IoT Link: LoRa vs. UNB. Part 1: Physics
The first of a series of articles devoted to the description of the main differences between low-power long-range radio communication technologies, which is now spreading in IoT systems: LoRa broadband from narrowband (UNB, Ultra Narrow Band) systems such as Sigfox and Stryzh
The topic of low-power radio communication, which allows, without going beyond the unlicensed ranges (that is, as a rule, for a power of 25 mW), to transmit low-speed data from 1-3 to 10-30 kilometers in Russia began to flourish in the past six months. That is - they talked about it before that, but practical applications were very rare, and there were very few developers and integrators who could do a project on such technologies.
Now we are on the verge of a turning point: although large projects are still only expected in the future (but we can already predict that this future is a matter of months, not years), integrators and customers have a serious interest in IoT communication technologies, and not only in words, but also in the immediate desire to try these technologies in action.
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The main competition in this segment right now is between the broadband connection LoRa and narrowband Sigfox (and specifically in Russia - the Stryzh Telematics technology similar to it). In the future, the Weightless UNB protocol will be added to this list, as well as the networks promoted by the suppliers of the classic cellular equipment - NB-IoT and LTE-M, but this will happen in two or three years.
So, what is the difference - and what to choose for a particular project? Go.
A common feature of all the listed technologies is that they allow you to organize a low-speed wireless communication channel at distances in units, and sometimes tens of kilometers, without going beyond the restrictions of unlicensed radio bands (usually, such systems operate in the range of 864–869 MHz with power up to 25 mW). Technically, we will talk about the restrictions on use imposed by business models of technology owners - the next time - this allows us to solve quite interesting problems, for example:
And all this is cheap, without the need to obtain a license to use the radio frequency spectrum and with the ability to power the end devices from batteries or solar cells of a small area.
However, exactly how this connection works, the technologies listed above are quite different - in fact, they fall into two groups: broadband UWB (Ultra Wide Band, only LoRa belongs to them) and narrowband UNB (Ultra Narrow Band, in our the case is Sigfox and Swift, as well as being developed by Weightless). This results in a number of differences, for which - not always honestly - and those who want to advertise this or that technology cling.
In Russia, in the range, conventionally named “868 MHz”, two frequency bands are officially available for non-specialized devices: 864.0-865.0 MHz with a period of active work of no more than 0.1% and a ban on work near airports and 868.7- 869.2 MHz without such restrictions. Simply put, in general we have only 500 kHz of available frequency band.
LoRa channels with a width of 125 kHz, obviously, only three of them fit into this band. Channels Sigfox or "Swift" - many hundreds. As a rule, the developers of UNB-systems this fact is presented as an obvious advantage - hundreds of thousands of devices can coexist on the air without interfering with each other.
However, in practice, everything is somewhat more complicated.
In UNB systems, one base station receiver can receive only one channel at a time. This is a fairly obvious and often forgotten thesis. The term "frequency separation" refers to the ability of the receiver to hook this channel out of the common ether so that it does not overlap the transmission in adjacent channels - and if we receive something on channel N over a given second, then N + 1 and N- 1 we can accept nothing at the same time.
UWB systems use not only frequency and time, but also code division of channels. In LoRa networks, the end device can select a specific modulation scheme - and the LoRa base station is designed so that it can separate data streams from several devices simultaneously operating on the same frequency channel with different modulation schemes. This scheme has its limitations, and in practice we are talking about the ability of the BS to decode a signal at the same time from just a few devices - but, nevertheless, to say that in UWB systems only one device can work at a time, and in UNB - hundreds , incorrectly.
Theoretically, the advantage of UNB-systems can be observed when several networks are deployed in one region - they can be easily spread by frequencies. However, first, up to three LoRa networks can also be spread to different frequencies (and if we make a network, for example, specifically for utilities and a 0.1% duty cycle, we are completely satisfied, then we can take it out at 864-865 MHz) secondly, the frequency separation of different networks in the unregulated spectrum is a utopia, as every Wi-Fi router owner in an apartment building knows.
Practical advice: when you hear about the advantages of UNB networks for using the spectrum, start with the predilection to interrogate the narrator, as in the system he promotes, frequency hopping is implemented, that is, the possibility of changing the operating frequency of devices on the fly.
UNB systems are extremely sensitive to frequency setting accuracy. The same obvious thesis is that if you have an entire frequency band of 100 Hz (Sigfox, "Swift"), then even a tiny frequency drift of the quartz resonator of the end device will throw its operating frequency out of the limits of the band indicated to it. Far beyond. You can calculate it yourself - a very good resonator has an error of 10 ppm, that is, 0.001%, at room temperature, and another 15 ppm (0.0015%) from above when the temperature changes from -40 to +85 ° C. The numbers seem tiny - but we take these percentages from 868,000,000 Hz and compare the result with 100 Hz ...
So what to do with the fact that the transmitter in UNB-systems broadcasts is not clear in which band? This is solved at the base station level: it should be able to see a signal in a wide range and tune in quickly. Unfortunately, implementing the same algorithms at the level of a small, cheap and cost-effective end device is problematic, so the bidirectionality of communication in UNB is not implemented in all systems and not in all conditions. At the same Sigfox connection has been strictly unidirectional for a long time.
UWB-systems provide a symmetrical communication channel. Thanks to a bandwidth of hundreds of kilohertz, LoRa provides a symmetrical connection with a frequency drift of as much as 25% of the channel width (31.25 kHz with a width of 125 kHz), which in the 868 MHz range means an allowable error of the resonator of 35 ppm. A good, but quite widespread crystal with a base error of ± 10 ppm and a temperature of ± 15 ppm allows the LoRa end device to feel normal in the full temperature range -40 ... + 85 ° C.
In addition, there is such an unpleasant thing for UNB networks as the Doppler effect. Sigfox loses the stability of work already at the speed of the end device in the region of 5-10 km / h, that is, making a bike monitoring system on Sigfox is already a task for real enthusiasts in their field. LoRa, in contrast, is sensitive to speeds a little - although generally it is worth considering acceleration, since Quartz resonators are sensitive to them.
Practical advice: when you hear about the benefits of UNB networks on using the spectrum, start with the predilection to interrogate the narrator, how symmetrical the connection is in this system, and under what conditions this symmetry works.
Alas, one cannot get away from the Kotelnikov-Shannon theorem: one cannot simply take and pull a megabit stream into the 100 Hz frequency band.
UNB systems operate at a fixed low speed . More specifically, Sigfox has a data transfer rate of 100 bps, while Strizha has a 50 bps data transfer rate.
UWB systems operate at adaptive speed . Depending on the signal strength, LoRa can operate at speeds from 30 bps to 50 kbps. In LoRaWAN cellular networks, the speed is automatically selected; in LoRa local networks, the speed can be fixed at a level that ensures reliable coverage of the desired object with a link.
In practice, this means both greater flexibility in the use of UWB-systems, and help for them in avoiding collisions in the air. The faster the subscriber unit transmits its data to the BS, the faster it will free up the air. Although LoRa, due to the complex modulation system, has a longer network packet length than UNB systems (longer preamble), this is more than offset by a higher data transfer rate.
In practice, this leads to quite severe restrictions on UNB systems: for example, in Sigfox the maximum amount of user data is 12 bytes, their transmission takes a few seconds, and the connection conditions to the Sigfox network determine that a single object can transmit no more than 140 messages per day .
Practical advice: having heard about millions of simultaneously working devices, start with an addiction to interrogate the narrator how many messages per day and how long one base station can receive.
In general - the same. The communication range in all such technologies very much depends on the conditions on the ground: so, if in the open area and with a high location of the antenna, the LoRa BS provides a range even higher than the promised 30 km, then in dense forest it drops to 1-2 km even at minimum speed .
The advantage of LoRa in this matter is that against the background of its competitors, LoRa is a fairly open technology, there are many companies in the world that are engaged in it, and therefore it is relatively easy to find various white papers and reviews indicating the actual range achieved.
In general, we can assume that all of these technologies provide a range of 1-3 km in urban areas and 15-20 km in open areas. The range can be increased due to the advantageous location of antennas: for example, the words “in urban development” can mean both subscriber devices located in the depth of buildings and equipped with compact printed antennas, as well as controllable street lights with ordinary whip antennas standing outdoors and a minimum five meters from the ground.
The power consumption of the end devices in all the listed technologies is determined by two points - the technological perfection of the transmitter chip and the time it spends on transmission.
In general, in any of the systems it is possible to ensure work for at least 5 years on one battery. UWB networks have an advantage over UNB when working at small distances, when their speed can exceed 1 kbps - which significantly reduces the time of the transmitter's activity.
Although in many cases the technologies UNB and UWB are equally applicable, there are noticeable differences between them that can play in favor of one or another solution. So, on the UNB-networks, a quick frequency hopping can be implemented to avoid collisions and interference - however, in the case of specific technologies, be it Sigfox or Stryzh, you need to additionally find out whether it is implemented as well as how and to what extent it works.
On the other hand, UWB networks based on LoRa technology have significantly greater flexibility of parameters, which allows them to be used in projects for which UNB networks are of little use. LoRa networks provide large potential data transfer speeds, symmetric bidirectional communication, less sensitive to temperature extremes and the speed of movement of the end device.
Interestingly, this also applies to possible applications of LoRa from a commercial point of view - at the moment this technology actually gives the business model and the details of the technical implementation of the project to the full discretion of the customer. But about this - in the next part.
Unwired Devices develops and manufactures communication modules for 6LoWPAN cellular networks and LoRa long-distance networks, as well as sensors and other terminals for these networks, including both hardware and firmware, supporting the necessary network technologies. In the case of LoRa networks, we develop all possible topologies: cellular and static radio relay networks, star-based object networks from a single BS, and devices for LoRaWAN global networks.
- IoT Link: LoRa vs. UNB. Part 1: Physics
- IoT Link: LoRa vs. UNB. Part 2: Business
- IoT Link: LoRa vs. UNB. Part 3: technical details
- IoT Link: LoRa vs. UNB. Part 4: LoRa networks and equipment
The topic of low-power radio communication, which allows, without going beyond the unlicensed ranges (that is, as a rule, for a power of 25 mW), to transmit low-speed data from 1-3 to 10-30 kilometers in Russia began to flourish in the past six months. That is - they talked about it before that, but practical applications were very rare, and there were very few developers and integrators who could do a project on such technologies.
Now we are on the verge of a turning point: although large projects are still only expected in the future (but we can already predict that this future is a matter of months, not years), integrators and customers have a serious interest in IoT communication technologies, and not only in words, but also in the immediate desire to try these technologies in action.
')
The main competition in this segment right now is between the broadband connection LoRa and narrowband Sigfox (and specifically in Russia - the Stryzh Telematics technology similar to it). In the future, the Weightless UNB protocol will be added to this list, as well as the networks promoted by the suppliers of the classic cellular equipment - NB-IoT and LTE-M, but this will happen in two or three years.
So, what is the difference - and what to choose for a particular project? Go.
A common feature of all the listed technologies is that they allow you to organize a low-speed wireless communication channel at distances in units, and sometimes tens of kilometers, without going beyond the restrictions of unlicensed radio bands (usually, such systems operate in the range of 864–869 MHz with power up to 25 mW). Technically, we will talk about the restrictions on use imposed by business models of technology owners - the next time - this allows us to solve quite interesting problems, for example:
- wireless collection of meter readings in housing and communal services on a large scale and wider;
- wireless monitoring of real-time state of technology at large open sites, from construction sites to quarrying;
- replacement of expensive in laying and servicing of low-current data collection networks at large objects, especially - square kilometers spread over the territory;
- construction of extended radio relay networks along power lines, pipelines, railways, etc. objects;
- the organization of cellular telemetry networks with continuous coverage and cost 1-2 orders of magnitude lower than that of classic cellular telephone networks.
And all this is cheap, without the need to obtain a license to use the radio frequency spectrum and with the ability to power the end devices from batteries or solar cells of a small area.
Use of the radio frequency spectrum
However, exactly how this connection works, the technologies listed above are quite different - in fact, they fall into two groups: broadband UWB (Ultra Wide Band, only LoRa belongs to them) and narrowband UNB (Ultra Narrow Band, in our the case is Sigfox and Swift, as well as being developed by Weightless). This results in a number of differences, for which - not always honestly - and those who want to advertise this or that technology cling.
- UWB: one channel occupies a band on the air with a width of 125 or 250 kHz
- UNB: one channel occupies a band in the air with a width of 100 Hz
In Russia, in the range, conventionally named “868 MHz”, two frequency bands are officially available for non-specialized devices: 864.0-865.0 MHz with a period of active work of no more than 0.1% and a ban on work near airports and 868.7- 869.2 MHz without such restrictions. Simply put, in general we have only 500 kHz of available frequency band.
LoRa channels with a width of 125 kHz, obviously, only three of them fit into this band. Channels Sigfox or "Swift" - many hundreds. As a rule, the developers of UNB-systems this fact is presented as an obvious advantage - hundreds of thousands of devices can coexist on the air without interfering with each other.
However, in practice, everything is somewhat more complicated.
In UNB systems, one base station receiver can receive only one channel at a time. This is a fairly obvious and often forgotten thesis. The term "frequency separation" refers to the ability of the receiver to hook this channel out of the common ether so that it does not overlap the transmission in adjacent channels - and if we receive something on channel N over a given second, then N + 1 and N- 1 we can accept nothing at the same time.
UWB systems use not only frequency and time, but also code division of channels. In LoRa networks, the end device can select a specific modulation scheme - and the LoRa base station is designed so that it can separate data streams from several devices simultaneously operating on the same frequency channel with different modulation schemes. This scheme has its limitations, and in practice we are talking about the ability of the BS to decode a signal at the same time from just a few devices - but, nevertheless, to say that in UWB systems only one device can work at a time, and in UNB - hundreds , incorrectly.
Theoretically, the advantage of UNB-systems can be observed when several networks are deployed in one region - they can be easily spread by frequencies. However, first, up to three LoRa networks can also be spread to different frequencies (and if we make a network, for example, specifically for utilities and a 0.1% duty cycle, we are completely satisfied, then we can take it out at 864-865 MHz) secondly, the frequency separation of different networks in the unregulated spectrum is a utopia, as every Wi-Fi router owner in an apartment building knows.
Practical advice: when you hear about the advantages of UNB networks for using the spectrum, start with the predilection to interrogate the narrator, as in the system he promotes, frequency hopping is implemented, that is, the possibility of changing the operating frequency of devices on the fly.
UNB systems are extremely sensitive to frequency setting accuracy. The same obvious thesis is that if you have an entire frequency band of 100 Hz (Sigfox, "Swift"), then even a tiny frequency drift of the quartz resonator of the end device will throw its operating frequency out of the limits of the band indicated to it. Far beyond. You can calculate it yourself - a very good resonator has an error of 10 ppm, that is, 0.001%, at room temperature, and another 15 ppm (0.0015%) from above when the temperature changes from -40 to +85 ° C. The numbers seem tiny - but we take these percentages from 868,000,000 Hz and compare the result with 100 Hz ...
So what to do with the fact that the transmitter in UNB-systems broadcasts is not clear in which band? This is solved at the base station level: it should be able to see a signal in a wide range and tune in quickly. Unfortunately, implementing the same algorithms at the level of a small, cheap and cost-effective end device is problematic, so the bidirectionality of communication in UNB is not implemented in all systems and not in all conditions. At the same Sigfox connection has been strictly unidirectional for a long time.
UWB-systems provide a symmetrical communication channel. Thanks to a bandwidth of hundreds of kilohertz, LoRa provides a symmetrical connection with a frequency drift of as much as 25% of the channel width (31.25 kHz with a width of 125 kHz), which in the 868 MHz range means an allowable error of the resonator of 35 ppm. A good, but quite widespread crystal with a base error of ± 10 ppm and a temperature of ± 15 ppm allows the LoRa end device to feel normal in the full temperature range -40 ... + 85 ° C.
In addition, there is such an unpleasant thing for UNB networks as the Doppler effect. Sigfox loses the stability of work already at the speed of the end device in the region of 5-10 km / h, that is, making a bike monitoring system on Sigfox is already a task for real enthusiasts in their field. LoRa, in contrast, is sensitive to speeds a little - although generally it is worth considering acceleration, since Quartz resonators are sensitive to them.
Practical advice: when you hear about the benefits of UNB networks on using the spectrum, start with the predilection to interrogate the narrator, how symmetrical the connection is in this system, and under what conditions this symmetry works.
Data transfer rate
Alas, one cannot get away from the Kotelnikov-Shannon theorem: one cannot simply take and pull a megabit stream into the 100 Hz frequency band.
UNB systems operate at a fixed low speed . More specifically, Sigfox has a data transfer rate of 100 bps, while Strizha has a 50 bps data transfer rate.
UWB systems operate at adaptive speed . Depending on the signal strength, LoRa can operate at speeds from 30 bps to 50 kbps. In LoRaWAN cellular networks, the speed is automatically selected; in LoRa local networks, the speed can be fixed at a level that ensures reliable coverage of the desired object with a link.
In practice, this means both greater flexibility in the use of UWB-systems, and help for them in avoiding collisions in the air. The faster the subscriber unit transmits its data to the BS, the faster it will free up the air. Although LoRa, due to the complex modulation system, has a longer network packet length than UNB systems (longer preamble), this is more than offset by a higher data transfer rate.
In practice, this leads to quite severe restrictions on UNB systems: for example, in Sigfox the maximum amount of user data is 12 bytes, their transmission takes a few seconds, and the connection conditions to the Sigfox network determine that a single object can transmit no more than 140 messages per day .
Practical advice: having heard about millions of simultaneously working devices, start with an addiction to interrogate the narrator how many messages per day and how long one base station can receive.
Communication range
In general - the same. The communication range in all such technologies very much depends on the conditions on the ground: so, if in the open area and with a high location of the antenna, the LoRa BS provides a range even higher than the promised 30 km, then in dense forest it drops to 1-2 km even at minimum speed .
The advantage of LoRa in this matter is that against the background of its competitors, LoRa is a fairly open technology, there are many companies in the world that are engaged in it, and therefore it is relatively easy to find various white papers and reviews indicating the actual range achieved.
In general, we can assume that all of these technologies provide a range of 1-3 km in urban areas and 15-20 km in open areas. The range can be increased due to the advantageous location of antennas: for example, the words “in urban development” can mean both subscriber devices located in the depth of buildings and equipped with compact printed antennas, as well as controllable street lights with ordinary whip antennas standing outdoors and a minimum five meters from the ground.
power usage
The power consumption of the end devices in all the listed technologies is determined by two points - the technological perfection of the transmitter chip and the time it spends on transmission.
In general, in any of the systems it is possible to ensure work for at least 5 years on one battery. UWB networks have an advantage over UNB when working at small distances, when their speed can exceed 1 kbps - which significantly reduces the time of the transmitter's activity.
Total
Although in many cases the technologies UNB and UWB are equally applicable, there are noticeable differences between them that can play in favor of one or another solution. So, on the UNB-networks, a quick frequency hopping can be implemented to avoid collisions and interference - however, in the case of specific technologies, be it Sigfox or Stryzh, you need to additionally find out whether it is implemented as well as how and to what extent it works.
On the other hand, UWB networks based on LoRa technology have significantly greater flexibility of parameters, which allows them to be used in projects for which UNB networks are of little use. LoRa networks provide large potential data transfer speeds, symmetric bidirectional communication, less sensitive to temperature extremes and the speed of movement of the end device.
Interestingly, this also applies to possible applications of LoRa from a commercial point of view - at the moment this technology actually gives the business model and the details of the technical implementation of the project to the full discretion of the customer. But about this - in the next part.
Unwired Devices develops and manufactures communication modules for 6LoWPAN cellular networks and LoRa long-distance networks, as well as sensors and other terminals for these networks, including both hardware and firmware, supporting the necessary network technologies. In the case of LoRa networks, we develop all possible topologies: cellular and static radio relay networks, star-based object networks from a single BS, and devices for LoRaWAN global networks.
Source: https://habr.com/ru/post/396869/
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