MARC 主機 00000nam 2200325 4500
001 AAI9802114
005 20050105135814.5
008 050105s1997 eng d
020 0591518023
035 (UnM)AAI9802114
040 UnM|cUnM
100 1 Schmidl, Timothy Mark
245 10 Synchronization algorithms for wireless data transmission
using orthogonal frequency division multiplexing (OFDM)
300 114 p
500 Source: Dissertation Abstracts International, Volume: 58-
07, Section: B, page: 3836
500 Adviser: Donald Clyde Cox
502 Thesis (Ph.D.)--Stanford University, 1997
520 Orthogonal frequency division multiplexing (OFDM) is a
multicarrier modulation method which provides efficient
bandwidth utilization and robustness against multipath
delay spread. In an OFDM system, finding the symbol timing,
the carrier frequency offset, and the sampling rate offset
at the receiver is important in the recovery of the
signal. Synchronization methods are needed which will work
well for signals passing through frequency selective
channels with large delay spreads. This thesis presents
methods to acquire synchronization for either a continuous
stream of data as in a broadcast application or for a
burst of data as in a wireless local area network. The
ratio of the number of overhead bits for synchronization
to the number of message bits must be kept to a minimum,
and low-complexity algorithms and rapid acquisition are
needed. The carrier frequency offset can be many
subcarrier spacings, so a large carrier frequency
acquisition range is necessary
520 A general method using two training symbols is presented
and analyzed. First the symbol/frame timing is found by
searching for a symbol in which the first half is
identical to the second half in the time domain. Then the
carrier frequency offset is partially corrected, and a
correlation with a second symbol is performed to find the
carrier frequency offset. This carrier frequency offset
estimate is shown to approach the Cramer-Rao lower bound
for variance. The symbol timing estimate can be refined
after the frequency correction by using matched filtering
in the time domain to determine the channel impulse
response. Simulations are presented over three types of
channels to compare several symbol timing estimators. The
maximum likelihood estimator for the sampling rate offset
is presented. This can be used if there will be a large
enough offset to cause a degradation in the received
signal. Another contribution is a synchronization method
requiring no training data. This could be useful for
systems with simple constellations such as QPSK
590 School code: 0212
590 DDC
650 4 Engineering, Electronics and Electrical
690 0544
710 20 Stanford University
773 0 |tDissertation Abstracts International|g58-07B
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