Fast Direct Acquisition of the L2 CL Code Through Utilizing the Code Properties and Wiener Filtering Techniques

Direct acquisition of the CL code using conventional techniques is resource exhausting because of the high processing and memory required to calculate the correlation over the code delay-Doppler shift search space. This paper introduces a novel approach that utilizes the code properties and Wiener filtering techniques to acquire the CL code with minimum resources. A shorter-length Doppler-free code is generated from the long CL code by dividing it into an even number of equal-length segments and multiplying the segments. The code generated from the received signal is sensitive to any change in the code length, and eliminating the Doppler shift does not eliminate the Doppler effect on the code length. A method is introduced to guarantee the generation of a code from the received signal that matches the local code. The method aims at correctly aligning the start of the multiplied segments to generate the required code. Several shorter-length, almost orthogonal, codes are generated from the received signal. Their lengths cover the change in length based on the Doppler shift range. Those codes either are added together and the resultant code is correlated with the local code, or each code is correlated separately with the local code. The increase in noise due to the multiplication process is circumvented by passing the received signal through a Wiener-based filter. The filter is designed to fit the spectrum shape of the L2C signal. The algorithm's computational complexity is derived and analyzed. The performance is assessed using signals with different carrier to noise ratios.