John P. Robinson

A class of binary recurrent codes with limited error propagation

A class of binary recurrent codes for correcting independent errors is given which has guaranteed error-limiting properties. These codes can be simply decoded using threshold decoding, and will recover from any decoding error caused by either an uncorrectable transmission error or a temporary malfunction of the encoder or decoder. A number of such codes are given along with a synthesis procedure. The results of a computer simulation are given which indicate that these codes perform better in some situations than other codes using threshold decoding.

Error recovery for variable length codes

When an error occurs in the encoded bit stream produced by a variable length code, the decoder may lose synchronization. A state model for synchronization recovery is developed, and a method for determining the expected span of source symbols lost is presented. The performance of various codes with respect to error recovery is discussed. Two examples are given where equivalent optimal codes have a marked difference in their error recovery characteristics. Some open problems are indicated.

An optimum nonlinear code

A systematic nonlinear code having length 15, minimum distance 5, and 256 code words is given in Boolean form. This is the maximum possible number of words for length 15 and distance 5. The distance spectrum of all pairs of code words is an exact multiple of the weight spectrum of the code words.

Random error and burst correction by iterated codes

We give a decoding algorithm for iterated codes that can correct up to the number of errors guaranteed by the product minimum distance, rather than about half that number when the iterated codes are decoded independently. This result is achieved by adapting Forneys generalized minimum distance decoding for use with iterated codes. We derive results on the simultaneous burst- and random-error-correction capability of iterated codes that improve considerably on known results.

Multiple Fault Detection in Combinational Networks

Combinational networks with no internal fan-out are considered from the point of view of testing for multiple faults. Several different approaches utilizing added inputs and observable outputs are considered and the tradeoffs are discussed.

A Unified View of Test Compression Methods

A unified treatment of the various techniques to reduce the output data from a unit under test is given. The characteristics of time compression schemes with respect to errors detected are developed. The use of two or more of these methods together is considered. Methods to design efficient test compression structures for built-in-tests are proposed. The feasibility of the proposed approach is demonstrated by simulation results.

Simultaneous signature and syndrome compression

A commonly used organization for built-in self-test of VLSI (very large-scale integration) circuits uses complete or pseudorandom test input generators followed by output data reduction. Two compression techniques which have been used are polynomial division (signature) and ones counting (syndrome). The simultaneous use of both of these approaches in parallel is investigated. Analytic and enumerative results indicate that the number of error patterns which are missed by both methods together is nearly the theoretical minimum. The conclusion extends to signature compression combined with any other counter-based compression method such as the use of Walsh spectral coefficients. Some suggestions for CAD (computer-aided design) implementations of test design are given based on these results. >

Error propagation and definite decoding of convolutional codes

The error-propagation effect in decoding convolutional codes is a result of the internal feedback in the usual decoding method, feedback decoding (FD). As a measure of this effect, the propagation length L of a system is defined as the maximum span of decoding errors following a decoding error when all succeding parity checks are satisfied. A relationship between L , the parity check matrix, and the decoding algorithm is developed. A decoding method having no internal feedback, definite decoding (DD), is formalized. It is shown that a code using FD with limited L exists if and only if that same code can be decoded using DD. When using DD a smaller class of errors is corrected. The self-orthogonal codes are shown to be decodable using FD with L small. The minimum possible value of L when using bounded distance decoding is given for some of these codes. Codes are given which minimize the spacing between single correctable errors using DD. These values of spacing are compared with those for similar (known) codes which use FD, and with the theoretical minimum spacing.

ESTprep: preprocessing cDNA sequence reads

MOTIVATION High accuracy of data always governs the large-scale gene discovery projects. The data should not only be trustworthy but should be correctly annotated for various features it contains. Sequence errors are inherent in single-pass sequences such as ESTs obtained from automated sequencing. These errors further complicate the automated identification of EST-related sequencing. A tool is required to prepare the data prior to advanced annotation processing and submission to public databases. RESULTS This paper describes ESTprep, a program designed to preprocess expressed sequence tag (EST) sequences. It identifies the location of features present in ESTs and allows the sequence to pass only if it meets various quality criteria. Use of ESTprep has resulted in substantial improvement in accurate EST feature identification and fidelity of results submitted to GenBank. AVAILABILITY The program is freely available for download from http://genome.uiowa.edu/pubsoft/software.html

Golomb rectangles

There are a number of communications problems involving two-dimensional arrays with constrained correlation functions. Golombs two classes of radar arrays and sonar arrays are examined. Improved bounds, optimal cases, and computational procedures are reported.