Blind Adaptive Channel Shortening Research Articles

Efficient Blind Adaptive CSE to Reduce Cyclic Prefix Length in Direct Detection Optical OFDM Systems

Abstract Direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems for a long-reach of standard single mode fiber (SSMF) require a large length of cyclic prefix (CP) to avoid the inter-symbol interference (ISI) effect caused by group velocity dispersion (GVD). Unfortunately, this method is inefficient due to the energy wasted in CP samples. In order to reduce the CP length and to mitigate the residual ISI, a novel blind adaptive channel shortening equalizer (CSE) is proposed in this paper. Based on the orthogonality between subcarriers in the fast Fourier transform (FFT) property, the proposed algorithm attempts to minimize the sum-squared correlation (SSCM) between each sample located in a well-defined window to update the CSE coefficients. Thus, the combined channel-CSE response is shortened. Therefore, it can cancel the residual ISI effect due to the GVD and the short CP length. The performance of the system is evaluated on basis of bit error rate (BER) versus optical signal to noise ratio (OSNR) for different CP lengths. The simulation results validate the new algorithm SSCM and show that it can reduce the CP length with a much better system improvement than existing algorithms.

Multi-carrier Equalization by Restoration of RedundancY (MERRY) for Adaptive Channel Shortening in Multi-carrier Systems

Abstract This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated and less complexity also involved by the simulation of the DST-DMT system. Keywords DFT, DMT, DST. 1. I NTRODUCTION Multi carrier modulation, particularly Discrete Multi-tone (DMT) modulation, is one of the most prominent modulation methods for high-speed digital communications. For the channel in the DMT system separated into self- regulating sub-channels. The full amount of bits transmitted over the channel would be the total amount of the bits transmitted in each sub-channel. The binary input data are passed onto a set of parallel, independent sub-channels, each of which is assigned a fixed number of bits during startup or system initialization. Given the measured SNR of each sub-channel during startup, the number of bits for each sub-channel is then determined [1]. Each sub-channel is encoded into a quadrature amplitude modulation (QAM) constellation of the appropriate size. For example, if four bits are assigned to tone

Minimum-Mean-Output-Energy Blind Adaptive Channel Shortening for Multicarrier SIMO Transceivers

In this paper, we propose a blind adaptive channel-shortening method for designing finite-impulse response time-domain equalizers (TEQs) in single-input multiple-output systems employing multicarrier modulations. The proposed algorithm, which relies on a constrained minimization of the mean-output-energy at the TEQ output, does not require a priori knowledge of the channel impulse response or transmission of training sequences, and admits an effective and computationally efficient adaptive implementation. Moreover, the proposed TEQ is narrowband-interference resistant and its synthesis only requires an upper bound (rather than the exact knowledge) of the channel order. Numerical simulations are provided to illustrate the advantages of the proposed technique over a recently developed blind channel shortener.

Fast-Converging Blind Adaptive Channel-Shortening and Frequency-Domain Equalization

Orthogonal frequency-division multiplexing (OFDM) is a popular transmission format for emerging wireless communication systems, including satellite radio, various wireless local area network (LAN) standards, and digital broadcast television. Single-carrier cyclic-prefixed (SCCP) modulation is similar to OFDM, but with all frequency-domain operations performed at the receiver. Systems employing OFDM and SCCP perform well in the presence of multipath provided that the channel delay spread is shorter than the guard interval between transmitted blocks. If this condition is not met, a channel-shortening equalizer can be used to shorten the channel to the desired length. In modestly time-varying environments, an adaptive channel shortener is of interest. All existing adaptive channel shorteners require renormalization to restrain the channel shortener away from zero. In this paper, we study the use of a unit-tap constraint rather than a unit-norm constraint on the adaptive channel shortener. We use this constraint to manipulate existing algorithms into a framework analogous to the recursive least squares algorithm, and we develop adaptation rules for blind and semiblind frequency domain equalizers for SCCP receivers. Simulations of the proposed algorithms show an order of magnitude improvement in convergence speed, as well as a reduced asymptotic bit error rate

Blind adaptive channel shortening by single lag autocorrelation minimisation

A blind adaptive channel shortening algorithm based on minimising the sum of the squared autocorrelations (SAM) of the effective channel was recently proposed. We submit that essentially identical channel shortening can be achieved by minimising the square of only a single autocorrelation. Our proposed single lag autocorrelation minimisation (SLAM) algorithm has very low complexity. We also constrain the autocorrelation minimisation with a novel stopping criterion so that the shortening signal-to-noise ratio (SSNR) of the effective channel is not minimised by the autocorrelation minimisation. The simulations show that SLAM achieves higher bit rates than SAM.