Upcoming new Wi-Fi technologies – IEEE802.11ac

on Oct 24, 2012

For how long will the speed competition between LTE and Wi-Fi continue? Since the emergence of IEEE802.11n, the speed of
Wi-Fi has accelerated dramatically and smartphone users have started to prefer Wi-Fi over 3G. That is not only because of the cost issue but also the speed of transferring data within the Wi-Fi zone. However, with the recent start of the LTE service, users are moving from Wi-Fi to LTE. Yet as IEEE802.11ac, the fastest Wi-Fi technology, started appearing in newspapers, Wi-Fi is once again attracting attention. The maximum speed of IEEE802.11n is 600Mbps, whereas that of IEEE802.11ac is 6.9Gbps. Let's take a look how high speed performance can be achieved.



Three factors for increasing speed – bandwidth, MIMO stream, 256QAM


Moving from 802.11n to 802.11ac, 3 factors increased the speed of Wi-Fi. IEEE802.11n supports up to 40MHz bandwidth, which is twice the basic 20MHz, thanks to channel bonding technology, while up to 160MHz of bandwidth, which is 8 times, is supported in IEEE802.11ac. Also, up to 4 MIMO streams can be supported in IEEE802.11n while 8 can be supported in IEEE802.11ac. For a better understanding, larger bandwidth can be seen as wider roads and more MIMO stream can be seen as more lanes that can be used at once. Also, IEEE802.11n support up to 64QAM, whereas IEEE802.11ac support up to 256QAM. 64QAM means that the minimum data unit sent at once is 6 bits and 256QAM means 8 bits. With these three factors, the speed increased by 4.35 times, two times, and 1.33 times, respectively, totaling up to 11.5 times. (Refer to the table below)

Item 802.11n 802.11ac Performance
Bandwidth 40MHz 160MHz 4.35 times 1)
MIMO Stream 4 8 2 times
QAM 64 256 1.33 times 2)
Total 11.5 times

Other than speed increase, there is Multi-User MIMO (MU-MIMO), which is another visible innovative technology. The existing MIMO technology concentrated on increasing speed by making one user to use various streams. In such a case, the number of streams could be increased to 8 by putting 8 antennas on AP. But it was nearly impossible for one device to support 8 antennas. Therefore, increasing the number of streams was meaningless. As for IEEE802.11n standard, up to 4 streams can be supported but there is no such device on the market because PCs, the main device, only support 3 streams. High performance PCs support up to 3 streams, but standard PCs only support up to 2 streams and smartphones support 1 stream only. However, with MU-MIMO, various users can share those 8 streams. That is, if there is a device that supports 2 streams, up to 4 devices can be used at the same time with one AP.

Also, the power saving technology of devices has been improved. Existing power saving repeatedly turned the sleep mode on and off to read the AP beacon and if any packet had been received, it made a request to the AP. However, this method lowers performance because reception is made in accordance with the on/off cycle. So, some did not even use this power saving technology or made the device turn to power saving mode only when there was no traffic for a certain period of time. If not in Power saving mode, even packets that are not sent to you are all received and then those that are not yours are discarded. This, therefore, consumes quite a large amount of power.

On the other hand, an IEEE802.11ac network uses information in the packet header to identify the packet and if it is not sent to you, the sleep mode goes on until the packet has been transmitted. Therefore, it saves a lot of energy.



Standardization: IEEE and Wi-Fi Alliance (WFA)


There are two Wi-Fi technology standardizing organizations called the Institute of Electrical and Electronics Engineers (IEEE) and Wi-Fi Alliance (WFA). The standard called IEEE802.11 is set by IEEE with experts in the academic and industrial circles, and the well-known Wi-Fi standard is an industrial standard that is set by experts from various industries, referring to the IEEE 802.11 standard series and focusing on the compatibility of devices. Therefore, IEEE should complete standardization of IEEE802.11ac, before WFA sets the industrial standard based on it.

According to this standardization process, the IEEE standardization for IEEE802.11ac will be complete by December 2013. Therefore, devices complying with the Wi-Fi standard are expected to be released after that date. However, WFA is trying to set a standard called IEEE802.11ac stage 1 (tentative) based on the draft IEEE802.11ac 3.0 by the end of 2012. Since it is making a Wi-Fi standard based on a draft standard, it only contains essential points that will not change in the final standard. Therefore, improved technologies such MU-MIMO or Power saving are not included. IEEE802.11ac stage 1 covers speed-related technology improvements such as 80MHz bandwidth, 3 streams and 256QAM. So, users who want fast speed at home might want to buy devices with this standard but they may not be suitable for work. The Wi-Fi devices that comply with the final version of standard are expected to be launched by the second half of 2014.



The 5GHz bandwidth wants more!


As explained above, IEEE802.11ac supports a wider bandwidth, which is not supported in 2.4GHz. Currently, there are 24 channels that can use Wi-Fi technology in the 5GHz bandwidth. Some channels cannot be used in some countries, and in the case of Korea, only 19 channels can be used. There are 13 channels that can be set in 2.4GHz bandwidth but there are only 4 that do not overlap. On the other hand, such confusion cannot be seen in the 5GHz bandwidth since overlapping is prohibited here.

19 channels may seem to be a lot but in IEEE802.11ac where 40MHz, 80MHz and even 160MHz channels can be bonded, the number of channels will once again be insufficient. When using 40MHz, there will be only 11 channels, in 80MHz, there will be only 5 channels and when using 160MHz, only 2 channels will be in place. Therefore, WFA is endeavoring to secure more channels colored in red in table 3) below.

5GHz Bandwidth



Concluding...


IEEE802.11ac boast a 6.9Gbps maximum transmission speed, support MU-MIMO that can communicate with various devices at the same time and have improved power saving. This technology is still in the process of being standardized at IEEE and WFA. IEEE802.11ac stage 1 devices that support the IEEE802.11ac technology, which is essential for improving speed, are expected to be launched in the first half of 2013, but devices with all standard technologies are expected to be on the market after that date since standardization is expected to be completed in December 2013.

  • Note 1. There are 108 sub-carriers in 40MHz and 468 sub-carriers in 160MHz,
                so, 468/108 = 4.35
  • Note 2. 256QAM is 8bit per symbol, 64QAM is 6bit per symbol, so, 8/6 = 1.33
  • Note 3. Source: VHT5G Marketing Group
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