Research On I/Q Imbalance Problems Of The OFDM-UWB System

This thesis mainly focus on the I/Q imbalance effect of the transmitter and receiver of the OFDM-UWB system, which is mainly caused by the mismatch of the hardware of the I branch and Q branch of the transmitter and receiver. The I/Q imbalance effect will introduce the image leakage phenomenon which will have a severe influence on the performance of the transmitter and receiver and the bit error rate (BER) of the whole OFDM-UWB system. For the above I/Q imbalance problem, the previous research have proposed the training signal approaches and the frequency domain blind compensation approaches. However, these approaches have the disadvantage of narrow application range, high computation complexity, low adaptiveness.Specially, almost all the researches are mainly focus on the I/Q imbalance problem of the receiver and few researches concern about the I/Q imbalance problem of the transmitter. This may cause the problem that the system still has an un-accapetable BER due to the distortion of the signal which is caused by the I/Q imbalance of the transmitter, which can not be estimated and compensated by current researches. This thesis proposes novel I/Q imbalance parameters estimation and signal pre-compensation schemes for the I/Q imbalance problem of the transmitter and receiver of the OFDM-UWB system. The I/Q imbalance parameters estimation is based on the statistical properties of the In-phase and Quadrature-phase parts of the signals of the transmitter and the receiver. And for the receiver, we compensate the LIF signals of the signals come out of the receiver according to the estimated parameters. For the transmitter, the pre-compensation scheme feedbacks the estimated imbalance parameters to the pre-compensation block and the pre-compensation block makes offsets to the In-phase and Quadrature-phase parts of the original low intermediate frequency (LIF) signal before they pass through the up-convertor of the transmitter and the outcome modulated radio frequency (RF) signal will be recovered. Both the signals for the estimation and pre-compensation are low intermediate frequency signals so the estimation and pre-compensation schemes are easy to realize on the digital domain. And the proposed schemes have the advantage of high adaptiveness.