Some optimal AMC codes (Corresp.)

A construction is given for low rate cyclic convolutional codes with optimal free distance. These codes are of the alternating maximum length sequence type.     

Some burst-error-correcting binoid codes (Corresp.)

In this paper we present a class of burst-error-correcting binoid codes derived from Samoylenko's codes. These codes, at high code rate, seem to be very useful for a not-too-noisy transmission channel when the encoding-decoding operations are performed by means of a general purpose computer.     

A class of composite codes (Corresp.)

Certain useful properties of the cyclic codeVare discussed with wordsV(x)=V_{1}(x)(l+x^{n})/(l+x^{n_{1}})+V_{2}(x)(l+x^{n})/(l+x^{n_{2}}), where fori=1,2,V_{i}(x)belongs to a binary codeV_{i}of lengthn_{i}.     

Some comments on N-orthogonal codes (Corresp.)

This correspondence points out that theN-orthogonal codes of Reed and footnote[1]{Scholtz} are equivalent to time-shifted phase-modulated signals. This leads to a simple geometric derivation of the probability of error and also directly determines the minimum distance of the code.     

Some new constant weight codes (Corresp.)

Nonlinear cyclic codes are constructed which improve on published lower bounds for the numberA(n,d,w)of codewords in a binary code of lengthn, constant weightw, and minimum distanced.     

Some efficient binary codes constructed using Srivastava codes (Corresp.)

In this correspondence, we construct a new class of binary codes by exploiting the symmetry properties of the parity check matrix of the Srivastava codes. The construction is a generalization of Goppa's construction [1]. A number of the binary codes constructed are proved equal, or superior, to the best codes previously known.     

Some construction of new burst-error-correcting codes (Corresp.)

We have investigated the existence of some optimal burst-error-correcting codes. Several constructions and some nonexistence theorems are presented.     

Some optimal type-B1 convolutional codes (Corresp.)

Ratefrac{3}{4}optimal type-B1burst-error-correcting convolutional codes have been discovered. Optimal codes of rate1/n_oandfrac{2}{3}are also given. A method of decoding is described.     

Optimal codes (Corresp.)

Some known results on the nonexistence of linear optimal codes can be very easily proved using results on the weight distribution of such codes.     

Duadic codes (Corresp.)

The notion of duadic codes over GF(2)is generalized to arbitrary fields. Duadic codes of composite length are constructed. An upper bound is given for the minimum distance of duadic codes of length a prime power.     

Multigram codes (Corresp.)

A multigram code is a list of codewords for multigrams (of various lengths) belonging to a setS. Three interrelated problems require designing a good setS, good codewords, and a good strategy for dissecting messages into multigrams ofS. Focus is placed on the dissection strategy and applications to English.     

Universal codes for a class of composite sources (Corresp.)

Fixed rate universal block source coding with a fidelity criterion is considered for classes of composite sources with a finite (fixed) set of modes not an unknown switch process. In particular, it is shown that weakly minimax universal codes of all rates with respect to an arbitrary distortion measure exist for such processes.     

A bound for cyclic codes of composite length (Corresp.)

An upper bound on the minimum distance of cyclic codes of composite length is presented. This upper bound proves the BCH bound to be exact for many cyclic codes.     

A bound for arithmetic codes of composite length (Corresp.)

This correspondence presents an upper bound on the minimum distance of arithmetic codes of composite lengthn = n_1 n_2. The tightness of this bound gives a rather good working estimate of the minimum distance of a prospective code.     

Superimposed concatenated codes (Corresp.)

A family of codes of lengthn=q^{s+l}over GF(q), with2s leq qare presented which are constructed by superimposing concatenated codes on a concatenated code. The raterand the distance ratiodeltaof the new codes satisfy the relationr=1-delta+delta ln (delta)for sufficiently large values ofnandq/s. The new codes are superior to the comparable Bose-Chaudhuri-Hocquenghem (BCH) codes, forsgeq 3, in the sense that they contain more codewords. An asymptotically good code constructed using these new codes has a distance ratio greater than those of other asymptotically good codes known to the authors for rates smaller than 0.007.