Wireless Performance - Three Stream
TRENDnet didn't like the jury-rigged third antenna I added to my standard Intel WiFi Link 5300 test client to run some initial three-stream tests. They said that my Dell Mini 12 test notebook and its two dual-band factory-installed antennas were "tuned" for a 2x2 client, so would not yield proper performance with a third antenna added.
They also said that their opinion was backed by an "Atheros engineer". Why TRENDnet would be using Atheros to back up their claims when the the two chipsets involved are Ralink (the router) and Intel (the client), I don't know.
Attempts to get a further explanation of "tuning" from TRENDnet were not satisfying, so I turned to Intel for an explanation, since, after all, I was using their client. I was passed from engineer to engineer until I reached a dead end (my last referral didn't respond).
Intel did provide a bit more information, however, saying that the client had to have "proper isolation between the three antennas", with "proper" defined as 20 dB. I'm no RF expert, but I know it doesn't take much to drop the first 20 dB of signal as you move away from an antenna. And given that my antenna was outside the notebook and about 6 inches from the closest internal antenna, I'm not really buying that explanation.
Since the only three stream N clients available are built into notebooks, I'm forced to buy a new notebook that I otherwise don't need in order to test three-stream N capability. At least D-Link has posted a list of notebooks that have Intel 5300 or 6300 three-stream adapters (and, hopefully three antennas to match!), since I had little luck plowing through online notebook specs to find such products. I'm not ready to take that leap yet, so for the meantime, I'll stick with my jury-rigged setup to at least get a glimpse of three-stream performance under best-base signal conditions.
For the three stream test, I switched from the Dell Mini 12 to an Acer Aspire 1810T, which has much easier access to the Intel 5300 card I installed. I used the same pigtail I scavenged from a dead DIR-655, but substituted a dual-band antenna borrowed from a D-Link DIR-825. (Thank you, D-Link for continuing to make routers with upgradeable antennas!) The antenna was connected to the Intel 5300 card's terminal 3 and positioned as shown in Figure 9.
Figure 9: Acer Aspire 1810T with third dual-band antenna added
I noted link rates close to the maximum 217 Mbps / 450 Mbps three-stream rates during each 2.4 GHz test run. Link rates seemed more consistent than those I observed during the TEW-691GR's testing, which bounced around and spent little time near the maximums.
But when testing the 5 GHz band, link rates tended to be lower than the maximums, although they were three-stream rates. I triple-checked the third antenna connection and made sure it was solid, so I'm not sure what caused the different behavior.
Figures 10 and 11 once again show the downlink and uplink summaries respectively, this time for the three-stream client.
Figure 10: D-Link DIR-665 wireless throughput summary - downlink, three-stream client
Figure 10: D-Link DIR-665 wireless throughput summary - uplink, three-stream client
I again ran simultaneous up and downlink tests to see if using more streams yielded higher total throughput. The highest result here was 114 Mbps (again using 2.4 GHz, 40 MHz mode). You can check out the IxChariot plots (2.4 GHz/20 MHz, 2.4 GHz/40 MHz, 5 GHz/20 Mhz, 5 GHz/40 MHz).
There didn't seem to be a lot of difference between the two-stream and three-stream results. So I pulled everything into two tables. Table 2 compares downlink rates for two and three stream test runs. Three stream rates are consistently higher, but by widely varying percentages.
|Test Description||Two stream
(2 to 3)
|2.4 GHz / 20 MHz||60.97||76.90||+ 26|
|2.4 GHz / 40 MHz||89.45||97.11||+ 8.6|
|5 GHz / 20 MHz||66.78||88.53||+32.6|
|5 GHz / 40 MHz||84.27||92.56||+ 9.8|
Table 2: Downlink two / three stream throughput comparison
Table 3 compares uplink rates. The percent change between two and three stream throughput again varies widely, even decreasing in one case.
|Test Description||Two stream
(2 to 3)
|2.4 GHz / 20 MHz||69.21||71.25||+ 2.9|
|2.4 GHz / 40 MHz||80.34||99.94||+ 24.4|
|5 GHz / 20 MHz||69.31||67.48||- 2.7|
|5 GHz / 40 MHz||94.83||96.19||+ 1.4|
Table 3: Uplink two / three stream throughput comparison
As I mentioned earlier, I'm not in a big hurry to invest in a new notebook just to test three stream N routers. I don't think "450 Mbps" routers are going to fly off the shelves until the wireless manufacturers deign to provide three-stream client options, or at least bridges, so that folks can upgrade both ends of their wireless connections.
My money is still on seeing three-stream bridges first. They can be made with existing PCI-e bus-based chipsets and provide the best option for folks looking to increase bandwidth for wireless HD video streaming. Notebook owners, however, will be caught in the same pickle that I find myself in. Why toss a perfectly good (and recently purchased) notebook / netbook just to get a little more speed?
I still have running the six location tests on both the D-Link and TRENDnet routers on my to-do list using the Intel two-stream N client. Although the best-case / strong-signal results seem to indicate that these routers can provide higher throughput than most two-stream products, I'm interested to see how fast that advantage fades as signal levels drop.