Pertti Henttu

Consecutive mean excision algorithm

A new adaptive excision algorithm called consecutive mean excision (CME) is presented. The CME algorithm separates iteratively the initial set of samples to two sets: outlier set and desired signal set. The initial threshold parameter required by the CME algorithm is calculated in advance based on statistical properties of the noninterfered signal. The same initial threshold parameter is shown to operate in various interference scenarios regardless of interference power and bandwidth. In this study the CME algorithm is attached to the adaptive FFT notch filter. The performance of the adaptive FFT CME notch filter is shown to overcome the basic adaptive FFT notch filter using the single mean or single median approach in various interference scenarios when attached to direct sequence communications systems.

Iterative multidimensional impulse detectors for communications based on the classical diagnostic methods

This letter introduces diagnostic impulse-detection methods in general, and, based on those, presents three iterative impulse detectors for communication receivers with an antenna array. These detectors are implemented either in a backward or forward search mode. The forward methods are shown to perform better. They can detect all the impulses, even though 90% of all the samples are corrupted.

Impulse detection and rejection methods for radio systems

Impulses that exist in the nature or are artificial may severely decrease the performance of any radio system including communication and interception receivers and radars. This paper investigates impulse detection in receivers that can have either a single antenna or an antenna array. The proposed detector uses either a backward or forward outlier search strategy and assumes zero mean signals and spatially and temporally white background noise. Signal need not to be weak, i.e., signal-to-noise ratio may be large and the methods still works. The backward method uses all the data in an initial step whereas the forward method uses smaller, (hopefully) clean set in an initial step. The forward method is expected to perform better. Simulations confirm this expectation. Indeed, the used forward method can detect outliers even if their contamination exceeds 90% of all the samples.

Transform-selective interference suppression algorithm for spread-spectrum communications

An adaptive method for suppressing interference with an unknown model is presented. The method is based on computation of several transforms in parallel and selecting the most suitable one depending on a priori unknown the interference type based on a compression gain (CG) metric, which is related to the interference concentration in the transform domain. It is also possible to estimate the a priori parameters required by some transforms. The method can be expanded to utilize an arbitrary number of transforms. It is shown through computer simulations that the CG is a good metric for choosing the proper domain for interference excision.

Method selection diversity approach to interference suppression

The interference suppression problem has introduced a large variety of suppression algorithms. A large majority of cases, the proposed algorithms are targeted against a specific type of interference and fail to suppress other types of interfering signals. We propose a SINR estimator based method to select between several relatively simple interference suppression methods to overcome this problem. We combine three suppression algorithms, namely CME-notch-, RLS- and polar-suppression filters. The approach is to use a DPSK-modulated hybrid direct sequence (DS) frequency hopping (FH) system model, but the suppression method is also applicable to pure DS-systems or MC-CDMA-systems. The performance results show that this approach has the capability of operating under a wide range of interference parameters.

A new interference suppression algorithm against broadband constant envelope interference

A new interference suppression method namely the polar exciser (PE) is proposed. We have simulated the BER performance of a direct sequence (DS) system with PE interference suppressor added in an environment where a strong broadband constant envelope interference perturbs the desired DS signal detection. Interference scenarios included are constant envelope BPSK, constant envelope FSK and sweeping interference.

Narrowband main beam interference mitigation algorithms for space-time adaptive processing

We investigate space-time adaptive processing (STAP) algorithms that can mitigate narrowband main beam interference. It will be shown, through simulations for direct sequence code phase estimation, that only a form of three possible Capon beamformer implementations can do the required mitigation. Alternatively, a novel time coherent combining beamformer can be used. Both algorithms have to function in a single sample per symbol or chip mode in order to avoid mutual correlation that decreases the performance.

Effective interference suppression using short overlapping regions of data and SVD

The interference suppression (IS) capability of a frequency hopping spread spectrum communication system can be increased by using additional IS algorithms. In this paper a new interference suppression algorithm called short overlapping singular value decomposition (SOSVD) is described. Many of the existing blind IS algorithms perform unsatisfactorily when interference is wideband. It is shown by simulations that the performance of the proposed SOSVD method clearly exceeds the performance of the blind recursive least squares (RLS) directed interpolation filter in a wideband interference environment. The computational complexity of the proposed method is tolerable because the size of the SVD input matrix is small and constant.

Interference suppression in DS/FH system using modified two sided adaptive filter

The detection properties of a modified two sided RLS (recursive least squares) adaptive filter is considered. The basic RLS whitening interpolation filter is modified by applying the Huber m-estimation principle. Two types of modified whitening interpolation filters are presented. The detection capability of the basic version and two modified versions are investigated through simulations in a nonstationary interference environment. Simulation results indicate that the detection performance of the filter is increased remarkably by the modifications.

Cyclic SVD method for broadband interference cancellation in FH/DS communications

A new method, called cyclic singular value decomposition (CSVD), for broadband interference cancellation is presented. CSVD method is a combination of intercept receiver and SVD based interference suppressor. CSVD utilizes the cyclostationary nature of many man-made interfering signals. In this paper the CSVD inteference suppressor is added to a FH/DS spread spectrum communication system simulation model and simulation results are presented. The interference scenario used is digitally modulated BPSK interference.