| Summary: | 碩士 === 國立清華大學 === 通訊工程研究所 === 92 === Orthogonal frequency division multiplexing (OFDM) is a popular research topic and has been employed in various applications in recent years. In OFDM systems, it is attractive to employ the direct conversion architecture in the radio frequency module of the receivers for the propose of low cost and low power consumption. But the main problem caused by using the direct conversion architecture is I/Q imbalance. In this thesis, we estimate and compensate the I/Q imbalance generated by the direct conversion receiver in OFDM systems. In previously proposed methods for I/Q imbalance compensation, the unknown multipath channel is usually not considered. In this thesis, the channels are considered to be multipath fading channels with additive white Gaussian noise (AWGN), and the channels are assumed quasi-static during an entire packet. Three methods for I/Q imbalance compensation are proposed: the maximum-likelihood (ML) estimation method, the least-square (LS) estimation method, and a heuristic method. Computer simulations are conducted for comparisons of the performance of three methods. Timing offset and frequency offset effects on performance are also considered. We find that the blind ML estimation method generally performs well and is robust against timing offset and frequency offset.
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