Tung Hai Ta

Partial Differential Postcorrelation Processing for GPS L2C Signal Acquisition

L2C is the second civilian signal introduced on the modernized block of GPS satellites. The two PRN sequences employed in L2C, named civil moderate (CM) and civil long (CL), have periods of 20 ms and 1.5 s, respectively. Stemming from the fact that using a full code period (CM or CL) for signal acquisition in GPS L2C receivers might not be necessary in normal situations (e.g. outdoor, light indoor, etc.), in this paper, we introduce a partial acquisition architecture using specially-designed matched filters (MFs) in order to relieve the computational complexity of the acquisition stage. The partial correlation loss is compensated by differential postcorrelation techniques. Three techniques, namely conventional differential combination (CDC), generalized differential combination (GDC), and modified generalized differential combination (MGDC), are investigated in terms of detection probabilities and mean acquisition time leading to the selection of MGDC as the most suitable technique for the L2C partial acquisition. By using this technique, a 2-dB sensitivity improvement with respect to the conventional noncoherent combination and a 94.5% reduction in mean acquisition time in comparison with the full code acquisition are shown for 1-ms partial correlation.

Development of real multi-GNSS positioning solutions and performance analyses

Till recently, for civil users worldwide, GPS was the only Global Navigation Satellite System (GNSS) for positioning purposes. However, the return of GLONASS as well as the appearance of Galileo and Beidou has brought many modern and advanced positioning services to the world. More importantly, the combinations of these systems in common multi-GNSS solutions promise much improvement in accuracy, availability and reliability of the positioning. This paper presents research works on development of multi-GNSS positioning solutions working with real signals collected from the recently launched satellites of the new Galileo and Beidou systems. The result analyses prove not only the readiness of the developed multi-GNSS solutions but also their real advantages over the stand-alone solutions.

Significance of Cell-Correlation Phenomenon in GNSS Matched Filter Acquisition Engines

Modern Global Navigation Satellite Systems (GNSS) are going to provide new signals with longer PRN codes and higher chipping rates, which aim to improve the positioning performance with respect to the current GPS. However, these new characteristics also cost GNSS receivers a high computational complexity. Due to their attractive acquisition time performance, matched filter (MF) correlators promise to be a good choice for GNSS signal acquisition engines. Existing methods to evaluate GNSS signal acquisition engine performance parameters, viz. detection probabilities and mean acquisition time, assume that the detections among the neighboring test cells are independent. However in a matched filter correlator, depending on the spacing between the test cells, due to the correlation of the local code with the noise component in the received signal at different time instances within a chip period, there can exist strong correlations, which affect these performance parameters. Also, the presence of cell correlations influences the acquisition threshold setting, which is a critical design parameter. This paper provides a detailed analysis of the significance of the cell-correlation phenomenon in MF correlators for the two widely used signal families in GNSS, namely BPSK and BOC, in particular BPSK(1) and BOC(1,1). Justifying the theoretical analysis with Monte Carlo simulations, it is shown that the maximum error in estimating the mean acquisition time without considering the cell-correlation phenomenon is shown to be about 10% for the BPSK(1) and about 12% for the BOC(1,1) signal.

Combined GPS L1C/A and L2C signal acquisition architectures leveraging differential combination

The GPS modernization program offers a new civil signal on the L2 band, which, together with the legacy L1 C/A signal, spurs the development of dual-frequency receivers for civil applications. This paper proposes a complete combined acquisition architecture dedicated to these receivers. The architecture fully utilizes the capacity of both signal channels as well as the advantages of differential signal processing. High detection sensitivity, finer parameter estimation, built-in bit synchronization mechanism, and acquisition-to-tracking transient time reduction are the advantages of the proposed architecture with respect to others in the literature.

Recent results in receiving and decoding signals from the Beidou system

Since December 27, 2012, the Beidou Navigation Satellite System officially started to operate. This event is a great opportunity for researchers in South East of Asia to receive and analyze the Beidou signals. After the official statement, the researchers at NAVIS centre monitored the broadcasted signal by using NAVISOFT- our Software Radio Receiver. This paper shows the analysis on the navigation message that was broadcasted by the Beidou satellites on the B1I bandwidth. In general, we were able to observe a valid ephemeris data on visible satellites. The successful PVT computation by using combinations of GEO and MEO/IGSO in static condition through code-phase measurements is indicated in this paper.

A differential joint data/pilot strategy for high sensitivity Galileo E1 signal acquisition

Global navigation satellite systems (GNSS) with the ability to provide accurate positioning and timing information have become very important for many essential applications of both military and civil purposes. Toward the objective of a high sensitivity GNSS receiver architecture capable of operating anywhere at anytime, this paper introduce a new acquisition strategy to adapt with the problem of low received signal power in indoor environments. The strategy combines the proved advantages coming from joint data/pilot acquisition strategies and differential integration technique to further improve the robustness of the acquisition process. Analytical expressions as well as Monte Carlo simulations in indoor scenarios are presented to describe and prove the strategy improvement with respect to other strategies in literatures.

A novel signal acquisition method for GPS dual-frequency L1 C/A and L2C receivers

Together with the 30-year-old signal L1 C/A, the new signal L2C, offered by the modernized GPS program, assures a future for civil GPS dual-frequency receivers which propose a better performance than the current single-frequency ones. This paper introduces a novel combined acquisition method dedicated to the GPS dual-frequency L1 C/A and L2C receivers. The method exploits the capacity of both the signal channels as well as the advantages of differential signal processing. High detection sensitivity at a reasonable complexity is the main advantage of the proposed method with respect to others in literature.

A robust acquisition architecture for GPS safety-of-life L5 Signal

The new GPS L5 signal with advanced characteristics in the signal structure is dedicated for safety-of-life applications that have strict requirements on accuracy, availability and integrity. To cope with this new signal, GPS receivers need to be upgraded with new signal processing blocks. This paper presents a robust acquisition architecture suitable for the L5 signal. The architecture can be considered as a combination of the Cross Ambiguity Function based; the energy-based; and the multiple channel acquisition methods.

A novel method for estimating residual carrier frequency offset in GPS L2C receivers

In a GPS receiver, the residual carrier frequency offset, which is the difference between the frequency estimated by the signal acquisition stage and the received one, cannot be neglected. This residual causes the receiver sensitivity loss and also the longer transient time from acquisition to tracking in the synchronization process. This paper proposes a novel estimation method for estimating this residual in GPS receivers working with the new L2C signal. The method utilizes the nature of advance differential signal processing, which is proved to be suitable with L2C signal acquisition, to produce reliable estimations with smaller bias and standard deviation values in comparison with the conventional method in literature.

Design and validation of a flexible software-based generator of realistic GNSS signals

N-FUELS (FUll Educational Library of Signals for Navigation) is a software-based generator of Global Navigation Satellite System (GNSS) signals [1]. One of the most relevant aspects of N-FUELS can be individuated in its versatility, being a collection of MATLAB® modules. This paper introduces a new module of N-FUELS suitable to simulate realistic GNSS signals from multiple satellites, with plausible code delays and Doppler frequency shifts. With the new module, N-FUELS can reproduce GNSS signals as received by both static and dynamic users. The work done to upgrade the software is described in the paper together with some examples of possible applications of the new version of the tool.