Frequently Asked Questions
From a data prospective, a gateway 15 km away from an end device can still perfectly receive the data in a rural environment. However, to be geo-located, you will need a minimum of three gateways receiving the message.
Keep in mind that the more gateways that are receiving the message, the more accurate will be the geo-location. If you are in the center of an imaginary triangle with one gateway at each corner, and each gateway is 15 km from you, you will be able to be geo-located with an accuracy of 20 to 50 meters.
DevEUI is a 64-bit number. It is the unique ID of the end-device.
AppEUI is a 64-bit number. It is the unique ID of the application server and is the destination of the messages sent by the end-devices. It must be unique so that the end-device knows where to send its messages. The AppEUI can be linked to either a single application (unique customer) or to several applications. In this last case, the manufacturer must re-route the messages to its end customers by using the DevEUI.
How to get them:
DevEUI key is linked to the end-device, this means end-device manufacturers should contact the IEEE to get a range of unique identifiers.
AppEUI is usually provided to the end-device manufacturers by the solution providers.
AppKey is a 128-bit key which is used to secure the communication between the source of the message (the end-device) and the destination of the message (the join server). This key is unique for each device and must be know by both sides. It is at the heart of the security and must only be known by the device and the join server. AppKey is never sent over the air and must remain secured over the lifetime of the end-device.
How to get it:
AppKey is typically a randomly-generated number that is programmed into the end-device and simultaneously communicated to the join server, so that it can authenticate the messages from the end-device.
There are currently no signs that this frequency band is being harmonized in Europe, so for now we are sticking to the 865-870 MHz frequency band.
There are some technical differences between LoRaWAN and alternative LPWAN technologies which enable a much broader set of applications to be addressed from a bi-directional connectivity, adaptive data rate and end point class perspective, but the key differentiator is the ecosystem, the Certification Program and standardization. If you look at successful technology adoption over the past 10 years all have followed this model. Having different business models, competition, and a diverse ecosystem with industry leaders is the only way to scale volume and deployments. An open standard is also a proven strategy to get acceptance and wide deployment versus proprietary technology, the choice of the various network components; gateways, end-devices, cloud network servers along with chips, development kits and end products from many different suppliers offers a low risk strategy for potential operators or end users.
Last but not least LoRaWAN protects data and privacy like no other LPWAN, it is the most secure solution available in the market with AES 128 encryption on multiple levels for all data from sensor to application server and back.
There is no such concept as a LoRa gateway or LoRaWAN gateway. A LoRa gateway can be connected to a LoRaWAN network server, in other words a server running LoRaWAN protocol, or to another server running another protocol. In fact, only gateways with eight channels or more are considered LoRaWAN-capable.
If I set the LoRa spreading factor to 7 and bandwidth to 500 kHz, could Channel Activity Detection (CAD) detect the preamble of a LoRa signal with spreading factor set to 7 and bandwidth to 125 kHz?
No, it may marginally pick up, but in principle the bandwidth and spreading factor must be coherent for the Channel Activity Detection (CAD) to work.
The following data shows the impedance of the two antennas on the SX1280 development kit, with the impedance matching. Here we see in excess of 16 dB of return loss which is good for a portable antenna.
The figure below shows a representation of the antenna system diversity performance, based upon the measured antenna S Parameters. (Based upon the method of Blanch et al). Here the red threshold indicates poor diversity performance, black acceptable diversity performance and green good, i.e. useful, antenna diversity performance.
The final plots show the simulated radiation patterns of the two diversity antennas. The pattern corresponding to the highlighted antenna (with the pattern in the same orientation as the board image).
There are two versions of kit that have been released. The first featured the version 1.0 bill-of-materials. This featured a standard crystal reference oscillator, this has since been replaced by a kit featuring a TCXO as can be seen in the Version 2.0 bill-of-materials. If you are unsure which version of the board you have it is possible to check quickly and simply by reviewing the reference design portion of the SX1280 PCB.As shown in the image below – if you have a crystal on the Q1 position (red cross) then you have a V1.0 BoM kit. If you have a V2.0 BoM kit, then the Q2 position (green circle) will be populated with a crystal (TCXO).The 2.0 version of the kit is recommended for the quickest and most efficient evaluation of the SX1280 ranging functionality.
Whilst the ranging performance accuracy is not dependent upon the received signal power (for an example of this and to see how to set up your first ranging measurements, see our application note for more details). It is important to note that the group delay of the transmitter will change depending upon the programmed transmit power.For this reason it is necessary to include a calibration setting for every programmed output power you intend to use in your final application. Our Introduction to Ranging application note gives more information on how to perform the calibration for your design.
The intermediate frequency of the SX1280 in receive mode is 1.625 MHz. This means that the image frequency can be found at twice the IF below the programmed RF centre frequency, i.e. FRF – 3.25 MHz.
The ranging accuracy can be degraded by one of several phenomenon, but we can eparate these into two broad categories: Design and hardware specific errors
- Environmental Errors
- We suggest using the SX1280 Development kit as the hardware for any initial evaluation, this should be updated with the very latest firmware compiled and downloaded from the Tools and SW area. With this configuration complete you should then have all of the design and hardware specific errors correctly calibrated by default. Moreover, the provision of a TCXO on the kit will protect the ranging measurement from temperature based environmental error.The main source of residual error then becomes the radio environement. The radio signal will follow an unpredictable path if there is no direct Line-of-Sight (LoS) between the two units. For this reason, it is necessary to initially evaluate the SX1280 in LOS conditions to ensure that the error is not due to multi-path and reflections specific to a given operating environment.For this reason we have a brief application note which walks you through the first steps of your evaluation that can be found in the Application Notes area of this Knowledge Base.
Recalling that SF11 and SF12 are inaccessible in ranging mode, the highest accuracy ranging setting is to use the highest bandwidth and the highest spreading factor (i.e. 1.6 MHz SF 10). To reduce the time on air of the ranging exchange, one should first decrease the SF then the bandwidth as the latter has the most profound effect on ranging accuracy.
There are no recommended settings for the FLRC modem, except that higher data rate (throughput) comes at the expense of reduced sensitivity. This is true of all modulation formats, more information on FLRC can be found in the SX1280 Datasheet.
All possible settings described in the SX1280 datasheet are acceptable configurations of the LoRa modem. However, depending upon the requirements of your application, it is certainly possible to configure the modem to one of several setting that will optimize performance.Longest Range Setting: This configuration is achieved by using the lowest bandwidth and highest spreading factor. Note that the increased sensitivity is achieved at the expense of a lower bitrate, so longer time on air.Highest Accuracy Ranging Setting: The highest accuracy ranging setting is achieved by setting the highest bandwidth and the highest spreading factor (1.6 MHz SF 10 in the case of ranging which does not operate at Spreading Factors above this).Lowest Energy / Highest Data Rate Setting: The lowest energy setting of the SX1280 LoRa modem, is to set the SF as low as possible and the bandwidth as high as possible. Note that this increased communication speed, comes at the expense of reduced sensitivity – so lower range.
The immunity of the SX1280 LoRa modem varies as a function spreading factor, bandwidth, the type of Wi-Fi interference and the frequency offset between the interferer and the wanted LoRa signal.For some OFDM types of Wi-Fi and with low bandwidth, low spreading factor we can get in excess of 60 dB co-channel immunity. The best mechanism to avoid WiFi interference, in general however, will be to avoid the interference by using unoccupied portions of the band. The image below shows our immunity at SF12 200 kHz as a function of frequency, here we see that on the same channel (0 Hz offset) we still have good immunity (45 dB) as we move further away in frequency (the ISM band is 80 MHz wide) we can get in excess of 100 dB of immunity. There is a little up-tick in the immunity at 0 Hz offset. The reason for this is shown in the second figure. Here the blue trace is the measured WiFi signal spectrum. You can also see here the actual measurement points (red dots). The precise immunity will depend upon the exact power level (here in 200 kHz) of the (blue) WiFi signal. More comprehensive coverage of this topic can be found in our WiFi immunity application note.
There are two versions of kit that have been released. The first featured the version 1.0 bill-of-materials (BoM). This featured a standard crystal reference oscillator, this has since been replaced by a kit featuring a TCXO as can be seen in the Version 2.0 bill-of-materials. If you are unsure which version of the board you have, it is possible to check quickly and simply by reviewing the reference design portion of the SX1280 PCB. As shown in the image below – if you have a crystal on the Q1 position (red cross) then you have a V1.0 BoM kit. If you have a V2.0 BoM kit, then the Q2 position (green circle) will be populated with a crystal (TCXO). The 2.0 version of the kit is recommended for the quickest and most efficient evaluation of the SX1280 ranging functionality.
To avoid re-work and modification of the component values on the RF output of SX1280 it is necessary to follow the reference design as closely as possible. The harmonic filter of SX1280 (magenta) and impedance match (cyan) in particular need to be replicated identically. Where possible the same family of components as specified in the BOM should also be used. It is possible, in some applications, that VCO leakage in receive mode can be seen. An effective remedy for this is to take the initial precaution of adding series resistances R7 to R10 to the digital lines. Moreover, a 4-layer design allows the DC-DC converter traces to be buried on internal PCB layer 3 (see below) between ground planes on layers 2 and 4.
The simplest technique to calculate the time on air for Master and Slave ranging exchanges is to consult the SX1280 calculator tool (available for download from the Tools and SW area). Under the LoRa tab, simply select the modem SF and bandwidth you intend using. The calculator will then show the LoRa symbol time as illustrated below:
The SX1280 development kit features a pair of antennas. The antennas are used to provide switched diversity to overcome fading, i.e. destructive interference of the wanted RF signal. The triangular patches are used to increase the bandwidth of the antenna and render it more immune to detuning by proximate objects – such as a user’s hand.