An OFDM system baseband design for broadband wireless access

Abstract

AB3:Työssä esitellään ja verrataan vain erilaisia karkean ajastuksen ja hienon taajuusvirheen estimointimenetelmiä. Luonnolliseksi valinnaksi tässä tutkielmassa kuvatun uuden OFDM siirtojärjestelmän synkronointiin osoittautuu algoritmi, joka estimoi samanaikaisesti ajastus- ja taajuusvirheen. Työn lopuksi tämä uusi järjestelmä esitellään yksityiskohtaisesti ja sen suorituskykyä eri parametrien arvoilla analysoidaan.

Due to the high sensitivity to synchronization errors in OFDM, special emphasis in this thesis is put on synchronization issues. The general synchronization process is first reviewed. It is shown that the cyclostationary nature of the OFDM symbol relaxes the timing requirements. It appears that in order to achieve very fast acquisition, algorithms should typically be implemented in time domain before FFFT. Moreover, loose requirements for timing and assumption for rather stabile transmitter and receiver oscillators result in the conclusion that fine timing and coarse frequency offset estimation methods can be omitted in this thesis. As a result, only different coarse timing and fine frequency offset estimation methods applicable to an OFDM system are studied in this work. It is shown that joint estimation of timing and frequency offset is a natural choice for an OFDM receiver. One of these methods is then selected as a basic synchronization scheme for a novel OFDM transmission system introduced in this thesis. The performance of this system is then carefully verified by simulations.