Lina Fagoonee

Nonlinear signal-processing model for signal generation in multilevel two-dimensional optical storage.

A two-dimensional optical storage (TwoDOS) format with binary modulation is being developed in which channel bits are arranged on a two-dimensional hexagonal lattice [W. M. J. Coene, in Optical Data Storage, Vol. 88 of OSA Trends in Optics and Photonics Series (Optical Society of America, Washington, D.C., 2003), pp. 90-92]. The aim is to increase the capacity by a factor of 2 and the data rate by a factor of 10 over third-generation Blu-ray Disc technology. Following a route similar to that used in one-dimensional conventional optical storage [Jpn. J. Appl. Phys. 42, 1074 (2003)] could lead to a further increase in capacity by the addition of another dimension to writing data, such as the use of multiple levels instead of the two levels (pit and land) used in the binary TwoDOS disk format. We present a nonlinear signal-processing model for signal waveform generation as a function of the M-ary channel symbols, as well as simulated signal readouts for multilevel TwoDOS.

PUM-Based Turbo Codes

Partial Unit Memory (PUM) codes have excellent distance properties and we show how to construct recursive code matrices for application into turbo schemes. An iterative max-log-MAP decoding scheme is proposed for the resulting trellises with multi-input labels.

Sequence Detection Based on a Variable State Trellis for Multidimensional ISI Channels

Near-optimum sequence detection in channels with intersymbol interference (ISI) is based on the Viterbi algorithm. However, its complexity increases exponentially with the number of taps within the span of the ISI and with the number of symbol levels. We present a low-complexity sequence detection scheme, based on the Viterbi detection algorithm, which is generalized for multidimensional ISI channels in the presence of the predominant signal-dependent noise. The proposed variable state trellis (VST) approach detects and discards in real time states that are unlikely to correspond to the survivor path, thus reducing the complexity of the sequence detection significantly. After analyzing and exploiting a number of criteria (such as a priori reliability information, channel characteristics, and probability of error occurrences among different symbol levels), we propose three approaches to implement the VST scheme. The VST can be applied to any multidimensional ISI channel, including magnetic and optical storage. We compare the performance of the VST and conventional Viterbi algorithms for the multilevel two-dimensional optical storage channel, where media noise is predominant, and show that, with negligible performance loss, the computational complexity is reduced significantly

Symbol detection for multilevel two dimensional optical storage using a non-linear channel model

We describe a symbol detection scheme for multilevel two dimensional optical storage (TwoDOS), where the channel is characterized by non-linear inter symbol interference and the dominant source of noise is media noise, both of which are characterized accurately by a non-linear channel model. Signal waveforms from the channel model are described as an explicit function of the channel symbols. Based on the non-linear model including media noise, we design and develop a practical symbol detection scheme for multilevel TwoDOS. This low complexity detection scheme is simulated for multilevel data for discs with different densities in the presence of media noise. Our proposed detection scheme exploits the properties of the 2D data format on the disc and is flexible enough to accommodate performance and complexity restrictions.

Experimental characterization for the binary two-dimensional optical storage channel

A new and challenging concept for optical storage is being developed, in which the information written on the disc has a two-dimensional characteristic, with the aim of realizing an increase of a factor of two in data density and a factor of ten in data rate over the current 3rd generation of optical storage (Blu-Ray Disc, BD). Experimental channel characterization provides insight into the magnitude of intersymbol interference, signal levels, modulation and noise distribution from the measured signal waveform. This information is used to evaluate the quality of the mastered discs, and provide feedback in the optimization process. It also yields essential input to the actual design of the signal processing solutions. The stages involved in characterizing the channel are downsampling and model fitting using a scalar diffraction model. The information gathered from channel characterization is demonstrated with experimental measurements from discs with an initial density of 1.4/spl times/BD using the same physical read-out system (blue laser and high-NA lens).

Two-Way Video Communication Based on Network Coding

We consider a practical system design for a wireless video conference application, where we exploit the broadcast nature of wireless radio links using network coding. With network coding, the number of necessary downlink transmissions from the intermediate node to the two users is reduced, and thus the throughput is increased. We develop two systems, one based on amplify-and-forward and another on decode-and-forward technique, and compare them to traditional communication systems that do not use network coding. Our practical designs exploit the latest in 3-D wavelet-based scalable video coding and channel coding. Simulation results confirm the advantages of the proposed video communication schemes over conventional ones.

Low complexity symbol detection method for multilevel 2-D optical storage based on a linear channel model

A symbol detection scheme based on the Viterbi algorithm that simultaneously processes subsets of 2-D data in the presence of Gaussian noise was recently proposed for binary 2-D optical storage (TwoDOS). In the case of multilevel TwoDOS, a straightforward full-fledged maximum likelihood symbol detector, or even the previous Viterbi-based algorithm, is not an ideal solution due to complexity restrictions. We propose a suboptimum low complexity symbol detector, which still performs within the accepted performance bound for optical storage. We describe the procedures involved in designing and developing a practical symbol detection scheme for multilevel TwoDOS by analyzing the signal values generated by a linear channel model in the presence of Gaussian noise. Our proposed detection scheme exploits the properties of the 2-D data format on the disk, and is flexible enough to accommodate performance and complexity restrictions for optical storage applications.

Application of turbo codes to tactical communications

A practical multifunctional system comprising a turbo decoder, low complexity turbo equalizer and turbo synchronizer is developed to compensate for frequency-selective channels with fading. The combined synchronizer, equalizer and decoder are based on a turbo scheme where soft extrinsic information is exchanged between these processes and between iterations. The turbo codes are based on Partial Unit Memory Codes, which may be constructed with higher free distance than equivalent recursive systematic convolutional codes and can achieve better performance than the latter. The purely digital multifunctional receiver is targeted for end-applications such as combat-radio and radio-relay, providing robust communication at low signal-to-noise ratio with performance approaching the Shannon limit. This paper presents design considerations for the multifunctional turbo-based receiver as well as simulation results for its performance in combat-radio communications channels.

EXIT Charts for PUM Woven Turbo Codes

Partial Unit Memory (PUM) codes are a class of low complexity, non-binary convolutional codes and have been shown recently to outperform equivalent convolutional codes. We present the Extrinsic Information Transfer (EXIT) charts of parallel concatenated PUM codes and PUM Woven Turbo Codes and analyse them to assess their performance compared with well-known turbo codes used by the third generation mobile UMTS standard. The EXIT chart analysis is supported by Bit Error Rate (BER) plots. We show that the concatenated PUM codes outperform the well-known turbo codes in the error floor region, with comparable performance in the waterfall region.

V-Shaped Viterbi Symbol Detection for Multilevel 2D Optical Storage

Recently, a symbol detection scheme based on the Viterbi algorithm was proposed for binary Two Dimensional Optical Storage (TwoDOS) in the presence of Additive White Gaussian noise (AWGN). In this paper, we extend the symbol detection scheme to allow for multilevel modulation. We demonstrate the proof of concept in a typical non-linear high density storage channel with intersymbol interference and AWGN. The relative performance, between multilevel and binary modulations is presented, where multilevel modulation provides better performance in higher capacities.