Wan Xianrong

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.

Sample rate conversion using Walsh-transform for radar receiver

Current SRC methods can consume a large fraction of the digital signal processor resources leaving limited computational power for other tasks. Reducing the computational requirements for SRC is a key element for the success and profitability of SWR systems. An efficient decimation architecture using Walsh transform for HF surface wave radar receivers is presented. The proposed takes into consideration the complexities of algorithm due to the relatively high data rate and the intensive filter operations involved in commonly used decimators, which substitute multiplication-addition for addition-subtraction imposed on filter. Performances illustrative are compared with that of other similar decimators. Experiments results show that the new decimators outperform others, which is suited for real time signal processing in DSP, such as ADSP2 1060.

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.

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.

Range sidelobes suppression for HF surface wave radar with discontinuous spectra

In order to improve the anti-interference performance, the high-frequency surface wave radar uses several discontinuous clear frequency bands for transmission. Spectral discontinuity causes high range sidelobes which influence detecting and identifying the targets. A novel modified CLEAN algorithm is proposed to remove the sidelobes interferences of the equivalent matched processing result of the received signals. The simulation results show that the method can not only suppress the range sidelobes efficiently but also enhance the range resolution greatly.

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.

Suppression of Ionospheric Es Clutter in HFSWR

Ionospheric clutters from sporadic E-layer are often observed in 200 km-coverage HFSWR. One kind of the Es-layer clutters is found to have coherent time much longer than that of sea echoes. The feature is exploited in the proposal of a new algorithm to suppress this kind of clutter based on eigen value decomposition and subspace projection

FPGA implementation of digital IF processing in HFGWR

Software radio has become the focus of research in communication. Radar based on software radio technology overcomes the simplicity and inflexibility of conventional radar. Digital IF, one of its key technologies, is a typical application of multirate signal processing theory. The paper studies the high decimation ratio of the digital downconverter in HF ground wave radar (HFGWR), and especially analyzes a multistage decimation algorithm based on a CIC (cascaded integrator-comb) filter and an HB (half-band) filter. By comparison, the optimal design can save 92.6% of the logic resources over that of a single stage polyphase design, and can be well implemented in a single FPGA chip (such as XC2S200) for four receiver channels. Furthermore, the filtering performance is better than design requirements.

Adaptive radio frequency interference mitigation for HF surface wave radar

The paper analyses the characteristics of radio frequency interference (RFI) in HF surface wave radar (HF-SWR) which adopts the linear frequency modulated interrupted continuous wave (FMICW). RFI will influence all the range cells including all the positive frequency and negative frequency, and the negative frequency range cells contain only the interference information. Based on the above characteristics, we introduce and analyze a new adaptive interference mitigation beamforming algorithm using the negative frequency range cells samples to estimate the interference covariance matrix. Experimental results confirm that this general and robust algorithm can achieve effective RFI suppression using the data recorded by the HFSWR, located near Zhoushan in Zhejiang China.

Optimal design of digital IF processing in HFGWR

Software radio has become the focus of research in communication. Radar based on software radio technology overcomes the simplification and inflexibility of conventional radar. Digital IF, one of its key technologies, is a typical application of multi-rate signal processing theory. The paper studies the high decimation ratio of the digital downconverter in HF ground wave radar (HFGWR), and especially analyzes a multi-stage decimation algorithm based on CIC (cascaded integrator-comb) filter and HB (half-band) filter. In comparison with the single stage polyphase design, the optimal design can save 92.6% of the logic resources, and it can be well implemented in one DSP chip (such as ADSP21062) for four receiver channels. Furthermore, the filtering performance is better than the design requirements.