說明 
114 p 
附註 
Source: Dissertation Abstracts International, Volume: 5807, Section: B, page: 3836 

Adviser: Donald Clyde Cox 

Thesis (Ph.D.)Stanford University, 1997 

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 lowcomplexity algorithms and rapid acquisition are needed. The carrier frequency offset can be many subcarrier spacings, so a large carrier frequency acquisition range is necessary 

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 CramerRao 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 

School code: 0212 

DDC 
Host Item 
Dissertation Abstracts International 5807B

主題 
Engineering, Electronics and Electrical


0544

Alt Author 
Stanford University

