> Q1: Where in Rx PHY is the matched filter being used exactly

Not at all / it is a rectangular filter.

802.11a is an OFDM system, and that means it's a multi-channel thing – it divides the wide channel into many narrow channels, each of which is *flat*, i.e. only a single complex coefficient. It uses a rectangular pulse shape on each of these.

Thus, there's no matched filter explicit anywhere in the receiver.


When you further your study of modulation techniques, you'll learn why OFDM *has* to use a (in time domain) rectangular filter for each subcarrier (because that achieves the zeros in frequency domain that make the "O" in OFDM).


> Q2: If matched filters are used in demodulator as I expect, how is it implemented for a complex demodulation scheme (i.e., 64-QAM).

Filtering is not part of the demodulator, but comes before (in systems that, unlike OFDM, do make use of it).