1,722,331 research outputs found
Calculating the Costs of Amino Acid Supplementation
Full text linkPesti, Gene; Tahir, Muhammad. (2013). Calculating the Costs of Amino Acid Supplementation. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/204381
A Novel Parallel Carrier Tracking Architecture for Weak GNSS Signals
No full textThe problem of designing robust architectures to track global navigation satellite system (GNSS) signals in harsh environments has gained high attention. The classical closed loop architectures, such as phase locked loops (PLL), have been used for many years for tracking, but in challenging applications such as weak signal and high dynamics, their design procedure becomes intricate. In weak signal conditions, the only option available is to increase the coherent integration time for successful operation of tracking loops. However, it is not possible to increase the integration time beyond certain limits which are set by different factors, one of them is the stability of the classical closed loop schemes. In this paper we investigate an alternative architecture for the tracking of weak GNSS signals where we aid the PLL from an independent architecture called quasi-open loop frequency estimator. The real motivation behind such a scheme lies on the fact that if we provide frequency aiding to PLL we can reduce the effective loop noise bandwidth which in turn allows us to increase the coherent integration time without worrying about loop instability problem. Simulation results are presented which indicate the feasibility of using such type of scheme in weak signal conditions where we can increase integration time in PLL scheme to larger extent which otherwise are not possible in classical closed loop scheme
Characterizing Different Open Loop Fine Frequency Estimation Methods for GNSS Receivers
No full textThe acquisition stage of any Global Navigation Satellite System (GNSS) receiver is responsible to coarsely estimate the code delay and Doppler from the received signals of all the visible satellites. From computational point of view during the acquisition stage the right strategy is to find the signal with as coarse frequency grid as possible in order to accelerate the search. After the coarse estimation has been performed, an additional frequency refinement could be possible for tracking loops which is equivalent to frequency offset estimation. In urban and moderate indoor applications closed loop schemes like Frequency Lock Loop (FLL) exhibit loss of lock behavior. In this paper, in order to avoid this behavior, we propose and characterize some alternatives for fine frequency offset estimation based on some classical techniques which can be considered as open loop schemes for fine frequency estimatio
Folding techniques for low complexity acquisition of modern GNSS signals
No full textIn global navigation satellite system (GNSS) because of the long pseudo-random-noise (PRN) code period and high chip rate of the code rapid code acquisition is challenging. The difficulty is how to rapidly detect the correct cell from numerous code frequency cells. To speed up the search process several folding techniques have been proposed in the literature which directly reduces the code phases to be searched by folding either the local signal or the incoming signal. Unfortunately all the folding techniques work on the basis of a non-realistic assumption that there is no sign transition in the data set due to the navigation message bits. In this study we consider different variants of the already available folding methods such as extended replica folding acquisition search technique (XFAST) and discuss their performance in the presence of data sign transitio
Performance analysis of pre-correlation differential acquisition scheme
No full textPre-correlation differential detection (PDD) scheme is studied for global navigation satellite systems (GNSS) receiver design. By performing a differential detection at the chip or sample level before correlation process, the effect of both data and residual carrier is eliminated which in turn allows for frequency independent code phase acquisition. Hence the search space and computational complexity is reduced to a large extent. The detection performance of this type of scheme is analysed in terms of receiver operating characteristic (ROC) curves and verified by simulatio
Two sequential acquisition techniques for weak GNSS signals
No full textTwo techniques to sequential acquisition of global navigation satellite system (GNSS) signals are investigated, one treats the GNSS signal acquisition problem as multiple hypothesis testing problem and the other treats the same problem as binary hypothesis testing problem. Both techniques do not rely on the generalized likelihood ratio test (GLRT), rather on a posteriori probabilities as test statistic. Mechanism of propagating the probabilities when a new measurement arrives, differes in both cases.
Simulation results have been presented comparing the detection performance of both schemes in different scenarios
Sequential bayesian detection of GNSS signals
No full textDetecting and processing global navigation satellite system (GNSS) signals indoors and in urban canyons has gained immense attention due to the problems of very weak signals and hostile environments. Satellite navigation signal detection problem applies a statistical test in which a signal coming from a specific satellite is declared present or absent. This paper considers a new approach to the detection of weak GNSS signals using a Bayesian technique. The proposed detection method selects some search space cells as candidate cells where each candidate cell is associated with a code delay and a Doppler frequency. For each candidate cell a vector of a posteriori probabilities is propagated for a fixed number of operation cycles. At the end of the process, maximum a posteriori probability (MAP) criterion is used to select the correct cell. Simulation results are presented indicating that the proposed method provides a significant performance advantage over classical techniques of acquisition which utilize non-coherent integration
A Novel Quasi Open Loop Frequency Estimator for GNSS Signal Tracking
No full textThe problem of designing the robust architectures for tracking the global navigation satellite system (GNSS) signals in harsh environments has gained immense attraction. The classical closed loop architectures like phase locked loop (PLL) have been used for many years for tracking purposes but for challenging applications their design procedure becomes intricate. This paper proposes and demonstrates the use of a quasi-open loop architecture to estimate the time varying carrier frequency of the GNSS signal. It is shown via simulation results that use of such type of scheme provides an additional degree of freedom for designing the whole architecture. Specially, we have shown that we can ease the design of the loop filter in harsh environments if we have this additional degree of freedo
A novel quasi-open loop architecture for GNSS carrier recovery systems
Full text linkThe problem of designing robust systems to track global navigation satellite system (GNSS) signals in harsh environments has gained high attention. The classical closed loop architectures, such as phase locked loops, have been used for many years for tracking, but in challenging applications their design procedure becomes intricate. This paper proposes and demonstrates the use of a quasi-open loop architecture to estimate the time varying carrier frequency of GNSS signals. Simulation results show that this scheme provides an additional degree of freedom to the design of the whole architecture. In particular, this additional degree of freedom eases the design of the loop filter in harsh environment
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