IEEE 802.11a systems use 20 MHz channels in the 5 GHz band. Speci_cally, let's consider an
802.11a system with a center carrier frequency of 5.16 GHz. 802.11a uses OFDM with a 64-pt
IFFT/FFT. However, only 52 of the 64 subcarriers are transmitted, primarily to minimize out-ofband
(a) What is the subcarrier bandwidth"?
(b) The cyclic prefix is added in the time domain, after the IFFT and parallel-to-serial conversion,
and adds an overhead of 20%. How long is the cyclic prefix, in microseconds? What about in
symbols (where each subcarrier modulates one symbol)?
(c) Of these 52 subcarriers, only 48 may be used for data. The minimum and maximum data rate
configurations in 802.11a utilize a r = 1/2 and r = 3/4 convolutional code with BPSK and
64QAM, respectively. Derive the minimum and maximum data rates in 802.11a.
(d) Assume that the worst-case delay spread scenario is when a user has the last-arriving
multipath component of appreciable energy travelling twice the distance of the first component.
What is the maximum delay spread for an ISI-free 802.11a system? How many taps v does this
correspond to assuming that the sample rate is 20 MHz.
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