why is dc carrier not used in wimax
Actually there are two questions in your question
The first one is "How can a DC subcarrier contains any frequency??”
& the second is ""RF centre frequency of the transmitting station." How this information is useful at receiver side?? "
The answer for the first question is the DC subcarrier is a DC without modulation (shift the channel to RF frequancy" or after doing demodulation you can find this subcarrier as a DC subcarrier.
And recommendation says that this subcarrier is null to simplify A/D & D/A operation.
The answer for second question is - I am not sure about it - as the following:
If you want to ask about how the receiver (subscriber station (SS)) can decide the center freq. and the bandwidth for the channel? I don't think that will happen from taking information from DC subcarrier may be - and again may be , I am not sure - from pilot subcarriers and it depends on if there is sub-channelization (802.16 d) or subcarrier permutation (802.16 e) .
If you ask about what is the function of DC subcarrier especially it will be null - according to the recommendation - I think they (the forum) want to keep a sort of symmetry in OFDM channel structure (for example, for 256 subcarrier channel , the remove 27 & 28 from each side for guard purpose & the remaining is 201 subcarrier ; 1 DC subcarrier (at center), 8 pilot subcarriers & 192 data subcarriers)
When I get the exact information I will let you know....