News

Netgear's newest MIMO WiFi gets full test: wakes up neighbours, and useless WEP

The test is a disaster for the IEEE and 802.11n. The good news is that the new WiFi MIMO technology really does reach throughput speeds of 100 megabits per second. The bad news: it utterly crushed a neighbouring network that used standard 802.11g.

The review is an astonishingly thorough technical analysis, complete with every kind of test of throughput you could imagine - as you would expect from Tom's Networking

What it shows is that the product is still very new, and not truly ready for market. For example, if you want the (very necessary) option of security, you had better not use WEP encryption! - as the reviewer says of the throughput tests:

"The results are indeed impressive and are the first time I've seen a wireless product of any flavour deliver usable throughput in excess of 100Mbps! What was not so impressive, however, is how throughput dropped over 30% when I enabled 128 bit WEP encryption!"

WPA works better: "Switching to the most secure WPA2 wireless security mode showed a negligible effect on throughput, which I attribute to a built-in AES encryption engine somewhere in the Airgo chipset."

But the products, the reviewer notes, are not yet tuned for public consumption. On its own, the device works much as predicted by the tech specs. But if you have neighbours, you could become unpopular: they set up the network so that it shared space with an ordinary Linksys 802.11g router.

What it was supposed to do (according to the advertising) is spot the legacy technology, and re-route to avoid causing interference. No such thing was actually done:

"In both Figure 20, which shows downlink and Figure 21, which shows uplink, you can see the RM240 (Airgo gen 3) pair drop below the throughput of the gen 2 pair when both are running! I would have expected more equal throughput sharing, if not a throughput advantage for the gen 3 chipset. Evidently, Airgo still has some performance tuning left to do!"

The result was caused by a bug (said the manufacturer) so the reviewer changed the firmware, and changed the test settings. The same bug was still there: "The bottom line at this point is that the ACE mechanism that is supposed to tune away from neighbouring wireless LANs is at best buggy and at worst currently broken. I should also note that Airgo told me that when it is working, it will take 5 to 10 minutes (!) to tune away from a neighbouring WLAN that is detected after the RM240 completes its initial power-up sequence—if the RM240 sees "lots of continuous traffic" in the neighbour.

In other words, use one of these, and you won't be popular when your neighbours work out what's going wrong. And if you think it will be "fixed in the next release," you're probably quite wrong:

"What happens when the legacy WLAN is parked on Channel 6? According to Airgo, both its products - and all 11n products - won't be able to 'tune away' from this situation. The reason has to do with fundamental design decisions that were made long ago with regard to the technology to be used in 802.11n, that resulted in the requirement for 40MHz of contiguous band. The result is that the Primary and Secondary channels for 802.11n 2.4GHz band operation will always be separated by four channels, i.e. 1P + 5S, 8P + 4S, 11P + 7S, etc. This means that even with an 802.11n WLAN channel forced to 1 or 11, there will be enough channel overlap from the 40MHz of occupied bandwidth to pretty much slow a legacy WLAN on channel 6 to a crawl, i.e. a few Mbps of throughput."

As suggested by NewsWireless this past week, the future for WLAN looks rotten, after the 802.11n dispute. If this is what happens with just two WLANs in the neighbourhood, what's going to happen when you set up an access point in an urban district? Answer: chaos. The thing will be capable of 100 megabits, in theory - but in the same way that a Ferrari is capable of more than 150 miles an hour, that capacity will be meaningless where real human beings live - in a city.

Tags: UWB, WiFi, Bluetooth, Bluetooth SIG, Hotspot, mesh