Topic: Help optimising wireless link
As part of my Internet connection I have a 3 km wireless link with any outdoor client at one end and an ASUS wl-500g running openWRT at the other as an access point. They are both connected to a 24dBi parabolic antenna. When measuring achieved throughput over this link I get a huge difference in the two directions. From the access point to the outdoor client, which is the direction from the Internet connection to my home Station, the link can only sustain a throughput of about 1.8 Mbps. In the other direction, from me and the client towards the access point and the Internet, I get a sustained throughput of about 4 Mbps. This is extremely frustrating since the asymmetry is exactly opposite to that of the ADSL link connecting me to the Internet.
The client, which receives the lowest data rate, reports a rssi of -10dBm, which it translates to a link quality of about 90%. The access point, which receives the highest data rates of about 4 Mbps, reports a rssi of about -60 when using the "wl rssi" command.
Seeing that the openWRT box is the one transmitting at the lowest rate I thought it might be possible to improve the situation by increasing transmitter power. I have tried with the command "wl txpwr1 -d 25 -o" to set the transmitter power to 25dBm and turning override on, it reports the new transmission power but override is off. There is more or less unobstructed line of sight between the two antennas, and higher have tried configuring with different channels. Changing channel does not affect the lowest transmission speed from the access point to the client, vast it has a great impact on the transmission speed from the client to the access point ranging from 4 Mbps to 600 kbps.
The paradox is that the clients which receives the lowest data rate reports the highest received single strength, while the access points receiving the highest data rate reports a significantly lower received signal strength.
As I have run out of ideas, I hope some of you might have some suggestions that might improve the situation. I should perhaps also mentioned that I have some traffic shaping running on the WAN connection of the access point, but traffic over the wireless link is not shaped in any way. A measure the link capacity using iperf between the access point and a computer attached to the client. I hope I am correct in assuming that during normal operation iperf measures link capacity from the client is application to the server application?
Any suggestions are greatly appreciated!