packet every hour, an SX1301 gateway can handle approximately 62,500 end devices.