Hybrid GNSS Receiver for Super Fast Acquisition Time, Five Times Faster than Conventional GNSS Receiver

摘要

Nowadays, fast acquisition is becoming very important in GNSS application especially in emergency application. But newly designed GNSS signal makes it more difficult, because upcoming Galileo, modernized GPS and GLONASS will require more complex and time consuming acquisition process. For example, Galileo E1 Open Service adopts a 4092-length code, four times longer code length than GPS L1 C/A and BOC (1,1) modulation for split spectrum[1]. Increase in number of GNSS signal and longer code length expands search space and BOC (1,1) causes ambiguity because of secondary peaks in autocorrelation function[2]. Of course, the performance of receiver hardware has been improved, such as high speed CPU. But the conventional receiver architecture and acquisition method couldn't make the most use of it. So we propose hybrid receiver architecture and corresponding acquisition scheme that needs very simple modification in receiver hardware design and can take advantage of improved processing power of CPU for fast acquisition. The modification enables the hardware receiver to use FFT-based acquisition method to help search process, in addition to the conventional sequential search conducted by hardware correlators. And it can be easily and cheaply implemented to current GNSS receiver. In this paper, the implementation issues and its performance will be presented. We implemented this scheme on the receiver that we made. It is based on Mitel (or Zarlink) GP2015 and GP2021 chipsets with ARM9 cored CPU. Test results show that the proposed receiver can acquire the signal 2-4 times faster than the conventional one with FFT-only operation. And it could be much faster if simultaneous operation of FFT and conventional search would be performed.