Abstract
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.
Highlights
The direct-sequence spread spectrum (DSSS) technique is a method in which a signal of narrow bandwidth is intentionally spread over a wider bandwidth in the frequency domain
The high complexity of the FFT-based acquisition is caused by (a) wide bandwidth of the incoming baseband signal which forces the device to deal with long FFT and inverse fast Fourier transform (IFFT) and (b) utilization of the conventional sequential search to estimate the Doppler frequency shift
5 Conclusion In this article, we propose a novel approach for FFT-based acquisition in Global Navigation Satellite Systems (GNSS) receivers
Summary
The direct-sequence spread spectrum (DSSS) technique is a method in which a signal of narrow bandwidth is intentionally spread over a wider bandwidth in the frequency domain. The high complexity of the FFT-based acquisition is caused by (a) wide bandwidth of the incoming baseband signal which forces the device to deal with long FFT and inverse fast Fourier transform (IFFT) and (b) utilization of the conventional sequential search to estimate the Doppler frequency shift. Note that sl(n) is the transmitted signal from the lth satellite and nl is the delay in samples, fdl is the normalized frequency shift due to the Doppler effect, L is the number of satellites in line of sight, and w(n) is additive white E w2(n) It is Gaussian noise with E possible to assume that s2l (n) each sl (n) is a wide-sense stationary (WSS) Gaussian process [2].
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