Monday, April 1, 2013

China Opened More Channels in 5 GHz & Embraced IEEE Std 802.11ac VHT80

Where can I find "clear air"?

In the past, WIFI users in China might find it was difficult to  access “clear 5 GHz”. However, with new regulation updates, it is all changed now.

In China, radio regulatory approval is supervised by Ministry of Industry and Information Technology (“MIIT”). Before 2013, MIIT only allowed WIFI vendors to use a limited 5 GHz spectrum at a precise measurement only from 5725 MHz to 5850 MHz. When users configured their WLAN routers or Access Points (“APs”) at HT40 under IEEE Std 802.11a/n, they could only use either channel 151 or 159. With limited non-overlapping channels, larger deployment cases were forced to reuse these two channels frequently. Installers usually found that these AP might interfere others or being interfered by neighbor devices due to co-channel interference (CCI). Without natural spectrum barriers, users may detect various AP broadcasting signals at same channel and at the same time. CCI could be more problematic when IT tended to support voice-over-WIFI or video applications. These use cases usually require a more dense deployment of APs. And, APs would sit closer together.

The problems were worsened when three major China Telco, China Mobile, China Telecom, and China Unioncom, promoted their high-powered Service Provider WLAN APs (“SP-AP”) either at indoor setting or outdoor environment. From 2010, China Telcos started to migrate their SP-AP to 5 GHz spectrum.  Those APs were equipped with modified power amplifier circuits and were capable of projecting 500 mW per chain. This powerful radio design could expand its physical coverage or extend its distance for DAS (Distributed Antenna System). However, its powerful design was also a double-edged sword which jam other APs due to co-channel interference.

A Promised Future

Good news finally arrived. On Dec. 31st, 2012, MIIT announced that they were releasing the usage of the open 5150 MHz ~ 5350 MHz usage to general public. There are additional eight (8) channels available in HT20, or four (4) channels available in HT40 cross both UNII-1 and UNII-2 bands.

The most exciting thing was that MIIT also allowed 80 MHz channel (VHT80) proposed by IEEE Std 802.11ac Draft. MITT opened a additional channel, CH155 in UNNII-3 (5725 MHz to 5850 MHz), to support IEEE Std 802.11ac Draft standard even though it is not ratified by IEEE yet. The available channel plan in China is shown as table below.You can also download such memorandum from URL link from MIIT China (

MIIT Memorandum 

The followings are my summary for MIIT’s memorandum;
  1. New available frequency: UNII-1, 5150 ~ 5250 MHz
  2. New available frequency: UNII-2, 5250 ~ 5350 MHz (DFS/TPC)
  3. Maximum EIRP: 200 mW (or 23 dBm)/EIRP (200 mW)
  4. EIRP Power density: 10 dBm/MHz
  5. New available 80 MHz channel: UNII-3, 5725 ~ 5850 MHz
The requirement is similar to European standards EN 301.893 V1.7.1 but, as usual, the type approval is required in-country test. That means vendors shall perform homologation test in China and then submit to MIIT locally. MIIT also opened the applications to enter UNII-2 Dynamic Frequency Selection (DFS) band. According to MIIT, applicants can have the choice to submit either DFS or DFC/Transmit Power Control (TPC) while TPC shall be less than 6 dB. If applicants do not submit TPC report, the transmit power in DFS channel must be 3 dB back off accordingly. MIIT also regulate deployment usage to strictly indoor environment only, and the devices shall be not located within 3 kilometer (1.8 miles) range from any satellite or radar station.


After MIIT announced this great news, many equipment vendors were rushing through tests and lining up at MIIT to receive approval stamps. I anticipate the first IEEE Std 802.11ac-based access device will arrive market in 2013 summer time.

Chun "Johnson" Hou