More AirFiber, good and different

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

    Unfortunately, this solution has obvious drawbacks, for example, the impossibility of legalization for a legal entity in the Russian Federation due to frequency inconsistency with the rules for using the air, dependence on rains due to the frequency range. This year, two new models of favorite radio-relay stations enter 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.

    Both new solutions, designed for the range 5 ( model without 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 according to the built-in indicators. Due to changes in the frequency range, the available modulations and 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 indication has become more convenient.

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

    System display unit - 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;
    • Isolation of the control interface from multicast traffic;
    • Built-in spectrum analyzer.

    Spectrum analyzer.

    Communicating with the AF24 system in early releases, remember that with a large amount of multicast traffic that did not even come to the vlan control, the processor was overloaded, because of which it was necessary to use out-of-band control. Using 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, which is available for the US market, has limited power for frequency channels below 5725 to 30 dBm, and radar detection, which is not required in Russia, is also included in this range. The use of ratings 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.

    Range of the American version of AirFiber 5:

    Radio use

    From the point of view of regulating the use of the frequency spectrum, AirFiber 5 can be regarded as a broadband access device, which makes it possible to obtain a frequency assignment of 1 nominal up to 40 MHz inclusive, and AirFiber 5U can also be interpreted as a radio relay station with the possibility of allocating a pair of frequencies of 40 MHz.
    It is technically possible for AirFiber 5 to file 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), apparent power:

    You can calculate the necessary frequency resources for the power and speed of interest in the built-in 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 is the more stringent requirements for channel planning: if the decay in the rain is the limiting factor for the high-frequency model, then interference and the frequency resource are critical for solving in the 5 GHz band.
    The use of high modulations led to a high sensitivity of the system to the reflection of its signal from the underlying surface and interference, therefore, the manufacturer provides the following recommendations for protecting the channel from damage by re-reflection, causing both a decrease in modulation and the triggering of radar signal detection: You can

    track the system switching to a different frequency rating by 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, the detection of a radar signal will switch the system to another frequency rating (if specified) and block the previous frequency for 30 minutes. Since the decision to switch the nominal frequency is made by each of the devices independently, in the temporary division mode of reception and transmission, a situation may arise when reception and transmission will be at different frequencies. Although the channel will continue to function, the frequency utilization efficiency will be halved. In some cases, as a radar signal, the system may also consider interference from other radio networks and the re-reflection of its transmitting signal from buildings.
    However, there is some benefit from the detection of the radar signal. In practice, using the frequencies subject to it, you can check the correct installation of the system - for this you do not need a full link, it is enough from one device to select the free face value from the ether analysis and start the device in it. If the device showed the presence of a radar signal and, especially, if the signal is not detected at the minimum power, but is detected with an increase, then we can talk about the presence of a significant re-reflection from the roof or neighboring 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 target not only reduces the signal-to-noise ratio, but can also block the operation of the system. At the time of adjusting the system, the manufacturer recommends using frequencies above 5725, select the TDD mode in the 10 MHz band to prevent the detection of the radar signal and the influence of interference on the alignment procedure. Then you can switch to the frequency of interest.

    Often forgotten moments 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 in the correspondence of the grounding potentials of the mast and injector, you can measure the difference in resistance between them - if you exceed a threshold of 4 Ohms, you should look for other options for inclusion.

    Measuring 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 AirFiber equipment.

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