Adaptive frequency correction method for enhanced sensitivity CDMA acquisition

Location based services with Galileo/GPS satellite receivers integrated in mobile phones are expected to experience a substantial market growth. Satellite signals are usually received on the earth surface with very low signal energy. Attenuation, shadowing, and multipath fading in urban canyons and moderate indoor environments impose challenging acquisition conditions for the state-of-the-art enhanced sensitivity mobile satellite receivers. Residual frequency deviations between the down-conversion frequency and the received signal frequency due to unknown Doppler frequency shifts significantly reduce the signal acquisition sensitivity of current satellite receivers. This paper shows how the residual frequency deviation can be reduced incrementally towards zero much faster than the CDMA code synchronization be detected with sufficient probability. This paper furthermore derives the probability density functions for the signal detection using the adaptive frequency correction method and illustrates the acquisition sensitivity gain of around 4 dB for different Galileo and GPS satellite receiver configurations.