Factors on low Throughput in WLAN

1) SIFS and ACK ( it occupies medium with some duration)

2) antenna direction

3) beamforming 

4) Access point angle 

5) tcp ack (sequence number)

6) software bug 

7) background traffic causes

8)need to  check re transmission happening or not

9) check RF side (rssi mcs rates)

10) Check if BT is enabled. since nowadays, single chip supports both WLAN/BT together, in some devices co-existence does not work properly

11) Rate statistics (BW, NSS, MCS) what is your dominant MCS, NSS, BW 

12)  check the AMSDU/AMPDU aggregation function. Lot of time it happens to be the issue with aggregation.

13)  Are there any wifi or non-wifi interferences (how busy is the medium without any wifi traffic ?) 

14)  How many clients are connected and being served by AP ?

15) Distance between AP and STA.

16) Obstacles (such as walls, floors, and ceilings).

 17) check the clock frequency. some times due to lower clock speed of the bus (sdio/pcie) over all

throughput might be less. 

18) Also, check how many physical antennas are connected and what is the spatial stream being configured in driver conf file. 

For example with 2x2 enabled in conf file but using only one antenna creates significant throughput drop. 

19) Check if BT is enabled. since nowadays, single chip supports both WLAN/BT together, in

some devices co-existence does not work properly. 

20 ) And lastly check the AMSDU/AMPDU aggregation function. Lot of time it happens to be the issue

with aggregation.