17717219
Construction of low-density parity-check codes based on balanced incomplete block designs
This correspondence presents a method for constructing structured regular low-density parity-check (LDPC) codes based on a special type of combinatoric designs, known as balance incomplete block designs. Codes constructed by this method have girths at least 6 and they perform well with iterative decoding. Furthermore, several classes of these codes are quasi-cyclic and hence their encoding can be implemented with simple feedback shift registers.
1486934
Linear block codes for error detection
The probability of undetected error of linear block codes for use on a binary symmetric channel is investigated. Upper hounds are derived. Several classes of linear block codes are proved to have good error-detecting capability.
41204462
Differential trellis decoding of convolutional codes
This paper investigates the principle of metric differences for trellis decoding of convolutional codes. Based on this differential method, a new algorithm, referred to as differential trellis decoding (DTD), is proposed. DTD offers an alternative to the conventional "add-compare-select" (ACS) method for implementing the Viterbi algorithm.
20336793
On linear structure and phase rotation invariant properties of block M-PSK modulation codes
Two important structural properties of block M(=2/sup '/)-ary PSK modulation codes, linear structure and phase symmetry, are investigated. An M-ary modulation code is first represented as a code with symbols from the integer group S/sub M-PSK/=(0,1,2,---,M-1) under modulo-M addition. Then the linear structure of block M-PSK modulation codes over S/sub M-PSK/ with respect to modulo-M vector addition is defined, and conditions are derived under which a block M-PSK modulation code is linear. Once the linear structure is developed, the phase symmetry of block M-PSK modulation codes is studied. In particular, a necessary and sufficient condition for a block M-PSK modulation code that is linear as a binary code to be invariant under 2/sup h/180 degrees /M phase rotation, for 1 >
45763221
Some Results on Linear Unequal-Error-Protection Codes Specified by their Generator Matrix
There are many applications in which it is required to design a code that protects messages against different levels of noise (or messages with different levels of importance over a noise stable channel). Examples of such situations are: broadcast channels, multi-user channels, and PCM digital telemetry systems, among others. A code that offers multiple levels of error protection is called an unequal-error-protection (UEP) code. In this paper, the UEP capabilities of certain classes of linear codes, obtained by combining shorter linear codes, are investigated. Linear UEP (LUEP) codes based on generator matrices of shorter codes were considered previously in [1], for the case of the \(\left| {\bar u\left| {\bar u + \bar v} \right.} \right|\)construction of MacWilliams and Sloane [3]. In this paper, we examine linear codes obtained from combining shorter codes using the more interesting constructions X and X4 of Sloane et al. [2]. Both construction X and construction X4 use cosets of a subcode in a linear code as building blocks, and constitute generalizations to the \(\left| {\bar u\left| {\bar u + \bar v} \right.} \right|\)construction. We provide specific examples of families of codes obtained from construction X, using very simple component codes, which yield good LUEP codes. Furthermore, we discuss two-stage decoding methods for LUEP codes obtained using these constructions. Finally, we present the alternative of using an LUEP code as one of the component codes in construction X. An example shows that in this way optimal LUEP codes may be constructed.
3084937
Bit-Error Probability for Maximum-Likelihood Decoding of Linear Block Codes and Related Soft-Decision Decoding Methods
In this correspondence, the bit-error probability P/sub b/ for maximum-likelihood decoding of binary linear block codes is investigated. The contribution P/sub b/(j) of each information bit j to P/sub b/ is considered and an upper bound on P/sub b/(j) is derived. For randomly generated codes, it is shown that the conventional approximation at high SNR P/sub b//spl ap/(d/sub H//N).P/sub s/, where P/sub s/ represents the block error probability, holds for systematic encoding only. Also systematic encoding provides the minimum P/sub b/ when the inverse mapping corresponding to the generator matrix of the code is used to retrieve the information sequence. The bit-error performances corresponding to other generator matrix forms are also evaluated. Although derived for codes with a generator matrix randomly generated, these results are shown to provide good approximations for codes used in practice. Finally, for soft-decision decoding methods which require a generator matrix with a particular structure such as trellis decoding, multistage decoding, or algebraic-based soft-decision decoding, equivalent schemes that reduce the bit-error probability are discussed. Although the gains achieved at practical bit-error rates are only a fraction of a decibel, they remain meaningful as they are of the same orders as the error performance differences between optimum and suboptimum decodings. Most importantly, these gains are free as they are achieved with no or little additional circuitry which is transparent to the conventional implementation.
14063870
Impact of Manufacturing Practices on Adoption of Plant Information Systems
Firms have invested over $15 billion in the past three years on new information technology and software in their manufacturing plants. In this study, we document how the implementation of new types of manufacturing practices has impacted the types of information technology investments in manufacturing plants. We present a conceptual model to develop hypotheses about relationships between manufacturing practices and the choice of information systems at the plant level. Analysis of cross-sectional survey data from 932 manufacturing plants provides strong empirical support for our hypotheses about how manufacturing practices influence decisions regarding adoption of plant-level IT applications.