improving performance of coherent coded ofdm systems using space time transmit diversity.pdf

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Improving performance of coherent coded It can be shown that if the channel estimates are perfect ( ˆ 1 = 1, ˆ 2 =
α
OFDM systems using space time transmit 2) diversity can be achieved:
diversity
. Stirling-Gallacher and Z. Wang However, to achieve this diversity, it is necessary that the channel does
not change significantly between received pilot symbols p1 and p2, so
The performance gain of space time transmit diversity (STTD) for α
that eqns. 5 and 6 are valid and the separate channel estimates ˆ 1 and
coded OFDM systems using space time block coding (STBC) is α
ˆ 2 can be made.
investigated. In particular, it is proposed to use pilot patterns, which are
orthogonal in both the frequency and time directions. Therefore, to
obtain channel estimates from the separate transmit antennas the
receiver can use either adjacent pilots in the frequency direction or
adjacent pilots in the time direction.
Introduction: Orthogonal frequency division multiplexing (OFDM) is
commonly used for high data rate wireless applications due to its inher-
ent ability bat inter-symbol interference (ISI). To achieve opti-
mum performance with such systems, time and frequency interleaving
are used with channel coding to yield the full benefits of time and fre-
quency diversity. However, to obtain time diversity, the size and corre-
sponding delay of the time int