A Novel L1 and L2C Combined Detection Scheme for Enhanced GPS Acquisition

Degraded signal environments such as indoors and urban canyons typically limit the scope of standard GPS receiver operation. For instance, GPS signals can be attenuated by 20 dB or more under these adverse conditions. In degraded signal environments, enhancing the processing gain by 20 dB or more requires a significant increase in coherent integration. However, the coherent integration time is decisively limited to less than 20 ms in the legacy GPS L1 signal due to the presence of navigation data modulation. Besides, the detection of weak PRN signals is also an issue owing to the limited correlation suppression performance of the L1 C/A code. Hence, the legacy GPS is currently being modernized to include improved signals at L2 and L5 frequencies. In particular, GPS L2C signal is not only attractive due to its immediate availability but also for its role in civilian GPS applications. The introduction of new signal structures necessitates the development of new acquisition algorithms. In this paper, we introduce a novel detection scheme that collectively utilizes the legacy GPS L1 C/A and L2C CM code signals to enhance the acquisition sensitivity. The proposed acquisition scheme derives its major impetus from the fact that the data, code and carrier are coherently related on the GPS L1 and L2 signals for a given PRN satellite. Secondly, it also uses both the non-coherent and differential detection outputs in its implementation for further sensitivity enhancements. A modified design of the developed acquisition scheme is introduced, which readily allows for an efficient implementation. The acquisition sensitivity performance of the proposed acquisition scheme was evaluated along with the traditional non-coherent acquisition scheme using hardware simulated and live GPS signals. Preliminary analysis corroborates the acquisition sensitivity