VeriWave tests 802.11 3x3 MIMO - Startling Results!

3x3 MIMO kicks in the nitro with measured throughput of more than 300 Mbps

Sustained data rates of over 300 Mbps are possible as measured by the VeriWave test equipment in back-to-back operation. However, as no commercially available enterprise-class and consumer-class AP’s support true 3x3 MIMO operation, measured data rates of these AP’s tops off at just over 160 Mbps.

For 802.11n to take off, all enhancements specified by the standard need to be implemented.

If AMPDU aggregation, 40 MHz channels and Short Guard Interval are not fully implemented, frame overhead will dominate and little performance gain will be seen for large frames, while small frame sizes will see no gain at all. Without these enhancements, one of two enterprise-class 802.11n AP’s tested was not able to maintain legacy 802.11g rates.

Looking at the AMPDU aggregation results in detail, the following has been observed:

• AMPDU aggregation really enables 802.11n to take off!
• The tests have shown that enabling AMPDU aggregation boosts throughput by a factor of 3, with peak rates greater than 100 Mbps with 20 MHz channels and 2x2
• Enterprise-class APs exhibit wide performance variation: while one can reach close to theoretical maximum throughput, another can barely maintain 802.11g rates

As expected, 40Mhz channels double capacity over 20Mhz channels

• 40 MHz channels enable sustained MAC data rates of approximately 250 Mbps to be met, typically over short distances, although it is sensitive to channel variations
• Enterprise-class AP’s have not yet fully realized this benefit, as only one of the tested AP’s exhibited better than basic 20 MHz forwarding capacity

Short Guard Interval increases efficiency – but only incrementally

• When frame size is large, a slight gain from shortening the Guard Interval between symbols from 800 to 400nSec is noticeable - data throughput increases from 242 Mbps to 266 Mbps
• This improvement will likely not noticeable in the field, as basic data path capabilities of the AP’s will dominate

It is all about co-existence

VeriWave’s test conclusively show that co-existence of various types of equipment has tremendous effect on the overall quality and capacity of the deployed network.

Adding 802.11a/g clients severely impacts today’s APs

• When allowing 802.11a/g clients to use an 802.11n network, theoretical performance drops by 50%, from approximately 225 Mbps to around 125 Mbps, but test results of actual enterprise-class APs show that the performance drop is much more significant to 50 Mbps or less – a 75% reduction!

20MHz / 40MHz coexistence issues need to be worked out

Enterprise-class APs show serious drop in performance at small frame sizes in this mode – to less than 50 Mbps - possibly due to high impact of coexistence provisions on smaller frame sizes.

Using Long Guard Interval in Short Guard Interval networks has little effect

Mixing long and short guard intervals results in “in-between” aggregate throughput, but current enterprise-class AP’s are too far below the achievable medium capacity to show this effect.

Enterprise class AP vs. Consumer class AP: you get what you pay for

Enterprise class APs are generally better than consumer grade APs and provide more consistent performance, however these devices are still evolving as can be seen here.

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