Amazing article, Gareth!
Remember Eric, AP throughput is not real:
- "marketing" throughput is aggregated for both radios, e.g. 1,75 Gbps for 11ac Wave 1 is 450 Mbps for 2.4 GHz and 1,3 Gbps for 5 GHz; so at best you could get 1,3 Gbps (BTW that's why some push you to buy double-port APs or 2.5 G interface switches), but...
- 802.11 MAC layer overhead, beacons and retransmissions and everything else - this reduces your throughput; it can eat about 50% of PHY throughput as mentioned (we go down to around 650 Mbps here);
- AP throughput is for full utilization of it's antennas; if the AP is 3x3:3 and your device is 2x2:2 for example, you can get two third of performance at most (despite the data rate might show some high PHY based on RF signal quality);
- same applies to channel width (20/40/80 MHz); mcsindex.com is a good point to see what PHY data rates are possible with different MIMO and channel widths for different 802.11 ammendments (then signal strength based on device sensitivity and SNR will imply actual data rate for AP-STA communication);
- in the end, all APs and STAs that talk on the same or adjacent channel interfere, so it drops your throughput even more; WiFi channel is one big collision domain with no option for collision detection so far (just CSMA/CA) so when two devices happen to talk at the same time, both might have their signals falsified.
From what you say, maybe it would be good to seek for interference (ACI/CCI) on 2.4 GHz. To many APs on the same/adjacent channel? 3rd pty SSIDs on the same/adjacent channel? Other 2.4 GHz devices with heavy blow (microwave, BT, sensors)? Too many clients on the same/adjacent channel? Perhaps the APs power is too high and with your environment they could have CCI on tens/hundreds of meters? Maybe your channel re-use plan for 2.4 GHz could be finetuned? If you are able, push dual-band clients to 5 GHz.
Those are basics, greatly enahnced within the article Gareth linked here.
Besides, IMHO AP throughput shouldn't be critical if it can reach around 20-30 Mbps per client. Unless you are doing some file transfer or multimedia streaming, typical office traffic is rather of hundreds of kbps per client on average.
My personal best so far was 200 Mbps with 2x2 Intel WLAN card on my PC (867 Mbps PHY), 11ac Wave 2 AP, 5 GHz, 5-7 meters away, conference room with small to none RF footprint around and no other clients connected. I don't remember the channel width unfortunately. I will check tomorrow in our office where I get great data rates, for the sake of curiosity.
Hope that helps,
Tomasz
