After I update the firmware of AR670W to DD-WRT build 13069, I found the signal quality of the Intel 5100 client is only around 23% at full Tx power (251mW) from the wireless status page. And it can only improves the throughput to ~35Mbits/s with
iperf -w 64k -c intel-5100. Then I started to adjust the following things:
- Orientation of the two antennas of AR670W: On one position I found the signal quality of Intel 5100 was improved to 34%.
- Manually set the channel number: After doing a site survey, I found the least crowded channel was not the one being picked up by DD-WRT. So I changed the channel number and the signal quality of Intel 5100 was improved to 40%
Then I tested the throughput again, and no surprise it's now ~80Mbits/s. Even if I further increase the TCP windows size of iperf from 64k to 10M or reduce the Tx power to half (126mW), the throughput remains at ~80Mbits/s (wired to wireless). Later I had to enable the N-only wireless mode on a D-link DIR-655 router to maximize the throughput of another Intel 5100.