Lihua Ma

The principle of a navigation constellation composed of SIGSO communication satellites

The Chinese Area Positioning System (CAPS), a navigation system based on geostationary orbit (GEO) communication satellites, was developed in 2002 by astronomers at Chinese Academy of Sciences. Extensive positioning experiments of CAPS have been performed since 2005. On the basis of CAPS, this paper studies the principle of a navigation constellation composed of slightly inclined geostationary orbit (SIGSO) communication satellites. SIGSO satellites are derived from GEO satellites which are near the end of their operational life and operating in inclined orbits. Considering the abundant frequency resources of SIGSO satellites, multi-frequency observations could be conducted to enhance the precision of pseudorange measurements and ameliorate the positioning performance. A constellation composed of two GEO satellites and four SIGSO satellites with an inclination of 5◦ can provide service to most of the territory of China with a maximum position dilution of precision over 24 h of less than 42. With synthetic utilization of the truncated precise code and a physical augmentation factor in four frequencies, the navigation system with this constellation is expected to obtain comparable positioning performance to that of the coarse acquisition code of the Global Positioning System (GPS). When the new method of code-carrier phase combinations is adopted, the system has the potential to possess commensurate accuracy with the precise code in GPS. Additionally, the copious frequency resources can also be used to develop new anti-interference techniques and integrate navigation and communication.

The Distributions of HDOP and VDOP in GNSS and a Corresponding New Algorithm of Fast Selecting Satellites

In Global Navigation Satellite System (GNSS), the accuracy of position estimates depends upon the measurement geometry and pseudorange measurement errors. The Dilution of Precision (DOP) provides a simple characterization of the user-satellite geometry. An in-depth study of DOP distribution characteristics is conducted in this paper, with emphasis on performance bounds of Horizontal Dilution of Precision (HDOP) and Vertical Dilution of Precision (VDOP) for four satellites in varied hypothetical constellations. The distributions of HDOP and VDOP in 16 major world cities are analyzed by simulated calculations using the TLE sets of GPS satellites. According to the theoretical analyses about the distributions of HDOP and VDOP, this paper also proposes a new algorithm of fast selecting satellites based on HDOP and VDOP, which requires a shorter computing time than the general method and provides a feasible way to quickly achieve a high-accuracy positioning.

Conical beam monopole antenna design for Chinese area positioning system

This article describes the operational principle of the satellite-based Chinese Area Positioning System (CAPS) and proposes a monopole antenna for a large anchored buoy platform in harshmarine environment. The proposed antenna is highly omnidirectional with sufficiently wide half-power beamwidth (HPBW) greater than 40° (i.e., not less than ±20° swing) by using a conical ground plane, taking into account the geostationary satellite position, link budget, sea conditions, volume and cost. The impedance bandwidth defined by 10 dB return loss is 750 MHz (5.60–6.35 GHz), and the main lobe direction and the half-power beamwidth are about 46° and 43° at the operating frequency 5.885 GHz, respectively. The antenna prototype has been installed on-site to test its performance in sea. The results confirm that the proposed antenna is a suitable candidate for a variety of CAPS applications in China.

Study of Ranging Using Dual Orthogonal Linear Polarized Antenna in Chinese Area Positioning System

The constellation for Chinese Area Positioning System (CAPS) consists of commercial communication satellites in the geosynchronous orbit. CAPS signals afford 3 dB polarization loss, since they are transmitted between linear polarized antenna of communication satellites and circular polarization antennas of receivers. In order to reduce the signal power loss, the receivers adopts a dual orthogonal linear polarized antenna to acquire signals from all directions with almost full power. In the current work, a method is proposed based on weighted combination of two pseudoranges measured by the dual orthogonal linear polarized antenna. The theoretical and simulation analysis show that this method improves the CAPS ranging precision approximately to that of signal with full power. Compared with 3 dB polarization loss of circular polarized antenna, this method is equivalent to 2.7 dB compensation for signal carrier to noise ratio. By applying the method to the experimental measured pseudoranges of the dual orthogonal linear polarized antenna, the precision of pseudorange is remarkably improved.