In this paper, we discuss crosstalk equalization technique for high-speed digital transmission systems. This equalization technique makes use of the cyclostationarity of the crosstalk interferer. We first analyze the eigenstructure of the equalizer in the presence of cyclostationary crosstalk interference. It is shown that the eigenvalues of the equalizer depend upon the folded signal and interferer power spectra, and the cross power spectrum between the signal and the interferer. The expressions of the minimum mean square error (MMSE) and the excess MSE are then obtained by using the equalizer's eigenstructure. Analysis and simulation results indicate that such peculiar equalizer's eigenstructure in the presence of cyclostationary interference results in significantly different initial convergence and steady-state behaviors as compared with the stationary noise case. We also show that the performance of the equalizer varies depending on the relative clock phase of the symbol clocks used by the signal and the crosstalk interferer.

In this paper, we analyze the convergence and steady-state behavior of the least mean-square (LMS) adaptive filtering algorithm for a finite-length phase-splitting hybrid-type decision feedback equalizer (H-DFE). With some approximations, we derive an iterative expression for the excess mean-square error (MSE) of the H-DFE, which is composed of three statistically dependent excess MSEs; that is, the excess MSEs of the feedforward filter (FFF), intersymbol interference predictive feedback filter (ISI-FBF), and noise predictive feedback filter (NP-FBF) taps. Computer simulation and analytical results show that the average eigenvalue of the input signal for the NP-FBF taps of the H-DFE is time-varying, whereas those for the FFF and ISI-FBF taps are fixed. Nevertheless, the H-DFE can be implemented with fixed step sizes that ensure the convergence of the LMS algorithm without performance degradation from the standpoint of convergence speed, as well as steady-state performance for digital subscriber line (xDSL) applications.

This paper discusses far-end crosstalk (FEXT) cancellation methods for multicarrier transmission system. A system arrangement and its tap update method are proposed when FEXT cancelers and a frequency-domain equalizer (FEQ) are jointly adapted to combat channel intersymbol interference, FEXT, and other additive noise. We present mathematical formulation of minimum mean-square error (MSE) and the optimum tap coefficients for the FEXT cancelers and the FEQ when FEXT cancellation techniques are introduced for multiuser discrete multitone (DMT) based very high-speed digital subscriber line (VDSL) transmission. It is shown that FEXT cancellation enhances the achievable bit rate in FEXT-limited systems. Computer simulation and analytical results show that the performance of jointly adapted FEXT cancelers and an FEQ is better than that of separately adapted FEXT cancelers and an FEQ.

By using multiple transmit antennas, wireless systems have a large capacity in time-varying multipath fading channels. Space-time block code (STBC), space-frequency block code (SFBC), and space-time-frequency (STF) block code are well-known techniques in transmitter diversity schemes. While the SFBC (or the STF block coded) system gives full diversity at frequency-nonselective channels, it breaks down when used in a frequency-selective environment. This is because the SFBC (or the STF block code) scheme disregards frequency selectivity of the channel by assuming that channel frequency responses (CFRs) at adjacent subcarriers are the same. In this paper, we propose efficient channel estimation and symbol decoding methods, which consider the difference between CFRs at the adjacent subcarriers of the SFBC (or the STF block coded) orthogonal frequency division multiplexing (OFDM) system in multipath fading channels. The proposed method gives initial channel information by designing a simple training symbol, and the CFRs at all the subcarriers and the differences between the CFRs are easily calculated by using an interpolation method or a discrete Fourier transform (DFT) operation.

We propose a new diversity scheme for orthogonal frequency division multiplexing/multi-input multi-output (OFDM/MIMO) systems. The proposed scheme, named turbo layered space-frequency coded OFDM (TLSFC-OFDM), exploits the turbo principle with space hopping (SH). The TLSFC-OFDM system with SH provides a spatial coding so that we can obtain the transmit diversity. We also introduce a successive interference cancellation (SIC) algorithm that requires no ordering and fewer iterations to converge. As a result, this scheme reduces computational complexity. Computer simulation results show that the unordered SIC-based TLSFC-OFDM system outperforms the OFDM/H-BLAST system. It is also shown that the proposed system can operate even with fewer receive antennas than transmit antennas.

This paper discusses a cyclic prefixed single carrier frequency-domain equalization (SC-FDE) scheme with two types of transmit diversity. Firstly, we propose a SC-FDE system with space-frequency block coding (SFBC). The transmit sequence of the proposed system is designed to have spatial and frequency diversities, which is equivalent to the SFBC. The corresponding combining receiver is derived under a minimum mean square error (MMSE) criterion. It is shown that the proposed system significantly outperforms the SC-FDE system with space-time block coding (STBC) over fast fading channels, while providing lower computational complexity than orthogonal frequency division multiplexing (OFDM) combined with SFBC. We verify the performance of two-branch transmit diversity systems including the proposed one through bit error rate (BER) analysis. Secondly, as a scheme that combines STBC and SFBC, a space-time-frequency block code (STFBC) SC-FDE system is presented. Computer simulation results show that the proposed STFBC SC-FDE system has better immunity to the distortion caused by both fast fading and severe frequency selective fading, compared to the SC-FDE system with the STBC or the SFBC scheme. Complexity analysis is also conducted to compare their computational loads of the transceiver. It is shown that the proposed STFBC SC-FDE system has lower computational complexity than the STFBC OFDM system.

In this paper, an efficient cyclic prefix reconstruction (CPR) technique with turbo equalization is developed for multi-antenna single-carrier frequency-domain equalization (SC-FDE) systems, which are for multi-input multi-output (MIMO), space-time block code (STBC), and space-frequency block code (SFBC) applications. The proposed method includes pre-processing estimation (PPE), weighted interblock interference cancellation (WIBIC), or residual intercarrier interference suppression (RICIS). PPE is employed to compute initial values of MIMO turbo equalization and the WIBIC is developed to cancel interblock interference (IBI) at the initial iteration of the CPR for STBC SC-FDE. RICIS is used to mitigate residual intercarrier interference (ICI) after each iteration of the CPR. By applying the proposed method to the multi-antenna SC-FDE system with insufficient cyclic prefix (CP), we can significantly improve its error performance, obtaining the benefits of spectral efficiency gain and multiplexing/diversity gain in MIMO/STBC/SFBC.

In this paper, a simple adaptive notch filter (ANF) scheme for reducing RFI over CAP/QAM-based VDSL systems is proposed. To alleviate the spectral null caused by notch filtering, a null reshaping scheme is introduced between the normal ANF and the decision feedback equalizer (DFE). The proposed filter scheme can control the width and depth of the null. The shallow and narrow null obtained by null reshaping reduces the loss of signal components and consequently improves the mean square error (MSE) at the output of the equalizer. The proposed null reshaping scheme also enables the infinite impulse response (IIR) type constrained ANF to have a smaller pole contraction factor α. This results in a fast convergence property in RFI frequency estimation with a recursive prediction error (RPE) algorithm. The performance variations of the proposed null reshaping are investigated with varying filter parameters. Compared to the conventional ANF, simulation results show that, at the expense of small system complexity, the proposed structure yields a 2-3 dB MSE gain and a fast convergence property for RFI estimation.

In this letter, we propose a low-complexity estimation method of cyclic-prefix (CP) length for a discrete multitone (DMT) very high-speed digital subscriber line (VDSL) system. Using the sign bits of the received DMT VDSL signals, the proposed method provides a good estimate of CP length, which is suitable for various channel characteristics. This simple estimation method is consistent with the initialization procedure of T1E1.4 multi-carrier modulation (MCM)-based VDSL Standard. Finally, simulation results with VDSL test loops are presented.

In this paper, we describe statistical properties of timing jitter of symbol timing recovery circuit for carrierless amplitude/phase modulation (CAP)-based very high-rate digital subscriber line (VDSL) system. Analytical expressions of the timing jitter for envelope-based timing recovery system, such as squarer-based timing recovery (S-TR) and absolute-value-based timing recovery (A-TR) schemes, are derived in the presence of additive white Gaussian noise (AWGN) or far-end crosstalk (FEXT). In particular, the analytical and simulation results of the timing jitter performance are presented and compared for a 51.84 Mb/s 16-CAP VDSL system. The A-TR system implemented digitally meets the DAVIC's VDSL system requirement, which specifies the maximum peak-to-peak jitter value of 1.5 nsec and the acquisition time of 20 msec.

In this paper, we discuss the performance and computational complexity of modulo-type Viterbi decoder (MVD) for high-speed digital transmission applications. It is shown that the MVD, which is a combination of modulo operation and Viterbi decoder at the receiver, has the same performance as a conventional Viterbi decoder (CVD) with extended constellations. We also show by complexity analysis that the MVD in conjunction with the Tomlinson-Harashima (TH) precoder at the transmitter reduces the system complexity significantly as compared to the CVD. The performance of the digital subscriber line (xDSL) system employing the MVD is investigated in the presence of near-end crosstalk (NEXT) and impulsive noise.