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In order to eliminate the voltage imbalance among battery cells when they are connected in series, the paper proposes a double-layer E-structure (DLE) equalizer based on bidirectional buck–boost converters, which has the advantage of quick equalization speed and can be applied to arbitrary number batteries. Furthermore, a novel two-stage equalization control strategy is proposed for the DLE equalizer to decrease maximum voltage gap between the maximum and minimum voltage cells. The paper analyses the working principle of proposed equalizer in detail and describes the detailed design of the control strategy and implement process. Simulation and experiment results show that the proposed equalizer can improve equalization performance of battery cells compared with adjacent cell-to-cell (AC2C) equalizer. [ABSTRACT FROM AUTHOR]

In this paper, a local area influence probabilistic (LAIP) detector for estimating magnetic grain interactions with coded data bits in two-dimensional magnetic recording is combined with a 2-D Bahl–Cocke–Jelinek–Raviv (BCJR)-based detector for joint removal of intertrack interference (ITI) and intersymbol interference (ISI). The LAIP detector sends log-likelihood ratio estimates of coded bits and an estimate of the local ISI/ITI convolution mask to a BCJR-based ISI/ITI detector followed by an irregular-repeat-accumulate decoder. Simulation results on a random Voronoi grain media model with ISI and ITI show that the concatenated LAIP/BCJR system, which detects three tracks simultaneously, achieves user information bit areal densities competitive or higher than results reported in a previous paper that employed the LAIP detector alone on a Voronoi grain channel without ISI/ITI. Simulation results on a grain-flipping probability media model based on micromagnetic simulations show that the proposed detector achieves an 11.3% bit error rate reduction compared to a recently proposed system with a 2-D linear equalizer followed by a two-track BCJR detector with 2-D pattern-dependent noise prediction. [ABSTRACT FROM AUTHOR]

With the widespread application of lithium-ion battery packs, it calls for efficient balancing methods to improve the performance of these battery systems. The relevant research has focused on the design of equalization circuits and control strategies while neglecting quantitative analysis and comparison of battery active equalization structures from the systematic level. In this paper, we propose an improved system-theoretic modeling approach for active equalization structures that takes into account the battery's constraints, including equalization current rate and SOC operation range. Accordingly, the mathematical models of various active equalization structures are derived that can describe their equalization dynamic behavior. Then, the analytical algorithms are developed to estimate the balancing time of active equalization structures online. Finally, extensive numerical simulations are conducted to evaluate and compare the average performance of these equalization systems in term of equalization time. It then comes up with a comprehensive comparison among them. Consequently, the Multicell-to-Multicell (MC2MC) balancing structure benefits the fast balancing speed and the lowest sensitive to initial batteries’ SOCs. The global structure has the lowest implementation cost and the series structure benefits the simplest control. Moreover, the module-based structures have faster balancing speed when each module contains about 4–6 batteries. [ABSTRACT FROM AUTHOR]

This paper proposes a joint read equalization scheme for interlaced magnetic recording (IMR) employing an array of readers, where multi-reader captured waveforms from asynchronously recorded tracks are jointly processed for single or multiple track data retrievals. In the array-reader-based IMR (ARIMR), the inter-track interference (ITI) collected from one reader is not necessarily synchronized to the other readers, especially in the case of a large cross-track separation (CTS) between the readers due to the linear density differentiation between the neighboring tracks. For the efficient mitigation of such asynchronous ITIs, an effective resampling-based joint equalization scheme is proposed in this paper, where multiple readbacks are digitally synchronized for designated target tracks, and joint processing of them suppresses the ITI in the equalized output. Furthermore, the proposed effective synchronization can be applied for joint multi-track retrievals when the CTS of the array reader is closed to the track pitch. For performance evaluations of the proposed joint read equalization scheme, numerical ARIMR channel simulations by the micro-pixelated magnetic channel model are conducted, and a bit error rate performance is evaluated under various configurations. In addition, waveforms captured from a dual-reader hard disk drive are evaluated with the proposed joint read equalization schemes for practical performance measurements of ARIMR. In both evaluations, unfavorable CTS conditions are investigated to account for the dominant skew effect in ARIMR, where the proposed joint equalization scheme enhances the off-track capability performance, especially with the customized configurations of interlaced recording. In overall, ARIMR with joint read equalization shows the potential of an areal density capability gain and a doubling of the data transfer rate over the conventional perpendicular magnetic recording and legacy IMR. [ABSTRACT FROM AUTHOR]

In this paper we propose a novel turbo equalizer based on the expectation propagation (EP) algorithm. Optimal equalization is computationally unfeasible when high-order modulations and/or large memory channels are used. In these scenarios, low-cost and suboptimal equalizers, such as those based on the linear minimum mean square error (LMMSE), are commonly used. The LMMSE-based equalizer can be efficiently implemented with a Kalman smoother (KS), i.e., a forward and backward Kalman filtering whose predictions are merged in a posterior smoothing step. Recently, it was shown that applying EP at the forward and backward stages of a KS equalizer could significantly improve its performance. In this paper, we investigate applying EP at the smoothing level instead. Also, we propose some further modifications to better exploit the information coming from the channel decoder in turbo equalization schemes. Overall, we remarkably reduce the computational complexity while highly improving the performance in terms of bit error rate. [ABSTRACT FROM AUTHOR]

In this paper, we design receivers for filter bank multicarrier-based (FBMC-based) massive MIMO considering practical aspects such as channel estimation and equalization. In particular, we propose a spectrally efficient pilot structure and a channel estimation technique in the uplink to jointly estimate all the users’ channel impulse responses. We mathematically analyze our proposed channel estimator and find the statistics of the channel estimation errors. These statistics are incorporated into our proposed equalizers to deal with the imperfect channel state information (CSI) effect. We revisit the channel equalization problem for FBMC-based massive MIMO, address the shortcomings of the existing equalizers in the literature, and make them more applicable to practical scenarios. The proposed receiver in this paper consists of two stages. In the first stage, a linear combining of the received signals at the base station (BS) antennas provides a coarse channel equalization and removes any multiuser interference. In the second stage, a per subcarrier fractionally spaced equalizer (FSE) takes care of any residual distortion of the channel for the user of interest. We propose an FSE design based on the equivalent channel at the linear combiner output. This enables the applicability of our proposed technique to small and/or distributed antenna setups such as cell-free massive MIMO. Finally, the efficacy of the proposed techniques is corroborated through numerical analysis. [ABSTRACT FROM AUTHOR]

This paper investigates the capacity of radio channels when iterative channel estimation, data detection, and decoding are employed. Knowing the capacity gain from iterative detection versus purely pilot-based channel estimation helps a designer compare the performance of an iterative receiver against a noniterative receiver and select the best balance between performance and cost. A bound is put on the linear minimum mean square error (LMMSE) channel estimation error, based on which a bound on the capacity is obtained. The attainable capacity is related to the channel estimation error of the receiver. The bounds take into account the uncertainty in symbol detection on channel estimation and incorporate the effect of channel estimation error on channel capacity. The interaction between the symbol detector and the decoder is analytically characterized and depicted in an extrinsic information transfer (EXIT) chart, where a bound on the detector curve is found. With optimal LMMSE pilot-based channel estimation, the results of this paper demonstrate that iterative channel estimation provides insignificant capacity advantage at fading rates below 1% of the symbol rate, although a computational-cost gain is still available. Iterative channel estimation provides a capacity benefit if suboptimal pilot signaling is used to provide initial channel estimates. [ABSTRACT FROM PUBLISHER]

This paper examines the improvement in performance of rotated and normally oriented heads by using the quasi-cyclic low-density parity-check (QC-LDPC) code in a two-dimensional magnetic recording (TDMR) system. This paper indicates that the significant improvement in performance in the rotated head compared to the normally oriented head can be attributed to the larger amplitude of its dibit response and the reduced overlap between conditional probability density functions. Simulation also indicates that maximum areal densities of 9.85 T/in ^2 and 6.64 T/in ^2 can be reached by the rotated head array (RHA) and normally oriented head array (NHA) at optimum bit aspect ratios of 0.67 and 3.5 for 5.5 nm Voronoi grains, respectively. After decoding, the performance of the NHA is about 8.5 dB worse than the RHA. With an oversampled signal, 2-D linear minimum mean-squared error (LMMSE) equalizer and LDPC codes, a user bit density near 10 Tbits/in ^2 is feasible for a rotated head array. [ABSTRACT FROM AUTHOR]

We present an extrinsic information transfer (EXIT) chart-based design technique for irregular repeat-accumulate (IRA) codes used in 2-D magnetic recording (TDMR) turbo-equalization systems. The channel model includes Voronoi magnetic grains, 2-D intersymbol interference (2D-ISI) and additive white Gaussian noise (AWGN). The receiver uses a 2D-ISI BCJR equalizer and an IRA decoder. For one outer equalizer-decoder iteration, we propose theory and simulation-based methods for computing EXIT curves. The simulation method calculates experimental EXIT curves for the check node decoder (CND) and the combination of the variable node decoder (VND) and an equalizer. The theoretical approach recursively calculates CND and VND Gaussian mixture model parameters in order to calculate EXIT curves. We then fit the VND and CND EXIT curves to find optimized variable node degree distributions. Simulation results show that the TDMR-optimized IRA codes achieve up to a 6.2% density increase in user bits/grain (U/G) compared with IRA codes designed for AWGN channels. The theory-based code designs achieve the same or better U/G as the simulation-based designs, but require 98% less design computation time. We also derive optimized IRA codes for iterative turbo-equalization; these codes can achieve simultaneous U/G gains and SNR savings compared with AWGN-optimized codes. [ABSTRACT FROM PUBLISHER]

Faster-than-Nyquist (FTN) signaling is regarded as a potential modulation format of 5G communication system for its high spectral efficiency. To further improve the spectral efficiency, researchers have extended the FTN signaling to the frequency dimension. However, the two-dimensional FTN signaling called multicarrier FTN (MFTN) signaling induces intersymbol interference and intercarrier interference (ICI), which challenges the receiver. Even the subcarriers are orthogonal, the MFTN signaling still induces the ICI. In this paper, we propose a new MFTN signaling transceiver with an FTN mapper and a linear minimum mean square error (LMMSE) equalizer. The FTN mapper is deployed on every subcarriers independently, which means that the MFTN is ICI-free. The proposed transceiver is compatible with the existing orthogonal frequency division multiplexing (OFDM) system and can detect the MFTN signal efficiently. The numerical results show that the bit error rate performance of the transceiver is close to the convolution code line. At the same time, the MFTN system with high-order modulation has power gains than the traditional OFDM system. [ABSTRACT FROM AUTHOR]

Shingled writing on bit patterned media (BPM) is a promising technology to further increase the areal density beyond 1 Tbit/in2 without drastic changes in writer design. In this paper, a shingled writer is modeled for writing a 2-D sector on BPM, and in particular, we investigate the potential benefit of leaving the last track in the 2-D sector untrimmed, making it fatter than the other tracks in that 2-D sector. During detection, the more reliable information from the last untrimmed (i.e., the fat) track is used as a priori information for detecting the data in the other tracks in that 2-D sector. The simulation results indicate that for 2-D sector with ten tracks (at 3.64 Tbits/in2 channel bit density) and 5% media noise and at a target bit error rate of 10^\mathrm -3 , using the fat track information, 2-D equalizer +2-D target + symbol-based pattern-dependent noise-predictive detector detecting a single track can provide about 2.9 dB SNR gain compared with that with the same joint detection method using uniform tracks at the same areal density. However, the latency increases due to the decision feedback detection. We can reduce this latency penalty by detecting three tracks at a time, but the SNR gain then reduces to 0.9 dB. [ABSTRACT FROM PUBLISHER]

This paper develops a novel voltage equalizer by combining wireless power transfer (WPT) and a voltage multiplier (VM) for series-connected energy storage cells. The physical isolation achieved by WPT can offer several unique benefits that traditional equalizers can hardly provide. In this paper, the characteristics of a multiple-output VM are analytically discussed and used to develop an equivalent one-output VM model. Based on this model, parameters of the WPT system are properly designed. The proposed design methodology can achieve a single-switch voltage equalizer without feedback control, which dramatically decreases the circuit complexity and cost. Moreover, this methodology can naturally ensure a robust system under small coil misalignment. In the experiment, the proposed system is built to balance four series-connected ultracapacitor modules. The system efficiency is 72.8% at a load power level of 10 W. [ABSTRACT FROM PUBLISHER]

Generalized frequency division multiplexing (GFDM) is one of the new waveforms with several attractive features such as lower out of band radiation, higher spectral efficiency, and better immunity to carrier frequency offset errors as compared with orthogonal frequency division multiplexing. However, it requires receivers with high computational complexity. Among different linear receiver structures, the joint minimum mean square error (joint-MMSE) receiver for GFDM achieves the best bit-error-rate (BER) performance, but it is the most computationally complex linear receiver. In this paper, we present a novel low complexity joint-MMSE receiver. We derive the closed-form expression for the joint-MMSE receiver filter by harnessing circulant properties of the matrices involved in the demodulation process. Amidst different operations involved in the receiver processing, inversion of a positive definite circulant-plus-diagonal matrix is found to be the costliest. Two low-complexity algorithms for the inversion of a positive definite circulant-plus-diagonal matrix are developed to design the low complexity receiver. We also propose a low complexity bias correction to improve BER performance. Our proposed receiver achieves a log-linear order of complexity without any noticeable loss in BER performance. [ABSTRACT FROM AUTHOR]

In the communication systems that use a linear modulation scheme for transmission, the fractionally-spaced (FS) samples of the received signal constitute a wide-sense cyclostationary time series. Hence, the standard Fourier transform techniques cannot be used to study the spectral characteristics of the received FS samples or to derive the transfer function (TF) of the corresponding digital minimum mean-square error (MMSE) receiver. In this paper, an analytical expression for the TF of the FS MMSE equalizer is derived, which includes the effects of the continuous-time to discrete-time (C/D) converter used at the receiver front end. Using this TF, the sources of instability of the FS least-mean-square (LMS) algorithm and the effects of the equalizer length and sampling phase on convergence of the LMS algorithm are explained. For stabilization of the FS LMS algorithm, conditions on the front-end C/D converter are provided, such that, when satisfied the LMS algorithm becomes more stable and the learning characteristics of the modified receiver are better than the leaky-FS LMS algorithm. Theoretical results are corroborated by simulations. [ABSTRACT FROM AUTHOR]

Bit-patterned media recording (BPMR) has been developed into a technology for the next generation of hard disc drives, which can push area density beyond 1 Tb/in2 for satisfying the ever increasing demand of storing massive amounts of data. One of the major challenges in BPMR systems is 2-D interference that is regarded as a gist of degrading the system performance. From a signal processing viewpoint, 2-D optimal detection schemes are very complicated for 2-D interference channels. In this paper, we propose a twin iterative detection scheme based on 1-D detectors and decoders in order to reduce the complexity. The performance of the proposed scheme is compared to that of a conventional simplified 2-D iterative detection scheme, and the results indicate that the proposed model is better by approximately 1 dB under the effect of 10% track misregistration. [ABSTRACT FROM AUTHOR]

Because of the explosion in data growth, the requirement for high-density storage systems has increased. Bit-patterned media recording (BPMR) is a candidate for the next-generation magnetic recording systems, and its many advantages facilitate the achievement of recording densities of 1 Tb/in2 and beyond. In BPMR, each information bit is represented by a magnetic island; however, due to the small spacings between the along- and across-track islands that are for the achievement of a high areal density, severe extents of the inter-symbol interference and inter-track interference appear. These error factors degrade the system performance of the recording system. In this paper, an iterative channel detection scheme with a low-density parity check (LDPC) product code for which the extrinsic information between the soft output Viterbi algorithm and the LDPC product code is used for the BPMR is proposed. For the improvement of the BPMR performance, the modified extrinsic information data are exploited. [ABSTRACT FROM AUTHOR]

The current cellular systems are conventional cell-centric based architectures, and thus the inter-cell interference greatly affects the quality of service (QoS) of users located at the border of those service areas. For that reason, future wireless systems will rely on a cell-less deployment by using an alternative promising network infrastructure known as cell-free (CF) technology. Here, in contrast to the current networks, there are no concepts of cells or cell boundaries since it is a disruptive paradigm where a large number of geographically distributed access points (APs) simultaneously and jointly serve a much smaller number of user terminals (UTs) to fulfill the exponentially increasing number of users. Therefore, this paper aims to contribute on this field and considers the design of hybrid analog/digital multi-user equalizer for broadband millimeter wave (mmWave) CF massive multiple-input multiple-output (mMIMO) systems, using a distributed beamforming approach (processing is distributed by APs and central unit (CU)) to reduce the fronthaul requirements. First, only a low complexity analog precoder is applied to the transmitter, while a joint design of APs hybrid equalizer and CU combiner are considered by minimizing the average mean square error (MSE) between the transmitted and CU estimated signals. To achieve this joint design, a cyclic minimization method is used to iterate between APs hybrid equalizer and CU combiner, where the information is exchanged between APs and CU based on a set of error variances to improve detection performance. The simulation results show that the proposed precoder and the hybrid linear equalizer can achieve performance results very close to those of the fully digital system. Moreover, just two iterations of the proposed algorithm are already enough to match the full centralized approach performance. [ABSTRACT FROM AUTHOR]

This paper presents the results of a comprehensive study of the shingled writing process and various signal processing and data detection approaches applied to the readback waveforms. The recording simulations include realistic head fields, a random granular media, magnetostatic and exchange interactions, and a READ head sensitivity function. Readback waveforms are examined in both one and two dimensions in terms of signal characteristics (linear and nonlinear), noise behavior (stationary and signal-dependent), and intertrack interference. Different equalization and detection approaches are compared and about a 10% density gain is reported for such 2-D magnetic recording compared with traditional single-track recording. These gains depend strongly on the number of readers, the reader positioning, and the reader width. [ABSTRACT FROM AUTHOR]

Two-dimensional magnetic recording (TDMR) was proposed in 2008 as a means of pushing beyond 1 Tbit/in ^2 areal-density yet staying with relatively conventional magnetic components. A density of approximately 1 Tbit/in ^2 is considered to be the limit for conventional perpendicular magnetic recording. The original concept for TDMR has evolved greatly since it was originally proposed. This evolution has occurred as more information has become available about the characteristics of shingled tracks and 2-D read-back signals and as constraints have become apparent in the implementation of recording components and electronics. With today’s technology, the projected gains are smaller than originally envisioned. As a very practical first step that introduces TDMR and provides modest gains without incurring undue complexity or cost, this paper focuses on the idea of a stacked two-element reader operating on shingled magnetic recording tracks and a two-input equalizer feeding a standard data detector. The dual-reader gains are assessed based on combining waveforms captured from a single reader at many off-track positions, track-pitches, and radii. [ABSTRACT FROM AUTHOR]

Two-dimensional magnetic recording (TDMR) relies on advanced signal processing and coding techniques to enable storage of data at higher densities. Various detection and decoding schemes have been proposed in the literature. In this paper, a recently proposed joint detection and decoding scheme known as the joint Viterbi detector decoder (JVDD) is presented for TDMR channels. The JVDD operates on a trellis and attempts to find a sequence in the trellis that belongs to a legal codeword with minimum metric. It does so by using a metric thresholding and parity checking technique over the same trellis structure. The iterative detector/decoder consisting of a soft-output Viterbi algorithm detector and low-density parity check decoder is used as a performance benchmark for the JVDD. In this paper, we perform the comparison with various equalization/detection techniques consisting of: 1) a 1-D general partial response equalization scheme followed by a 1-D-detector as used in today’s Partial Response Maximum Likelihood Detection (PRML) channels; 2) a 2-D equalization scheme that equalizes to a 1-D target [fully equalizing away the intertrack interference (ITI)], followed by a series of parallel 1-D-detectors to handle the intersymbol interference (ISI); and 3) a 2-D-equalization scheme followed by 2-D detector to combat both ITI and ISI. [ABSTRACT FROM AUTHOR]

Nonlinearity is one of the key issues that hinder the development of high-capacity optical short reach systems. This paper proposes three variants of kernel affine projection (KAP) algorithms, all of which combine kernel mapping and affine projection in a reproducing kernel Hilbert space for compensating nonlinear impairments in optical short reach systems. An intensity modulation/direct detection system with a single digital-to-analogue converter, a packaged externally modulated laser and a packaged InP photo-detector is used for experimental demonstration, achieving 238-Gbps (net rate 222-Gbps). Experimental results show that the KAP algorithms can mitigate nonlinear impairments in short-reach communications while maintaining low complexity in reproducing kernel Hilbert space. [ABSTRACT FROM AUTHOR]

In this paper, a battery balancing circuit is proposed for the series-connected lithium-ion battery cells based on the principle of synchronous rectification. The proposed balancing circuit, also referred to as an equalizer, mainly includes a buck–boost converter (BBC), a multiport half-bridge converter (MHBC), and a driving circuit. The MHBC is coupled with a multiwinding transformer. Compared with the conventional congeneric methods, the number of transformer windings is almost reduced by half, leading to a more compact size and lower cost. Moreover, the secondary mosfets of the MHBC are synchronously driven by the primary half-bridge converter (HBC) without the need of additional isolated mosfet gate drivers and power supplies, dramatically reducing the circuit cost and complexity. In addition, the proposed equalizer can realize the module-to-multi-cell (M2MC) equalization under severe imbalance conditions to improve the balancing speed, and work at the any-cell-to-any-cell (AC2AC) self-balancing mode under slight imbalance conditions to improve the balancing efficiency and effectiveness, which achieves a good trade-off between balancing speed and effectiveness. The expressions of the equalization current and efficiency are derived and verified by experimental results. The proposed equalizer is experimentally evaluated for a string with 12 series-connected lithium-ion cells. [ABSTRACT FROM AUTHOR]

To achieve a high track density, two-dimensional magnetic recording (TDMR) is combined with shingled magnetic recording (SMR). SMR makes it possible to record 1 bit on a few grains. However, the performance will be remarkably deteriorated by the increased media noise, the inter-track and inter-symbol interference (ITI and ISI). Therefore, the application of effective equalization and error control coding are required. In this paper, we investigate a simple block-based neural network equalizer (NNE) that mitigates the influence of ITI and ISI. We compare the equalization effects of the NNE and a conventional 2-D equalizer with low-density parity-check (LDPC) coding based on a random Voronoi grain media model. Simulation results show the proposed block-based NNE achieves better bit error rate performance than the conventional 2-D linear equalizer followed by the a posteriori probability (APP) detector and a sum-product (SP) decoder. In addition, we find the block-based NNE is sensitive to write errors. [ABSTRACT FROM AUTHOR]

This paper aims to build a supervised classifier for dealing with imbalanced datasets, uncertain class proportions, dependencies between features, the presence of both numeric and categorical features, and arbitrary loss functions. The Bayes classifier suffers when prior probability shifts occur between the training and testing sets. A solution is to look for an equalizer decision rule whose class-conditional risks are equal. Such a classifier corresponds to a minimax classifier when it maximizes the Bayes risk. We develop a novel box-constrained minimax classifier which takes into account some constraints on the priors to control the risk maximization. We analyze the empirical Bayes risk with respect to the box-constrained priors for discrete inputs. We show that this risk is a concave non-differentiable multivariate piecewise affine function. A projected subgradient algorithm is derived to maximize this empirical Bayes risk over the box-constrained simplex. Its convergence is established and its speed is bounded. The optimization algorithm is scalable when the number of classes is large. The robustness of our classifier is studied on diverse databases. Our classifier, jointly applied with a clustering algorithm to process mixed attributes, tends to equalize the class-conditional risks while being not too pessimistic. [ABSTRACT FROM AUTHOR]

High-order modulation formats with high symbol rates are promising candidates for meeting the growing traffic requirements of digital coherent transmission. In using these modulation formats, the impact of transceiver impairment on the signal quality becomes significant. In this paper, we propose an 8×2 widely linear (WL) multiple-input multiple-output (MIMO) equalizer with independent complex filtering on IQ signals to mitigate linear transceiver impairments. Furthermore, we extend the equalizer for digital subcarrier (SC) multiplexing. Accordingly, a 16×4 WL MIMO equalizer is also proposed to mitigate linear transceiver impairments, through application to a pair of SC inputs. Experimental results show that, for transmission of a 58-GBaud polarization-multiplexing 64 quadrature amplitude modulation (PM-64QAM) single-carrier signal, the proposed method effectively compensates for various receiver impairments and also mitigates transmitter (Tx) impairments. Q-penalties of 0.1 dB up to a 10-ps skew, 2.5-dB gain imbalance, 7.2-degree phase error, and –15-dB crosstalk in Tx were achieved for 100-km standard single-mode fiber transmission. Moreover, for a 29-GBaud PM-64QAM dual-SC signal, the proposed 16 × 4 WL MIMO equalizer shows transceiver impairment mitigation performance similar to that in the single-carrier case, even though dual-SC transmission is less tolerant of laser phase noise. [ABSTRACT FROM AUTHOR]

This paper presents a scheme that utilizes soft feedback information obtained from a decoder to eliminate detrimental interference in bit-patterned media recording (BPMR) systems. BPMR is a promising technology that can increase the storage area density of magnetic storage systems, but one of the main challenges is to overcome 2-D spatial interference. The performance of the proposed scheme is compared with that of a conventional iterative detection scheme, and the results indicate that the proposed model is better by approximately 1 dB at 20% track misregistration. In particular, the performance of the system is quite superior, allowing the design of systems with higher area densities. [ABSTRACT FROM AUTHOR]

Chained turbo equalization (CHATUE) has been recently recognized as a low-complexity frequency-domain turbo equalization technique that eliminates the necessity of transmitting the cyclic prefix (CP), and hence allows for spectrally efficient signaling in wireless communications. However, two issues arise from the original version of CHATUE (referred to as CHATUE1) as a consequence of eliminating the CP, which are the noise enhancement and the latency due to the time-concatenated structure. This paper proposes a new version of CHATUE (referred to as CHATUE2) to solve the noise enhancement problem. CHATUE2 retrieves the circulant structure of the channel matrix, originally inherent within the CP transmission, by utilizing composite replica signals that combine the received signals and the soft reference signals replicated from the log-likelihood ratio (LLR) fed back from the decoder. For this purpose, this paper determines the optimal combining ratio based on the minimum-mean-square-error (MMSE) criterion. CHATUE2 is hence able to achieve an improvement in bit-error-rate (BER) performance over CHATUE1. In addition, this paper provides a solution to solving the latency problem by making a practical assumption on the training sequence (TR) transmission, which is required to perform channel estimation generally, in practical systems. Furthermore, this paper proposes a new channel estimation technique, i.e., chained turbo estimation (CHATES), which improves the spectrum efficiency and asymptotically achieves the Cramér–Rao bound (CRB). CHATES assumes that the TR length is exactly equal to the channel impulse response (CIR) length, although the conventional technique requires twice as long or even longer TR lengths. Numerical results show that CHATUE2 with CHATES achieves a gain of 1 dB over conventional turbo equalization with a CP at a BER of \10^-5 in realistic propagation scenarios represented by channel sounding measurement data and in model-based frequency-selective fading channels. [ABSTRACT FROM PUBLISHER]

This paper presents a different interpretation of the cyclic Wiener filter (CWF) for digital (in-phase/quadrature) IQ-modulated signals, such as phase-shift keying (PSK) or quadrature amplitude modulations (QAM). We demonstrate that the CWF can be implemented as a multirate filter instead of the frequency-shift (FRESH) filter implementation found in the literature. The multirate implementation consists of a fractionally spaced equalizer (FSE) followed by a pulse shaping filter, thus establishing a direct relationship between the CWF and FSEs. Afterwards, the results from the study are applied to develop a simple blind adaptive algorithms for signal estimation, which are benchmarked against the most common CWF implementation based on FRESH filters. [ABSTRACT FROM AUTHOR]

Hardware structure is a basic characteristic of a battery management system (BMS), which influences the overall performance of battery packs. This paper presents a novel BMS architecture based on the power/data time division multiplexing transmission technique. In the proposed system, a common bus is employed to transfer power and data simultaneously, so the system wiring is simplified. The system consists of a pack management unit and several cell management units (CMUs). The circuit of the CMU is compact and achieves conventional management functions like status monitoring and active cell balancing; thus, it can be integrated with battery cell to be an intelligent cell. The timing sequence of the system is presented, and the design considerations are discussed in detail, including terminal resistance selection, maximum node number calculation, and power consumption analysis. Finally, a simulation based on MATLAB is carried out and an experimental prototype system with six nodes is built, which verifies the correctness of the architecture and proves the feasibility in practical applications. [ABSTRACT FROM AUTHOR]

Compared with the conventional hard switching battery equalizers, hierarchical battery equalizer based on the bipolar continuous-conduction mode buck–boost units could effectively reduce the switching loss and improve the conversion efficiency. This paper mainly addresses the key technical challenges associated with the optimal design of this battery equalizer. The inductor current is controlled to enter into the negative region. Thus, the mosfet body diode provides a freewheeling path for the inductor current during the dead band. This ensures zero-voltage switching turn-on of both power mosfets in each buck–boost unit without auxiliary snubbers. Therefore, the switching losses are significantly reduced. Meanwhile, the integral of the inductor negative current is precisely controlled to minimize the circulating current. This guarantees both minimized conduction losses and suitable equalization speed. Furthermore, an equalization algorithm, which compensates the battery internal resistance induced state-of-charge error, is proposed to improve the equalization accuracy. The operating principles and design considerations are analyzed in detail. An experimental prototype to balance four series-connected lithium-ion battery cells is implemented. The experimental results validate the design of the equalizer and demonstrate obvious efficiency enhancement over the conventional method. [ABSTRACT FROM AUTHOR]

Increasing areal density in bit patterned media recording systems increases the 2-D interference from the adjacent islands in the down-track and cross-track directions. Also, nonlinear effects due to the track mis-registration (TMR) and media noise become severe as the areal density increases and degrade the bit error rate (BER) performance. In this paper, we proposed a new detection scheme based on multi-layer perceptrons (MLPs) to alleviate the nonlinear effects. Two MLPs are used in the proposed detection scheme and learn the channel with the nonlinear effects in the training procedure. One MLP is used for TMR estimation and the other MLP is used for data detection. The MLP-based TMR estimator estimates the TMR from the readback signals. Then, the MLP-based data detector equalizes the channel reflecting the estimated TMR and media noise and detects the data bit. Therefore, the detection scheme is robust to the effects of the TMR and media noise. The proposed detection scheme provides the improved BER performances compared to the conventional detection scheme using the 2-D equalizer filter, 1-D generalized partial response target, and Viterbi detector in the channel with the TMR and media noise. [ABSTRACT FROM AUTHOR]

Charge equalization for a series-connected battery string is necessary to enhance usage life and performance of cells. In this paper, an isolated bidirectional dc–dc converter with quasi-resonant zero-voltage switching (ZVS) is proposed for centralized charge equalization system. Through the quasi-resonant operation, the proposed converter can achieve ZVS operations in both boost and buck modes, which decreases switching losses and improves the efficiency. The energy in leakage inductance is released to output side in the boost mode and recycled to the input side in the buck mode, which eliminates the voltage spike. Moreover, the proposed converter has fewer components than existing converters used in the centralized charge equalization system. The operating principle and theoretical derivation of the proposed converter are presented. The ZVS implementations and conditions are analyzed and illustrated in detail. Finally, the experiments using a 7.2 Ah battery string of 13 cells are conducted. The results verify the validity of the proposed converter and show that the equalizer achieves good performance in terms of equalizing speed and efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the performance of a filter-bank multicarrier-quadrature amplitude modulation (FBMC-QAM) system with two prototype filters. We analyze the effective channel and derive the signal-to-interference ratio for additive white Gaussian noise channels and multipath fading channels. Based on the analysis, the characteristics of the effective channel according to various prototype filter sets and channel models are investigated. Utilizing the effective channels, we design two types of per-tone channel equalizers and evaluate the bit error rate performances by Monte Carlo simulations. The simulation results show that the FBMC-QAM system with two prototype filters can achieve almost the same bit error rate performance as orthogonal frequency division multiplexing with cyclic prefix by adopting the signal-level per-tone channel equalizer. Finally, the computational complexity of per-tone channel equalizers is analyzed. [ABSTRACT FROM AUTHOR]

For the high areal density bit patterned media recording (BPMR) systems, various multi-track equalization and detection techniques were proposed to mitigate the inter-track interference (ITI) so as to recover recorded data from the detecting tracks efficiently, but most works rarely aim to recover the recorded data on the sidetracks concurrently. As anticipation of that the readback signal has the intense contributions from the sidetracks due to high areal density, in this paper, we attempt to estimate the recorded data from the sidetracks as well as the detecting tracks by a multi-track joint detector that processes multi-track readback signals jointly in a single detector. To avoid the high complexity, which is the main shortfall in realizing the multi-track joint detector, we propose to employ a multi-track joint detector with a reduced complexity trellis for multi-head multi-track systems, in particular, four-head four-track (4H4T) BPMR system. To reduce the number of states in the trellis, the signals are equalized to 2-D generalized partial response targets whose cornered ITI coefficients are set to zero. The parallel branches are also incorporated in the trellis to estimate the data on the sidetracks. Moreover, we propose a two-head four-track (2H4T) system which generates the estimates of the recorded data on the four tracks by processing the signals from only two tracks. According to the simulation results, the proposed detector performs well on the data estimation of the detecting tracks as well as the sidetracks in both 4H4T and 2H4T systems. [ABSTRACT FROM AUTHOR]

Reduced-complexity multiuser interference equalization and group decoding (ME-GD) is an attractive way to improve performance of multiuser transmissions for narrow-band additive white Gaussian noise channels. ME-GD receivers have been investigated in the past for convolutionally coded synchronous multiple-access channels (MACs). In this paper, we propose a new ME-GD for trellis-coded asynchronous MACs. The coding information of a subset of users and the multiuser interference are jointly taken into account in the branch metric computation using per-survivor processing. The novel approach leads to a family of Viterbi decoders which offers a good tradeoff between performance and complexity. As a second contribution of this paper, we derive theoretical bounds for the performance of ME-GD considering the effect of error propagation, which is critical for asynchronous MACs. Numerical results show the excellent accuracy of the proposed bounds. Finally, based on the novel theoretical analysis, we derive a new criterion to achieve good tradeoffs between performance and complexity. [ABSTRACT FROM AUTHOR]

A plethora of new applications will be enabled by next generation wireless networks. These demand sophisticated medium access control and physical layer protocols in order to fulfill the requirements in terms of spectral efficiency, bit error rate (BER), energy efficiency, reliability, and security, among others. This paper develops an advanced space-time multiple-input, multiple-output (MIMO) solution that builds on the concept of space-time shift keying (STSK) for single-carrier frequency domain equalization (SC-FDE). STSK-aided SC-FDE, or SSF, ensures space-time and frequency diversity in dispersive channels, but can only support suboptimal linear receiver schemes. We therefore introduce a turbo equalizer for SSF in frequency-selective multipath channels. It enables inter-symbol-interference cancellation by means of iterative space-time processing. We coin it the iterative space-time block equalizer (SSF-ISTBE). We provide the mathematical formulation for the proposed SSF-ISTBE framework in non-linear channel conditions. We demonstrate that the SSF-ISTBE achieves a substantial 4 dB gain in terms of BER over the linear minimum mean square error equalizer while significantly reducing the computational complexity of the optimal maximum likelihood SSF. When considering practical transceivers, in particular non-linear power amplifiers, the gain of the SSF-ISTBE becomes more prominent over state-of-the-art approaches, demonstrating its robustness against non-linear distortion. [ABSTRACT FROM AUTHOR]

The move from traditional single-track magnetic recording to two-dimensional magnetic recording (TDMR) with squeezed tracks and multiple readers opens up new design degrees of freedom beyond the track pitch and bit-aspect ratio, including the widths, spacing, and crosstrack positions of the readers. In this paper, we present a systematic method for determining the combination of multi-reader geometry, track pitch, and bit-aspect ratio that maximizes the areal density of a TDMR system using single-track detectors. The method combines realistic modeling of the medium and write/read processes, advanced signal detection, and information-theoretic tools. For the particular head and medium we consider, the two-reader geometry that maximizes areal density with zero skew and zero misregistration was found to use different-sized readers (the smaller having a full-width at half-maximum width, i.e., 96% of the track pitch and the larger having a width, i.e., 148% of the track pitch) with significant overlap in the crosstrack direction (centers spaced by one eighth of the track pitch). The optimal bit-aspect ratio was 2.2. At the optimal operating point, the information rate per coded bit is 0.8. [ABSTRACT FROM AUTHOR]

In the past several years, the single-reader read channel scheme reached its performance limitation. Thus, a new multiple-reader system is evaluated in this paper to have more than one read back signal to improve the hard disk drive performance and capacity. The novel control loops, equalization, and detection are discussed on how to handle the multiple read back signals, estimate head positions based on preamble signal-to-noise ratio, jointly equalize two stream signals as well as detect the final output using pattern-dependent detection. [ABSTRACT FROM AUTHOR]

Recent magnetic recording technologies have opened the possibility of reaching densities of 10 Tb/in2. A 2-D magnetic recording (TDMR) scheme has pointed out one of the key technologies for increasing areal density. From the viewpoint of signal processing for TDMR, a recording system is desirable or preferable to be capable of allowing to get readback signals from a group of adjacent parallel tracks and detect recorded data written in these tracks simultaneously. This paper proposes a novel signal processing scheme with coding and detection for bit-patterned media recording (BPMR) which is considered to be TDMR using bit-patterned media. Actually, the proposed signal processing scheme for BPMR gets mixed readback signal sequences from the parallel tracks using a single reading head and these readback signal sequences are equalized to a frequency response given by a desired 2-D generalized partial response system. In decoding process, a single maximum likelihood sequence detector is capable of detecting the equalized signal sequence, and it leads to an increase in the effective transfer rate because the recorded data on the parallel tracks are decoded for each time slot. [ABSTRACT FROM AUTHOR]

One limitation of many battery charge equalizers is their slow equalization speed, especially when there are a large number of batteries in the series-string in high-voltage and high-power applications. This paper presents a new architecture for battery charge equalization. In this architecture, independent equalizers are placed in different layers and all the layers can equalize the corresponding batteries simultaneously, thus reducing equalization time by 50%. We explore the operation, performance characteristics, and the design of the architecture. Both simulation and experimental results are presented to validate the analysis in this paper. [ABSTRACT FROM AUTHOR]

Battery equalizers are widely used in multibattery systems to maintain balanced charge among individual battery cells. While the research on the hardware realization of battery equalizers has received significant attention, rigorous analysis of the battery equalization process at the system level remains largely unexplored. In this paper, we study three types of battery equalization system structures: series-based, layer-based, and module-based. Specifically, we derive mathematical models that describe the system-level behavior of the battery equalization processes under these equalization structures. Then, based on the mathematical models, analytical methods are developed to evaluate the performance of the equalization processes. In addition, we carry out statistical analysis to compare the performance of the three equalization structures considered. [ABSTRACT FROM PUBLISHER]