Research On Compensation Techniques Of Non-ideal Channel On Navigation Satellite

In order to make satellite navigation system provide services with high precision and diversity, to meet the development direction of product diversification and the comprehensive needs of users, a series of new modulation methods represented by BOC modulation are proposed. The navigation signal with new modulation has better code tracking accuracy and anti-multipath performance if the quality of transmitted signal is guaranteed. The navigation signal usually having a larger bandwidth with such modulation, when it goes through the transmitting channel of the payload, is distorted inevitably so that the navigation signal quality is decreased, resulting in the distance of actual navigation system performance compared with which is determined by the navigation signal quality. Therefore research on compensation techniques of non-ideal channel is of great significance.For the purpose of evaluating the distortion effect on navigation signal quality introduced by non-ideal channel, and evaluating the degree of improvement for signal quality by compensation techniques, the receiving theory and quality evaluation indices are introduced in this paper. The block diagram of the transmitting channel is showed, and core devices of the payload are modeled respectively including I/Q modulator, high power amplifier with memory effect, bandpass filter, their influence on signal quality is analyzed by simulation. GMP predistortion model for power amplifier with memory effect without the presence of I/Q imbalance(direct conversion) is showed, and the simulation results show that this method has obvious inhibitory effect on the spectral band regeneration, improves the quality of navigation signal significantly. Joint predistortion model for power amplifier with memory effect in the presence of I/Q imbalance(orthogonal mixing) is introduced, and the simulation results show that this method can compensate the carrier leakage caused by I/Q imbalance, at the same time, also can inhibit the spectral band regeneration caused by HPA, improves the quality of navigation signal. Type-based group delay equalization technique for bandpass filter is given, simulation shows that this method has obvious improvement on zero-crossing offset index, improves the quality of navigation signal. This paper proposes a group delay compensation technique which is available for the navigation signal with the same modulation for all components, there is only one parameter of this model, and it is simple to extract parameter. The simulation results show that this method can achieve the equivalent compensation effect compared with the previous equalization technique.