Hello everyone,
I'm facing a big issue on one of my AP.
It's a RB435G with 4 radios Atheros AR92xx.

Each radio is connected to a 120° antenna to get a 360° coverage of the area.

They all have the same settings.

It always worked good but during the last month it became unstable and now it has a super-low throughput versus most of CPEs.
My expected throughput from AP to CPE is 10Mbps.

There are 57 CPEs connected:
wlan1 -> 10 CPEs
wlan2 -> 26 CPEs
wlan3 -> 17 CPEs
wlan4 -> 4 CPEs

Frequencies are:
wlan1 -> 5280MHz
wlan2 -> 5500MHz
wlan3 -> 5620MHz
wlan4 -> 5520MHz

Protocol is:
- nstreme, framer policy none, framer limit 2800, polling enabled, csma enabled, hw retries 15

Except a few CPEs, almost everyone have not more than 3-4 Mbps (TX from AP, RX from CPE). Lots of them have less than 1Mbps.

CPEs get signal from -80 to -50, SNR from 27 to 53.
Even CPEs with great signal have terrible speed.
Some of them disconnects every 2-3 minutes.

I tried almost everything:
- Change frequencies
- Reset all interfaces
- Change lots of CPEs
- Switch from WPA2 TKIP to WPA2 AES
- Switch from 5GHz-A to 5GHz-A/N (not all CPEs have N support)
- Switch from nstreme to nv2 or 802.11
- Activate Adaptive Noise Immunity
- Change radio cards

This is wlan2 configuration export (they all have the same conf)

ros code

/interface wireless set [ find default-name=wlan2 ] adaptive-noise-immunity=ap-and-client-mode country=italy disabled=no frequency=5620 \
    ht-rxchains=0,1 ht-txchains=0,1 hw-retries=15 l2mtu=2290 mode=ap-bridge name=wlan3 nv2-cell-radius=15 radio-name=\
    Radio3 security-profile=aes_profile ssid=RADIO3 tdma-period-size=6 tx-power=25 tx-power-mode=card-rate
    wireless-protocol=nstreme
/interface wireless nstreme set wlan1 enable-nstreme=yes framer-limit=2800

This is interface info:

ros code

1 interface-type=(unknown) chip-info="mac:0x80/0x2, phy:0xd0, a5:0xc0, a2:0x0, eeprom:0x0" pci-info="00:12.0" 
   capabilities=tx-power-control,ack-timeout-control,virtual-ap,alignment-mode,noise-floor-control,scanning,nstreme,sniffing,power-channel,ht40-a,
             ht40-g,wmm,spectral-scan,nv2,no-ant-mode 
   supported-bands=2ghz-b,5ghz-a,2ghz-g,5ghz-10mhz,5ghz-5mhz,2ghz-10mhz,2ghz-5mhz,5ghz-n,2ghz-n,5ghz-n-10mhz,2ghz-n-10mhz,5ghz-n-5mhz,2ghz-n-5mhz 
   2ghz-b-channels=2412:0,2417:0,2422:0,2427:0,2432:0,2437:0,2442:0,2447:0,2452:0,2457:0,2462:0,2467:0,2472:0 
   5ghz-channels=5180:0,5185:0,5190:0,5195:0,5200:0,5205:0,5210:0,5215:0,5220:0,5225:0,5230:0,5235:0,5240:0,5245:0,5250:0,5255:0,5260:0,5265:0,5270:0,
              5275:0,5280:0,5285:0,5290:0,5295:0,5300:0,5305:0,5310:0,5315:0,5320:0,5500:0,5505:0,5510:0,5515:0,5520:0,5525:0,5530:0,5535:0,5540:0,
              5545:0,5550:0,5555:0,5560:0,5565:0,5570:0,5575:0,5580:0,5585:0,5590:0,5595:0,5600:0,5605:0,5610:0,5615:0,5620:0,5625:0,5630:0,5635:0,
              5640:0,5645:0,5650:0,5655:0,5660:0,5665:0,5670:0,5675:0,5680:0,5685:0,5690:0,5695:0,5700:0 
   2ghz-g-channels=2412:0,2417:0,2422:0,2427:0,2432:0,2437:0,2442:0,2447:0,2452:0,2457:0,2462:0,2467:0,2472:0 
   5ghz-10mhz-power-channels=5175:0,5180:0,5185:0,5190:0,5195:0,5200:0,5205:0,5210:0,5215:0,5220:0,5225:0,5230:0,5235:0,5240:0,5245:0,5250:0,5255:0,
                          5260:0,5265:0,5270:0,5275:0,5280:0,5285:0,5290:0,5295:0,5300:0,5305:0,5310:0,5315:0,5320:0,5325:0,5495:0,5500:0,5505:0,
                          5510:0,5515:0,5520:0,5525:0,5530:0,5535:0,5540:0,5545:0,5550:0,5555:0,5560:0,5565:0,5570:0,5575:0,5580:0,5585:0,5590:0,
                          5595:0,5600:0,5605:0,5610:0,5615:0,5620:0,5625:0,5630:0,5635:0,5640:0,5645:0,5650:0,5655:0,5660:0,5665:0,5670:0,5675:0,
                          5680:0,5685:0,5690:0,5695:0,5700:0,5705:0 
   5ghz-5mhz-power-channels=5175:0,5180:0,5185:0,5190:0,5195:0,5200:0,5205:0,5210:0,5215:0,5220:0,5225:0,5230:0,5235:0,5240:0,5245:0,5250:0,5255:0,
                         5260:0,5265:0,5270:0,5275:0,5280:0,5285:0,5290:0,5295:0,5300:0,5305:0,5310:0,5315:0,5320:0,5325:0,5495:0,5500:0,5505:0,
                         5510:0,5515:0,5520:0,5525:0,5530:0,5535:0,5540:0,5545:0,5550:0,5555:0,5560:0,5565:0,5570:0,5575:0,5580:0,5585:0,5590:0,
                         5595:0,5600:0,5605:0,5610:0,5615:0,5620:0,5625:0,5630:0,5635:0,5640:0,5645:0,5650:0,5655:0,5660:0,5665:0,5670:0,5675:0,
                         5680:0,5685:0,5690:0,5695:0,5700:0,5705:0 
   2ghz-10mhz-power-channels=2412:0,2417:0,2422:0,2427:0,2432:0,2437:0,2442:0,2447:0,2452:0,2457:0,2462:0,2467:0,2472:0 
   2ghz-5mhz-power-channels=2412:0,2417:0,2422:0,2427:0,2432:0,2437:0,2442:0,2447:0,2452:0,2457:0,2462:0,2467:0,2472:0 ht-chains=0:chain0,1:chain1

I really don't know what I can do anymore.
Can you please help me?

Thank you

Use 20 Mhz bandwidth pleace

It's already on 20MHz, not 20/40

I think interference from the other radio cards.
What is your ccq from the badest link?
Try the channels from the radiocards so far as possible from each other

25% TX
15% RX

I tried to switch off all radios and I tried each allowed channel on wlan1 but I can't find a good one where each client has a good speed.
Only a few users can get 9-10mbps with a good CCQ.

Unfortunately, it's a noisy area.

This is clearly noise.

Try to reduce the output power from your accesspoints and see that of it is better

Let me know

Thank you for your time!
I reduced output power but I can't see any improvement
Some CPEs are also unstable: they disconnect from the AP every minute, also with good signal...

there are questions you have to answer:

1. What version of Routeros you are using?
2. Switch protocol to NV2
3. Use 4 separte boxes with 1 wireless card in each (RB912)
4. equalize the clients signal strength to not more the 5db difference (use at client side different antenna size to get more or less gain)

test first with one sektor and post results

Thank you sonny for your answer!

1. It was 6.9, now 6.10, no improvement at all
2. Tried NV2, i had worser speed than nstreme
3. Why do you suggest this? I always use RB433 with two wireless card, this is an exception I'll avoid in the future. Do you think using one wireless card for board is better? Why?
4. I try to equalize clients but there are lots of variables that don't allow me to set a threshold like 5dB. At the moment here's my registration table: What I can do (and I'm doing it as I can't find a better solution) is to move the AP closer to my clients to try to get a better signal for everyone, but I would like to understand why I'm having this situation.

5500 is to close to 5520

Also RF schielding does help!

I tried to change channel without improvement... I don't have lots of free channels as it's an area with other WISPs

RF Shielding is a good point! What do you suggest to shield exactly?

I was wondering why some users, on the same AP, same wireless card, same CPE, same distance don't have problems...

Interference from other devices