Assessment And Compensation Of I/Q Delay Mismatch In Navigation Satellite Channel

With the continuous improvement of the Global Navigation Satellite System and the wide application of the diversification services, there has appeared a series of new modulation shemes in response to the problem of limited spectrum resources. The premise of a good performance is that the quality of the signals under the new modulation shemes is assured to be good. However, the devices used in the satellite emmited chanel can not be totally perfect in project, which always results the degration of the signal quality. Among the devices, the orthogonal frequency conversion unit will introduce the I/Q impairment. Although as an aspect of I/Q impairment, the I/Q delay mismatch is always ignored, while the other aspects such as the gain imbalance, the phase imbalance and the DC offset are taken into account. However, the I/Q delay mismatch will affect both the relevance of the navigation signals and the quality of them. Therefor, it is particularly necessary to study the difference and connection between the impact of the I/Q delay mismatch on signals at different frequencies in emission channel and to compensate for this distortion.In this paper, we will introduce several new modulation shemes used in BeiDou Navigation Satellite System, describe the overall model of the emission channel and depict the navigation signal from baseband to antennas. We will describe the partial model of the I/Q delay mismatch and give distortion model of the orthogonal frequency inverter which only exists the I/Q delay mismatch. We will also introduce three assessment indicators relavant to the signal quality, and analyze the impacts of the I/Q delay mismatch for signals at different frequencies of B1, B2, B3 in the system due to the I/Q low pass filters' characteristics not completely same. Finnaly, we will propose a method by the square of the ideal I and Q signals and the instantaneous power of the distortion signal with a few iteration to estimate the delay and compensate for it using the characteristics of correlation function, and verify the results from three aspects of signals at frequencies of B1, B2, B3, and explain the particularity of the results of signals at frequency of B1.