Showing papers by "Evangelos Eleftheriou published in 2002"

Filtered multitone modulation for very high-speed digital subscriber lines

Abstract: A filter-bank modulation technique called filtered multitone (FMT) and its application to data transmission for very high-speed digital subscriber line technology are described. The proposed scheme leads to significantly lower spectral overlapping between adjacent subchannels than for known multicarrier techniques such as discrete multitone (DMT) or discrete wavelet multitone. FMT modulation mitigates interference due to echo and near-end crosstalk signals, and increases the system throughput and reach. Signal equalization in an FMT receiver is accomplished in the form of per-subchannel symbol-spaced or fractionally spaced linear or decision-feedback equalization. The problem of channel coding for this type of modulation is also addressed, and an approach that allows combined removal of intersymbol-interference via precoding and trellis coding is described. Furthermore, practical design aspects regarding filter-bank realization, initial transceiver training, adaptive equalization, and timing recovery are discussed. Finally, simulation results of the performance achieved by FMT modulation for very high-speed digital subscriber line systems, where upstream and downstream signals are separated by frequency-division duplexing, are presented and compared with DMT modulation.

"Millipede": a MEMS-based scanning-probe data-storage system

Abstract: Ultrahigh storage densities of up to 1 Tb/in./sup 2/ or more can be achieved by using local-probe techniques to write, read back, and erase data in very thin polymer films. The thermomechanical scanning-probe-based data-storage concept called Millipede combines ultrahigh density, small form factor, and high data rate. After illustrating the principles of operation of the Millipede, a channel model for the analysis of the readback process is introduced, and analytical results are compared with experimental data. Furthermore, the arrangement of data-storage fields as well as dedicated fields for servo and timing control is discussed, and system aspects related to the readback process, multiplexing, synchronization, and position-error-signal generation for tracking are introduced. Finally, the application of (d,k) modulation coding as a means to further increase areal density is presented, and the effect on the user data rates discussed.

Low-density parity-check codes for digital subscriber lines

Abstract: The paper investigates the application of low-density parity-check (LDPC) codes to digital subscriber-line (DSL) transmission systems that employ discrete multitone modulation. A family of linear-time encodable binary LDPC codes that are well-suited for DSL transmission is introduced. Encoding and symbol mapping for multilevel modulation are described. Simulation results show that even under tight latency constraints good net coding gains can be achieved. Implementation complexity is analyzed and compared with that of trellis-coded modulation as employed in current asymmetric DSL transceivers. The incorporation of powerful LDPC coding techniques into next-generation DSL modems appears to be possible with reasonable increase in transceiver complexity.

Decoding low density parity check codes

Abstract: A method for decoding Low Density Parity Check (LDPC) codes comprises executing a sum product algorithm to recover a set of information bits from an LDPC code represented as a bipartite graph of symbol nodes and check nodes, the sum product algorithm being responsive to input log likelihood ratios associated with the symbol nodes. The check nodes are updated by generating a set of forward difference metrics and a set of backward difference metrics in dependence on the ratios of logarithmic probabilities each associated with a corresponding symbol node of the LDPC code, updating each metric in the set of forward difference metrics in dependence on the absolute value of the log likelihood ratio associated with the symbol node and the absolute value of the previous metric in the set, updating each metric in the set of backward difference metrics in dependence on the absolute value of the log likelihood ratio associated with the symbol node and the absolute value of the previous metric in the set, and generating log likelihood ratios to be propagated back to each symbol node in dependence on the updated sets of forward and backward difference metrics.

Irregular progressive edge-growth (PEG) Tanner graphs

Abstract: A general method for constructing Tanner graphs having a large girth by progressively establishing edges between symbol and check nodes in an edge-by-edge manner, called progressive edge-growth (PEG) construction, is proposed. Such an approach is powerful for generating good regular and irregular LDPC codes of short and moderate block lengths.

Perpendicular and longitudinal recording: a signal-processing and coding perspective

Abstract: Equalization and noise prediction followed by sequence detection and postprocessing are studied for double-layer perpendicular recording channels that are corrupted by electronics and transition noise. The performance of various outer coding schemes, such as conventional Reed-Solomon codes with 8and 10-bit symbols and low-density parity check codes, is evaluated, and a signal-processing and coding perspective is presented for both longitudinal and perpendicular recording channels. Finally, the capacity of recording channels is characterized.

Block coding for multilevel data communication

Abstract: Methods, apparatus and systems for multilevel data communication comprises dividing a set of information bits to be transmitted into a first group and a second group; encoding the first group to generate a block code, selecting a subset of symbols in a constellation of symbols in dependence on the block code according to a Gray-coded mapping function, selecting a symbol within the subset in dependence on the second group according to a Gray-coded mapping function, and transmitting the selected symbol.

Low density parity check encoding method and device for data

Abstract: PROBLEM TO BE SOLVED: To provide a parity check matrix connected to an LDPC code having the encoding complexity of a linear time. SOLUTION: This data low density parity check (LDPC) encoding method comprises a step for defining a first M×N parity check matrix, a step for generating a second parity check matrix having M×M triangle part matrix based on the first parity check matrix, and a step for mapping the data to the LDPC code word based on the second parity check matrix. This method is made valid especially for a data communication application, and also may be used for another application such as a data storage.

Near optimal reduced-complexity decoding algorithms for LDPC codes

Abstract: In this paper, two families of reduced-complexity algorithms for decoding low-density parity-check (LDPC) codes based on incorporating either a normalization or a correction term in the check-node update are presented. A simplified symbol-node update can also be used. Using simulations, it is shown that these simplified belief propagation (BP) approaches provide near optimum performance with different classes of LDPC codes.

Low-density parity-check codes for multilevel modulation

Abstract: The application of low-density parity-check (LDPC) codes to multilevel modulation systems is studied. A family of binary LDPC codes that offer good performance and do not suffer from error-floor effects at low bit-error rates is introduced. A number of properties render these codes attractive for practical applications: they are specified via a small number of parameters, are encodable in linear time, and the generation of their parity-check matrix is deterministic, involving a small number of preprocessing operations. In addition, the symbol-mapping technique based on "double Gray-code labeling" for obtaining coded multilevel transmit symbols is described. Finally, it is shown that the proposed LDPC coding technique is well suited for multicarrier digital-subscriber-line transmission applications as it permits a wide range of trade-offs between latency, complexity, and system performance.

Data detection for local probe data storage devices

Abstract: Apparatus for detecting data in a sensor signal generated by a read sensor (10) in a local probe data storage device comprises a differentiation (110) for subtracting a value of the sensor signal from the succeeding value of the sensor signal to generate a ternary difference signal ; and a convertor (120) connected to the differentiator for converting the difference signal into a binary output signal indicative of the detected data. A local probe data storage device comprising such apparatus is also described.

On the information-theoretic capacity of magnetic recording systems in the presence of medium noise

Abstract: The compound behavior of the magnetic recording channel is modeled by combining the Lorentzian read-back pulse, the microtrack channel model, and additive white Gaussian noise (AWGN). By noting that at the output of this model the read-back signal is cyclostationary, the average autocorrelation function and corresponding power spectral density over one period are computed. The average power spectral density is then used to characterize the capacity of the magnetic recording channel for various linear density and medium noise scenarios by using the conjectured Shamai-Laroia lower bound. It is shown that from a capacity point of view, medium noise is better in certain cases than AWGN.

The millipede, a very dense, highly parallel scanning-probe data-storage system

Abstract: Ultrahigh storage densities of up to 1 Tbit/in2. can be achieved by local-probe techniques to write, read back, and erase data in very thin polymer films. The thermo-mechanical scanning-probe-based data-storage concept called Millipede combines ultrahigh density, terabit capacity, small form factor, and high data rate. After illustrating the principles of operation of the Millipede, we introduce a channel model for the analysis of the read back process, and compare analytical results with experimental data.

CMOS sensor array with cell–level analog–to–digital conversion for local probe date storage

Abstract: A scalable CMOS sensing architecture for highly parallel readback of signals from large two-dimensional local probe arrays for AFM(atomic force microscope)-based data storage is presented. The main challenge to the detection scheme comes from the fact that information signals are superimposed on carrier signals that are more than three orders of magnitude higher. In addition, local memories are needed because of carrier variations, and parallel operation requires local data conversion. Therefore, analog-to-digital conversion of the probe signals is performed locally in a two-dimensional scheme fitting the probe array. A scalable prototype array fabricated in a 0.35 µm CMOS technology demonstrates the required functionality and performance for future large arrays of 32 × 32 or more AFM cantilevers.

Computing information rates of magnetic recording channels in the presence of medium noise

Abstract: An information-theoretic method is presented for computing information rates of magnetic recording channels with medium noise, assuming 0.5-Bernoulli as well as optimized Markov input processes. The method is based on the well-known conjectured Shamai-Laroia bound. The compound behavior of the magnetic recording channel is modelled by combining the Lorentzian read-back pulse, the microtrack channel model, and additive white Gaussian noise (AWGN). Numerical results are provided that show that from an information theoretic viewpoint in certain cases medium noise is preferable to AWGN.

Data encoding systems

Abstract: A method and apparatus for encoding a plurality of successive m-bit binary data words to produce a plurality of successive of n-bit binary code words, where n and m are positive integers and n is greater than m, for supply to a magnetic recording channel. Each m-bit binary data word is partitioned into a plurality of blocks of bits, and at least one said blocks of bits in each m-bit binary data word is encoded in accordance with a finite-state coding scheme to produce a plurality of successive n-bit binary code words. At least one stage of violation correction which transforms the plurality of successive n-bit binary code words. Violation correction includes detecting the occurrence of any of a plurality of prohibited bit patterns at one or more predetermined locations within each n-bit binary coded word, and replacing any prohibited bit pattern so detected by a corresponding substitute bit pattern. The finite-state coding scheme, the prohibited bit patterns, and corresponding substitute bit patterns are predetermined such that in a serial bit-steam comprising the successive n-bit binary code words, the maximum number of consecutive bits of a first value is limited to a first predetermined number j, where b greater or equal to 2, and the maximum number of consecutive bits of the a second value is limited to a second predetermined number k.