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Challenges with 80 MHz bandwidth signals
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on Jul 6, 2011
on Jul 6, 2011 by tabbott
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What new challenges do 80 MHz bandwidth signals present that I haven't seen before?
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Jul 6, 2011 3:56 PM
Hi Gladys -
Glad you asked. There are challenges in making a transmitter, or receiver, that is double the bandwidth than it was in 802.11n. The analog path must be wider, and the baseband clock rate is twice as large.
But there are a few issues which may not be quite as obvious:
a. The spectral mask requirement in 802.11ac has a transition region that is 2 MHz wide. On an 80 MHz signal, the transition region is proportionally narrower than on a 40 MHz signal. Transmitter designers will need to keep this in mind when designing any windowing or filtering to meet the spectral mask requirement.
To help mitigate the above issue, the spectral flatness requirement in 802.11ac is looser, allowing more variation in subcarrier amplitude.
b. Related to the above, there are only 6 lower guard subcarriers and 5 upper guard subcarriers on both 40 MHz and 80 MHz signals. A receiver may use filtering to attenuate signals in adjacent carriers, and that filtering will require a proportionately narrower transition region on an 80 MHz signal.
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