Throughput vs. Path Loss
I used the Azimuth ACE to plot throughput vs. path loss curves for uplink and downlink and 300 Mbps and 145 Mbps modes. Figure 15 was generated using the Compare Benchmarks tool of our new Wireless Charts feature.
NOTE: We no longer refer to "range" in these plots, but instead use the more accurate "Path Loss". For an explanation, see the How we Test Wireless article.
Figure 15: Throughput vs. Path Loss - both modes
The 300 Mbps (auto 20/40 MHz channel) mode clearly provides a throughput advantage over the 145 Mbps mode, with downlink besting uplink throughput, as seems to be the pattern for MIMO products. But the steep drop-off around the 90 dB path loss point shows that work remains to be done in the link rate adjust algorithms for both up and downlink.
By comparison in the 145 Mbps (20 MHz channel) mode, throughput falls off more gradually and actually beats 300 Mbps mode speeds from 88 to 97 dB of path loss. But beyond 97 dB, both modes are down to 802.11b speeds.
Turning again to the Wireless Charts tools, I created 20 MHz channel mode up and downlink comparison plots for the draft 11n routers I've tested so far: the Netgear 854T, D-Link DIR-655 and Buffalo WZR-AG300NH. Note that the Buffalo router is not yet Wi-Fi Draft 2.0 certified.
For sake of comparison between 802.11g and draft 11n, I included results for the ol' standby: the Linksys WRT54G. Since the WPC54G card that I used for the WRT54G test would not allow direct cabled connection to the Azimuth system, I had to use a near-field antenna. Since the antenna introduces additional path loss, the Linksys plot starts at a higher path loss value. A 100 Mbps Ethernet reference line is also included to fix the Y axis scale for easier visual comparison.
Figure 16: Throughput vs. Path Loss product comparison - downlink
Since all Wi-Fi certified Draft 2.0 11n routers (as well as some non-certified products) will come set to 20 Mhz channel mode, the comparisons in Figures 16 and 17 are representative of "out of the box" performance. What I find most interesting is that all products manage to stay connected at high path loss values.
This is why you'll see the "X" speed and range claims that manufacturers have now turned to as their front-of-the-box buyer bait have lower "X" values for range than for speed. And, of course, you never get both "X" values at the same time... but you knew that already, right?
Figure 17: Throughput vs. Path Loss product comparison - uplink
If you don't like these comparisons, you can run your own using the Wireless Charts tools!