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 
856    |u 
856 40 |u