Optical Recording Channels Research Articles

Enumerative Encoding of TMTR Codes for Optical Recording Channel

We propose a new time-varying maximum transition run (TMTR) code for DVD recording systems, which has a rate higher than the EFMPlus code and a lower power spectral density (PSD) at low frequencies. An enumeration method for constructing the new TMTR code is presented. Computer simulations indicate that the proposed TMTR code outperforms the EFMPlus code in error performance when applied to partial response optical recording channels.

Performance Evaluation of the Reed Solomon and Low Density Parity Check Codes for Blu-ray Disk Channels

In this paper, we evaluate the performances of the Reed–Solomon (RS) and low density parity check (LDPC) codes in order to propose an efficient coding system for the outer code in high density optical recording channels. Hard decision decoding (HDD) RS code, iterative soft decision decoding (SDD) RS code or LDPC code is used as the outer code and LDPC code is used as the inner code. We compare the bit error rate (BER) performance of each coding system for various code rates, code lengths and burst errors. Simulation results show that the LDPC code has a better BER performance than the HDD RS and iterative SDD RS codes as the outer code in high density optical channels. Therefore, the LDPC code could be more attractive as the outer code than the RS code in high density optical channels.

Distance-Enhancing Constrained Codes with Parity-Check Constraints for Data Storage Channels

This paper proposes efficient distance-enhancing constrained codes with parity-check (PC) constraints for data storage channels. We first propose simple and efficient finitestate encoding methods to design various distance-enhancing constrained codes, including a repeated minimum transition runlength (RMTR) code for optical recording channels, as well as a maximum transition run (MTR) code for magnetic recording channels. We further propose a general and systematic code design methodology, which can efficiently combine constrained codes with PC codes. The constrained codes can be any distanceenhancing constrained codes. The PC codes can be any linear binary PC codes. The rates of the designed codes are only a few tenths of a percent below the theoretical maximum. The proposed method enables soft information to be available to the PC decoder and soft decoding of PC codes. Examples of several newly designed distance-enhancing constrained PC codes are illustrated. Simulation results with blu-ray disc (BD) systems show that the proposed new RMTR code and RMTR constrained 4-bit PC code perform 0.2 dB and 0.85 dB better than the standard 17PP code, respectively, at error correction code (ECC) failure rate (EFR) of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> and high recording density.

Capacity Approaching Run-Length-Limited Codes for Multilevel Recording Systems

We propose two constructions for multilevel run-length-limited (RLL) block codes for which the rates are very close to the capacity. For each code construction, we propose a variation that has the advantage of low complexity of encoding and decoding. We conducted a simulation to see the combined effect of channel coding and our proposed RLL coding over an optical recording channel.

Design of close-to-capacity constrained codes for multi-level optical recording

We report a new method for designing (M,d, k) constrained codes for use in multi-level optical recording channels. The method allow us to design practical codes, which have simple encoder tables and decoders having fixed window length. The codes presented here for the d = 1 and d = 2 cases, achieve higher storage densities than previously reported codes, and come within 0.3 - 0.7% of capacity.

Constrained Code and Partial-Response Maximum-Likelihood Detection for High Density Multi-Level Optical Recording Channels

A new efficient four-ary (1,4) run-length limited (RLL) code is presented, which is intended for high density multi-level optical recording channels. By using proposed hybrid DC control scheme, the new code can achieve acceptable DC suppressing characteristics while maintaining high code rate. The bit error rate (BER) performances of this new code on blue laser recording systems are evaluated by using partial-response maximum-likelihood (PRML) detection. The feasibility of using four-ary RLL modulation and PRML detection is studied in this paper, and these techniques show great potential to be applicable in high-density multi-level optical recording channels.

New Efficient Run-Length Limited Code for Multilevel Read-Only Optical Disc

Multilevel recording with run-length limited (RLL) modulation is a novel way to significantly increase the recording density without changing the optical or mechanical units of current optical disc systems. In this paper, a new efficient 4-ary RLL(2,13) code with special constraint is designed for four-level RLL modulation on read-only digital versatile disc (DVD-ROM). This code can result in alternate multilevel pits and lands on the disc, and reduce the difficulty of multilevel disc replication. Further more, simulation results show the symbol error rate (SER) performance can be improved about 3 dB when the proposed code is used for optical recording channel with partial-response maximum-likelihood (PRML) detection.

DC-Free Four-Ary (2,8) Run-Length Limited Code for Multi-level Recording Channels

A new high efficient DC-free (2,8) run-length limited (RLL) code for four-level optical recording channels is proposed. The proposed code can be represented by a finite state diagram (FSM) with three states and implemented easily. The code rate and density ratio of the code are 5/6 bits/symbols and 2.50 bits/minimum-recorded-mark, respectively. On the basis of the experimental results, the performances of the code are evaluated by using partial-response maximum-likelihood (PRML) technology, which is suitable for detecting multi-level RLL signals. By using four-ary (2,8)RLL modulation and PRML technology, one can increase the recording density 66.7% relative to conventional binary RLL modulation currently used in digital versatile disc (DVD), meanwhile the bit error rate (BER) still be acceptable.

Modulation Codes for Multi-wavelength and Multi-Level Photochromic Optical Recording Channel

Multi-wavelength and multi-level optical recording with photochromic materials is a novel way to increase recording density and data transfer rate significantly. Modulation codes for multi-wavelength and multi-level recording channel are discussed. Firstly, two-dimensional (2-D) run-length-limited (RLL) (dx,dy,k;n) codes are introduced for multi-wavelength recording. An example of 2-D RLL(1,1,6;2) code is shown to effectively combat the crosstalk in a two-wavelength recording model. Then, a DC-free four-ary RLL(2,8) code is designed with code rate of 8/10 (bits/symbol), and a partial-response maximum-likelihood (PRML) detector is used for the four-level RLL(2,8) modulation recording channel. We also introduce 2-D RLL(M,1,∞) codes for the joint multi-wavelength multi-level recording channel. Some numerical results on the capacities are derived, and an example of 2-D (5,1,∞) code is constructed via state splitting algorithm. These proposed codes show great potential to be applicable in high-density 2-D and multi-level optical recording channels.

Partial Response Maximum Likelihood Detection Using Signal Quality Measure Method for Asymmetric Optical Recording Channels

This paper presents a partial response maximum likelihood (PRML) detection method using partial response signal-to-noise ratio (PRSNR) that evaluates the signal quality of asymmetric optical recording channel. We confirm that the maximum PRSNR value is given by the equalizer that is the most properly adapted to the asymmetric optical recording channel. This result denotes that it is sufficiently useful for selecting the optimum equalizer. The proposed PRML detection using this result has 2.5 dB SNR gain at 4.0×10-6 bit error rate compared to PRML detection using typical adaptive equalizer.

A New Four-Ary Run-Length-Limited (2,12) Code for Multilevel Optical Recording Channels

In this paper, we introduce a new four-ary run-length-limited (d,k)=(2,12) code for multilevel optical recording channels. This code has a simple one-codeword look-ahead encoder and a sliding block decoder. The code rate is 4/5 (bits/symbol), and the density ratio is 2.4 bits/Tmin, which is larger than that of binary codes used for typical optical recording systems. The encoding and decoding rules of the proposed code are simple and easy for implementation. With the bit error rate (BER) performance evaluation, this code shows feasible to be applied in high-density multilevel optical storage systems.

Parity-check codes and post-processing for d=1 optical recording channels

We have developed an advanced detection approach with parity-check (PC) codes and post-processing for optical recording channels. In seeking the advanced detection approach, we investigated different types of PC codes, existing as well as new. We developed a novel remedy scheme to minimize the miscorrection of error events that are split across codeword boundaries. Simulation shows that the performance of the developed PC codes approaches the corresponding bit-error-rate bounds, at both nominal density and high density.

Turbo decoding for a new DVD recording system

The modulation code used in a digital versatile disc (DVD) recording system is referred to as the EFMPlus code with a rate of 8/16. We present a new time-varying maximum transition run (TMTR) code for DVD recording systems, which has a rate 8/11 higher than the EFMPlus code and a lower power spectral density (PSD) at low frequencies. Computer simulations indicate that the proposed TMTR code outperforms the EFMPlus code when applied to a partial response optical recording channel. The turbo (iterative) decoding for the TMTR-coded partial response optical recording channel is also investigated, in which the TMTR-coded partial response channel is viewed as the inner code and two parallel concatenated convolutional codes (PCCC's) as the outer code. The error performance of the proposed coding scheme is investigated and compared with the conventional coding scheme, in which both the TMTR code and partial response channel are decoded or detected independently. Simulation results reveal that a coding gain of more than 3 dB can be achieved over the conventional coding scheme.

Adaptive Equalization Using Expanded Maximum-Likelihood Detector Output for Optical Recording Systems

For high-density optical recording systems, the effectiveness of the partial–response maximum-likelihood (PRML) detection scheme is limited by the channel asymmetry. Hence, to solve the problem and improve detection performance, we present an adaptive equalization scheme using the output of an expanded maximum-likelihood (ML) detector. The proposed PRML detection method adapts well to the asymmetric optical recording channels and has better bit error rate performance than the conventional PRML detection method.

A New 9-Level Run-Length-Limited (1, 3) Code for Multilevel Optical Recording Channels

In this paper, we propose the M=9 run-length-limited (d,k)=(1,3) code for multilevel recording channels. The code rate is 5/3 (bits/symbol), and the code has a simple 3-state encoder and a sliding block decoder. During the decoding process, the maximum error propagation of input data is seven bits. The structures of the encoder and decoder of the proposed code are very simple, so it may be easily implemented for high-density multilevel recording systems.

Asynchronous zero-forcing adaptive equalization

Digital data receivers often operate at a fixed sampling rate 1/Ts that is asynchronous to the baud rate 1/T. A digital equalizer that processes the incoming signal will also be asynchronous, and its adaptation is commonly based on extensions of the LMS algorithm. In this paper, we develop and analyze a much simpler approach that is based on zero-forcing adaptation techniques. Numerical results for an idealized optical recording channel serve to illustrate the merits of the approach. LMS-like performance is found to be within reach at a fraction of the cost of LMS. Copyright © 2004 AEI.

3-ary (2,10) run-length limited code for optical storage channels

An efficient and simple 3-ary (2,10) run-length limited (RLL) code for a three-level optical recording channel is presented. The proposed code can be represented by a finite state diagram with three states. The density ratio of the new code is 2.14 bits/minimum-recorded-mark, which is larger than that of the previous 3-ary (2,10) RLL code yet presented. The encoding and decoding rules for the code are also introduced and the method for reducing the DC content of the coded sequence is also discussed.

The event-related optical signal to electrical stimulation of the median nerve

The event-related optical signal (EROS) uses near-infrared light to study changes in neuronal optical properties in response to stimuli and endogenous events. EROS responses to electrical stimulation of the median nerve at 1, 5, and 8 Hz were collected from 80 channels in 7 subjects. Optical recording channels were spatially aligned by co-registering the digitized fiber locations with structural magnetic resonance images (MRI) for each subject separately. The co-registered data sets were then transformed into Talairach space to permit alignment across subjects. After alignment, data from channels underlying pixels of a surface projection were combined to produce maps of Z statistics. Waveforms associated with voxels within an a priori region of interest (ROI) over the hand area of primary somatosensory (SI) cortex were compared across the three stimulus frequencies. Reliable early increases in light propagation time (i.e., increased phase delay) were found in SI as early as 16–32 ms of poststimulus for all three frequency conditions, and both an increase in phase delay and a decrease in signal intensity were observed over SI at longer latencies. A split-half analysis of the 8 Hz condition demonstrated the replicability of the response. This represents the first direct comparison of intensity and delay measures of these components of the somatosensory response; further, it shows that these early cortical components are replicable across subjects and correspond well to individual subjects' anatomical landmarks for SI.

Nonlinear signal-processing model for scalar diffraction in optical recording.

A nonlinear signal-processing model is derived for the optical recording channel based on scalar diffraction theory. In this model, the signal waveform is written in closed form as an explicit function of the channel bits that are stored on an optical disk, thereby comprising both linear and nonlinear terms. Its explicit dependence on the channel bits makes this model well suited for signal-processing purposes. With the model it is also convenient to assess the importance of nonlinear contributions to the signal waveform. The model is applied for one-dimensional optical storage as well as for two-dimensional (2D) optical storage in which bits are arranged on a 2D hexagonal lattice. Signal folding is addressed as a typical nonlinear issue in 2D optical storage and can be eliminated by recording of pit marks of sizes considerably smaller than the size of the hexagonal bit cell. Further simplifications of the model with only a limited number of channel parameters are also derived.

Combining nonlinear equalization and simple detection for high-density optical recording channels

This paper discusses new systems for nonlinear optical recording channels. The systems combine neural network structure into simple detectors such as the multilevel decision-feedback equalizer (MDFE) and the discrete matched filter (DMF). The latter (denoted as DFNE/DMF) provides powerful nonlinear tolerance, while the former (denoted as NMDFE) shows poor tolerance because of conditional training property in the MDFE. When compared with a partial response neural equalizer with maximum-likelihood (PRNE/ML), the proposed DFNE/DMF proves to be very hardware-efficient and able to support high data rates. Simulation results show that the DFNE/DMF increases bloom tolerance up to roughly 30% at a density of S = 6.