Sincronismo de tempo e frequência em receptores OFDM

Abstract

This work proposes a new time and frequency synchronization system for OFDM (Orthogonal Frequency Division Multiplexing) receivers. Presently, the OFDM technique is adopted in nearly all wireless broadband systems (IEEE 802.16 WiMax, 3GPP-LTE, IEEE 802.22, etc). It is also used in the ISDB-T digital television system, adopted in Brazil. The proposed synchronization system controls the receiver timing and frequency in a closed loop, adjusting the FFT window delay and the local oscillator frequency. The loop error is measured in the frequency domain, based on reference symbols inserted on pilot carriers in the transmitter. Initialization of the closed loop operating point is performed with base on the guard interval generated at the transmitter. Di erently of the usual sync implementations for OFDM systems, the proposed system actuates in the time domain, instead of the frequency domain. Also, in order to avoid loop instabilities due to the transport delay intrinsic to the OFDM demodulation process, the proposed system uses a prediction algorithm for loop stabilization.