Zhengyu Zhao

Design and implementation of hardware architecture in ionospheric oblique backscattering sounding system

The ionospheric oblique backscattering sounding system can not only be used to detect the state of ionosphere and the condition of high frequency channel in real time, but also be used for over-the-horizon sounding. So, it has a very high military and civil value. For the characteristics of ionospheric oblique backscattering sounding, such as long sounding distance, wake echo, strong background noise, slow moving target, etc., a hardware platform of ionospheric oblique backscattering sounding system is designed. This platform adopts the technology of software radio and is designed as a new kind of general-purpose, modularized, software-based ionosonde that is based on VXI (Versa module eurocard eXtensions for Instrumentation) bus. At present, this hardware platform has been successfully used in actual ionospheric oblique backscattering sounding, and the experimental results demonstrate that this system can satisfy the demands of ionospheric oblique backscattering sounding preferably.

A new location precision model for multi-static over-the-horizon radar system

In this paper, a multi-static system working in an active way is made up of ionospheric oblique backscatter sounding system (IOBSS) and two separate receiving stations, which adopts discontinuous wave mechanism. We have advanced a new model that contains skywave condition to locate over-the-horizon targets. We use a single quasi-parabolic (QP) ionosphere model and an analytic ray-tracing program to obtain the coordinate registration (CR) index, which changes skywave group range to ground range. Also, IOBSS and other two receiving stations use this distance information to locate the target which is far away from the system. The analytic expression for the geometric dilution of precision (GDOP) under different station deployments are obtained, which shows GDOP is influenced by the system measurement precision, the stations’ coordinates, and CR index. By computer simulation, we find that GDOP of isosceles right triangle deployment is smaller than that of line deployment and location precision will be improved with increasing base line length. The results indicate that this model is practicable with an acceptable range of error (less than 500 m under certain conditions in this paper).

An improved algorithm for blind carrier frequency estimation with burst MPSK transmissions

This paper presents an improved non-data-aided algorithm for carrier frequency estimation for burst M-ary PSK signals when modulation order M and training symbols are unknown. Unlike data-aided estimation, a phase clustering algorithm is used first to estimate M and modulated information is removed by a variable interval linear phase unwrapping. Then, a high-order correlation algorithm with proper correction is present, which reduces the probability of phase ambiguity and promotes anti-noise capability of the estimation. Simulations are given to analyze the unbiased estimation range, and the asymptotic performance and symbol number are needed to compare with the former algorithms. The new algorithm has a large estimation range close to the theoretical maximum value for non-data-aided estimation and has a better performance than earlier non-data-aided techniques for large frequency offset, low signal-to-noise ratio, and limited symbol numbers.

Radio wave propagation effects produced by chemical releases in the ionosphere

As an effective means to actively modify the ionosphere, chemical release can produce artificial ionospheric holes as a consequence of ionization depletion, which can greatly impact on radio wave propagation. In this paper, on the basis of the pre-study results on ionospheric disturbances produced by some representative chemical releases, the radio waves propagation effects of ionospheric holes that are produced by two different release species, water (H2O) and sulfur hexafluoride (SF6), had been investigated and simulated by the three-dimensional (3-D) numerical ray tracing. The results show that ➀ the appearance of various artificial ionospheric holes can lead to certain decrease of critical frequency in the ionosphere, and ➁ when the wave frequency exceeds the critical frequency, the rays should be multiple reflections or penetrate through the ionospheric hole and focus afterwards with the focus altitude elevated for higher frequencies. This work may provide the necessary theoretical support for chemical release experiments and the evaluation of radio wave propagation effects.

Design of the signal processor for an ionospheric sounding system

On the basis of the analysis of the system sounding principle, this paper introduced a new type of ionospheric oblique backscattering sound system, which is based on the pseudo- random noise phase modulated pulse compression. According to the high requirements of real-time and a large amount of computation and echo characteristics, a high-speed real-time signal processing system was established and the design of system hardware and software was focused on. The sounding results indicate that the system is equipped to handle the data fast and has a high degree of software features. It is of great significance for the realization of fast, real-time ionospheric sounding means.

Analysis and correction for systematic error of ionospheric monostatic system

In the ionospheric monostatic system the echo is affected by systematic error. A real-time method using the special characters of direct wave existing in monostatic radar to correct systematic error is advanced. In the condition of large-amplitude direct wave, time delay of maximum amplitude of echo is considered as system time delay; in the condition of small-amplitude direct wave, the mathematical model of time delay error is built to approach after direct wave test. And a method using large-amplitude direct wave to correct phase distortion is advanced. It achieves good effect using this method in practice, which can improve the quality of sound result obviously.