Ke Hengyu

Adaptive cochannel interference suppression based on subarrays for HFSWR

The paper analyzes the characteristics of cochannel interference (CCI) in the high-frequency (HF) surface wave radar (HFSWR), which adopts the linear frequency modulated interrupted continuous wave (FMICW). CCI will influence all the range bins, including all the positive and negative frequencies, and the negative frequency range bins contain only the external interference information. Based on the above characteristics, we introduce a new adaptive coherent side-lobe cancellation (CSLC) algorithm based on subarrays that use the negative frequency range bin samples to estimate the interference covariance matrix and correlation vector. Experimental results confirm that the general and robust algorithm can achieve effective CCI suppression using the data recorded by the Ocean State Monitor and Analysis Radar (OSMAR2003, manufactured in 2003), located near Zhoushan in Zhejiang, China.The paper analyzes the characteristics of cochannel interference (CCI) in the high-frequency (HF) surface wave radar (HFSWR), which adopts the linear frequency modulated interrupted continuous wave (FMICW). CCI will influence all the range bins, including all the positive and negative frequencies, and the negative frequency range bins contain only the external interference information. Based on the above characteristics, we introduce a new adaptive coherent side-lobe cancellation (CSLC) algorithm based on subarrays that use the negative frequency range bin samples to estimate the interference covariance matrix and correlation vector. Experimental results confirm that the general and robust algorithm can achieve effective CCI suppression using the data recorded by the Ocean State Monitor and Analysis Radar (OSMAR2003, manufactured in 2003), located near Zhoushan in Zhejiang, China.

Porting from Wishbone Bus to Avalon Bus in SoC Design

Motivated by the increasing IP (intellectual property) based SoC (system-on-chips), designers have begun using an IP based SoC design methodology that permits reuse of key SoC functional components. The Wishbone bus is a common interface between IP cores, and the Avalon interface is designed to accommodate peripheral development for the SoC environment. It is necessary to port the Wishbone bus to Avalon bus when we use an IP core with a Wishbone interface in an Avalon bus system. We port the Wishbone interface I2C controller IP to Avalon bus and design a master/slave simulation model to test the Avalon bus compatible I2C controller IP core. The experimental results confirm that the Avalon bus compatible I2C controller IP works well in the Avalon based SoC.

Sporadic-E ionospheric clutter suppression in HF surface-wave radar

The unwanted radar echoes from the ionosphere are collectively called ionospheric clutter. It has proved to be the greatest impediment to achieving consistently good performance in long-range detection of surface vessels and sea state monitoring for HF surface wave radar (HFSWR). Ionospheric clutter can mask target/sea echoes having similar Doppler shifts. Main characteristics of sporadic-E ionospheric clutter (Es-layer clutter) are described. A new time domain coherent side-lobe cancellation (CSLC) algorithm based on subarrays is proposed to suppress this type of ionospheric clutter. Experimental results confirm that the general algorithm can achieve effective ionospheric clutter suppression while not decreasing the strength of the first-order sea echo using the data recorded by the OSMAR2003 (ocean state monitor and analysis radar, manufactured in 2003), located near Zhoushan in Zhejiang China.

Broad Beam HFSWR Array Calibration Using Sea Echoes

A novel technique to calibrate nonlinear array of HFSWR (HF surface wave radar) by exploiting single-DOA (direction of arrival) sea echoes only is presented. It works online to supply precise channel unmatching factors in real time without interrupting regular radar operating. The technique exhibits excellent robusticity and practicability when applied to the OSMAR (ocean state monitoring and analyzing radar) HFSWR system developed by Wuhan University

Main beam cochannel interference suppression by range adaptive processing for HFSWR

The performance of high-frequency (HF) surface wave radar degrades significantly due to cochannel interferences (CCIs) in the user-congested HF band (3-30 MHz). Most of the conventional techniques generally follow a simple spatial adaptive processing (SAP) only in the presence of spatially structured interference, but sometimes, we cannot rely on SAP to cancel interference received through the main beam. In this letter, the correlation function of CCI applied in range domain is analyzed, and a new range adaptive processing technique is utilized to suppress the CCI. Real and simulated data results are presented that the general and robust algorithm can achieve effective CCI suppression without comprising the target detection.

Super-resolution ocean surface current algorithm based on MUSIC for OSMAR2000

Owing to the decametric wavelength, a large aperture antenna array is needed for high frequency (HF) ground radar to obtain high angular resolution with conventional beam forming (CBF); for the case of a compact antenna or small aperture array, spatial super-resolution algorithms are used to get satisfactory angular resolution. Wuhan Universitys ocean state measuring and analyzing radar (OSMAR2000) is expected to real-time extract ocean surface current, wave and surface wind information at medium-range and long-range. To obtain long-range (i.e. 200 km) current mapping, the radar frequency must be selected in the lower region of the HF band, e.g. 7.5 MHz. Digital beam forming (DBF) is applied with the 120 m-long phased array to determine the bearings of the sea echo with 15/spl deg/ resolution for wave and wind extraction. The angular resolution is, however, too coarse for current mapping, especially when the ocean current detection range is as far as 200 km. Consequently, a super-resolution ocean surface current algorithm based on multiple signal classification (MUSIC) is developed for OSMAR2000. The relative theory basis, processing procedure and preprocessing and postprocessing associated with the algorithm are given. The comparison of OSMAR2000 measurements with the measurements from a current meter and the Seasonde system shows the ocean surface current algorithm based on MUSIC for OSMAR2000 can meet the requirements of the project contract successfully.

Ionospheric Clutter Suppression in HF Surface Wave Radar OSMAR

Experimental trials conducted from 2003 to 2005 in east China sea demonstrated that HF surface wave radar (HFSWR) OSMAR (ocean state monitor and analysis radar) could be strongly affected by scattering from ionospheric structures and irregularities. A large database acquired during those trials has been used in detailed investigations of the phenomenology of this ionospheric clutter, leading to the development of effective mitigation techniques based on the characteristics of ionospheric clutter. In this paper the 2-D angle of arrival of ionospheric clutter has been analyzed and the spatial adaptive processing based on 2-D antenna array is introduced to suppress ionospheric clutter. Experimental results confirm that the above technique can achieve effective ionospheric clutter suppression using the field experimental data recorded by the OSMAR2003.

Detection of the number of signals in super-resolution ocean surface current algorithm for OSMAR2000

Super-resolution ocean surface current algorithm based on MUltiple SIgnal Classification (MUSIC) is used for current mapping of Wuhan Universitys ocean state measuring and analyzing radar (OSMAR2000), in which MUSIC is applied to estimate the bearings of the first-order sea echo signals. The premise of MUSIC processing is that the number of signals is known in advance. In fact, the number of signals is unknown, and needs to be estimated from received data. In the case of discrete targets, the problem can be perfectly solved using information theoretic criteria such as the Akaike Information Criterion (AIC) or the Minimum Description Length (MDL) criterion. However, these criteria are proved unsuccessful for sea echo signals both in simulation and in actual application, since sea surface is essentially a continuum. Therefore, an ad hoc method of detection of number of signals, a bit different from the existent methods, is developed for the current algorithm of OSMAR2000. The underlying idea is to determine the number of signals based on the variance of MUSIC spectra structure under different candidate number of signals.

Scattering from Rough Surfaces Using the 'Shooting and Bouncing Rays' Technique

The “shooting and bouncing rays” (SBR) technique is used to analyze the electromagnetic scattering characters of ocean rough surfaces varying with time. Some numerical results are presented and compared with the method of moments, and some factors, such as the incident angle, polarization and frequency are investigated which influence on electromagnetic scattering characters of ocean rough surfaces.

The relationship between mutual coefficient errors and the amplitude and phase errors of channels

In general, an accurate mutual coupling correlation is necessary for an array antenna to reach ideal sideiobe level. If the mutual coefficient matrix of an array antenna is perfectly known, one can completely compensate the effect of mutual coupling and realize the desired sidelobe level in theory. However, the mutual coefficient matrix obtained wherever by calculation on by measurement has a limited precision. In this paper, the requirements on the precision of matrix coefficient for compensation in low sidelobe array antenna are discussed. The relationship between mutual coefficient errors and the amplitude and phase errors of channels is derived.