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ABSTRACT: We propose two practical schemes for the cancellation of nonlinear distortions caused by the power amplifiers (PA) in Orthogonal Frequency Division Multiplexing (OFDM) systems. The algorithms are iterative and located at the receiver. They utilize a soft channel decoder to improve the capabilities of the distortion estimation and relay all the computational complexity to the receiver. Simulation results show that the algorithm can improve the coded bit error rate (BER) to levels close to the linear system case.
Signal Processing Advances in Wireless Communications (SPAWC), 2010 IEEE Eleventh International Workshop on; 07/2010
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ABSTRACT: This paper proposes a practical receiver cancellation technique for removing nonlinear power amplifier (PA) distortion in OFDM systems. By performing the estimation of the PA model parameters at the receiver, the implementation complexity of the transmitter can be reduced. Furthermore, a simple adaptation rule is provided to enable tracking of the PA model parameters. As a consequence, cancellation of nonlinear distortion can be achieved without assuming that the PA model is known a priori at the receiver. Simulation results show that good levels of distortion cancellation are possible for a system with a broadband PA with memory.
Signal Processing Advances in Wireless Communications, 2007. SPAWC 2007. IEEE 8th Workshop on; 07/2007
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ABSTRACT: We present a novel channel estimator for fading channels using basis function approximations and Kalman filtering. The proposal results in a low complexity estimator that is robust to the shape of the channel Doppler spectrum and allows different Doppler spectra for each channel coefficient in a frequency-selective scenario. The estimator is based on the description of channel variations via truncated discrete cosine transform (DCT). We show that DCT can be approximated by a set of linear narrow-band passband filters that can be inserted into a Kalman filter formulation that track a set of decoupled parameters. This estimator attains close to perfect channel knowledge performance with only 1% training symbols in a data frame with Doppler frequencies up to 0.8 times the frame frequency.
Signal Processing Advances in Wireless Communications, 2007. SPAWC 2007. IEEE 8th Workshop on; 07/2007
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ABSTRACT: This paper proposes a new channel estimation approach for MIMO-OFDM systems subject to power amplifier nonlinearities. The harmful effect of nonlinear distortion on the system performance can be reduced by applying an iterative distortion cancellation technique. However, such an approach requires accurate channel estimates to yield good performance. In our approach, initial channel estimation is carried out in frequency domain (FD) followed by time domain (TD) processing of the received signal. In the TD step, the equalized signals from the FD processing is used to remove the nonlinear distortion and to improve the initial channel estimate. Simulations verify that the combined channel estimation and nonlinear cancellation strategy has a performance close to the case of perfectly known channel. Furthermore, a substantial improvement in the system performance is achieved with the proposed technique when compared with conventional methods in terms of mean square error and BER
Personal, Indoor and Mobile Radio Communications, 2006 IEEE 17th International Symposium on; 10/2006
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Signal Processing and Communications, 2004. SPCOM '04. 2004 International Conference on; 01/2005
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ABSTRACT: A canonical piece-wise-linear filter (CPWL) realization is proposed as part of the scheme for nonlinear time-domain equalization (TEQ) aiming impulsive noise interference reduction in xDSL transmission systems. The resulting structure is discussed in the context of a VDSL system using the usual Reed-Solomon (RS) coding to prevent impulsive noise effects. Also, a recently introduced impulsive noise model is used in order to evaluate the new methodology. The scheme for impulse noise reduction presented can be used to obtain an alternative compromise between RS correcting capabilities and interleaving delay. Results obtained using probability of error as performance measure indicate promising results. Computer simulations are included that allow to verify the interesting properties of the training algorithm for the nonlinear TEQ proposed.
Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on; 06/2004
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Signal Processing Symposium, 2004. NORSIG 2004. Proceedings of the 6th Nordic; 02/2004
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ABSTRACT: A complex-allpass-based multiple notch IIR filter is pro- posed to suppress Radio Frequency Interference (RFI) that affect VDSL systems. A notch filter realization based on complex allpass cascaded second-order sections is presented and evaluated in this paper. Two different algorithms, us- ing the Recursive Prediction Error (RPE) method and an al- ternative (similar to the Steiglitz-McBride) method, are pro- posed to update the adaptive notch filter coefficients. Simple stochastic gradient algorithms can be obtained using allpass cascaded second-order sections whose regressors are formed by orthogonal functions which is not the case for the conven- tional complex cascade realization. Comparisons with other multiple-notch realizations evaluating convergence rate and residual interference levels are included. The novel structure using the RPE method reaches the lowest residual interfer- ence level with the fastest convergence rate. Furthermore us- ing the novel techniques stability check is not needed, which reduces their implementation complexity.
