364 research outputs found
Analysis and Design of Finite Alphabet Iterative Decoders Robust to Faulty Hardware
This paper addresses the problem of designing LDPC decoders robust to
transient errors introduced by a faulty hardware. We assume that the faulty
hardware introduces errors during the message passing updates and we propose a
general framework for the definition of the message update faulty functions.
Within this framework, we define symmetry conditions for the faulty functions,
and derive two simple error models used in the analysis. With this analysis, we
propose a new interpretation of the functional Density Evolution threshold
previously introduced, and show its limitations in case of highly unreliable
hardware. However, we show that under restricted decoder noise conditions, the
functional threshold can be used to predict the convergence behavior of FAIDs
under faulty hardware. In particular, we reveal the existence of robust and
non-robust FAIDs and propose a framework for the design of robust decoders. We
finally illustrate robust and non-robust decoders behaviors of finite length
codes using Monte Carlo simulations.Comment: 30 pages, submitted to IEEE Transactions on Communication
An Introduction to Quantum Error Correction and Fault-Tolerant Quantum Computation
Quantum states are very delicate, so it is likely some sort of quantum error
correction will be necessary to build reliable quantum computers. The theory of
quantum error-correcting codes has some close ties to and some striking
differences from the theory of classical error-correcting codes. Many quantum
codes can be described in terms of the stabilizer of the codewords. The
stabilizer is a finite Abelian group, and allows a straightforward
characterization of the error-correcting properties of the code. The stabilizer
formalism for quantum codes also illustrates the relationships to classical
coding theory, particularly classical codes over GF(4), the finite field with
four elements. To build a quantum computer which behaves correctly in the
presence of errors, we also need a theory of fault-tolerant quantum
computation, instructing us how to perform quantum gates on qubits which are
encoded in a quantum error-correcting code. The threshold theorem states that
it is possible to create a quantum computer to perform an arbitrary quantum
computation provided the error rate per physical gate or time step is below
some constant threshold value.Comment: 46 pages, with large margins. Includes quant-ph/0004072 plus 30 pages
of new material, mostly on fault-toleranc
Fault and Defect Tolerant Computer Architectures: Reliable Computing With Unreliable Devices
This research addresses design of a reliable computer from unreliable device technologies. A system architecture is developed for a fault and defect tolerant (FDT) computer. Trade-offs between different techniques are studied and yield and hardware cost models are developed. Fault and defect tolerant designs are created for the processor and the cache memory. Simulation results for the content-addressable memory (CAM)-based cache show 90% yield with device failure probabilities of 3 x 10(-6), three orders of magnitude better than non fault tolerant caches of the same size. The entire processor achieves 70% yield with device failure probabilities exceeding 10(-6). The required hardware redundancy is approximately 15 times that of a non-fault tolerant design. While larger than current FT designs, this architecture allows the use of devices much more likely to fail than silicon CMOS. As part of model development, an improved model is derived for NAND Multiplexing. The model is the first accurate model for small and medium amounts of redundancy. Previous models are extended to account for dependence between the inputs and produce more accurate results
Density Evolution and Functional Threshold for the Noisy Min-Sum Decoder
This paper investigates the behavior of the Min-Sum decoder running on noisy
devices. The aim is to evaluate the robustness of the decoder in the presence
of computation noise, e.g. due to faulty logic in the processing units, which
represents a new source of errors that may occur during the decoding process.
To this end, we first introduce probabilistic models for the arithmetic and
logic units of the the finite-precision Min-Sum decoder, and then carry out the
density evolution analysis of the noisy Min-Sum decoder. We show that in some
particular cases, the noise introduced by the device can help the Min-Sum
decoder to escape from fixed points attractors, and may actually result in an
increased correction capacity with respect to the noiseless decoder. We also
reveal the existence of a specific threshold phenomenon, referred to as
functional threshold. The behavior of the noisy decoder is demonstrated in the
asymptotic limit of the code-length -- by using "noisy" density evolution
equations -- and it is also verified in the finite-length case by Monte-Carlo
simulation.Comment: 46 pages (draft version); extended version of the paper with same
title, submitted to IEEE Transactions on Communication
Improving the tolerance of stochastic LDPC decoders to overclocking-induced timing errors: a tutorial and design example
Channel codes such as Low-Density Parity-Check (LDPC) codes may be employed in wireless communication schemes for correcting transmission errors. This tolerance to channel-induced transmission errors allows the communication schemes to achieve higher transmission throughputs, at the cost of requiring additional processing for performing LDPC decoding. However, this LDPC decoding operation is associated with a potentially inadequate processing throughput, which may constrain the attainable transmission throughput. In order to increase the processing throughput, the clock period may be reduced, albeit this is at the cost of potentially introducing timing errors. Previous research efforts have considered a paucity of solutions for mitigating the occurrence of timing errors in channel decoders, by employing additional circuitry for detecting and correcting these overclocking-induced timing errors. Against this background, in this paper we demonstrate that stochastic LDPC decoders (LDPC-SDs) are capable of exploiting their inherent error correction capability for correcting not only transmission errors, but also timing errors, even without the requirement for additional circuitry. Motivated by this, we provide the first comprehensive tutorial on LDPC-SDs. We also propose a novel design flow for timing-error-tolerant LDPC decoders. We use this to develop a timing error model for LDPC-SDs and investigate how their overall error correction performance is affected by overclocking. Drawing upon our findings, we propose a modified LDPC-SD, having an improved timing error tolerance. In a particular practical scenario, this modification eliminates the approximately 1 dB performance degradation that is suffered by an overclocked LDPC-SD without our modification, enabling the processing throughput to be increased by up to 69.4%, which is achieved without compromising the error correction capability or processing energy consumption of the LDPC-SD
Simulation and Synthesis of Efficient Majority Logic Fault Detector Using EG-LDPC Codes to Reduce Access Time for Memory Applications
This paper presents an error-detection method for Euclidean Geometry low density parity check codes with majority logic decoding methodology in VHDL language and the output is verified with the help of Xilinx12.1. Majority logic decodable codes are suitable for memory applications due to their capability to correct a large number of errors. However, they require a large decoding time that impacts memory performance. The proposed fault-detection method significantly reduces memory access time when there is no error in the data read. The technique uses the majority logic decoder itself to detect failures, which makes the area overhead minimal and keeps the extra power consumption low. Starting from the original design of the ML decoder introduced, the proposed ML Detector/Decoder (MLDD) has been implemented using the Euclidean Geometry low density parity check codes. The proposed improved majority logic detector/decoder to perform data error correction in simple way using additional error correction technique and also reducing the delay time by detecting the errors in parallel manner. Hence the decoding process uses less number of cycles which reduces the delay
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