Blind Interference Suppression Research Articles

Spread Spectrum Symbol Detection With Blind Interference Suppression in FBMC-SS

Recent works have demonstrated Filter Bank Multicarrier Spread Spectrum (FBMC-SS) to be a robust communication scheme in the presence of high-power interferers. Existing FBMC-SS symbol detector designs based on analysis filter banks (AFB) suggest using an optimal combining scheme to suppress the interferers, necessitating some noise/interference power estimation method. In this paper, we introduce a symbol detector with blind interference suppression by extending a recently developed packet detection method. We then provide an analysis to show that the existing AFB-based symbol detector and the one proposed in this paper are equivalent in typical usage scenarios. A fully-fledged receiver design is proposed utilizing this symbol detector, with specifics presented for estimation of the channel impulse response and carrier frequency offset (CFO). We also outline a method of iterating upon the channel and CFO estimations to improve the quality of both parameters. Moreover, a modification to allow improved performance of the symbol detector at high SNR is provided. Finally, simulated performance results are presented to corroborate these findings and demonstrate the efficiency of this receiver design.

Stabilised blind interference suppression of constant modulus‐based adaptive array over Rayleigh fading channels by initial antenna selection

This article proposes an initial antenna selection for constant modulus-based blind interference suppression algorithms to stabilise their prominent interference suppression performance. Constant modulus algorithm (CMA) is a well-known blind adaptive array scheme, but it cannot suppress the interference when signal-to-interference power ratio (SIR) is <0 dB. It faces strong limits on their applicable region over Rayleigh fading channels where instantaneous channel gain fluctuates over 10 dB range. Even if the expected desired signal strength is larger than interference, CMA may still miscapture the interference and incorrectly suppress the desired signal. The authors’ proposal is simplified approach to select the antenna element whose reception power is maximal. Certain antenna element can be expected to capture the desired signal precisely under the condition where SIR is statistically positive, so that the CMA processor can utilise it as an initial input. This condition will be ensured by increasing antenna element number, supported by the trends that base station antenna elements are going massive. Computer simulations verifies improved interference suppression performance provided by the proposed scheme. This article also verified applicability for multi-modulus algorithm to accommodate M-ary quadrature amplitude modulation (QAM) use.

Uplink Interference Suppression by Semi-Blind Adaptive Array With Decision Feedback Channel Estimation on Multicell Massive MIMO Systems

This paper proposes a novel semi-blind uplink interference suppression scheme for multicell multiuser massive multiple-input multiple-output (MIMO) systems. The inter-cell interference (ICI) becomes intenser when a number of users are spatially multiplexed via massive MIMO. Here arises a pilot contamination problem due to the limitation of orthogonal sequence set and thus inter-user interference (IUI) also remains unsuppressed. Our proposal employs a constant modulus algorithm (CMA) known as a blind interference suppression scheme and exploits channel state information (CSI)-aided minimum mean square error (MMSE) postcoding weight as an initial weight of CMA. Although MMSE weight cannot suppress ICI and IUI due to the pilot contamination, it can help subsequent CMA to capture the desired signals which is required for CMA to effectively work. Since CMA can fully exploit degree of freedom of massive arrays by using uncorrelated data signal part, derived weight successfully suppresses ICI/IUI while resolving the pilot contamination problem. A decision feedback channel estimation (DFCE) is then introduced to further improve CSI estimation accuracy and subsequent interference suppression performance. A series of signal processing, MMSE–CMA–DFCE, can be iteratively performed. The computer simulation reveals that our proposal can improve outage probability and it satisfies below the fifth percentile of cumulative distribution with saved symbol amount.

Blind Interference Suppression Scheme by Eigenvector Beamspace CMA Adaptive Array with Subcarrier Transmission Power Assignment for Spectrum Superposing

Blind Interference Suppression Scheme by Eigenvector Beamspace CMA Adaptive Array with Subcarrier Transmission Power Assignment for Spectrum Superposing

Beampattern Synthesis With Blind Interference Suppression

We suggest an adaptive blind interference suppression (BIS) beamformer that synthesizes a desired beampattern. For a strong interference, the principal eigenvector of the data sample covariance matrix approaches the array response at the interference direction. The beamformer weight vector minimizes the distance from a desired beampattern subject to a zero response to this principal eigenvector. For a strong interference, uncorrelated with the desired signal, the asymptotic array gain (AG) of the BIS beamformer achieves the AG of the minimum power distortionless response (MPDR) beamformer. Simulations demonstrate that, for a finite number of samples, the AG of the BIS beamformer outperforms that of the MPDR beamformer and that it is not sensitive to sensor gain and phase errors.

Improved DSE-CMA error function for blind multiuser interference suppression in DS/CDMA systems

This paper presents an improved error function of dithered signed-error constant modulus algorithm (IDSE-CMA) for blind multiuser interference suppression in DS/CDMA systems. It uses a different error function to replace the former one in sign operation of the DSE-CMA and compares their performance in multiple access interference (MAI) suppression ability. Simulations indicate that the new algorithm has better performance than the similar CMA in terms of convergence speed and steady-state performance.

Joint blind channel estimation and interference suppression with efficient implementation for OFDM systems

A joint blind channel estimation and interference suppression scheme with efficient implementation for orthogonal frequency-division multiplexing (OFDM) systems is presented. In particular, an equalising filterbank is designed and the channel estimate from a lower bound of the filterbank output power is derived. The proposed scheme and exhibits low sensitivity to unknown narrowband interference. It compares favourably with a subspace blind channel estimator.

Advanced ICA-based receivers for block fading DS-CDMA channels

In this paper we propose two types of receivers, which perform blind interference suppression. The receivers are suitable for the third generation mobile communications systems, which are based on direct-sequence code division multiple access (DS-CDMA). We especially consider the statistical technique called independent component analysis (ICA) as a tuning element attached to an existing single-user or blind multiuser detector. By doing this, the statistical independence of the users’ signals can be exploited. In addition, it makes it possible to alleviate the performance drop due to the erroneous parameters estimation in the receiver. From the ICA point of view, the receiver observes a mixture of users’ original signals, determined by the user-specific spreading codes, the data symbols, and the state of the propagation channel. Since all of them might be complex valued by nature, complex ICA is needed. In the paper, a proof of global convergence is given for the kurtosis-based FastICA algorithm in the case of complex valued source signals with circular distribution, and considered as the ICA component of the advanced receivers. Two types of receivers, RAKE-ICA and MMSE-ICA, are proposed and studied in a Rayleigh block fading channel. Extensive numerical simulations indicate that the performance of RAKE and subspace MMSE detector, respectively, can be greatly improved. Quite significantly, their performance is close to the theoretical bound of an equal length MMSE detector.

Orthogonalizing matched filtering (OMF) detector for DS-CDMA mobile communication systems

This paper proposes a new blind interference suppression scheme for direct-sequence code-division multiple-access (DS-CDMA) mobile communication systems. The proposed detector, the orthogonalizing matched filtering (OMF) detector, consists of a bank of despreading filters and a signal combiner. The received composite signal is first despread by the filters in the bank. The despreading filter outputs are then weighted and combined. The weight vector is adaptively determined and updated so that the average combined signal power is minimized while keeping the combiner's response to the desired signal constant. The proposed algorithm for OMF weight updating requires neither knowledge about other users' spreading sequences nor desired user's signal reference. The similarity between the proposed OMF detector and Applebaum's sidelobe canceller adaptive array is discussed in detail. Results of computer simulations are shown to demonstrate the OMF performance in various mobile communications environments.