UBNT promotes it's AC gear as new highly efficient system, that outperforms all 802.11N based system ( also it's old airmax 802.11N ) and competitors.
Let's see how ubnt АС really works.
1) Point To Point scenario.
АС chip has 256QAM5/6 modulation and is able to achieve max 135-140 MBps ( UL+DL) in 20 MHz channel bandwidth, 270-280 Mbps in 40 MHz. Wi-Fi AC chip requires for 256QAM5/6 modulation CINR =signal/( interference+ termal noise ) >34dB. Taking into account 3 dB fade margin required CINR for stable link at 256QAM5/6 should be 37 dB. It means that when interference + noise is -85 dBm ( typical interference at base station locations in 5 GHz), then signal should be > -48 dBm. So max distance, for example, PB AC 500 ( antenna 27 dBi, and Tx 18 dBm@ 256QAM5/6) in real life noisy environment (about -85 dBm) is 3km ( it is able to achieve max 135-140Mbps in 20 MHz at 256QAM 5/6 ).
UBNT AC shows (at web) measured by AC radiochip it's (interference + noise) level and CINR, but ubnt system can not adapt it's modulation according measured CINR. And when distance is longer then 3 km or interference is higher then -85 dBm ubnt АС tries to works at 256QAM5/6 at CINR lower then 37 dB. For example, we very often may see that ubnt AC works at 256QAM 5/6 at indicated at it's web CINR 26-29 dB that leads to huge packet losses and big TCP/IP throughput degradation.
See screen of TCP duplex test, that made by Bandwidth Test Mikrotik for link 13km at PB AC 500, 40 MHz, antenna dish 27 dBi, (interference+noise)= -86 dBm, CINR 23-29 dB, but PB works at 256QAM/64QAM
It was got 170M download +18M upload TCP duplex. Test was done by experienced ubnt fanboy , and it was best result ,that PB AC 50 was able to show at 13 km in such condition. If download to remain 170Mbps and upload to increase up to 20 Mbps, then link latency became over 80-100 ms. So AC at 256QAM 5/6 shows in 40 MHz TCP 188 Mbps ( UL+DL). It is much better then old Airmax N ( for example PB M5 400) in the same link, but it is almost the same as ePMP Force with 25 dBi dish is able to show TCP 170+20 Mbps at 64QAM 5/6, 40 MHz in the same conditions. But ePMP also is able to achieve symmetric dupleх 100+100М, when UBNT AC – not ( when current CINR less required CINR).
So main problems of ubnt AC are high required CINR for 25QAM5/6 and luck of ability to manage it's modulation according current CINR.
Second problem is Airmax AC high packet error rate (PER). For example we may see in UBNT AC big difference between UDP test throughput ( that does not take into account packet losses) and TCP test throughput, that degrades when packet losses occur. Both problems are Airmax protocol issues, and it may be resolved only by complete Airmax redesign, that is impossible.
2) Point to multipoint.
As we know UBNT Airmax N is able to achieve in 20 MHz point to point max 90-100 Mbps. In multipoint scenario with 25-30 Subscribers ( 6-8+ simultaneously active SS) ubnt sector throughput capacity is 22-25 Mbps ( UL+DL) , in 4 times less then in p2p. Also we know, that ubnt is able to serve with acceptable quality max 30-35 CПЕ per sector ( with max 25 Mbps sector throughput).
If AC able to achieve 140 Mbps at 256QAM 5/6 in 20 Mhz in p2p, we may suppose, that in multipont with 30 SS it may give only 35 Mbps. Why AC should give more then 35 Mbps in 20 MHz multipoint throughput? Why ubnt AC should serve more then 30 СПЕ sector Airmax N ? It seems, Airmax AC multipoint protocol remains the same as Airmax N, so nothing is changed and all problems are the same.
Let's assume , that ubnt Rocket AC and all CPE ( PB AC ) 25-30 q-ty are working in multipoint at 64QAM modulations , - at the same modulations as, for example, ubnt AP Rocket Ti with CPE - PB M5. Total sector throughput of Rocket AC and Rocket Ti with 25-30 CPE at 64QAM will be the same - about 25 Mbps (UL+DL). Will total sector throughput increase in twice- till 50 Mbps, if all CPE AC , that are working with Rocket AC AP increase it's modulation up to 256QAM ? No. Max sector throughput capacity growth due to increasing CPE modulations from 64QAM to 256QAM will be about 30-40%. So it will be max 35 Mbps. May be 40 Mbps, no more
Somebody may say, that Rocket AC has ASIC Airmax accelerator. But throughput and max quantity CPE per sector does not depends on CPU power. So ASIC can not significantly improve UBNT AC Airmax performance.
We have never seen yet in multipoint above 30 CPEs per UBNT AC sector and above 30-35 Mbps sector throughput with 25-30 active CPEs. All that was shown by UBNT fans in their forum, it is some kind of p2p throughput, when 20 CPE are idle, and only one CPE is working and shows point -to point speed.
Also if we take into account how many CPEs are able to work in multipoint at 256QAM5/6 ( because for 256QAM CPE should have 27-30 dBi dish at 2-3 km LOS distance from base station) we can understand that UBNT AC gear is not able to improve UBNT multipoint service.
In comparison with ePMP multipoint. We know and we have examples, when ePMP 20 MHz sector serves 120 CPEs with throughput sector capacity total 70 Mbps download + 8 Mbps upload ( MRTG daily graph) So conclusion is:
- in point to point UBNT AC is able to compete with ePMP in throughput only with high gain dish antenna at short distance in low noisy environment.
- in multipoint UBNT AC is not able to compete with ePMP in total sector throughput and max CPEs per sector.