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Communication Dans Un Congrès Année : 2009

Pseudo-range multipath mitigation technique based on the Subcarrier x PRN Reference code replica

Résumé

The multipath represents a serious source of error that damages the pseudo-range measurement carried out by GNSS (Global Navigation Satellite Systems) receivers. It also affects the carrier phase measurement but its effect is more significant on the pseudo-range. Since several years the scientific community has studied the multipath problem and promising results have been proposed. For instance, the Narrow Correlator technique [1], the strobe Correlator technique [2], the MEDLL (Multipath Insensitive Delay Lock Loop) technique [3], the ELS (Early Late Slope) technique [4], the multi-antenna based technique [5], among others. These techniques greatly improve the code measurement when compared to the standard Delay Lock Loop (DLL). This paper deals with a technique developed in order to further reject medium and long multipaths. It is simple to implement and does not require any post-processing of observables. The idea is taken from the Galileo open signal architecture on E1. The agreement of 2004 between the European Council and the United States led to a BOC(1,1) signal for the Galileo open service (OS) on E1. The BOC(1,1) sequence is the product of a square wave subcarrier (having a frequency of 1.023 MHz) and a PRN sequence (the current Galileo E1-OS signal is a Multiplexed BOC (MBOC), agreement of 2006 [6]). Reference [7] showed that the correlation between the BOC(1,1) signal and the same PRN sequence (without subcarrier) leads to a Correlation Function having two triangles (that we call CF2). Each peak of the CF2 has a width of 1 chip (remember that the autocorrelation function is 2 chips wide). The idea is to track the peak of the CF2 using only the first triangle. The benefit of this is the fact that multipaths having relative delays greater than 0.5+Δ/2 chip do not affect the early and late correlations, therefore they do not effect the pseudorange measurement. The use of the standard ACF (AutoCorrelation Function) rejects multipath of delays greater than 1+Δ/2 chips. As a result, this technique allows to enhance the multipath rejection capability of the code loop. Based on this idea, dealing with the C/A code of GPS, we propose a DLL that uses a new reference code. In this case, the received sequence is the PRN and the local replica code will be the product of the C/A code and a square wave subcarrier (that we call just "subcarrier"). This technique is generalized for subcarrier having a frequency of n*1.023 MHz leading to more multipath rejection capability of the DLL. One shows that the DLL using the Correlation Function (CFn) is insensitive to multipath having relative delays greater than 1/2n+Δ/2 chip. This technique suffers from power loss and is more sensitive to thermal noise than the standard DLL. For this reason, the prompt replica used by the PLL (Phase lock Loop) is the standard prompt obtained by the C/A autocorrelation. This led to reduce the power loss on the carrier tracking loop. Thermal noise performance degradation is therefore compensated by the multipath rejection capability of the new code loop. This technique was implemented using MatLab/Simulink and results show a significant improvement of the C/A code measurement for medium and long multipaths.
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Dates et versions

hal-00445838 , version 1 (11-01-2010)

Identifiants

  • HAL Id : hal-00445838 , version 1

Citer

Nabil Jardak, Alexandre Vervisch-Picois, Nel Samama. Pseudo-range multipath mitigation technique based on the Subcarrier x PRN Reference code replica. ITM '09 : the 2009 International Technical Meeting of the Institute of Navigation, Jan 2009, Anaheim, Ca, United States. pp.187-195. ⟨hal-00445838⟩
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