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Hello, When looking at the
WirelessMAN-OFDM PHY profiles defined in the standard in Section 12.3.2, I am
finding some inconsistencies which I cannot seem to resolve regarding the bandwidth
of the signals. For example, for the 1.75MHz
channel bandwidth profile (ProfP3_1.75), table 405 defines Tb (total symbol
period) as 128us. Since there are 256 subcarriers, the basic 'chiprate' would
be 256/128us = 2MHz. Since of those 256 subcarriers, only 200 are actually
used, the real double-sided bandwidth of the signal would be 2MHz*200/256 =
1.5625MHz. This value indeed fits within the 1.75MH channel bandwidth for this
profile. No problem here nor for the 3.5MHz and 7MHz profiles. If I however do the same
calculation for the 3MHz channel bandwidth profile (ProfP3_3), table 408
defines Tb as 73*99/437us = 16.538us. This leads to a double sided bandwidth of
256/16.538us * (200/256) = 12.09MHz. This value does not even come close to the
specified 3MHz channel bandwidth?! The same problem exists for the 5.5MHz and
the 10MHz profiles: the real double sided bandwidth does not fit within the
specified channel bandwidth! Could anyone explain where
the error in my reasoning is? Best
regards, Steven Thoen |