To Be Faster – 2: Wide Band
Last week I discussed the performance benefits of multi-streaming. This week I will cover wide band technology. Have you ever heard of “HT20/HT40 mode” for 802.11n? Conventional wireless LAN (802.11a/b/g) uses 20MHz bandwidth for 1 channel. 802.11n has a new mode using 40MHz bandwidth as an option. When I mentioned last week that “each stream offers up to 150Mbps”, it assumed HT40 mode. The speed is reduced by half (75Mbps) with HT20 mode. The IEEE802.11ac standard is now under development which will be an evolving version of HT40 and provide extended band (80MHz or 160MHz) to achieve two or four times faster speed.
The wide band technology doesn’t require antennas like multi-streaming, so it is available for small portable devices. Moreover, the inner circuit design doesn’t need to be changed so no new parts are needed. It sounds good but it is not that easy. The number of channels available is decreased as the bandwidth is increased. As the number of available channels decreases, “interference” tends to occur. Neighboring wireless systems may occasionally suffer interference from each other which can result in decreased performance.
Japan allows the use of 13 channels in the 2.4GHz frequency range. Channels are overlapping in the 2.4GHz band, so there are only 3 channels available without interference for HT20. There is only one channel for HT40. Therefore, it is impractical to increase the speed in 2.4GHz with the wide band technology.
In the 5GHz frequency range, there are 3 bands (5.2, 5.3, 5.6GHz) assigned in Japan. There are 8 channels in the HT20 bandwidth that don’t overlap in 5.2GHz and 5.3GHz. In 5.6GHz (the newest frequency range), 11 channels (HT20) are reserved. Consequently, it seems the 802.11ac has ability to achieve higher speed. But this condition is just applicable in Japan.
Availability of channels in 5GHz is regulated by country. Some countries, including China and Korea, allow the use of HT20 channels only. It is impractical to increase the speed in such regions.
Wide band technology is also capable of achieving higher speed transfer without dramatic improvement of current technology. It is also good for smaller/lower-power products. However, there aren’t many channels available to secure the necessary bandwidth. It is hard to avoid interference which results in decreasing performance. 802.11ac might be popular as an upgraded version of HT40. It depends on the radio law by country and interference environmental condition to achieve two/four times higher speed transfer. The wide band technology is still unreliable as a resource for high speed.