Wireless local-area networking (WLAN) was birthed to support computers in the home and office as well as on the road. Today, however, the usage models have moved far beyond such basic functionality. They now incorporate wireless display, high-definition-television (HDTV) distribution, rapid upload/download, backhaul, outdoor campus/auditorium, and the manufacturing floor. Two new IEEE project groups have emerged to provide very high-throughput capabilities: Working Groups TGac (focused on IEEE 802.11ac) and TGad (proposing IEEE 802.11ad). The standard that is the focus of the latter is detailed at length in a newly available application note from Agilent Technologies titled, “Wireless LAN at 60 GHz—IEEE 802.11ad Explained.”
The 28-page application note explains that IEEE 802.11ad is being jointly proposed by its working group and the Wireless Gigabit Alliance (WiGig; http://wirelessgigabitalliance.org). The goal of the standard, which is expected to be finalized by the end of this year, is to provide throughput to 7 Gb/s using roughly 2 GHz of spectrum at 60 GHz over a short range. All of the IEEE 802.11 standards are tasked with backward compatibility. Thus, IEEE 802.11ac and 802.11ad are compatible at the medium-access-control (MAC) or data-link layer. They differ only in their physical-layer (PHY) characteristics. As a result, devices could have three radios: a 2.4-GHz radio for general use, which may suffer from interference; a 5-GHz radio for more robust, higher-speed applications; and a 60-GHz radio for ultra-high speed within a room. Session switching between all three radios would be supported.
The application note provides in-depth information on various facets of the standard. For example, a discussion of the choice of 60 GHz explains that transmission at that frequency covers less distance for a given power. For the most part, this is due to the increased free-space path loss (68 dB over 1 m at 60 GHz, which is 21.6 dB worse than at 5 GHz). It is compounded by propagation losses through materials and human-body shadowing (losses from, say, 3 to 30+ dB).
Another concern raised about the 60-GHz band is the range limitation caused by the substantial RF absorption peak, which is due to a resonance of atmospheric oxygen molecules. Yet this absorption effect only begins to grow significant beyond 100 m. As a result, it does not impact low-power transmissions. With IEEE 802.11ad, it is considered an advantage that low-power transmissions will not propagate very far. In addition to reducing the likelihood of co-channel interference, such limited propagation increases the possible frequency re-use density.
Among other benefits are reduced opportunities for protected content to be stolen by eavesdropping on nearby transmissions; the emergence of low-cost microwave-component fabrication techniques; and the fact that high path loss can be mitigated by increasing antenna gain. In-depth information also is provided on topics like a regulatory overview, the standard’s PHY, and testing. By covering so many aspects surrounding IEEE 802.11ad, the note succeeds in addressing both the requirements and challenges of supporting today’s unwired world.
Agilent Technologies, Inc., 5301 Stevens Creek Blvd., Santa Clara, CA 95051; (408) 345-8886, FAX: (408) 345-8474, www.agilent.com.