The Ruckus Room

Let the N Testing Begin...

Computer Reseller News (CRN) just published some of the first competitive 802.11n testing. 

Not surprisingly, they had problems getting anyone (read Aruba, Cisco, Trapeze, etc.)  to even participate - go figure (CSCO even blogged about why they didn't show up...hmmmm).

Well, we're risk takers.  We believe you just need to build good products and put them out there. Like any vendor, we'd love to be able to control reviewers, dictate test plans, influence test results. But we're also realists. We just don't have the clout.

And 802.11n is hard to test. There are so many variables.  Meanwhile vendors do nothing but spew data rates that users will never see.  Then they never seem to show up when the curtain rises.

With 802.11g the maximum physical rate is 54Mbps, but actual UDP performance is capped at roughly 35Mbps with maximum TCP throughput still lower. When using higher 802.11n, physical data rates the problem is even more dramatic. But at a 300Mbps phy-rate with no channel bonding or block acknowledgment, the effective maximum UDP throughput for 802.11n is no more than 68Mbps.

At CRN we received top marks for performance at 20MHz with the AP doing about 66Mbps. With 40MHz channelization (in the 2.4GHz band no less) we saw TCP data rates exceeding 125Mbps - but this wasn't even reported.What a lot of people don't understand is that to see any kind of substantial performance increase, three things need to happen:

1. spatial multiplexing/multipath (with more than one stream)
2. 40MHz channelization (i.e. channel bonding) and
3. frame aggregation and block acknowledgment.

But today's 802.11n systems do next to nothing to increase the likelihood that these fundamental techniques are actually utilized. This is because they have little or no control over the RF domain and the path that Wi-Fi signals take. So they can do almost nothing to mitigate interference and packet lose which are essential to ensuring spatial multiplexing and channel bonding (for instance).

Pretty much every 802.11n AP today uses multiple omni-directional antennas for different streams. These omni antennas are equally polarized, thereby reducing the likelihood of sufficient multipath, especially over short distances.

Smart antenna technology is ideally suited for spatial multiplexing. Because of the control over signal path direction and timing, smart antenna arrays maximize pattern de-correlation. It is the de-correlation of the different antenna configurations that provides the bulk of the statistical gain delivered through the use of such systems.

By independently steering or routing each spatial stream over the most optimum RF path, smart antennas exploit the utility of spatial multiplexing by increasing the percent of time that spatial multiplexing communication is possible.

Hopefully as more 802.11n tests come so will the vendors.  Like Woody Allen says "Ninety percent of life is just showing up."

Demo Diva Raises Ruckus at CableLabs...

With her back up against the wall at the recent CableLabs Winter Conference in Colorado Springs, our CEO, Selina Lo, was all business (sometimes she's good and sometimes she's REALLY good. This day she was in some sort of zone).

Out of nine companies innovating new  technology for services provider, Ruckus was asked to present within CableLabs' "innovators showcase." 

So we demonstrated our latest 802.11n Smart Wi-Fi system to an audience of around 200 cable executives.  They were impressed enough to vote it the "best product idea most likely to succeed." Go figure. I thought cable companies loathed Wi-Fi?  Not any more.

For the demo (we have some of the coolest demos), we streamed three MPEG-2 high defnition multicast streams concurrently. We then made a UMA/VoIP over Wi-Fi call using the newest Blackberry Curve and T-Mobile's UMA service over the same network. 

Going for broke, we pulled up some content off a Sling Box in Lake Tahoe and surfed the Internet - all over the same 802.11n network.  See for yourself.

802.11n without Channel Bonding is Just Stupid

802.11n is a good choice. 802.11n without channel bonding is not.

Perhaps the most important thing (in addition to MIMO and frame aggregation) that makes 802.11n 802.11n is 40Mhz channelization, aka channel bonding.

Channel bonding boosts bandwidth by combining two adjacent 20 MHz channels into a single 40 MHz channel. The throughput increase is actually a bit more than double since the guard band between the two bonded channels can also be removed.

Since only three non-overlapping 20 MHz channels are available in the 2.4 GHz (2.4 GHz to 2.4835 GHz) spectrum band used by the IEEE 802.11b and IEEE 802.11g WLAN communication standards, channel bonding is often thought to be difficult in noisy environments with dumb Wi-Fi systems that have no proper adaptive controls.

But here's the real deal. Without channel bonding 802.11n is handicaped. Limiting clients (e.g. Centrino and other laptops) to 20MHz-only is essentially misguided and actually hurts 802.11n as a whole. People that think that 40MHz operation causes extra interference don't actually understand RF issues.

Yes, 40Mhz operation consumes twice the bandwidth, but the packets are half as long (relative to time) so there is no net increase in interference. APs and clients should be smart enough to dynamically determine the correct mode of operation.  Smart Wi-Fi systems do just that.

Smart Wi-Fi systems continuously pay attention or listen to (my engineer says i must say "monitor") the RF environment, picking the best performing signal paths and RF transmission parameters for a given client.

This results in less interference since the link is occupied for a shorter period of time.  There you go.  Now tell someone who really cares.