Iterative block decision feedback equalization

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Frequency-domain multiuser detection for CP-assisted DS-CDMA signals

Frequency-domain multiuser detection for CP-assisted DS-CDMA signals

To avoid significant noise enhancement, the FDE is usually optimized under the MMSE (Minimum Mean-Squared Error) criterion [10]. Since an MMSE FDE does not perform an ideal channel inversion, when this type of equalizer is employed in DS-CDMA systems we are not able to fully orthogonalize the different spreading codes. This means that we can have sig- nificant residual interference levels when different users have different powers. To avoid this problem, a promising nonlinear receiver structure was proposed in [11] which employs an IB- DFE (Iterative Block Decision feedback Equalization) [12] especially designed for DS-CDMA signals. The IB-DFE can be regarded as a blockwise DFE where the feedforward and feedback parts are implemented in the frequency domain. Since the feedforward and feedback coefficients take into account the blockwise reliability, we have a turbo-like behavior, with small error propagation (in fact, the IB-DFE can be regarded as a low-complexity turbo equalization scheme [13], since the feedback loop does not use the channel decoder output).
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A spectrally efficient transmission scheme for signals with large bandwidth

A spectrally efficient transmission scheme for signals with large bandwidth

interference (ACI) levels. As an alternative, we can design a receiver able to cope with strong ACI. By taking advantage of the cyclostationary nature of digital signals [4], [5], we can design receivers for channels with strong ACI [6], [7]. This concept can be extended to SC-FDE schemes [8], [9], [10]. A promising receiver for SC-FDE schemes with strong ACI levels is the multiuser frequency-domain receiver proposed in [8] that can be regarded as an iterative block decision feedback equalization (IB-DFE) receiver [11], [12] with multiuser de- tection and ACI cancellation, allowing excellent performance in the presence of strong ACI levels.
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Iterative Equalization and Interference Alignment for Multiuser MIMO HetNets with Imperfect CSI

Iterative Equalization and Interference Alignment for Multiuser MIMO HetNets with Imperfect CSI

Single-carrier frequency division multiple access (SC- FDMA) has a lower peak-to-average power ratio (PAPR) than OFDMA [14]. As the mobile terminals are low power devices SC-FDMA has been adopted, for the uplink, as the multiple access scheme of the current long-term evolution (LTE) cellular system [13]. It is also a promising solution technique for high data rate uplink communications in future cellular systems. Single-carrier frequency domain equalization (SC- FDE) is widely recognized as an excellent alternative to OFDM, especially for the uplink of broadband wireless systems [15, 16]. The SC-FDE based schemes may be either linear or nonlinear. Optimized linear frequency domain equalization (FDE) is widely used in conventional SC-FDE schemes. However, it suffers from high residual interference levels, leading to poor performance, that is, several dB from the matched filter bound (MFB) [17]. On the other hand, nonlinear FDE even if more complex do not suffer from this drawback. For this reason, the designing of nonlinear FDE in general and decision-feedback FDE in particular, with the iterative block decision-feedback equalization (IB-DFE) being the most promising nonlinear FDE [17] has gained significant attention lately. IB-DFE was originally proposed in [18] and was extended for a wide range of scenarios in the last years, ranging between diversity scenarios, multiplexing MIMO, and MC-CDMA systems, among many others [19– 26].
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Iterative Multiuser Equalization for Subconnected Hybrid mmWave Massive MIMO Architecture

Iterative Multiuser Equalization for Subconnected Hybrid mmWave Massive MIMO Architecture

The performance of the pure-analog techniques is limited by constraints on the amplitudes of phase shifters and due to the phases of the ones quantized. Therefore, analog beamforming is usually limited to single-stream transmission [15]. These limitations are overcome by doing some signal processing at an analog level and the rest at the digital level. These architectures are called hybrid analog/digital architectures and have been addressed in [15, 16]. Precod- ing and/or combining/equalization designs for single-user systems have been addressed for fully connected hybrid architectures in [17–19]. In these architectures, each of the RF chains is connected to all receive-and-transmit antennas. In [17], a hybrid spatially sparse precoding/combining approach was designed for mmWave mMIMO systems. The spatial structure of mmWave channels was used to transform the single-user multistream precoding and combining scheme into a sparse reconstruction problem. In [18], joint turbo-like beamforming was designed to compute transmit/receiving analog beamforming coefficients; however the digital pro- cessing part was not considered. In [19], codebook design approaches were addressed for single-stream transmissions through an analog beamforming structure. For multiuser systems, some beamforming approaches have been proposed for fully connected hybrid architectures [20–22]. The authors of [20] proposed uplink receiving beamforming where they assume only single antenna user-terminals (UTs), and at both stages analog and digital ones dealt with multiuser interfer- ence. Reference [21] proposed for the downlink a limited feedback analog/digital two-stage precoding and combin- ing algorithm. Transmit/receiving analog beamforming are jointly computed in the first stage to maximize the power of the desired signal, and then the interference is explicitly mitigated using conventional linear zero-forcing (ZF) pre- coding in the second stage, that is, in the digital domain. An efficient hybrid iterative block space-time multiuser equalizer was proposed in [22]. This equalizer was designed based on the iterative block decision feedback equalization (IB-DFE) principle [23]. IB-DFE was originally proposed in [24]. It does not need the feedback loop of the channel decoder output, and it can be considered as a low complexity turbo equalizer. IB-DFE has been extended to several scenarios, like diversity scenarios and conventional and cooperative MIMO systems, among many others [25–30].
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Approaching universal frequency reuse through base station cooperation

Approaching universal frequency reuse through base station cooperation

Base Station (BS) architectures are a promising cellular wireless solution to miti- gate the interference issues and to avoid the high frequency reuse factors implemented in conventional systems. Combined with block transmission techniques, such as Orthog- onal Frequency-Division Multiplexing (OFDM) for the downlink and Single-Carrier with Frequency-Domain Equalization (SC-FDE) for the uplink, these systems provide a signifi- cant performance improvement to the overall system. Block transmission techniques are suitable for broadband wireless communication systems, which have to deal with strongly frequency-selective fading channels and are able to provide high bit rates despite the chan- nel adversities. In BS cooperation schemes users in adjacent cells share the same physical channel and the signals received by each BS are sent to a Central Processing Unit (CPU) that combines the different signals and performs the user detections and/or separation, which can be regarded as a Multi-User Detection (MUD) technique. The work presented in this thesis is focused on the study of uplink transmissions in BS cooperations systems, considering single carrier block transmission schemes and iterative receivers based on the Iterative-Block Decision Feedback Equalization (IB-DFE) concept, which combined with the employment of Cyclic Prefix (CP)-assisted block transmission techniques are appro- priate to scenarios with strongly time-dispersive channels. Furthermore, the impact of the sampling and quantization applied to the received signals from each Mobile Terminal (MT) to the corresponding BS is studied, with the achievement of the spectral characterization of the quantization noise. This thesis also provides a conventional analytical model for the BER (Bit Error Rate) performance complemented with an approach to improve its results. Finally, this thesis addresses the contextualization of BS cooperation schemes in clustered C-RAN (Centralized-Radio Access Network)-type solutions.
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Estimation of the Feedback Reliability for IB-DFE Receivers

Estimation of the Feedback Reliability for IB-DFE Receivers

Copyright © 2011 F´abio Silva et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. single-carrier (SC) modulation with frequency-domain equalization (FDE) combined with iterative (turbo) FDE schemes has been shown to be suitable for cyclic-prefix (CP)-assisted block transmission within broadband wireless systems. Its excellent performance in severely time-dispersive channels, makes it a promising candidate for future broadband wireless systems. In this paper we investigated the impact of the correlation factor estimation in the performance of iterative block decision feedback equalization (IB-DFE) receivers. Since the correlation factor represents a key parameter to ensure the good performance of these receivers, reliable estimates of this factor are needed in the feedback loop. We present several methods to estimate the correlation coefficient. We also propose a technique to compensate the inaccuracy of the estimation.
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Joint turbo equalization and cancelation of nonlinear distortion effects in MC-CDMA signals

Joint turbo equalization and cancelation of nonlinear distortion effects in MC-CDMA signals

However, since the transmission over time-dispersive channels destroys the orthogonality between spreading codes, an FDE (Frequency-Domain Equalizer) is required before the despreading operation [3]. To avoid significant noise enhancement for channels with deep in-band notches, the FDE is usually optimized under an MMSE criterion (Minimum Mean-Squared Error) [3]. The performances can be further improved by employing the iterative receiver proposed in [4]. That receiver, which is based on the IB- DFE (Iterative Block Decision Feedback Equalizer) pro- posed for block transmission with single-carrier modula- tions [5, 6], allows significant performance improvements as we increase the number of iterations, especially for fully loaded systems and/or in the presence of high interference levels. The asymptotic performances can be close to the single-code performance, provided that we have severely
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High Performance Faster-than-Nyquist Signaling

High Performance Faster-than-Nyquist Signaling

A much less known fact is that it is possible to achieve optimum asymptotic performance with a bandwidth below the minimum Nyquist band. In fact, by employing the so-called Faster-than-Nyquist (FTN) signaling the transmission band can be reduced to around 80% without compromising the minimum Euclidean distance between differente binary sequences, in spite of the inherent ISI levels [3]. This remarkable result was almost completely ignored for over 30 years mainly because the optimum receiver with FTN signaling was too complex. However, due to spectrum scarcity and advances in signal processing there is a renewed interest in FTN (see [4] and references within). Faster-than-Nyquist signaling is particularly interesting for broadband wireless systems. However, the scenario is even more complex if we consider that the ISI inherent to FTN signaling is combined with the ISI associated to multipath time-dispersive effects, which leads to much higher ISI levels that cannot be handled by conventional FTN receivers (even the simplified receivers from [5], [6] are too complex). Block transmission techniques combined with Frequency-Domain Equalization (FDE) such as Orthogonal Frequency Division Multiplexing (OFDM) [2] and Single-Carrier with FDE (SC-FDE) [7] are widely recognized as the best candidates for the downlink and uplink, respectively [8], [9]. Although a linear FDE is suitable for OFDM, it is far from optimum for SC-FDE. In that case, the most promising FDE is the so-called nonlinear IB-DFE (Iterative Block Decision-Feedback Equalizer) [10].
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An iterative frequency-domain decision feedback receiver for CDMA systems

An iterative frequency-domain decision feedback receiver for CDMA systems

Block transmission techniques, with appropriate cyclic ex- tensions and employing FDE techniques (Frequency-Domain Equalization), have been shown to be suitable for high data rate transmission over severe time-dispersive channels. In fact, due to the Fast Fourier Transform (FFT) implementation, the number of operations per symbol grows logarithmically with the block duration (and, therefore, the ISI (Inter-Symbol Interference) span), instead of linearly (at least) with the ISI span, as with conventional time-domain equalizers.

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Interference-aware iterative block decision feedback equalizer for single-carrier transmission

Interference-aware iterative block decision feedback equalizer for single-carrier transmission

equalization (SC-FDE) is often preferred due to its lower PAPR, while still being robust in ISI inducing channels [3]. This hybrid approach with OFDM for the downlink and SC for the uplink has been adopted by several wireless standards like the 3GPP Long Term Evolution (LTE) [4]. Although it is possible to employ low complexity linear receivers in SC schemes the performance is far from the matched filter bound (MFB) [5]. In order to improve the performance, nonlinear schemes like decision feedback equalizers (DFE) can be used instead [6] with one of the most promising being the IBDFE [7]-[9] based on the minimum mean squared error (MMSE) criterion. It employs feedforward and feedback filters implemented in the frequency domain and has been shown to be capable of performing close to the MFB in rich multipath propagation channels, especially when combined with diversity techniques [5][10].
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Interference Aware Iterative Block Decision Feedback Equalizer for Single Carrier Transmission

Interference Aware Iterative Block Decision Feedback Equalizer for Single Carrier Transmission

equalization (SC-FDE) is often preferred due to its lower PAPR, while still being robust in ISI inducing channels [3]. This hybrid approach with OFDM for the downlink and SC for the uplink has been adopted by several wireless standards like the 3GPP Long Term Evolution (LTE) [4]. Although it is possible to employ low complexity linear receivers in SC schemes the performance is far from the matched filter bound (MFB) [5]. In order to improve the performance, nonlinear schemes like decision feedback equalizers (DFE) can be used instead [6] with one of the most promising being the IBDFE [7]-[9] based on the minimum mean squared error (MMSE) criterion. It employs feedforward and feedback filters implemented in the frequency domain and has been shown to be capable of performing close to the MFB in rich multipath propagation channels, especially when combined with diversity techniques [5][10].
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Parallel Iterative Algorithms with Accelerate Convergence for Solving Implicit Difference Equations

Parallel Iterative Algorithms with Accelerate Convergence for Solving Implicit Difference Equations

Theorem: Segment classic implicit iterative algorithm with accelerated convergence (9) for solving diffusion Eq. 1-3 is convergent. Its convergent rate is better than SCII algorithm, and the property of gradual approach convergence can approach ( ) r 2

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Multisensory Tracking of Objects in Darkness: Capture of Positive Afterimages by the Tactile and Proprioceptive Senses.

Multisensory Tracking of Objects in Darkness: Capture of Positive Afterimages by the Tactile and Proprioceptive Senses.

While the data above provide tentative evidence for the role of auditory information in the afterimage fading effect, these data are unable to tease apart the relative contribution or neces- sity of proprioceptive, tactile, or reafferent signals. Hogendoorn et al. [10] showed that proprio- ception, rather than reafferent motor signals, drive the afterimage fading effect for a body part which is moved in the dark, but in the case of held objects we must still find a way to test the effects of proprioception independent of touch and touch independent of proprioception. That was the aim of our third experiment. In one set of conditions, we manipulated the mass of an object dropped in the dark while holding other sensory information constant. If the afterimage fading effect scales with the strength of proprioceptive feedback, it would provide evidence that proprioception plays a role above and beyond the effects of touch. In another set of conditions, we manipulated tactile information while holding other sensory information constant. If the afterimage fading effect still occurs, it will provide evidence that tactile information alone is sufficient to capture vision, and will provide further evidence that the fading of a moved object's afterimage is independent of the object being held (and hence, unlikely to be explained as an effect of held objects being assimilated into the body schema).
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A Robust Reach Set MPC Scheme for Control of AUVs

A Robust Reach Set MPC Scheme for Control of AUVs

to control formations of AUVs is presented and discussed. These features are critical for AUV systems as they operate in contexts of scarce resources and high uncertainty or environmental variability. The proposed control structure, and the various underlying results, enabling the articulation of resources optimization with state feedback control while keeping the onboard computational burden very low, were developed in the context of 2 , and were partially published in a number of papers, 3,4 . The key idea to tackle this challenge consists in, by taking advantage of time-invariant data underlying the formulation of the involved optimization problems, computing a priori (i.e., o ff-line) a number of, as comprehensive as possible, simple building blocks required for optimal or sub-optimal control synthesis as a function of a set of parameters associated with a satisfactory number of more likely typified on-line situations. This, possibly large, amount of data is stored on onboard in appropriate look-up tables. Then, the actual on-line control synthesis is performed by computing the parameter values that take into account the sampled data to retrieve the best control values from the look-up table. The scheme is such that the computation involved in the on-line adaptivity requires several orders of magnitude less time and computational power relatively to the conventional MPC schemes. For a recent reference, see 5 .
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O feedback no contexto do trabalho entre alunos com o geogebra

O feedback no contexto do trabalho entre alunos com o geogebra

Resumo. Apresentamos neste artigo dois episódios relativos a uma experiência de ensino com alunos do 7.º ano onde é dado relevo ao trabalho com o computador na aprendizagem da geometria. Tentamos tirar partido das potencialidades da utilização de um ambiente de geometria dinâmica no processo de ensino/aprendizagem. Focamo-nos no trabalho desenvolvido por um grupo de dois alunos em sala de aula. Este estudo desenvolve-se num contexto de ensino/aprendizagem onde se dá primazia às relações não hierárquicas (interação aluno-aluno). Adotando um modelo co-construtivista damos relevo aos diálogos entre alunos e adotamos uma metodologia qualitativa do tipo interpretativo com o objetivo de perceber o papel e a relevância do feedback entre alunos para a sua aprendizagem, na classificação e na semelhança de triângulos utilizando o Geogebra. A aplicação empírica e a interpretação de um modelo de fases do feedback (Performance; Surgimento de Feedback; Receção de Feedback e Revisão) permite-nos elaborar um conjunto de comentários finais que revelam a importância do feedback para a compreensão e aprendizagem dos alunos.
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CD18.R7: Tax equalization plan

CD18.R7: Tax equalization plan

Member Government, in the proportion of its assessment for the financial year concerned. That there shall be charged against the credits of the individual Member Government an amount[r]

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Automatic street lighting using plc

Automatic street lighting using plc

Function Block Diagram using TIMER PROG Block, SUMMER/WINTER Block, Timer A-C Block and LOGIC GATES :. Figure3.[r]

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Low complexity detection for SC-FDE massive MIMO systems

Low complexity detection for SC-FDE massive MIMO systems

Block transmission techniques, with appropriate cyclic prefixes and em- ploying FDE techniques, have been shown to be suitable for high data rate trans- mission over severely time-dispersive channels [19]. Two possible alternatives based on this principle are OFDM and SC modulation using FDE (or SC-FDE). Due to the lower envelope fluctuations of the transmitted signals and, implicitly a lower PAPR (Peak-to-Average Power Ratio), SC-FDE schemes are especially interesting for the uplink transmission (i.e., the transmission from the mobile ter- minal to the base station), being considered for use in the upcoming LTE cellular system.
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Adaptive equalization for Interchip Communication

Adaptive equalization for Interchip Communication

In chapter 4 are presented a a set of CTLE transfer curves created through optimization in ADS. While in this chapter are also presented Verilog A models created to describe the behavior of the DFE and the receiver. Then using both ADS, Matlab and Hspice the equalization structure proposed in chapter 3 was simulated and it was verified that many of the channel induced ISI could be eliminated using the proposed structure. Finally in chapter 5 is made a study of the applicability of the methods described in chapter 2 to adapt the equalizing filters to the interface. It was possible too observe that the methods that consisted in making the voltage histograms of the waveform after the equalizers correctly selected the optimum setting. Although the success in selecting the proper setting for the interface the algorithm presented too much of a a heavy load in terms of computation power required for the interface. So next it was tested a simplification of the algorithm that was based on DC balance of data transmitted by the interface, unfortunately the algorithm was not robust enough in making the correct selection of the settings for the equalizers. Next, it was tested a new algorithm for the adaptation of both filters that consisted in making the histogram of the passing through zero of the waveform after the equalizer.The algorithm states that the setting for the equalizer that minimizes the variance of the edge histogram is the the optimum setting for the equalizer. The algorithm showed promising results, providing the interface with a robust and simple method to perform adaptation of both the DFE and the CTLE. For the adaptation of the DFE was also tested the least mean squares algorithm, this algorithm also was capable of selecting the correct value for the DFE taps during channel adaptation.
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Comput. Appl. Math.  vol.30 número3

Comput. Appl. Math. vol.30 número3

The form of (1.2) frequently occurs in a large number of applications, such as the (linearized) Navier-Stokes equations [21], the time-harmonic Maxwell equations [7, 8, 10], the linear programming (LP) problem and the quadratic pro- gramming (QP) problem [17, 20]. At present, there usually exist four kinds of preconditioners for the saddle point linear systems (1.2): block diagonal precon- ditioner [22, 23, 24, 25], block triangular preconditioner [15, 16, 26, 27, 28, 37], constraint preconditioner [29, 30, 31, 32, 33] and Hermitian and skew-Hermitian splitting (HSS) preconditioner [34]. One can [12] for a general discussion.
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