FCC to Free Up Wi-Fi Spectrum: Part II

February 7, 2013, 8:53 am

Our recent blog post, FCC to Free Up Wi-Fi Spectrum to Boost Speeds, discusses how the FCC plans to expand the unlicensed spectrum in the 5 GHz frequency band for use by Wi-Fi® devices.  While most Wi-Fi client devices are confined to the overcrowded 2.4 GHz band, consumer devices such as the Apple iPhone 5 are beginning to support the 5 GHz band.  Consumer device support for 5 GHz will increase as 802.11ac radios become more prevalent in the market.

In the United States and other countries that adhere to FCC policy, the 5 GHz band is divided into four sub-bands referred to as Unlicensed National Information Infrastructure (UNII) bands. Each UNII band is subdivided into channels.  A standard Wi-Fi channel is 20 MHz wide.  802.11n supports channel widths of 20 MHz and 40 MHz, where the latter is the combination of two adjacent 20-MHz channels.  With 802.11ac, four adjacent 20-MHz channels to be combined into a single channel that is 80 MHz wide.

How many 20-MHz channels exist today?  How many will be added?  The answer to the first question depends on whom you ask:

  • UNII-1: Everyone agrees that there are four channels – 36, 40, 44, and 48.
  • UNII-2: Everyone agrees that there are four channels – 52, 56, 60, and 64.  All four require Dynamic Frequency Selection (DFS).
  • Intermediate: Most vendors support eight DFS channels – 100, 104, 108, 112, 116, 132, 136, and 140.  A few support three more – 120, 124, and 128 – although the FCC has removed those channels to protect a special kind of weather radar being developed by the Federal Aviation Administration for airports.  Even fewer support one more – 144.
  • UNII-3: Some vendors, such as Cisco and Laird, support four channels – 149, 153, 157, and 161.  Others add a fifth – 165.

Most vendors support 20-24 of the 25 channels that are defined.

If the FCC follows through, then the following channels will be added to 5 GHz:

  • Intermediate: The three channels – 120, 124, and 128 – that were removed
  • New band 1 (5.350-5.470MHz): Five new channels, possibly 72, 76, 80, 84, 88, and 92
  • New band 2 (5.850-5.925MHz): Four new channels, possibly 170, 174, 178, and 182

12 new channels will add capacity for enterprise networks, which present greater operational challenges and more stringent requirements than residential and commercial Wi-Fi networks. For more information on optimizing operation in the 5 GHz band in enterprise deployments, read our white paper on this topic.

So what will happen next? The press release issued by the FCC is not an official plan of action. On February 20, the FCC now will issue a "notice of proposed rulemaking", or NPRM, with a public comment period. The FCC will proceed with caution because portions of the current 5 GHz are used by weather and military radar systems which have priority over Wi-Fi devices. The FCC will need to decide which new channels will require support for two features that are part of the 802.11h specification: Transmit Power Control (TPC) and DFS.