Hardware Architecture for Acquisition in IRNSS Receiver using Serial Search Method

Indian regional navigation satellite system (IRNSS) is a navigation system developed by the Indian Space Research Organisation (ISRO), India. The IRNSS receiver granted by Space Application Centre (SAC), ISRO, Ahmedabad is installed at SVNIT, Surat, India. A solar flare is a natural event that occurs when an unpredicted flash of distended Sun's illumination is observed near its surface. The ionosphere is greatly ionised by solar radiations. Hence it is a current challenge to investigate effects of ionospheric scintillation on IRNSS signals. This study examines impact of major solar flare events like Class ‘C’ solar flare happened on 22 July 2016 and class ‘M’ solar flare occurred on 23 and 24 July 2016, on IRNSS signals with measurement of total electron content (TEC). Real-time ionospheric scintillation monitoring (RTISM) model based on empirical mode decomposition (EMD) and second-order Daubechies (db2) wavelet is used for comparing measured and denoised TEC. The RTISM model is also used for determining automatic threshold using Neyman–Pearson detector, probability of detection and probability of false alarm. It is proven with analysis that EMD is giving more sharp results as compared to db2 wavelet for determining fluctuations in TEC during the solar flare events.

Indoor navigation has become increasingly important for various applications such as emergency services and consumer devices. The performance of Indian Regional Navigation Satellite System (IRNSS) receiver degrades in indoor environment due to attenuation of signal levels in addition to ionospheric scintillations. For indoor navigation applications such as position finding in a multi-story building, the effect of scintillation may result in the loss of lock signal rather than reduced accuracy. The objective of this paper is to investigate the effect of ionospheric scintillations on IRNSS receiver performance for indoor navigation by estimating the receiver phase lock loop (PLL) and Delay locked loop (DLL) tracking error variance iitter). Our initial results indicate that severe scintillation could cause loss of lock.

The Indian Regional Navigational Satellite System (IRNSS) satellites provide two services namely standard Positioning Service (SPS) and Restricted Service (RS). L5 and S are the frequency bands from which both the services are utilized. To transmit the navigational information in SPS downlink gold codes are used. Most of the GNSS will work on the principle of CDMA where PRN sequences are the heart of the system. In this paper Pseudo Random Noise (PRN) codes are generated for an SPS signal which is called as SPS PRN code. A CDMA signal is generated using these sequences by using BPSK modulation. The analysis is done based on a time domain signal basis and is used to derive the Power Spectral Density of a CDMA signal. The spectrum analyser optimal operating conditions are observed by using the analytical results. To generate these codes, the polynomials Gl & G2 are selected, which are similar to ones used by GPS C/ A signal and are as per the preconditions provided in IRNSS_SPS_ICD_June 2014. This paper also covers the process of selection of codes to be computed and the properties of PN-sequence are also analysed. The Xilinx ISE test system and Mat lab apparatus were used for the simulation of SPS PRN codes and additionally the implementation of PRN code is done on FPGA hardware wherein positive results have been obtained. These obtained simulated test results are within the theoretical limits.

The Indian Regional Navigation Satellite System (IRNSS), also known as NavIC- Navigation with Indian Constellation provides real time positioning and timing services. The NavIC receivers provide information related to both satellite and receiver. There are multiple algorithms which can be used for position estimations. In this paper, Iterative Least Squares and Extended Kalman Filter algorithms are proposed to estimate the unknown receiver position by taking clock bias of the receiver into consideration.

Navigation with Indian Constellation (NavIC), also known as Indian Regional Navigation Satellite System (IRNSS), is the Indian regional satellite navigation system. NavIC relies on a vast network of one-way ranging reference stations for its precise orbit determination and time synchronisation (OD&TS) functions. These reference stations are equipped with reference receivers which act as measurement engines and provide the raw code and carrier phase measurements to the OD&TS process. NavIC provides navigation services in two Radio Frequency (RF) bands, namely L5 and S. L5 band, centred at 1176.45 MHz is susceptible to pulsed interference from Distance Measuring Equipment used for civil aviation. ISTRAC is currently undertaking the development of an indigenous tri band reference receiver for the one way ranging stations of the NavIC ground segment. An asynchronous Pulse Blanker has been implemented for the in-house NavIC Tri-band Reference receiver for the detection and mitigation of the pulsed interference in L5. Furthermore, implementation of digital pulse blanking has been designed to be independent of the RF band and thus can provide benefits to NavIC receivers operating at frequencies other than L5, i.e. S with its known dense interference environment.

Integrals that are of interest in the analysis, design, and optimization of concentrating solar thermal systems (CST), such as the annual optical efficiency of the light collection and concentration (LCC) subsystem, can be accurately computed or estimated in two distinct ways: on the time domain and on the spatial domain. This article explores these two ways, using a case study that is highly representative of the commercial CST systems being deployed worldwide. In the time domain, the computation of these integrals are explored using 1-min, 10-min, and 1-h solar DNI input data and using The Cyprus Institute (CyI)’s High-Performance Computing (HPC) system and an open-source ray tracer, Tonatiuh++, being actively developed at CyI. In the spatial domain, the computation of these integrals is explored using SunPATH, another open-source software tool being actively developed at CyI, in tandem with Tonatiuh++. The comparison between the time and spatial domain approach clearly indicate that the spatial domain approach using SunPATH is dramatically more computationally efficient than the time domain approach. According to the results obtained, at least for the case study analyzed in this article, to compute the annual energy delivered by the LCC subsystem with a relative error less than 0.1%, it is enough to provide SunPATH with 1-h DNI data as input, request from SunPATH the sun position and weights of just 30 points in the celestial sphere, and run Tonatiuh++ to simulate these 30 points using 15 million rays per run. As the test case is highly representative, it is expected that this approach will yield similar results for most CST systems of interest.

There are three signal acquisition approaches mainly: the serial search algorithm, circular correlation and the delay-and-multiply approach. The serial search algorithm searches for a satellite sequentially at each possible code delay and Doppler shift in time domain. Because only addition and multiplication operations are needed, it is easy to implement in time domain. This approach has been extensive applications. Because the serial search algorithm has to do much glide correlation in a real GPS receiver, this exhausting correlation also tends to be the main weakness of the serial search acquisition. To overcome the shortage of the serial search algorithm, the objective of the study is to shorten the amount of correlation, and a new method is given. It can decrease the amount acquisition time efficient. If this method is implemented in civil GPS receivers, the serial search algorithm will become more feasible and popular. The method aim at not only the GPS coarse code, but also the method of research is suitable for other CDMA systems.

The Steel Catenary Riser (SCR) concept offers advantages over other riser concepts and has been widely deployed worldwide. The first deepwater SCR was installed in the Gulf of Mexico in 1994. Since then, more than 100 SCRs have been installed for many types of deepwater floaters (Spars, TLPs, SEMIs, and FPSOs) in the deepwater fields of West of Africa, the Gulf of Mexico (GoM), and Offshore Brazil. As the second of two companion papers, this paper presents the state-of-the-art of key analysis techniques of deepwater SCRs while the first paper addresses the design methodology [R. Song, P. Stanton, Ref. 4]. First of all, the procedure for analysis of deepwater SCRs is discussed and presented in more detail than given in the first paper and is also illustrated in an analysis flowchart. Wave theory applicable to deepwater SCR analysis and time domain vs. frequency domain analysis approaches are described and discussed. More focus is given to the strength analysis including discussion and comparison of regular wave and random wave approaches. Attention is paid to the vortex induced vibration (VIV) analysis including discussion of modal response analysis and VIV parameter selections. For SCRs on semisubmersibles and FPSOs, vessel heave-induced VIV needs to be taken into account, and a corresponding time-domain approach is presented. Similarly, for Spars and deep draft semisubmersibles, vortex-induced motion (VIM) fatigue damage of SCRs is discussed in more detail. Particular attention is also given to the analysis of SCR compression in the touch-down zone (TDZ) and corresponding acceptance criteria are presented. The application of fracture mechanics to engineering criticality assessment (ECA) is explored. Two examples of deepwater SCRs corresponding to a semi and a Spar are given to illustrate the presented methodology.

Third order time and frequency analysis has exhibited great potential for correlation analysis of multi-sensor datasets, but is usually presented as separate time domain and frequency domain approaches. A combined framework of both frequency domain and time domain has rarely been used. This paper proposes a non-parametric third order time and frequency domain framework which used two dimensional Fourier transforms to bridge the gap between time domain and frequency domain. A unified framework offers flexibility and efficiency to apply to data. In this paper we study neural spike train data treated as stochastic point processes. In time domain direct analysis, third order cumulant densities of spike trains are applied, which need all first-, secondand third order product densities to be calculated before constructing the third order cumulant density, which brings additional challenges. The novelty in this study is that a new framework is proposed which can offer an alternative approach without calculating lower order quantities and can reveal nonlinear relationship between neural recordings. The results show that the present framework provides a novel non-parametric method to estimate both time and frequency domain measurements which is applicable to neural spike trains.

By using the direct approach to the analysis of the serial-search spread-spectrum code acquisition, the author presents the approximate analysis of the cumulative probability density function (CDF) of the acquisition time. This approach is based on the binomial approximation to the distribution of the partial acquisition times, instead of the Gaussian one used previously. The binomial approximation gives very accurate results but, more importantly, it shows that the analysis of the arbitrary detection/verification scheme can be reduced to the much simpler analysis of the equivalent single-dwell system, whose parameters depend only on the mean test times and not on their distribution. Based on the exact results, simple closed-form approximations are derived for the CDF in the case of the straight-line serial search with uniform a priori distribution, which might be useful in practice.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The use of ultrawide bandwidth (UWB) signals requires highly accurate timing, and, hence, presents significant challenges from the standpoint of acquisition receiver design. Improving the acquisition performance is important, especially for time-critical applications that cannot tolerate long processing delay. This paper deals with the design and analysis of UWB rapid acquisition receivers. In particular, we consider serial-search strategies that employ a multi-dwell detector with optimal thresholds. Specific contributions include derivation of lower and upper bounds on the asymptotic mean acquisition times for both the conventional and the optimal serial search strategies. The bounds serve as ultimate performance limits of acquisition receivers that operate in high and low signal-to-noise ratio regimes. We propose a search strategy that is near-optimal in these asymptotic regimes. The results in this paper are valid for environments with arbitrary power dispersion profiles, provided that some mild assumptions about the channel and the receiver design are satisfied.

There are mainly three well-known techniques to acquire a GNSS signal. The first, called Serial Search Acquisition, consist in correlating the Pseudo-Random Noise (PRN) codes for all the codes phases and all the frequency bins. The two others make use of the Fourier Transform in order to parallelize the search, either in the frequency space (Parallel Frequency Space Search Acquisition) or in the code space (Parallel Code Space Search Acquisition). The last two methods make parallelization inherently, but it is also possible to make parallelization with the first method by using multiple correlators testing several code phases at the same time. This paper provides an assessment of the resources required for each method, in terms of circuit, memory and processing power for the case of a hardware based receiver implemented into a FPGA. The associated performances are also provided and compared. The study is based on GPS L1 signal, but the methodology can easily be applied to others GNSS signals.

Recently, digital Intermediate Frequency (IF) waveform generators and receivers are introduced in modern radar systems to reduce the cost, size, and achieve better performance. Moreover, digital IF waveform generators achieve the requirements of high resolution and complex modulation schemes. Digital receivers have better sensitivity, wider dynamic range and lower noise Figure than analog receivers. Digital IF waveform generators and receivers work well in conjunction with a high-speed Analog to Digital Converters (ADC) and Digital to Analog Converters (DAC). In this paper, the design and implementation of high-speed data acquisition circuits (ADC and DAC) to generate and acquire IF waveforms are presented. Different modulated waveforms are generated digitally using Field Programmable Gate Array (FPGA). The corresponding digital receiver, including digital phase detection and matched filtering, is designed and implemented on the same FPGA chip. Design and implementation of a Printed Circuit Board (PCB) including FPGA chip and its required circuitry are introduced. The proposed design is simulated using Computer-Aided Design (CAD) tools and verified experimentally through laboratory testing.

A formulation of simultaneous optimization a passively damped structure and active controller has been attempted. In this study, viscoelastic materials (VEMs) have been utilized as one of device to enhance damping passively. The formulation needs to adopt the modeling method that is capable of designing not only the viscous passive damping but also the active controller adequately. For such requirement, the time domain approach that results the accurate model on the time domain is employed for the modeling of the viscoelastic structures. In order to create the reduced order model (ROM) for system design, the complex modal analysis has been developed, and the ROM is obtained with using both truncation and the balanced realization method. The accuracy of the ROM has been investigated based on a cantilevered partially viscoelastic beam example. The numerical results indicate that the time domain approach is more appropriate than the modal strain energy (MSE) method for creation of the ROM. Moreover, the strategy to derive the ROM is included into the formulation of simultaneous optimization of a viscoelastic structure and active controller. The formulation is applied to the design of a sandwich beam like space structure. The optimization results indicate that the optimization of viscous passive damping is useful for the total system cost reduction.

The floating bridge bears the dead weight and live load with buoyancy, and has wide application prospect in deep-water transportation infrastructure. The structural analysis of floating bridge is challenging due to the complicated fluid-solid coupling effects of wind and wave. In this research, a novel time domain approach combining dynamic finite element method and state-space model (SSM) is established for the refined analysis of floating bridges. The dynamic coupled effects induced by wave excitation load, radiation load and buffeting load are carefully simulated. High-precision fitted SSMs for pontoons are established to enhance the calculation efficiency of hydrodynamic radiation forces in time domain. The dispersion relation is also introduced in the analysis model to appropriately consider the phase differences of wave loads on pontoons. The proposed approach is then employed to simulate the dynamic responses of a scaled floating bridge model which has been tested under real wind and wave loads in laboratory. The numerical results are found to agree well with the test data regarding the structural responses of floating bridge under the considered environmental conditions. The proposed time domain approach is considered to be accurate and effective in simulating the structural behaviors of floating bridge under typical environmental conditions.