Tak jsem si v tom trochu pocet a zjistil jsem, ze jejich HDD znamena krutopresne nacasovane odesilani dat. Zatimco vysilac odesila data na klienta, data od klienta jsou uz ve vzduchu a "doleti" na vysilac presne, kdyz skonci s vysilanim a na klienta zase v momente, kdy on dovysilal. Zadny cekani na data, kazdy vi, kdy protistrana dovysila, tak ji uz s predstihem posila data, aby tam byla presne na cas. Timto se oproti klasickemu TDD systemu zvysuje efektivita, ktera roste se zvysujici se vzdalenosti. V tom dokumentu je popsana tato technologie i v PTMP verzi.
Jinak mi to nedalo a trochu jsem si s UBNtakama psal a dovedel jsem, ze anteny maji slant (45st) jelikoz nejsou tolik nachylne na slabnuti signalu kvuli odrazum a maji stejne vyzarovaci diagramy v obou rovinach.
U tohoto spoje si mohu zvolit, bud simplex (HDD) s pevnym pomerem UP&DOWN a nebo TDD, pricemz primaci a vysilaci frekvence jsou pochopitelne kazda jina a mohu si zvolit i rozdilnou sirku pasma.
airFiber 5X Uses Dual Polarized Slant 45 antennas, or you can upgrade a Rocket™link that uses a RocketDish™ RD‑5G30/RD‑5G34* antenna.
A dipole, which is set at a slant of +45° when viewed from the front, will appear to be vertically polarized when viewed from
the side and will then appear at a slant of -45° when viewed from the rear.
Slant 45° antennas are more robust than traditional horizontal and vertical cross polarized solutions. Horizontal and vertical as cross polarizations can suffer fading due to reflections from buildings, vehicles and the general environment, these reflections
occur more easily than ±45°.
The radiation pattern from both ports of a ±45° Linear Polarization antenna are symmetrical and almost overlap whereas horizontal and linear polarized patterns differ substantially. Slant 45 degree antenna delivers more reliable coverage areas with less drop-outs.
Channel width flexibility allows you to independently configure TX and RX channel frequencies and place them anywhere within the radio band to avoid local interference.
You have two choices with AF 5X:
1) HDD - TX and RX on same frequency,
2) Frequency Duplex Division, TX and RX on different frequencies, sending data independently on each other
Thanks!
Shaibaz Khan
Ubiquiti Networks
Kdo chce může si počíst:
Guys,
If you want a little bit of insight on what we did for our TDD/HDD protocol (at least one early limited instantiation of it), you could peruse the following light reading:
https://www.google.com/patents/US201300 ... CC0Q6AEwAg
To answer the question posed about GPS sync and latency, I can tell you there is zero impact to latency with the AF/AFX implementation.
This is a real-time hardware based implementation and has been pointed out is far more robust than anything possible with WiFi based systems. WiFi based PTP/PMP systems are generally limited to interrupt driven sync implementations so timing accuracy and timing resolution is very constrained. In pretty much all WiFi based systems, the designer is limited to trying to "fool" the chipset to support a pseudo-frame, which results in serious performance impacts, problems with ACK timing and a bunch of other stuff. WiFi chips are fantastic in their intended environment (indoor, high amounts of multipath to ensure path orthogonality, high loss exponents) but they have serious underlying limitations for transporting large amounts of data with low overhead and low latency at long range while trying to elegantly coexist at the same time.
Gary
