In this article, we develop a novel algorithm for Doppler acquisition in fast Fourier transform (FFT)-based Global Navigation Satellite System (GNSS) receivers. The Doppler estimation is carried out in FFT domain by finding the frequency shift which maximizes the energy of the correlation vector. Subsequently, energy detection is used for preliminary decision about the presence of the target code. Then, the final decision and code phase estimation are done in the time domain after taking the inverse fast Fourier transform (IFFT). It is shown that the proposed algorithm has the potential for reducing the average number of required IFFTs in the acquisition process. For improving the sensitivity of the proposed approach, time-domain block averaging and FFT-domain non-coherent integration are investigated as alternative methods. They exhibit rather similar performance improvement, but the non-coherent integration approach is found to be computationally more effective.

In this article the effect of decimation before acquisition stage in conventional Parallel Code Phase Search Acquisition (PCPSA) is discussed. In PCPSA, correlation function of the incoming signal and a locally generated Pseudo Random Noise (PRN) code is extracted by taking the Fast Fourier Transform (FFT) of the incoming signal and multiplying by conjugate FFT of a locally PRN code. Afterward, the IFFT of the resultant signal is carried out and required information is extracted.The incoming signal in acquisition stage inherits a fixed sampling frequency from ADC which causes long FFT and IFFT. Since long FFT and IFFT are not very welcome from implementation point of view one of the solution is using decimation before the acquisition stage.The fact that the most important part of the signal is centralized in a bandwidth of 2Mhz makes it possible to utilize a decimation block before the correlation stage without losing the important information. Decimation catalyzes lower Acquisition Margin (AM) and in order to compensate its effect a coherent integrator is applied at the beginning of the procedure. Thus the peak of correlation function is enhanced and the noise level is attenuated. By comparing AM for conventional PCPSA with modified structure there is an improvement of 2.3848dB in AM when CN R = 36(dB : 1Hz). In addition, modified PCPSA works in average better than conventional one.

This paper proposes

In this article, we introduce a variation of binary search algorithm for the estimation of Doppler frequency shift in the acquisition stage of a GNSS receivers. It is shown in this article that the proposed modified binary search on average reduces the number of search steps by 25% in compare to traditional sequential search which is conventionally used in this context. This saving for the worst case scenario is as high as 100%.

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