Impulse response shortening for discrete multitone transceivers
TL;DR: Various methods of determining the coefficients for this time-domain finite impulse response (FIR) filter are explored and an optimal shortening and a least-squares approach are developed for shortening the channel's impulse response.
Abstract: In discrete multitone (DMT) transceivers an intelligent guard time sequence, called a cyclic prefix (CP), is inserted between symbols to ensure that samples from one symbol do not interfere with the samples of another symbol. The length of the CP is determined by the length of the impulse response of the effective physical channel. Using a long CP reduces the throughput of the transceiver, To avoid using a long CP, a short time-domain finite impulse response (FIR) filter is used to shorten the effective channels impulse response. This paper explores various methods of determining the coefficients for this time-domain filter. An optimal shortening and a least-squares (LS) approach are developed for shortening the channel's impulse response. To provide a computationally efficient algorithm a variation of the LS approach is explored. In full-duplex transceivers the length of the effective echo path impacts the computational requirements of the transceiver. A new paradigm of joint shortening is introduced and three methods are developed to jointly shorten the channel and the echo impulse responses in order to reduce the length of the CP and reduce computational requirements for the echo canceller.
Citations
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Book•
30 Apr 2013
TL;DR: This book offers a unified presentation of OFDM theory and high speed and wireless applications, in particular, ADSL, wireless LAN, and digital broadcasting technologies are explained.
Abstract: From the Publisher:
Multi-carrier modulation, in particular orthogonal frequency division multiplexing (OFDM), has been successfully applied to a wide variety of digital communications applications for several years. Although OFDM has been chosen as the physical layer standard for a diversity of important systems, the theory, algorithms, and implementation techniques remain subjects of current interest.
This book is intended to be a concise summary of the present state of the art of the theory and practice of OFDM technology. This book offers a unified presentation of OFDM theory and high speed and wireless applications. In particular, ADSL, wireless LAN, and digital broadcasting technologies are explained.
It is hoped that this book will prove valuable both to developers of such systems, and to researchers and graduate students involved in analysis of digital communications, and will remain a valuable summary of the technology, providing an understanding of new advances as well as the present core technology.
755Â citations
TL;DR: Identifiability results are provided, showing that in the (theoretical) situation where channel zeros are located on subcarriers, the algorithm does not ensure uniqueness of the channel estimation, unless the full noise subspace is considered.
Abstract: This paper proposes a new blind channel estimation method for orthogonal frequency division multiplexing (OFDM) systems. The algorithm makes use of the redundancy introduced by the cyclic prefix to identify the channel based on a subspace approach. Thus, the proposed method does not require any modification of the transmitter and applies to most existing OFDM systems. Semi-blind procedures taking advantage of training data are also proposed. These can be training symbols or pilot tones, the latter being used for solving the intrinsic indetermination of blind channel estimation. Identifiability results are provided, showing that in the (theoretical) situation where channel zeros are located on subcarriers, the algorithm does not ensure uniqueness of the channel estimation, unless the full noise subspace is considered. Simulations comparing the proposed method with a decision-directed channel estimator finally illustrates the performance of the proposed algorithm.
318Â citations
TL;DR: A novel subspace approach for blind channel identification using cyclic correlations at the OFDM receiver and Simulations of the proposed channel estimator along with its performance in OFDM systems combined with impulse response shortening and Reed-Solomon coding are presented.
Abstract: Transmitter-induced cyclostationarity has been explored previously as an alternative to fractional sampling and antenna array methods for blind identification of FIR communication channels. An interesting application of these ideas is in OFDM systems, which induce cyclostationarity due to the cyclic prefix. We develop a novel subspace approach for blind channel identification using cyclic correlations at the OFDM receiver. Even channels with equispaced unit circle zeros are identifiable in the presence of any nonzero length cyclic prefix with adequate block length. Simulations of the proposed channel estimator along with its performance in OFDM systems combined with impulse response shortening and Reed-Solomon coding are presented.
272Â citations
Cites background or methods from "Impulse response shortening for dis..."
...This problem can be eliminated by employing decision feedback [16] or impulse response shortening [9]....
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...We estimate the channel as before but look at MMSE equalization with and without the use of impulse response shortening [9] and RS (15;11) coding....
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...5), which consists of designing a prefilter a(n) such that the composite channel a(n)?h(n) has energy concentrated in the desired duration chosen for the cyclic prefix [9]....
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TL;DR: An alternative receiver structure is presented for discrete multitone-based systems that is modified into a structure with a (complex) multitap FEQ per tone by solving a minimum mean-square-error problem, resulting in a larger bit rate while complexity during data transmission is kept at the same level.
Abstract: An alternative receiver structure is presented for discrete multitone-based systems. The usual structure consisting of a (real) time-domain equalizer in combination with a (complex) 1-tap frequency-domain equalizer (FEQ) per tone, is modified into a structure with a (complex) multitap FEQ per tone. By solving a minimum mean-square-error problem, the signal-to-noise ratio is maximized for each individual tone. The result is a larger bit rate while complexity during data transmission is kept at the same level. Moreover, the per tone equalization is shown to have a reduced sensitivity to the synchronization delay.
272Â citations
TL;DR: This work develops two TEQ design methods to maximize the bit rate and proposes a minimum-ISI method that generalizes the MSSNR method by weighting the ISI in the frequency domain to obtain higher performance.
Abstract: In a discrete multitone receiver, a time-domain equalizer (TEQ) reduces the intersymbol interference (ISI) by shortening the effective duration of the channel impulse response. Current TEQ design methods such as the minimum mean-squared error (MMSE), maximum shortening SNR (MSSNR), and maximum geometric SNR (MGSNR) do not directly maximize bit rate. We develop two TEQ design methods to maximize the bit rate. First, we partition an equalized multicarrier channel into its equivalent signal, noise, and ISI paths to develop a new subchannel SNR definition. Then, we derive a nonlinear function of TEQ taps that measures the bit rate, which the proposed maximum bit rate (MBR) method optimizes. We also propose a minimum-ISI method that generalizes the MSSNR method by weighting the ISI in the frequency domain to obtain higher performance. The minimum-ISI method is amenable to real-time implementation on a fixed-point digital signal processor. Based on simulations using eight different carrier-serving-area loop channels, (1) the proposed methods yield higher bit rates than MMSE, MGSNR, and MSSNR methods; (2) the proposed methods give three-tap TEQs with higher bit rates than 17-tap MMSE, MGSNR, and MSSNR TEQs; (3) the proposed MBR method achieves the channel capacity (as computed by the matched filter bound using the proposed subchannel SNR model) with a five-tap TEQ; and (4) the proposed minimum-ISI method achieves the bit rate of the optimal MBR method.
257Â citations
Cites background from "Impulse response shortening for dis..."
...BACKGROUND This section introduces necessary background information for the derivation of a new subchannel SNR definition in the next section and reviews the MGNSR TEQ design method....
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...The second approach estimates the channel impulse response and designs a TEQ that minimizes the energy of the impulse response outside of a target window or, equivalently, maximizes the shortening signal-to-noise ratio (SSNR) [9], [10]....
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...A three-tap TEQ designed by either of the two proposed methods outperforms 17-tap equalizers designed by MMSE, MSSNR, and MGNSR TEQ methods....
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References
More filters
TL;DR: In this article, a new estimate minimum information theoretical criterion estimate (MAICE) is introduced for the purpose of statistical identification, which is free from the ambiguities inherent in the application of conventional hypothesis testing procedure.
Abstract: The history of the development of statistical hypothesis testing in time series analysis is reviewed briefly and it is pointed out that the hypothesis testing procedure is not adequately defined as the procedure for statistical model identification. The classical maximum likelihood estimation procedure is reviewed and a new estimate minimum information theoretical criterion (AIC) estimate (MAICE) which is designed for the purpose of statistical identification is introduced. When there are several competing models the MAICE is defined by the model and the maximum likelihood estimates of the parameters which give the minimum of AIC defined by AIC = (-2)log-(maximum likelihood) + 2(number of independently adjusted parameters within the model). MAICE provides a versatile procedure for statistical model identification which is free from the ambiguities inherent in the application of conventional hypothesis testing procedure. The practical utility of MAICE in time series analysis is demonstrated with some numerical examples.
47,133Â citations
TL;DR: A discrete multitone (DMT) transceiver design for high bit rate digital subscriber line (HDSL) access is presented and analyzed and is an excellent candidate for HDSL implementation.
Abstract: A discrete multitone (DMT) transceiver design for high bit rate digital subscriber line (HDSL) access is presented and analyzed. The DMT transmitter and receiver structure and algorithms are detailed, and the computational requirements of DMT for HDSL are estimated. At a sampling rate of 640 kHz, using an appropriate combination of a short finite-impulse-response (FIR) equalizer and a length-512 DMT system, 1.6 Mb/s data transmission is possible within the carrier serving area (CSA) at an error rate of 10/sup -7/ on a single twisted pair. A significant performance margin can be achieved when two coordinated twisted pairs are used to deliver a total data rate of 1.6 Mb/s. In terms of a performance-per-computation figure of merit, the DMT system is an excellent candidate for HDSL implementation. >
549Â citations
23 May 1993
TL;DR: Several algorithms for designing the time-domain equalizer, which use adaptation in the frequency domain and windowing in the time domain in order to minimize the mean squared error of the equalized response, are described.
Abstract: In a multicarrier data transmission system the length of a symbol is often limited by the maximum permissible delay of data from input to output. If the length of the impulse response of the channel is not negligible compared to the permitted symbol length, the impulse response can be shortened by passing the received signal through a time-domain equalizer before modulation. The best performance for a given computational complexity can then be achieved by appending to each block of samples of the transmit signal a cyclic prefix that has the same length as the shortened impulse response. Several algorithms for designing the time-domain equalizer, which use adaptation in the frequency domain and windowing in the time domain in order to minimize the mean squared error of the equalized response, are described. >
221Â citations
14 Jun 1992
TL;DR: Results indicate that near-optimum performance can be achieved by using the general optimum class of structures derived that includes the decision feedback equalizer and the lesser-known autoregressive moving average filters at a great computational reduction.
Abstract: Equalization structures for maximum likelihood (ML) reception of data transmitted over intersymbol interference channels are studied. The equalizer that is best for the ML receiver is derived from a general theory of decision-aided equalization. The resulting optimum equalizers are linear and do not use previous decisions. If the equalizer complexity is permitted to be infinite, then a general optimum class of structures is derived that includes the decision feedback equalizer and the lesser-known autoregressive moving average filters. When a complexity constraint is also imposed on the equalizer, one of the structures in this class will be best for a given ML receiver. The best structure is found by a simple search procedure, which is given. The results indicate that near-optimum performance can be achieved by using this approach at a great computational reduction. >
140Â citations
01 Dec 1980
TL;DR: In this paper, the extension of the all-pole (AR) exact least-squares ladder algorithms to the pole-zero (ARMA) case is presented, based on a general set of recursions obtained by a geometric approach.
Abstract: The extension of the all-pole (AR) exact least-squares ladder algorithms to the pole-zero (ARMA) case is presented. The algorithms are based on a general set of recursions obtained by a geometric approach. The recursions obtained are square-root normalized and have much simpler structures than the unnormalized case. The white input as well as the possibly non-white unknown input case are discussed.
80Â citations