| Summary: | 碩士 === 國立交通大學 === 電子工程系所 === 95 === This thesis introduces the synchronization problems, algorithms, and imple- mentation issues of IEEE 802.16e OFDMA system.
In DL synchronization, the (mobile station) MS receiver needs to perform initial synchronization upon its initial entrance to the network. There are timing offset, carrier frequency offset (CFO), and preamble index needed to be estimated during initial synchronization. We use the information of the first DL subframe to estimate the more accurate timing and fractional CFO by cyclic prefix (CP) correlation. Then, we consider the joint detection of integer CFO and preamble index using the compensated preamble in the frequency domain. The preamble sequences and the feature of preamble symbol are exploited and a number of detection methods of different complexity are introduced.
In subsequent subframe, the MS only needs to track the timing offset and fractional CFO. We use CP correlation with exponential average over the symbols in the subframe to obtain a more accurate estimation. Besides, we also afford a data-aided method to estimate the symbol timing since we already know the preamble index during normal synchronization. This method exploits the quasi-orthogonality among the preamble sequences. We verify our system in floating-point computation, and simulate our system in both AWGN and multipath Rayleigh fading channel, which the speed is as high as 120 km/h, and see the performance.
In the end, we modified these methods into fixed-point version, and then optimize the speed of our programs on the digital signal processor (DSP) platform. Although the performance is degraded because of fixed-point modification, the results still can be accepted. After DSP optimization, the synchronization tasks can achieve the real-time requirement.
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