Interference Suppression Performance Research Articles

Blind Multiple Access Interference Suppression Algorithm Based on Relaxed Subgradient Projection for DS/CDMA Systems

A novel blind multiple access interference suppression algorithm based on relaxed parallel subgradient projection is proposed for DS/CDMA systems. The qualification “relaxed” is manifest in two aspects: first, the new expression for updating the interference suppression filter coefficients vector relaxes paralleled projection fields and reduces computation complexity. In addition, the relaxation parameter in the updated process is adaptively determined to guarantee the interference suppression filter coefficients vector falling into fields containing the optimal filter coefficients vector after several iterations. Theoretical analysis and simulation results conclude that this algorithm has a fast convergence speed, steady interference suppression performance, low computation and low bit error rate.

Target detection and parameter estimation for MIMO radar systems

We investigate several target detection and parameter estimation techniques for a multiple-input multiple-output (MIMO) radar system. By transmitting independent waveforms via different antennas, the echoes due to targets at different locations are linearly independent of each other, which allows the direct application of many data-dependent beamforming techniques to achieve high resolution and excellent interference rejection capability. In the absence of array steering vector errors, we discuss the application of several existing data-dependent beamforming algorithms including Capon, APES (amplitude and phase estimation) and CAPES (combined Capon and APES), and then propose an alternative estimation procedure, referred to as the combined Capon and approximate maximum likelihood (CAML) method. Via several numerical examples, we show that the proposed CAML method can provide excellent estimation accuracy of both target locations and target amplitudes. In the presence of array steering vector errors, we apply the robust Capon beamformer (RCB) and doubly constrained robust Capon beamformer (DCRCB) approaches to the MIMO radar system to achieve accurate parameter estimation and superior interference and jamming suppression performance.

Broadband Interference Suppression Performance of Minimum Redundancy Arrays

The broadband interference suppression performance of the minimum redundancy array (MRA) used in the linearly constrained minimum variance (LCMV) beamformer is studied in this paper. The ideal continuous-time, infinite-length filter instead of the realistic finite-order digital filter is assumed in the array processor. The expressions of the power spectrum of the beamformer output in different scenarios are derived to compute the mean output power. Several original properties of the performance of the MRA compared with that of the uniform linear array (ULA) are obtained by mathematical proofs and numerical studies.

A two-stage binaural speech enhancement approach for hearing aids with preserving binaural benefits in noisy environments

Speech enhancement is one of the most crucial functions, if not the most, in hearing aids, as hearing impaired people have great difficulty in understanding speech in noisy environments. In this paper, we propose a two-stage binaural speech enhancement approach for hearing aids, which consists of interference estimation by pre-trained adaptive filters and speech enhancement using the Wiener filters. Main attention is then paid to the theoretical analysis of this system and the experimental comparisons with the traditional binaural speech enhancement approaches. The comparisons are conducted with the following two considerations: interference suppression performance and the ability in preserving binaural cues which give birth to listener's own “binaural gain.” We finally give the general discussion on this proposed binaural speech enhancement algorithm from the viewpoints of theory, through implementation, to evaluation.

Resource allocation with CCI suppression for multiuser MIMO-OFDM downlink in correlated channels

To minimize the overall transmit power while maintaining a constant data rate and target BER, a downlink adaptive resource allocation algorithm with jointing the exclusive manner and the shared manner is proposed for multiuser MIMO-OFDM system in correlated channels. The algorithm allocates all the subcarriers to different users according to their spatial correlations. The users with high spatial correlation are allocated in the same group and the exclusive manner is applied. The shared manner with an improved null broadening method, which improves the performance of co-channel interference (CCI) suppression and decreases the number of transmit antennas required, is applied between the different group users. As the user's direction of departure (DOD) changes very slowly, a looking up table method is used to reduce the computational complexity. The simulation results show that despite the angle spread of DOD, when compared with the exclusive manner, the proposed algorithm improves the spectral efficiency, and when compared with the TDMA-ZF (zero forcing) shared manner, the proposed algorithm decreases the total transmit power by at least 1 dB.

Designing Amplitude/Phase Response of the Frost Beamformer

In this correspondence, three methods are proposed to design the look-direction amplitude/phase response to optimize the Frost beamformer. With some constrained optimization criteria, the new constraint vector and thus the new weight vector are designed to improve the output signal-to-interference-plus-noise ratio (SINR) relative to the beamformer with the distortionless constraint. Simulation results are presented to demonstrate the improved interference and noise suppression performance of the optimized beamformer

Subcanceller: adaptive generalised sidelobe canceller with optimum subband decomposition

This paper presents a subband beamformer with the generalised sidelobe canceller (GSC) as the underlying structure. This new beamformer, referred to as the subcanceller, determines the statistically optimum filter bank succeeding the blocking matrix of the GSC based on the minimum mean-square error criterion. As a consequence, the signals passing through the lower branch of the GSC are decomposed into more appropriate subband components by such filter banks according to the input data statistics to enhance the interference suppression capability. The determination of the filter bank coefficients, however, calls for computationally demanding nonlinear optimisation. To alleviate the computational overhead, an iterative procedure is also proposed, which solves the Rayleigh quotient in each iteration. Furthermore, a detailed performance analysis of the proposed beamformer is conducted, which includes the development expression of the output signal to interference-plus-noise ratio and its implications, and the analysis of the convergence characteristic. Furnished simulations show that the new scheme yields superior interference suppression performance with a faster convergence rate compared with previous studies.

Approximate comparative analysis of interference suppression performance between antenna and beam selection techniques

Multiple antenna systems can greatly improve the performance of wireless systems by providing better link quality, capacity and immunity to interference. A very simple structure for smart antennas is a fixed beamforming network (FBN) with beam selection. In Y.S. Choi and S.M. Alamouti (2004) the performance of antenna and beam selection/combining techniques are compared. The channel model in that paper is a statistical, clustered propagation model in a correlated Rayleigh fading channel. In this paper we derive the approximate density function of the signal-to-interference-and-noise power-ratio (SINR) of beam selection with eigen-beamforming. We also analyze the outage probability and capacity of beam selection with a fixed beamforming network (FBN) with correlated fading between the antennas. We compare the performance of this system with antenna selection avid independent fading between the antennas. We also investigate the impact of erroneous beam or antenna selection. We show that beam selection outperforms antenna selection in the presence of interference.

A software antenna configuration having robustness for strong interference signal that arrives suddenly—Utilizing the power inversion characteristics in the second eigenvector beam output

AbstractAn environment is assumed in which a strong interference wave is suddenly incident. To produce an antenna robust to such an environment, a method is proposed in which an eigenvector beamspace adaptive array (EBAA) is formed by using the weight of the eigenvector for the first eigenvalue in the case of weak interference, but the weight of the eigenvector for the second eigenvalue in the case of strong interference. The performance of the interference suppression in the latter case (desired wave power ≪ interference wave power) is analyzed by numerical calculations and simulations. Also, this EBAA is superior in terms of configuration and performance to the well‐known power inversion adaptive array (PIAA). Based on the results, a software antenna configuration method for real‐time understanding of the propagation environment and adaptive switching of the algorithm is discussed. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 86(8): 20–28, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10099

Performance of reduced-rank linear interference suppression

The performance of reduced-rank linear filtering is studied for the suppression of multiple-access interference. A reduced-rank filter resides in a lower dimensional space, relative to the full-rank filter, which enables faster convergence and tracking. We evaluate the large system output signal-to-interference plus noise ratio (SINR) as a function of filter rank D for the multistage Wiener filter (MSWF) presented by Goldstein and Reed. The large system limit is defined by letting the number of users K and the number of dimensions N tend to infinity with K/N fixed. For the case where all users are received with the same power, the reduced-rank SINR converges to the full-rank SINR as a continued fraction. An important conclusion from this analysis is that the rank D needed to achieve a desired output SINR does not scale with system size. Numerical results show that D=8 is sufficient to achieve near-full-rank performance even under heavy loads (K/N=1). We also evaluate the large system output SINR for other reduced-rank methods, namely, principal components and cross-spectral, which are based on an eigendecomposition of the input covariance matrix, and partial despreading. For those methods, the large system limit lets D/spl rarr//spl infin/ with D/N fixed. Our results show that for large systems, the MSWF allows a dramatic reduction in rank relative to the other techniques considered.

Performance of adaptive linear interference suppression in the presence of dynamic fading

Adaptive linear interference suppression for direct-sequence (DS) code-division multiple access (CDMA) is studied in the presence of time- and frequency-selective fading. Interference suppression is achieved with an adaptive digital filter which spans a single symbol interval. Both decision-directed and blind adaptive algorithms, which do not require a training sequence, are considered. Modifications to least squares adaptive algorithms are presented which are compatible with differential coding and detection. For frequency-selective fading, adaptive algorithms are presented based upon different assumptions concerning knowledge of the desired user's channel. Specifically, the cases considered are as follows: (1) perfect knowledge of the desired channel; (2) knowledge of only the relative path delays; and (3) knowledge of only one delay corresponding to the strongest path. Computer simulation results are presented which compare the performance of these algorithms with the analogous RAKE receivers. These results show that for case (3), even slow fading can cause a significant degradation in performance. Effective use of channel parameters in the adaptive algorithm reduces the sensitivity to fade rate, although moderate to fast fading can significantly compromise the associated performance gain relative to the RAKE receiver.

Adaptive linear interference suppression for packet DS‐CDMA

AbstractThe performance of adaptive linear interference suppression is studied in the context of packet DS‐CDMA. A multi‐cell system is assumed with stochastic arrivals and departures of asynchronous users, and additive Gaussian noise as the only channel impairment. Interference suppression is achieved with a tapped‐delay line filter, where the filter spans a single symbol interval. Adaptive algorithms considered include the stochastic gradient (LMS), exponentially‐weighted Least Squares (LS), block LS, and a reduced‐rank LS algorithm. The reduced‐rank LS algorithm first projects the received signal onto a signal sub‐space spanned by eigenvectors of the averaged outer product matrix of received vectors. The purpose of the projection is to eliminate low‐level background interference and noise. Both decision‐directed and blind algorithms, which do not require a training sequence, are compared. Computer simulation is used to obtain error rates as a function of traffic load, and algorithm and system parameters (including timing offset). Results indicate that the adaptive algorithms offer a significant increase in capacity (nearly a factor of two at moderate error rates), and are insensitive to variations in received power over the user population.

Linear Arrays Pattern Synthesis with Multiple Broad Nulls Using Partial Amplitude Control

The purpose of this paper is to present a simple procedure for partial amplitude control to suppress multiple wide band interferences in linear arrays. The partial element excitations are determined to meet a specified array pattern using the simplex method of linear programming to solve an overdetermined system of linear equations. The procedure achieves the minimum number of controlled edge elements for the prescribed sidelobe level (SLL), main beam width (MBW), and multiple wide band interference suppression in arbitrary directions. The performance of multiple interference suppression using this technique is independent of the number of array elements.

On full decoding of truncated ranges for ST/MST radar applications

In a coding system that uses a complementary code pair of length N, the first N-1 sampled ranges are not normally fully decoded due to truncation. However, these ranges can be fully decoded by performing two processing stages. In the first stage, the truncated ranges are partially decoded and during the second stage, the vector of the fully decoded values is obtained as a product of the vector of the partially decoded values and a decoding matrix. Three performance parameters appropriate to the full decoding of truncated ranges are considered. These are the signal-to-noise power ratio degradation of the truncated ranges, the interference suppression performance of the codes, and a parameter related to the magnitudes of the elements of the decoding matrix which may influence the complexity of implementation. It is shown that by choosing suitable code pairs significant performance improvements can be obtained. >