Co-channel interference rejection for MIMO-OFDM systems

A method based on the maximum a posteriori probability （MAP） criterion is proposed to estimate the channel frequency response （CFR） matrix and interference- plus-noise spatial covariance matrix （SCM） for multiple input and multiple output orthogonal frequency division multiplexing （MIMO-OFDM） systems. An iterative solution is proposed to solve the MAP-based problem and an interference rejection combining （IRC） receiver is derived to suppress co-channel interference （CCI） based on the estimated CFR and SCM. Furthermore, considering the property of SCM, i. e., Hermitian and semi-definite, two schemes are proposed to improve the accuracy of SCM estimation. The first scheme is proposed to parameterize the SCM via a sum of a series of matrices in the time domain. The second scheme measures the SCM on each subcarrier as a low-rank model while the model order can be chosen through the penalized-likelihood approach. Simulation results are provided to demonstrate the effectiveness of the proposed method.

Cyclostationary Model Based Multiple-Tone Interference Rejection in DSSS Communication Systems

Multiple-tone interference is a kind of narrow band interference appears in Direct Sequence (DS) Spread Spectrum (SS) communication system frequently that degrades the system performance. Most open literature studies on narrowband interference rejection assumed stationary SS signal and interference. SS signal and interference are modeled as cyclostationary and based on cyclostationary model, an interference rejection algorithm is proposed. Through computer simulation, it is shown that the performance of the SS system can be improved considerably after adopting this algorithm.

HOS AND GA BASED INTERFERENCE REJECTION IN DS SS COMMUNICATION SYSTEMS

A new interference rejection filter based on Higher Order Statistics (HOS) and Genetic Algorithm (GA) is introduced. The advantages over the adaptive filters based on secondorder statistics or gradient algorithm are shown through computer simulation.

HOS AND GA BASED INTERFERENCE REJECTION IN DIRECT SEQUENCE SPREAD SPECTRUM COMMUNICATION SYSTEMS

A new Higher Order Statistics (HOS) and Genetic Algorithm (GA)-based interference rejection filter is introduced. Compared with the adaptive filters based on second-order statistics and gradient algorithm, the HOS and GA-based filter can reject the interference more efficiently, is independent of uncorrelated Gaussian noise, tends to converge to the optimum solution and is much less sensitive to the choice of the step size parameter. Computer simulations show that the method can reject narrowband interference efficiently.

An improved WPM interference rejection system using an adaptive LMS algorithm

Based on the good time-frequency localization of the wavelet packet modulation （WPM） system and the analysis of the muhitone （MT） interference, an improved WPM narrow band interference （NBI） rejection system using an adaptive least mean square （LMS） algorithm is discussed in this paper. In the WPM interference rejection system, according to the structure of the wavelet packet tree （WFF） and the characteristic of the MT interference, the demodulated WPM signal which contains the interference component is filtered using an adaptive LMS filtering implementation. Theoretical analysis and simulation resuits show that the proposed method improves the bit error rate （BER） performance of the WPM system in the presence of MT interference.

Rejection of Linear FM Interference in DSSS System Based on Fractional Fourier Transform

A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the receiver with an interference exciser is also presented. Based on the property that the fractional Fourier transform of a signal is equivalent to rotating the signal in the time-frequency plane, the received signal is transform into a certain fractional Fourier domain, this transform will result in the least spectrum overlap between the signal and interference. Then, a narrowband filter is exploited to extract most of the interference energy. The performance analyses show that remarkable improvements in signal-to-noise ratio (SNR) and bit-error-ratio (BER) are obtained.

Rejection of Direct Blast Interference Based on Signal Phase-Matching Array Processing

In bistaic acoustic testing, there will be strong direct blast interference. An algorithm based on signal phase-matching array processing that rejects direct blast interference in bistatic acoustic testing has been studied, through which the object scattering signal is accurately extracted. Characteristics of bistatic acoustic testing and signal phase matching processing principle are fully integrated in this algorithm. Firstly, the direct blast interference is calculated from the receiving signal based on three subarrays signal phase matching processing. Secondly, the direct blast is rejected by subtraction from the receiving signal. In this way the limitations of the high signal to noise ratio that signal phase matching processing required for direct calculating the object scattering signal can be avoided. Simulation and sea trial results show that, when the ratio of signal to interference is greater than -20 dB, this algorithm of direct blast interference rejection based phase matching signal processing can accurately extract the object scattering signal.

Low-complexity transceiver design scheme based on channel null-space feedback

To reduce the negative impact of channel quantization errors, a low-complexity transceiver joint design scheme for both the transmit beamformers and receive combining vectors is proposed in the two-user multiple-input multiple-output （MIMO） system. In the scheme, the channel nullspace quantization vector is used as the transmit beamformer of the interference user directly based on channel null-space feedback. Since the interference can be determined at the receiver, interference rejection combining （IRC） is jointly utilized to cancel the inter-user interference. Simulation re- sults show that the proposed scheme can provide substantial sum-rate improvement especially at high SNR.

Technological Research on Navigation System Interfered by Harmonic Wave

Electromagnet interference troubles are more and more and complex with each pass day along with improvement of large system electronization. This article will analyze the interference problems caused by harmonic waves in large system. The generation,characteristic and perniciousness of harmonic waves will be qualitatively analyzed for summarizing practical experience to provide mentality and method for settling the large system electromagnet interference trouble. This article raises the approach and method of harmonic suppression from the root of harmonic generation during ultrashort wave transmission and through actual test and analyzing verification. The effectivity and correctness of the methods adopted are certified by theoretical analysis and experimental verification.