HostAP digest, Vol 1 #61 - 14 msgs

[Dave Edwards]

Mike, BB,

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The Diversity circuit of the receiver will compare the phase difference
of the two received signals, delay the more advanced of the two so that
it is phased up with the other signal, then combine them together to
produce one composite stronger signal, which can be de-modulated more
effectively.

This technique has been used in the cellphone industry for around 20+
years.

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If you are using an intersil based radio (i.e. Prism 2/2.5) then antenna 
diversity is rather limited. This is because the radio only has a single 
RX channel and a switch to select the receive antenna. Due to this, the 
device can only listen on one port at a time and so mixing the received 
signals is not possible.

The Prism Baseband chip makes it's decision about antenna diversity by 
sampling the received signal on each of the antenna ports during the 
synchronization portion of the RF transmission. This is one of the 
reasons for having a preamble on the radio. Once the BB chip has 
selected a port it will then stick with it until the end of the reception.

Hope this clarifies things

Dave