Most of the recently proposed hardware realizations for non-binary low-density parity-check decoders are ASIC oriented as they employ multiplierless computation units. In this article, we present a different decoder d...
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Most of the recently proposed hardware realizations for non-binary low-density parity-check decoders are ASIC oriented as they employ multiplierless computation units. In this article, we present a different decoder design approach that is specifically intended for an FPGA implementation. We reformulate the mixed-domain FFT-BP decoding algorithm and develop a decoder architecture that does not exclude the multiplication units. This allows mapping a part of the algorithm to the multiplier cores embedded in an FPGA, thus making use of all the types of FPGA resources. Then, the throughput limit achievable in a single FPGA by the proposed decoder is significantly increased. We also consider another important optimization of the decoder implementation, mainly an efficient realization of the permutation units and an approximated evaluation of the nonlinear functions of messages. Another motivation is to make the decoder easily scalable for FPGA devices of different sizes. To achieve this goal, the configurable semi-parallel decoder architecture is applied operating for the structured subclass of codes.
The Deletion-Insertion Correcting Code construction proposed by Davey and MacKay consists of an inner code that recovers synchronization and an outer code that provides substitution error protection. The inner code us...
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ISBN:
(纸本)9781424464043
The Deletion-Insertion Correcting Code construction proposed by Davey and MacKay consists of an inner code that recovers synchronization and an outer code that provides substitution error protection. The inner code uses low-weight codewords which are added (modulo two) to a pilot sequence. The receiver is able to synchronise on the pilot sequence in spite of the changes introduced by the added codeword. The original bit-level formulation of the inner decoder assumes that all bits in the sparse codebook are identically and independently distributed. Not only is this assumption inaccurate, but it also prevents the use of soft a-priori input to the decoder. We propose an alternative symbol-level inner decoding algorithm that takes the actual codebook into account. Simulation results show that the proposed algorithm has an improved performance with only a small penalty in complexity, and it allows other improvements using inner codes with larger minimum distance.
We introduce a novel message passing (BP) algorithm, named Analog-Digital Belief Propagation (ADBP). The algorithm works with factor graph over linear models and uses messages in a particular class of parameterized Ga...
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ISBN:
(纸本)9781457720536
We introduce a novel message passing (BP) algorithm, named Analog-Digital Belief Propagation (ADBP). The algorithm works with factor graph over linear models and uses messages in a particular class of parameterized Gaussian-like distributions by tracking their parameters. With respect to the regular Gaussian BP, this algorithm adds two operations to the factor graph, namely the wrapping and the discretization of variables. This addition allows to use ADBP to construct iterative decoders for mod-M ring encoders that have a complexity independent from the size of the alphabets, thus opening the possibility to construct efficient decoders for systems with unbounded spectral efficiencies. In this paper we derive the updating rules of ADBP and show some possible simplifications of them that make ADBP suitable for implementation in practical systems.
To simultaneously mitigate the linear and nonlinear channel impairments in high-speed optical communications, we propose the use of non-binary low-density-parity-check-coded modulation in combination with a coarse bac...
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ISBN:
(纸本)9780819480170
To simultaneously mitigate the linear and nonlinear channel impairments in high-speed optical communications, we propose the use of non-binary low-density-parity-check-coded modulation in combination with a coarse backpropagation method. By employing backpropagation, we reduce the memory in the channel and in return obtain significant reductions in the complexity of the channel equalizer which is exponentially proportional to the channel memory. We then compensate for the remaining channel distortions using forward error correction based on non-binary LDPC codes. We propose non-binary-LDPC-coded modulation scheme because, compared to bit-interleaved binary-LDPC-coded modulation scheme employing turbo equalization, the proposed scheme lowers the computational complexity and latency of the overall system while providing impressively larger coding gains.
Code-modulated visual evoked potentials (c-VEPs) have potential as a reliable and non-invasive control signal for brain-computer interfaces (BCIs). However, these systems need to become more user-friendly. non-binary ...
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ISBN:
(纸本)9783031430770;9783031430787
Code-modulated visual evoked potentials (c-VEPs) have potential as a reliable and non-invasive control signal for brain-computer interfaces (BCIs). However, these systems need to become more user-friendly. non-binary codes have been proposed to reduce visual fatigue, but there is still a lack of adaptive methods to shorten trial durations. To address this, we propose a nonparametric early stopping algorithm for the non-binary circular shifting paradigm. The algorithm analyzes the distribution of unattended commands' correlations and stops stimulation when the most probable correlation is considered an outlier. This proposal was evaluated offline with 15 healthy participants using p-ary maximal length sequences encoded with shades of gray. Results showed that the algorithm could stop stimulation in under two seconds for all sequences, achieving mean accuracies over 95%. The highest performances were achieved by bases p = 2 and p = 5, attaining 98.3% accuracy with ITRs of 164.8 bpm and 121.7 bpm, respectively. The proposed algorithm reduces required cycles without compromising accuracy for c-VEP-based BCI systems.
In this work, fluid antenna channels are investigated from the diversity and coding gain perspectives. From the dominant eigenvalues of the channel correlation matrix, the maximum diversity of the channel is estimated...
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ISBN:
(纸本)9798350393194;9798350393187
In this work, fluid antenna channels are investigated from the diversity and coding gain perspectives. From the dominant eigenvalues of the channel correlation matrix, the maximum diversity of the channel is estimated based on the Jakes' correlation model. Two examples of Reed-Solomon-coded QAM constellations are then proposed that achieve the diversity limits of the channel. In addition, transmit port selection is analyzed, and finally two code constructions that achieve the diversity-security tradeoff of fluid compound channels are proposed. Results show that, for a fixed array width, diversity (and coding gain) quickly saturates with the increasing number of antennas where the performance is dictated by the number of dominant eigenvalues. Also, in absence of CSI at the transmitter side, the best option is to transmit over all ports rather than selecting a subset of ports by minimizing their correlation.
Background and Objectives: Code-modulated visual evoked potentials (c-VEPs) have marked a milestone in the scientific literature due to their ability to achieve reliable, high-speed brain-computer interfaces (BCIs) fo...
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Background and Objectives: Code-modulated visual evoked potentials (c-VEPs) have marked a milestone in the scientific literature due to their ability to achieve reliable, high-speed brain-computer interfaces (BCIs) for communication and control. Generally, these expert systems rely on encoding each command with shifted versions of binary pseudorandom sequences, i.e., flashing black and white targets according to the shifted code. Despite the excellent results in terms of accuracy and selection time, these high-contrast stimuli cause eyestrain for some users. In this work, we propose the use of non-binary p-ary m-sequences, whose levels are encoded with different shades of gray, as a more pleasant alternative than traditional binarycodes. The performance and visual fatigue of these p-ary m-sequences, as well as their ability to provide reliable c-VEP-based BCIs, are analyzed for the first time. Methods: Five different m-sequences were evaluated with 16 healthy participants, following the circular shifting paradigm: base 2 (63 bits), base 3 (80 bits), base 5 (124 bits), base 7 (48 bits), and base 11 (120 bits). Signal processing consisted of a 3-filter bank (1-60 Hz, 12-60 Hz and 30-60 Hz), followed by a canonical correlation analysis. Raster latency correction and artifact rejection approaches were also applied to compute command templates. For each m-sequence, users performed a 30-trial calibration stage, followed by an online spelling task of 32 trials. In addition, qualitative measures regarding visual fatigue and satisfaction were collected. Results: Users were able to achieve an average accuracy of over 98% for all p-ary m-sequences. The differences between m-sequences were not significant in terms of accuracy, but they were in terms of visual fatigue. The higher the base, the less eyestrain perceived by users for both presentation rates of 60 Hz and 120 Hz. All p-ary m-sequences were also significantly less annoying when displayed at 120 Hz compared to 60 Hz.
We introduce a novel message passing (BP) algorithm, named Analog-Digital Belief Propagation (ADBP). The algorithm works with factor graph over linear models and uses messages in a particular class of parameterized Ga...
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ISBN:
(纸本)9781457720529
We introduce a novel message passing (BP) algorithm, named Analog-Digital Belief Propagation (ADBP). The algorithm works with factor graph over linear models and uses messages in a particular class of parameterized Gaussian-like distributions by tracking their parameters. With respect to the regular Gaussian BP, this algorithm adds two operations to the factor graph, namely the wrapping and the discretization of variables. This addition allows to use ADBP to construct iterative decoders for mod-M ring encoders that have a complexity independent from the size of the alphabets, thus opening the possibility to construct efficient decoders for systems with unbounded spectral efficiencies. In this paper we derive the updating rules of ADBP and show some possible simplifications of them that make ADBP suitable for implementation in practical systems.
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