# John R. Barry's research while affiliated with Georgia Institute of Technology and other places

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## Publications (154)

The industry standard for single-track detection in magnetic recording is partial-response equalization followed by a trellis-based sequence detector. We extend for the first time the partial-response paradigm to the case of multitrack detection when the multiple tracks being jointly detected were written asynchronously, with different bit phases a...

A magnetic recording read channel has numerous parameters that must be carefully tuned for best performance; these include not only the equalizer coefficients but also any parameters inside the soft-output detector, some of which may be pattern dependent, including signal levels, predictor coefficients, and residual noise variances. Conventional tu...

A dominant impediment in magnetic recording is pattern-dependent media noise, and its impact will only grow more severe as areal densities increase. A widely used strategy for mitigating media noise in a trellis-based detector is pattern-dependent noise prediction (PDNP); in this approach, each bit pattern (which determines a trellis branch) will h...

Two-dimensional magnetic recording (TDMR) is an emerging storage technology that aims to achieve areal densities on the order of 10 Tb/in
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>
, mainly driven by innovative channels engineering with minimal changes to existing head/media designs within...

A bottleneck in multiple-input multiple-output communications systems is the complexity of detection at the receiver. The complexity of optimum maximum-likelihood detection is often prohibitive, especially for large numbers of antennas and large alphabets. A suboptimal tree-search-based detector known as the K-best detector is an effective scheme t...

Two-dimensional magnetic recording promises to increase areal density through the joint detection of multiple tracks of interest. This paper concerns the problem of joint detection of multiple tracks that are written asynchronously, meaning that neither the bit boundaries (phase) nor the bit rate (frequency) are aligned between neighboring tracks....

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. Readb...

We analyze the general form of the extrinsic information transfer curve of polar codes viewed as multilevel codes with multistage decoding. Based on this analysis, we propose a graphical design methodology to construct polar codes for intersymbol interference channels. The method matches the extrinsic information transfer curve of the code to that...

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...

In this paper, we study the performance of hybrid automatic repeat request (HARQ) with incremental redundancy over double Rayleigh channels, a common model for the fading amplitude of vehicle-to-vehicle communication systems. We investigate the performance of HARQ from an information theoretic perspective. Analytical expressions are derived for the...

The state-of-the-art soft-output decoder for polar codes is a message-passing algorithm based on belief propagation, which performs well at the cost of high processing and storage requirements. In this paper, we propose a low-complexity alternative for soft-output decoding of polar codes that offers better performance but with significantly reduced...

We propose a detection strategy for the two-dimensional magnetic recording channel with multiple read heads, in which intertrack interference is suppressed by a combination of linear combining and soft interference cancellation. This suppression reduces the detection problem to a traditional one-dimensional detection problem, so that we may leverag...

A widely used soft-output decoder for polar codes is a message-passing algorithm based on belief propagation, which performs well at the cost of high processing and storage requirements. In this paper we propose a low-complexity alternative for soft-output decoding of polar codes that offers comparable performance but with significantly reduced pro...

We propose an algorithm to allocate streams and find the corresponding beamforming and combining weights that maximize the sum rate of a set of interfering multiple-input multiple-output (MIMO) links. Our algorithm iteratively computes the beamforming and combining weights of each link and determines how many streams, if any, are allocated to each...

We describe an error-correcting system that combines polar codes with turbo equalization for partial response channels. The successive cancellation decoder, originally proposed by Arikan for polar codes, does not produce the soft outputs needed for turbo processing. The belief propagation decoder, on the other hand, requires many iterations and has...

We tackle the problem of determining the beamforming and combining weights in a network of interfering multiple-input multiple-output (MIMO) links. We classify any strategy for computing these weights as either unilateral or bilateral. A unilateral strategy is one for which the responsibility of cancelling interference from one node to another is p...

We consider the problem of combining the signals received from a decode-and-forward relay with those received from the source. As an alternative to the high-complexity maximum-likelihood combining strategy, we propose a bit-wise combining strategy in which the received signals are first converted to log-likelihood values before being combined. We s...

The golden code is a full-rate full-diversity space–time code for the two-input two-output channel with good performance but
high decoding complexity. The overlaid Alamouti codes were recently proposed as an alternative; in exchange for a slight performance
penalty, they have lower decoding complexity on quasistatic channels with QAM alphabets. How...

In this paper, we study the performance of hybrid automatic repeat request (HARQ) with incremental redundancy (IR) over double Rayleigh channels. Such channels can be used to model the fading amplitude for vehicle-to-vehicle (V2V) communications. We study the performance of HARQ from an information theoretic perspective. Analytical expressions are...

In this letter, we present indoor multipath dispersion characteristics for visible light communications (VLC). Since the VLC uses a wide spectrum between 380 nm and 780 nm, the conventional narrowband model for infrared may not apply. We generalize the Barry's model by including wavelength-dependent white LED characteristics and spectral reflectanc...

The modulation and demodulation blocks in an orthogonal frequency-division multiplexing (OFDM) system are typically implemented digitally using a fast Fourier transform circuit. We propose an analog implementation of an OFDM demodulator as a means for reducing power consumption. The proposed receiver implements the discrete Fourier transform (DFT)...

Because each golden code codeword conveys four information symbols from an M-ary QAM alphabet, the complexity of an exhaustive-search decoder is proportional to M<sup>4</sup>. In this paper we prove that the golden code is fast-decodable, meaning that maximum-likelihood decoding is possible with a worst-case complexity proportional to only M<sup>2....

We propose a new family of high-rate space-time block codes called embedded orthogonal space-time (EOS) codes. The family is parameterized by the number of transmit antennas, which can be any positive integer, and by the rate, which can be as high as half the number of transmit antennas. The proposed codes are based on a new concept called embeddin...

We present a soft-output multiple-input multiple-output (MIMO) detection algorithm that achieves near max-log optimal error rate performance with low- and fixed-computational complexity. The proposed smart ordering and candidate adding (SOCA) algorithm combines a smart-ordered QR decomposition with smart candidate adding and a parallel layer-by-lay...

Over the last two decades, wireless communications has gained enormous popularity, offering attractive options for many personal and organizational communication needs due to major intrinsic characteristics such as flexibility, cost effectiveness, and mobility.

Soft-output detection of the golden code is an important but computationally difficult task. We propose a low-and fixed-complexity soft-output detector for the golden code that uses linear equalization to simplify the task of finding a list of candidate values for one pair of information symbols, and then - for each pair on the list - it uses decis...

Three desirable properties of a four-antenna spacetime block code are full rate, full diversity, and single-symbol decodability. Previously reported space-time codes that achieve all three properties do so at the expense of the peak-to-average power ratio (PAPR). A fourth desirable property of a space-time block code is that its PAPR be the same as...

Consider a communications system where the detector generates a mix of hard and soft outputs, which becomes fed to a soft-input channel decoder. In such a setting, it is of interest to find the optimal soft representation for the hard detected bits, which minimizes the probability of error at the decoder output. In this contribution we prove that f...

The golden code is a full-rate full-diversity space-time code for two transmit antennas that has a maximal coding gain. Because each codeword conveys four information symbols from an M-ary QAM alphabet, a maximum-likelihood decoder based on a conventional sphere detector has a worst-case complexity of M<sup>4</sup>. In this paper we present a new a...

We introduce a new family of space-time codes called embedded Alamouti space-time (EAST) codes which offer high rate, a nonvanishing determinant and low decoding complexity. The family is parameterized by both the number of transmit antennas, which can range from two to eight, and by the rate, which can range from one to half the number of transmit...

Suboptimal detection schemes, such as list MIMO detection, often face the challenge of having to ldquoguessrdquo at the decision reliability for some of the detected bits. A simple yet effective way of doing this is to set the maximum magnitudes of the associated log-likelihood-ratios (LLRs) to a certain predefined value: LLR clipping. However, the...

Three desirable properties of a four-antenna space time block code are full rate, full diversity, and single-symbol decodability. Previously reported space-time codes that achieve all three properties do so at the expense of the peak-to-average power ratio (PAPR). A fourth desirable property of a space-time block code is that its PAPR be the same...

Orthogonal-frequency-division multiplexing (OFDM) transforms a frequency-selective multiple-input multiple-output (MIMO) fading channel into a MIMO-OFDM channel that has a well-defined outage capacity. A transmitter with channel knowledge can achieve this capacity by a combination of eigenbeamforming and water-filling; the eigenbeamforming transfor...

We introduce a new family of detectors for multiple-input multiple-output (MIMO) channels. These detectors are called Chase detectors because they can be interpreted as a translation of the Chase error-control decoding algorithm from time to space. The Chase detector is parameterized by only four parameters; nevertheless, it reduces to a wide range...

The fifteen articles in this special issue are devoted to new equalization techniques for wireless communications, including new the latest theories and applications.

Tree search schemes are an efficient means for solving the detection problem in multiple-input multiple-output systems. One option for implementing such a tree search is the smart candidate adding approach: using first an unconstrained search for the MAP estimate and then multiple constrained searches for counter-hypotheses. An inherent disadvantag...

We introduce a new family of detectors for multiple-input multiple-output (MIMO) channels called Chase detectors because of their resemblance to the well-known Chase algorithm for soft decoding of error-control codes. A Chase detector is fully specified by only three simple parameters; nevertheless, it reduces to a wide range of previously reported...

We propose a new cooperation protocol for the fading multiple-access channel called space-division relay (SDR). It is similar to the protocol of Laneman, Tse and Wornell (LTW), except that the relays use space- division instead of time-division multiplexing. The result is a nonorthogonal cooperation protocol with a higher rate that nevertheless ach...

We present a new detection algorithm for multiple-input multiple-output channels called the CLAM algorithm. The CLAM algorithm is similar to the classical M algorithm for searching the detection tree, except that it varies from one stage to the next the number of children extended from each retained node. These numbers are optimized based on knowle...

The BLAST-ordered decision-feedback (BODF) detector is a nonlinear detection strategy for multiple-input multiple-output (MIMO) channels that can significantly outperform a linear detector. However, for some applications even the BODF detector is too complex. We propose the partial decision-feedback (PDF) detector, a stripped-down version of the BO...

The BLAST-ordered decision-feedback (BODF) detector is a nonlinear detection strategy for multiple-input multiple-output (MIMO) channels that can significantly outperform a linear detector. However, for some applications even the BODF detector is too complex. We propose the partial decision-feedback (PDF) detector, a stripped-down version of the BO...

A new laser architecture emitting alternate multiwavelength picosecond pulses at room temperature is proposed. The generation is based on a single active component, an unbalanced Mach-Zehnder interferometer, inserted in an actively mode-locked erbium-doped fiber ring laser to provide both intensity modulation and tunable filtering. Control of the e...

Lattice basis reduction is a powerful technique that enables a hard-output detector for a multiple-input multiple-output channel to approach maximum-likelihood performance with low complexity. In this work we propose a soft-output detector that combines lattice- reduction-aided detection and list decoding. The proposed algorithm performs nearly as...

We consider the problem of timing recovery for bandlimited, baud-rate sampled systems with intersymbol interference and a timing offset that can be modeled as a combination of a frequency offset and a random walk. We first derive the Crameacuter-Rao bound (CRB), which is a lower bound on the estimation error variance for any timing estimator. Conve...

Phase jitter is the major impairment of long-haul phase-shift keying systems. In this letter, we propose and investigate a novel experimental method to estimate the optical phase variance of return-to-zero differential phase-shift-keyed (RZ-DPSK) systems. The means and variances of the power detected before and after DPSK demodulation are the only...

We consider the problem of timing recovery for bandlimited, baud-rate sampled systems with intersymbol interference and a timing offset that can be modeled as a combination of a frequency offset and a random walk. We first derive the Cramer–Rao bound (CRB), which is a lower bound on the estimation-error variance for any timing estimator. Convention...

The influence of spectral inversion on the phase jitter of a soliton propagating in single-channel arbitrary dispersion-managed systems is studied with a semianalytic moment method. The results are similar to those previously observed in constant-dispersion links and show that the transmission-system reach can signifi-cantly be increased.

The complexity of a turbo equalizer based on the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm is manageable only for mildly dispersive channels having a small amount of memory. To enable turbo equalization of highly dispersive channels, we propose the soft-feedback equalizer(SFE). The SFE combines linear equalization and soft intersymbol-interference...

We report the experimental generation of alternate multiwavelength pulse trains in a mode-locked fiber ring laser containing an unbalanced Mach-Zehnder interferometer at an aggregate repetition rate of 18.8 GHz. These results are compared with simulations.

An inner space-time code, i.e., one that is complemented by an outer error-control code, calls for vastly different design strategies than a space-time code that stands alone. This letter investigates the design of a linear inner space-time code for a t-input r-output Rayleigh fading channel by examining its outage capacity, which assumes an ideali...

The generation of alternate multiwavelength pulse trains in an actively mode-locked erbium-doped fiber laser containing an unbalanced Mach-Zehnder interferometer is analyzed using numerical simulations and a theoretical Gaussian pulse analysis. The results obtained allow the interpretation of recent experimental results reporting multiwavelength pu...

Two powerful techniques for improving the performance of a detector in a multiple-input multiple-output communications channel are decision feedback and lattice reduction. We propose a new detector, the DOLLAR detector, that combines decision feedback and lattice reduction in a novel way. The DOLLAR detector is based on a simple lattice reduction a...

We demonstrate a new modulation format based on differential phase-shift keying (DPSK) with a duobinary-shaped modulating signal for applications in optical communications. Compared to conventional DPSK and using the 20-dB full-width criterion, numerical and experimental data show a bandwidth reduction by a factor of two resulting in a better toler...

The decision-feedback (DF) detector is a nonlinear detection strategy for multiple-input multiple-output (MIMO) channels that can significantly outperform a linear detector, especially when the order in which the inputs are detected is optimized according to the so-called Bell Labs Layered Space-Time (BLAST) ordering. The DF detector may be impleme...

The combination of partial response and trellis-based maximum-likelihood sequence detection that dominates magnetic recording is known as PRML. The receiver front-end includes an analog filter whose role is to essentially shorten the impulse response of the underlying channel; this filter transforms the channel response into a target partial respon...

A (full-complexity) per-survivor iterative timing recovery scheme, which jointly performs timing recovery, equalization, and error-correction decoding, was recently proposed [1] to deal with the problem of timing recovery operating at low signal-to-noise ratio. Although it outperforms other iterative timing recovery schemes, it has very high comple...

We consider a wireless system over a MIMO Rayleigh-fading channel with successive-cancellation detection. The outage probability (OP) of such a system is strongly dependent on two choices: the order in which the layers are detected, and the rate-allocation strategy at the transmitter. We propose the rate-normalized ordering algorithm, a generalizat...

The performance of a decision-feedback detector on a fading multiple-input multiple-output channel is limited by the low diversity of the first symbol detected. We propose a new family of detection techniques which overcomes this bottleneck by using a list detector for the first symbol; the list detector is then combined with a parallel bank of dec...

40 Gbit/s signal format conversion from NRZ to RZ using a Mach-Zehnder delay interferometer has been demon-strated for the first time. The converted RZ signal has high receiver sensitivity and shows significantly improved trans-mission performance.

Per-survivor iterative timing recovery was proposed to jointly perform timing recovery, equalization, and error-correction decoding. In this paper the robustness of per-survivor iterative timing recovery against thermal asperity (TA) and in ultra-high media noise environment in perpendicular recording channels was investigated.

We propose space-time active rotation (STAR), a new layered space-time architecture for fading multiple-input multiple-output channels. The vertically layered V-STAR architecture is similar in spirit to the popular V-BLAST architecture, but by rotating the set of active antennas it achieves better performance with comparable complexity. We derive t...

The modified Cramer-Rao bound (CRB) on frequency estimation error variance for magnetic recording channels is derived as a function of training symbol locations, and it is shown that placing the known symbols half at the beginning and half at the end of the sector minimizes the CRB. Simulation results show a 1.5 dB gain in loss-of-lock rate over ha...

We analyze the impact of a time-varying Rayleigh-fading channel on the performance of an Alamouti transmit-diversity scheme. We propose several optimal and suboptimal detection strategies for mitigating the effects of a time-varying channel, and derive expressions for their bit-error probability as a function of the channel correlation coefficient...

We will experimentally demonstrate 10 Gbit/s repeaterless transmission over a record length of standard fiber (SMF-28) using a modified duo-binary RZ signal generated by one dual-drive LiNbO3 modulator. Our results show that the MD-RZ signal can tolerate a certain dispersion tolerance range.

A conventional receiver performs timing recovery and equalization separately. Specifically, conventional timing recovery is based on a phase-locked loop that relies on the decision provided by its own symbol detector. We propose a new timing recovery scheme based on per-survivor processing (PSP) that jointly performs timing recovery and equalizatio...

The BLAST ordered decision-feedback (ODF) detector is a nonlinear detection strategy for multiple-input multiple-output channels that can significantly outperform a linear detector at the expense of the increased computational complexity. We propose the partial decision-feedback (PDF) detector, a simplified version of the ODF detector that only fee...

We present new trellis codes based on multiple-pulse-position modulation (MPPM) for wireless infrared communication. We assume that the receiver uses maximum-likelihood sequence detection to mitigate the effects of channel dispersion, which we model using a first-order lowpass filter. Compared to trellis codes based on PPM, the new codes are less s...

We optimize linear space-time codes for the case when the receiver uses successive cancellation decoding. Specifically, the proposed codes minimize the perfect cancellation bound on word error probability, which assumes error-free cancellation of previously detected symbols. Assuming perfect cancellation, we prove that to minimize the error probabi...

The last decade has seen the development of iteratively decodable error-control codes of unprecedented power, whose large coding gains enable reliable communication at very low signal-to-noise ratio (SNR). A by-product of this trend is that timing recovery must be performed at an SNR lower than ever before. Conventional timing recovery ignores the...

We propose the adaptive minimum symbol-error rate algorithm, which is a low-complexity technique for adapting the coefficients of a linear equalizer in systems using pulse-amplitude or quadrature-amplitude modulation. The proposed algorithm very nearly minimizes error probability in white Gaussian noise and can significantly outperform the minimum-...

The binary error-control schemes of Chapter 12 were designed specifically for binary modulation formats. They are ideally suited for the low-SNR regime where the target spectral efficiency is small. This chapter treats the problem of error control when the target spectral efficiency is large. In this scenario, one might be tempted to concatenate a...

We propose the adaptive minimum symbol-error rate algorithm, which is a low-complexity technique for adapting the coefficients of a linear equalizer in systems using pulse-amplitude or quadrature-amplitude modulation. The proposed algorithm very nearly minimizes error probability in white Gaussian noise and can significantly outperform the minimum-...

In Chapter 5 we described transmitter and receiver design using PAM. In this chapter we extend to other modulation schemes. We begin by considering a general form of modulation called M-ary modulation, in which one of M signals is transmitted every signaling interval. In this general setting, we present the correlation and projection receivers as p...

Soft-output equalizers that exploit a priori information on the channel inputs play a central role in turbo equalization. Such equalizers are traditionally implemented with the forward-backward or BCJR algorithm, whose complexity is prohibitive for channels with large memory. Many reduced-complexity alternatives to the BCJR algorithm have been prop...

Prior chapters were concerned with communication across a single-input single-output (SISO) channel for which the channel input and channel output were scalar-valued signals. In this chapter we study the problem of communicating across a multiple-input multiple-output (MIMO) channel, for which the channel input and output are vector-valued signals....

The previous chapter examined MIMO communications from an abstract point of view, with an eye towards all types of MIMO applications. In contrast, this chapter specializes to wireless MIMO applications, which suffer from not only additive noise and multiuser interference but also from multipath fading

We propose a new iterative timing recovery scheme based on per-survivor processing that jointly performs timing recovery and turbo equalization on partial response channels with error-correction codes. The scheme embeds the timing recovery process inside the Bahl, Cocke, Jelinek, and Raviv (BCJR) equalizer, using per-survivor processing. This per-s...

An information-bearing signal must conform to the limitations of its channel. While the bit streams we wish to transmit are inherently discrete-time, all physical media are continuous-time in nature. Hence, we need to represent the bit stream as a continuous-time signal for transmission, a process called modulation

Performance analysis of iterative timing recovery schemes, which perform timing recovery, equalization, and error-correction decoding jointly, is difficult because of their complexity. In this paper, we apply the extrinsic information transfer chart (EXIT chart) analysis as a tool to compare and predict their performances. Simulation results indica...

In PAM, intersymbol interference (ISI) results from linear amplitude and phase distortion in the channel that broadens the pulses and causes them to interfere with one another. The Nyquist criterion specifies a condition on the received pulses under which there is no ISI. Generally this or a similar condition is not satisfied unless we equalize the...

In the late 1940’s, Claude Shannon of Bell Laboratories developed a mathematical theory of information that profoundly altered our basic thinking about communication, and stimulated considerable intellectual activity, both practical and theoretical. This theory, among other things, gives us some fundamental boundaries within which communication can...

Timing recovery is an essential part of the state-of-the-art read channels employed by high-density data storage systems. It is utilized to adjust the sampling phase offset used to sample the received analog signal so that the sampler output will be synchronized with the transmitted symbol. Conventional timing recovery is performed in the analog do...

A fundamental problem in digital communications is the corruption of the transmitted signal by noise. The minimum-distance philosophy for receiver design is reasonably robust in the presence of noise, but two questions arise: when is it optimal? And what should be done when it is not? In this chapter we start with the statistics of the noise and de...

This book is for designers and would-be designers of digital communication systems. The general approach of this book is to extract the common principles underlying a range of media and applications and present them in a unified framework. Digital Communication is relevant to the design of a variety of systems, including voice and video digital cel...