A Rapid Code State Computing Algorithm for L2C Code Phase Control

摘要

The ability to control code phase is important in GNSS receiver design for fast signal acquisition or signal reacquisition. This often requires that local PRN codes be created in desired code phase at designated time. An easy way to do this is to set shift registers of PRN code generator with previously prepared register states, which are called as code state. This paper discloses a rapid code state-computing algorithm for code phase control of the new L2 civil signal. Comparing to conventional code state calculation of state by state, this paper proposes a matrix method to calculate code states that can be separated from initial state. The matrix has a property of that it only dependents on the phase difference from the calculated state to initial state no matter where they are located in. This property helps us save memory in code state calculation. In order to combine the matrix method into code state computation, this paper introduces a hierarchical architecture together with decimated code state tables and conventional code state calculation. Mathematic details of the proposed algorithm have been given in this paper. Software implementation of the algorithm has been tested in real time. Furthermore a hardware accelerator of the algorithm is also provided. It makes the code state computing quite suitable for low power CPU that is often required in embedded GNSS receiver modules.