More AirFiber, good and different

Since the advent of Ubiquiti AirFiber 24 , which we previously wrote about , more than a year has passed. During this time, an inexpensive relay station with more than 700 Mbit / s of FDD capacity has found its place among many operators, and the functionality of the system has been significantly expanded.

Unfortunately, this solution also has obvious drawbacks, for example, the impossibility of legalizing a legal entity in the Russian Federation due to the inconsistency of frequencies with the rules for using the ether, depending on rainfall due to the frequency range. This year, two new models of beloved radio relay stations are entering the market - we meet airFiber 5 and 5U. Let their capacity be 500 Mbit / s instead of 750, but the range of reliable communication promises to be greater, and the frequency plan allows you to register them in the Russian Federation.
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Both new solutions, designed for band 5 ( model without an index ) and 6 GHz ( model U ), continue the ideology of the first device: an inexpensive relay station FDD or TDD with the ability to control in a separate vlan and adjust by built-in indicators. Due to the change of the frequency range, the available modulations, system capacity have changed.

The main parameters of AirFiber systems:



From the point of view of appearance, the antenna system has changed: instead of a metallized reflector, two metal reflectors are used, and the display has become more convenient.


General view of the AF5 and "combat" placement of the device.


System indication block - adding an indication of the remote side of the link allows you to more accurately and easily align the system. The indicator reflects the state of the radio channel, the modulation used.

Equipment functionality

In the new models appeared (and in the old, high-frequency ones, they were added):

• Jumbo frame support;
• Isolating the management interface from multicast traffic;
• Built-in spectrum analyzer.

Spectrum analyzer.

Those who communicated with the AF24 system in early releases remember that with a large amount of multicast traffic coming not even into the control vlan, the processor was overloaded, which made it possible to use out-of-band-control. The use of multicast isolation has solved this problem.



But, of course, the most interesting in the new product is the opportunity to get a full frequency assignment and independence from precipitation.
We calculate the range of the American frequency plan systems, using the already proven methodology from the previous publication and the data provided by the manufacturer:



Capacity (Mbps), duplex, as a function of distance, maximum frequency bands:


We see that the range of the new solution is several times higher than the high-frequency model.
Unfortunately, due to the requirements of US regulators, AirFiber 5, produced for the American market, has limited power for frequency channels below 5725 to 30 dBm, and this area also includes detection of a radar signal, which is not required in Russia. The use of nominal values ​​without attenuation leaves only frequencies from 5725 to 5950, which may not be enough to build a communication center with several radio channels, given the presence of other radio networks.

The range of the American version of AirFiber 5:

Use of radio

From the point of view of regulating the use of the frequency spectrum, AirFiber 5 can be regarded as a broadband access device, which allows you to receive a frequency assignment of 1 nominal up to 40 MHz inclusive, and AirFiber 5U can be interpreted as a radio relay station with the possibility of allocating a 40 MHz frequency pair.
It is technically possible for AirFiber 5 to submit a second application with the same network identifier and receive a second 40 MHz band to use the system in duplex.

We calculate the range taking into account the limitations of the frequency regulation of the Russian Federation (40 MHz TDD for 5 GHz, 40 MHz FDD for 6 GHz), the total power:


The required frequency resources for the required power and speed can be calculated in the integrated radio planning application - the system shows the possible modulation and the minimum frequency plan for the technical task:

Communication channel design

The main difference from the AF24 model are more stringent channel planning requirements: if for the high-frequency model the limiting factor is rain attenuation, then for a solution in the 5 GHz band, interference and frequency resource are critical.
The use of high modulations has led to a high sensitivity of the system to the reflection of its signal from the underlying surface and interference, so the manufacturer makes the following recommendations to protect the channel from being affected by re-reflections, causing both a decrease in modulation and a triggering of the radar signal detection:



You can track the switching of the system to another frequency rating by the system log, SNMP, graphical menu:


The signal of the neighboring radio network is recognized as radar.

For frequencies of 5725 MHz and higher, using the system in such a situation will lead to a decrease in modulation to 64QAM and lower, while at frequencies below 5725 MHz, detection of the radar signal leads to switching the system to another frequency rating (if specified) and blocking the previous frequency for 30 minutes. Since the decision to switch the nominal frequencies is made by each of the devices independently, in the time mode of receiving-transmitting time, a situation may arise when reception and transmission will be conducted at different frequencies. Although the channel will continue to function, the frequency use efficiency will be halved. In some cases, as a radar signal, the system may consider interference from other radio networks, and re-reflection of its transmitting signal from buildings.
However, there is some benefit from detecting a radar signal. In practice, using frequencies that are susceptible to it, you can check the installation of the system — you do not need a full link, it’s enough to select a free rating from one device by analyzing the ether and start the device in it. If the device has shown the presence of a radar signal and, especially, if the signal is not detected at minimum power, and is detected with an increase, then we can speak of the presence of significant reflections from the roof or adjacent buildings.

The second factor important for frequency planning is interference from extraneous networks. Before installing the equipment, it is recommended to conduct an air survey, since the ingress of an extraneous signal into the antenna array not only reduces the signal-to-noise ratio, but can also block the operation of the system. At the time of the system alignment, the manufacturer recommends using frequencies above 5725, select the TDD mode in the 10 MHz band in order to avoid triggering the detection of the radar signal and the effect of interference on the alignment procedure. Then you can switch to the frequency of interest.

Often forgotten points in the installation of systems is grounding. Recently, the manufacturer clarified the requirements - now the recommended connection looks like this:



I will add that if there is uncertainty about the correspondence between the potentials of the mast and the injector earthing, you can measure the resistance difference between them - if you exceed the 4 ohm threshold, you should look for other switching options.


Measurement of the potential difference of the connection points.

In the near future, wait for the publication of a kind of success story - the results of the deployment of several channels on the equipment AirFiber.