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Tutorial Topic Sections
Intended to be read in sequence

1 - Establishment of the 802.11ac and 802.11ad Standards 6 - QAM Modulation and OFDM Symbols
2 - Transmit Output Power 7 - Comparing 802.11ac and 802.11ad QAM and OFDM Implementation
3 - Oxygen Absorption of RF at 60 GHz 8 - Real-World Expectations for 802.11ac and 802.11ad
4 - Channel Width and Guard Interval 9 - Antenna Differences: Beamsteeering, Gain and Range
5 - MIMO and Implementation of Multiple Spatial Streams 10 - Overall Perspective and Conclusions

Antenna Differences: Beamsteering, Gain and Range

A pair of outdoor 60 GHz bridges can interconnect up to roughly 3000 feet (but more typically closer to 2500 feet). 60 GHz outdoor bridges use very high gain directional antenna pairs (i.e. 40 dBi with a 1.4 degree beamwidth) for 80 dB of link gain. For perspective, a pair of 5 GHz bridges with 80 dB of link gain could operate with a LOS range greater than 50 miles! Transmission at 60 GHz is subject to extreme attenuation due to the resonant frequency of oxygen. Because in-building 802.11ad requires omnidirectional coverage it’s not possible to use antennas with the directional gain achieved outdoors. 802.11ad specifies a beamsteering mechanism to provide a limited degree of signal strength directionality. It’s reasonable to assume that, unlike 802.11ac beamsteering, 802.11ad will implement beamsteering in early-to-market equipment. It’s unlikely that mobile 802.11ad devices will implement multiple antennas and sophisticated beamsteering due to size and complexity limitations.

Consider that today most 802.11n mobile devices implement, at most, 2-stream MIMO and the 4 streams in the standard are never implemented. 802.11ad devices will inherently have significantly less power output than outdoor 60 GHz bridge radios. 802.11ad devices will not benefit from very high gain, directional antennas as are found with outdoor bridge equipment. 802.11ad mobile devices may only have omnidirectional antennas (it’s unknown at this time) and may have low power output (to save battery). Using only omnidirectional antennas (no beamsteering) a 60 GHz 802.11ad transmission is not expected to have a range much greater than 10 feet. Human bodies (high water content) will impact Line-of-Sight 60 GHz transmission and beamsteering APs may partially mitigate these effects. Beamsteering has the ability to attempt to find a reflected path around obstructions (like people) in a room. If beamsteering is implemented then 802.11ad is expected to perform well even when many people are in a room (like a conference room). Because 802.11ac operates in the 5 GHz spectrum it is less impacted by people in a room than equipment in the 60 GHz spectrum.