8,810 research outputs found
Design of LDPC Codes: A Survey and New Results
No full textThis survey paper provides fundamentals in the design of LDPC codes. To provide a target for the code designer, we first summarize the EXIT chart technique for determining (near-)optimal degree distributions for LDPC code ensembles. We also demonstrate the simplicity of representing codes by
protographs and how this naturally leads to quasi-cyclic LDPC codes. The EXIT chart technique is then extended to the special case of protograph-based LDPC codes. Next, we present several design approaches for LDPC codes which incorporate one or more accumulators, including quasi-cyclic accumulatorbased codes. The second half the paper then surveys several
algebraic LDPC code design techniques. First, codes based on finite geometries are discussed and then codes whose designs are based on Reed-Solomon codes are covered. The algebraic designs lead to cyclic, quasi-cyclic, and structured codes. The masking technique for converting regular quasi-cyclic LDPC codes to irregular codes is also presented. Some of these results and codes have not been presented elsewhere. The paper focuses
on the binary-input AWGN channel (BI-AWGNC). However, as discussed in the paper, good BI-AWGNC codes tend to be universally good across many channels. Alternatively, the reader may treat this paper as a starting point for extensions to more advanced channels. The paper concludes with a brief discussion of open problems
Quasi-cyclic Generalized LDPC codes with low error floors
No full textIn this paper, a novel methodology for designing structured generalized LDPC (G-LDPC) codes is presented. The proposed design results in quasi-cyclic G-LDPC codes for which efficient encoding is feasible through shift-register-based circuits. The structure imposed on the bipartite graphs, together with the choice of simple component codes, leads to a class of codes suitable for fast iterative decoding. A pragmatic approach to the construction of G-LDPC codes is proposed. The approach is based on the substitution of check nodes in the protograph of a low-density parity-check code with stronger nodes based, for instance, on Hamming codes. Such a design approach, which we call LDPC code doping, leads to low-rate quasi-cyclic G-LDPC codes with excellent performance in both the error floor and waterfall regions on the additive white Gaussian noise channel
Quick response codes and libraries
No full textPurpose: This article explains the nature of QR (Quick response) codes and their possible applications in libraries.
Design/methodology/approach: Existing uses; applications and functionality of QR codes are looked, before turning to the limited existing use of QR codes in libraries. The Author then suggests many different ways QR codes could be used in our libraries.
Findings: Most of our users are likely to be able to use QR codes if they install a free reader onto their camera 'phones or other mobile device. An already high and further increasing number of people own suitable devices. There are many ways QR codes can be used, with the most exciting applications relying on the use of the internet from mobile devices. The main restrictions on their take up is likely to be increasing awareness of QR codes and carefully marketing services based on QR codes to our users.
Originality/value: Outside Japan few libraries have implemented services based on QR codes. This article is the first of it's kind aimed at libraries and it shows how we can use them to take advantage of the mobile devices in many of our users' pockets
Multilevel structured low-density parity-check codes for AWGN and Rayleigh channels
No full textWe propose a novel class of protograph low-density parity-check (LDPC) codes having a combinatorial rather than a random structure, which are termed multilevel-structured (MLS) LDPC codes. It is demonstrated that they posses a strikingly simple structure and, thus, benefit from reduced storage requirements, hardware-friendly implementations, and low-complexity encoding. Our simulation results provided for both additive white Gaussian noise (AWGN) and uncorrelated Rayleigh (UR) channels demonstrate that these advantages accrue without compromising the attainable bit error ratio (BER) and block error ratio (BLER) performance, when compared with their previously proposed more complex random-construction-based counterparts, as well as with other structured codes of the same length
MFangPDA/PDA-codes: v1.0.0
No full textThis file contains the PDA source codes for reconstructing air temperature of the NH during the last millennium. Author: M. Fang
Building Codes Division ... annual report
No full textThis archived document is maintained by the Oregon State Library as part of the Oregon Documents Depository Program. It is for informational purposes and may not be suitable for legal purposes.Began with 2015.Mode of access: Internet from the Oregon Government Publications Collection
The Effectiveness of Business Codes: A Critical Examination of Existing Studies and the Development of an Integrated Research Model
No full textBusiness codes are a widely used management instrument. Research into the effectiveness of business codes has, however, produced conflicting results. The main reasons for the divergent findings are: varying definitions of key terms; deficiencies in the empirical data and methodologies used; and a lack of theory. In this paper, we propose an integrated research model and suggest directions for future research.Ethics;Business codes;Effectiveness;Organization
Near-capacity iterative decoding of binary self-concatenated codes using soft decision demapping and 3-D EXIT charts
No full textIn this paper 3-D Extrinsic Information Transfer (EXIT) charts are used to design binary Self-Concatenated Convolutional Codes employing Iterative Decoding (SECCC-ID), exchanging extrinsic information with the soft-decision demapper to approach the channel capacity. Recursive Systematic Convolutional (RSC) codes are selected as constituent codes, an interleaver is used for randomising the extrinsic information exchange of the constituent codes, while a puncturer helps to increase the achievable bandwidth efficiency. The convergence behaviour of the decoder is analysed with the aid of bit-based 3-D EXIT charts, for accurately calculating the operating EbN0 threshold, especially when SP based soft demapper is employed. Finally, we propose an attractive system configuration, which is capable of operating within about 1 dB from the channel capacity
Downlink Space–Time Spreading Using Interference Rejection Codes
No full textIn this paper, the authors will investigate the performance of a loosely synchronized (LS) code-based space–time spreading (STS) scheme in comparison to that of classic Walsh code and pseudonoise code-based STS when communicating over dispersive Nakagami-m multipath channels. Closed-form formulas are derived for characterizing the bit-error-rate performance as a function of the number of resolvable paths L and the number of users K. Our numerical results suggest that the employment of LS code-based STS scheme is beneficial in a low-user-load and low-dispersion channel scenario, where a near-single-user performance can be achieved without a multiuser detector. Index Terms—Code-division multiple access (CDMA), Gaussian approximation, interference-free window (IFW), large area synchronized (LAS) codes, loosely synchronized (LS) codes, Nakagami-m fading
Short author list codes
No full textThe literature contains articles on community-developed codes such as AstroPy (Astropy Collaboration et al. 2013, 2018) and yt4 (Turk et al. 2011), their importance in research, and the need for supporting these important codes and those who devote time and effort building and sustaining these resources (Turk 2013; Muna et al. 2016), but has comparatively little about the body of software written by 1, 2, or 3 people, what we here refer to as short author list (SAL) codes. A recent examination of the 1978 entries currently in the Astrophysics Source Code Library (ASCL,ascl.net) (Nemiroff & Wallin 1999) reveals that 1348 of them, 68%, are SAL codes
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