Proceedings of the Institute of Navigation ... International Technical Meeting, Feb 13, 2020
This paper investigates the impact of non-line-of-sight (NLOS) and multipath signals on frequency... more This paper investigates the impact of non-line-of-sight (NLOS) and multipath signals on frequency-locked loops (FLLs), which are commonly used to obtain Doppler shift measurements for velocity estimation in radio navigation. A salient result is that, in the absence of a direct signal, a single NLOS signal does not corrupt Doppler observables if the angle-of-arrival (AOA) is known. Another striking result is that, in a multipath environment involving two signals, the arctangent discriminator (averaged over the beat frequency) tracks only the higher amplitude signal. Our investigation has particular significance for radio navigation in urban environments, either using global navigation satellite system (GNSS) signals or ground-based cellular signals.
A New SIMD Correlator Algorithm for GNSS Software Receivers to Process Complex IF Data
Springer eBooks, 2013
GNSS software receivers implement digital signal processing algorithms on programmable software p... more GNSS software receivers implement digital signal processing algorithms on programmable software platform (such as PC, DSP), which traditional ones execute on dedicated hardware. It is highly flexible, convenient for debug and could be adapted to a platform for GNSS algorithm research. However, the computation of down shifting of the GNSS signal to baseband and correlation with the locally generated ranging code is too expensive for normal GNSS software receivers to work in real time. The computational cost could be reduced by utilizing Single Instruction Multiple Data (SIMD) operations. The article proposes a new SIMD correlator algorithm for complex GNSS IF signal processing on x86 processors. It firstly demonstrates why normal GNSS software receivers couldn’t achieve real-time processing by using Single Instruction Single Data (SISD) operations and the improvements achieved by using existing SIMD algorithms; then proposes a new SIMD correlator algorithm, outlines its implementation principle and compares it with the SISD and the existing SIMD algorithms. Performance gains achieved via the new SIMD algorithms are then demonstrated in an analysis. Finally, the implementation and experimental results of the new algorithm are presented. The experimental results show that compared to the SISD and existing SIMD algorithms the new SIMD algorithm can effectively reduce the computation of down shifting of the GNSS signal to baseband and correlation with the locally generated ranging code.
The correlation process in a GNSS receiver tracking module can be computationally prohibitive if ... more The correlation process in a GNSS receiver tracking module can be computationally prohibitive if it is executed on a central processing unit (CPU) using singleinstruction single-data algorithms. An efficient replacement for a CPU is a graphics processing unit (GPU). A GPU is composed of massive parallel processors with high floating point performance and memory bandwidth. It can be used to accelerate the burdensome correlation process in GNSS software receivers. We propose a novel GPU-based correlator architecture for GNSS software receivers, which is independent of the GPU device, the number of the processing channels, the signal type, and the correlation time. The proposed architecture is implemented and optimized using CUDA, a parallel computing platform and programming model for GPUs. We focus on the following aspects: the design and the time complexity analysis of the proposed GPU-based correlator algorithm, the tests that verify the correctness and the optimization of the implementation, and the performance evaluation of the optimized GPU-based correlator. Moreover, we introduce some new CUDA features that can be applied in a GPUbased correlator. Keywords Global navigation satellite system (GNSS) Á Software receivers Á Correlation Á CUDA Á Real time Á Graphics processing unit (GPU)
Embedding various sensors with powerful computing and storage capabilities in a small communicati... more Embedding various sensors with powerful computing and storage capabilities in a small communication device, smartphones have become a prominent platform for navigation. With the increasing popularity of Apple CarPlay and Android Auto, smartphones are quickly replacing built-in automotive navigation solutions. On the other hand, smartphones are equipped with low-performance Micro Electro Mechanical Systems (MEMS) sensors to enhance their navigation performance in Global Navigation Satellite System (GNSS)-degraded or -denied environments. Compared with higher-grade inertial navigation systems (INS), MEMS-based INS have a poor navigation performance due to large measurement errors. In this paper, we present laboratory test results on the stochastic and deterministic errors observed in MEMS inertial sensor measurements of five different smartphones from different manufacturers. Then, we describe and discuss the short-term effects of these errors on the pure inertial navigation performan...
Modeling Multipath Effects on Frequency Locked Loops
This paper investigates the impact of non-line-of-site (NLOS) and multipath signals on frequency-... more This paper investigates the impact of non-line-of-site (NLOS) and multipath signals on frequency-locked loops (FLLs), which are commonly used to obtain Doppler shift measurements for velocity estimation in radio navigation. First, we use theory to model the effects of NLOS signals on the Doppler estimate produced by a conventional FLL with an arctangent discriminator. Next, we use experiments to verify theoretical predictions. A salient result is that, in the absence of a direct signal, a single NLOS signal does not corrupt Doppler observables if the angle-of-arrival (AOA) is known. Another striking result is that, in a multipath environment involving two signals, the arctangent discriminator (averaged over the beat frequency) tracks only the higher amplitude signal. Our investigation has particular significance for radio navigation in urban environments, either using global navigation satellite system (GNSS) signals or ground-based cellular signals.
Proceedings of the Institute of Navigation ... International Technical Meeting, Feb 13, 2020
This paper investigates the impact of non-line-of-sight (NLOS) and multipath signals on frequency... more This paper investigates the impact of non-line-of-sight (NLOS) and multipath signals on frequency-locked loops (FLLs), which are commonly used to obtain Doppler shift measurements for velocity estimation in radio navigation. A salient result is that, in the absence of a direct signal, a single NLOS signal does not corrupt Doppler observables if the angle-of-arrival (AOA) is known. Another striking result is that, in a multipath environment involving two signals, the arctangent discriminator (averaged over the beat frequency) tracks only the higher amplitude signal. Our investigation has particular significance for radio navigation in urban environments, either using global navigation satellite system (GNSS) signals or ground-based cellular signals.
A New SIMD Correlator Algorithm for GNSS Software Receivers to Process Complex IF Data
Springer eBooks, 2013
GNSS software receivers implement digital signal processing algorithms on programmable software p... more GNSS software receivers implement digital signal processing algorithms on programmable software platform (such as PC, DSP), which traditional ones execute on dedicated hardware. It is highly flexible, convenient for debug and could be adapted to a platform for GNSS algorithm research. However, the computation of down shifting of the GNSS signal to baseband and correlation with the locally generated ranging code is too expensive for normal GNSS software receivers to work in real time. The computational cost could be reduced by utilizing Single Instruction Multiple Data (SIMD) operations. The article proposes a new SIMD correlator algorithm for complex GNSS IF signal processing on x86 processors. It firstly demonstrates why normal GNSS software receivers couldn’t achieve real-time processing by using Single Instruction Single Data (SISD) operations and the improvements achieved by using existing SIMD algorithms; then proposes a new SIMD correlator algorithm, outlines its implementation principle and compares it with the SISD and the existing SIMD algorithms. Performance gains achieved via the new SIMD algorithms are then demonstrated in an analysis. Finally, the implementation and experimental results of the new algorithm are presented. The experimental results show that compared to the SISD and existing SIMD algorithms the new SIMD algorithm can effectively reduce the computation of down shifting of the GNSS signal to baseband and correlation with the locally generated ranging code.
The correlation process in a GNSS receiver tracking module can be computationally prohibitive if ... more The correlation process in a GNSS receiver tracking module can be computationally prohibitive if it is executed on a central processing unit (CPU) using singleinstruction single-data algorithms. An efficient replacement for a CPU is a graphics processing unit (GPU). A GPU is composed of massive parallel processors with high floating point performance and memory bandwidth. It can be used to accelerate the burdensome correlation process in GNSS software receivers. We propose a novel GPU-based correlator architecture for GNSS software receivers, which is independent of the GPU device, the number of the processing channels, the signal type, and the correlation time. The proposed architecture is implemented and optimized using CUDA, a parallel computing platform and programming model for GPUs. We focus on the following aspects: the design and the time complexity analysis of the proposed GPU-based correlator algorithm, the tests that verify the correctness and the optimization of the implementation, and the performance evaluation of the optimized GPU-based correlator. Moreover, we introduce some new CUDA features that can be applied in a GPUbased correlator. Keywords Global navigation satellite system (GNSS) Á Software receivers Á Correlation Á CUDA Á Real time Á Graphics processing unit (GPU)
Embedding various sensors with powerful computing and storage capabilities in a small communicati... more Embedding various sensors with powerful computing and storage capabilities in a small communication device, smartphones have become a prominent platform for navigation. With the increasing popularity of Apple CarPlay and Android Auto, smartphones are quickly replacing built-in automotive navigation solutions. On the other hand, smartphones are equipped with low-performance Micro Electro Mechanical Systems (MEMS) sensors to enhance their navigation performance in Global Navigation Satellite System (GNSS)-degraded or -denied environments. Compared with higher-grade inertial navigation systems (INS), MEMS-based INS have a poor navigation performance due to large measurement errors. In this paper, we present laboratory test results on the stochastic and deterministic errors observed in MEMS inertial sensor measurements of five different smartphones from different manufacturers. Then, we describe and discuss the short-term effects of these errors on the pure inertial navigation performan...
Modeling Multipath Effects on Frequency Locked Loops
This paper investigates the impact of non-line-of-site (NLOS) and multipath signals on frequency-... more This paper investigates the impact of non-line-of-site (NLOS) and multipath signals on frequency-locked loops (FLLs), which are commonly used to obtain Doppler shift measurements for velocity estimation in radio navigation. First, we use theory to model the effects of NLOS signals on the Doppler estimate produced by a conventional FLL with an arctangent discriminator. Next, we use experiments to verify theoretical predictions. A salient result is that, in the absence of a direct signal, a single NLOS signal does not corrupt Doppler observables if the angle-of-arrival (AOA) is known. Another striking result is that, in a multipath environment involving two signals, the arctangent discriminator (averaged over the beat frequency) tracks only the higher amplitude signal. Our investigation has particular significance for radio navigation in urban environments, either using global navigation satellite system (GNSS) signals or ground-based cellular signals.
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Papers by Liangchun Xu