Codex Corporation

About: Codex Corporation is a based out in . It is known for research contribution in the topics: Signal & Network packet. The organization has 189 authors who have published 241 publications receiving 32205 citations.

Convolutional codes. II - Maximum-likelihood decoding. III - Sequential decoding

Abstract: Maximum-likelihood decoding is characterized as the determination of the shortest path through a topological structure called a trellis. Aspects of code structure are discussed along with questions regarding maximum-likelihood decoding on memoryless channels. A general bounding technique is introduced. The technique is used to obtain asymptotic bounds on the probability of error for maximum-likelihood decoding and list-of-2 decoding. The basic features of sequential algorithms are discussed along with a stack algorithm, questions of computational distribution, and the martingale approach to computational bounds.

A Custom VLSI Chip Set for Digital Signal Processing in High-Speed Voiceband Modems

Abstract: Systems modems intended for use in relatively large private networks are characterized by high performance, reliability and flexibility to support network management, and multiple modes of operation and user features. This paper describes a programmable digital signal processor which is teamed with a 16-bit microprocessor in a dual processor architecture satisfying the requirements of high-speed voiceband systems modems. The architecture of the two custom integrated circuits which form the basis of the signal processor is presented. This processor has novel arithmetic, data structure address generation, and program flow-control capabilities, which result in a high utilization of the arithmetic unit and a low program overhead for housekeeping tasks. Some of these features are illustrated by programming examples.

Novel device and method for precoding___________________________

Abstract: A novel precoding technique (900) and device (100) allows transmission of a stream of signal points over a channel h(D) to provide efficient data transfer in the presence of intersymbol interference and noise at data rates approaching channel capacity. This new technique may be combined with trellis-coded modulation and works with any signal constellation. In addition, the present invention allows decoupling signal constellation shaping, a significant improvement over prior precoding techniques. Thus, the present invention simplifies shaping and allows signaling at fractional rates without constellation switching.

Real-time implementation of a 9600 bps subband coder with time-domain harmonic scaling

Abstract: This paper describes the real-time implementation of a high quality 9600 bps speech coder on the microprocessor based GTE MARK IV voice digitizer. The speech processing technique programmed is a combination of the subband coding (SBC) with the Time-Domain Harmonic Scaling (TDHS) algorithm. The SBC employs a bank of eight quadrature mirror filters to partition the speech bandwidth into subbands. An adaptive bit allocation scheme is incorporated to assign the quantizer bits dynamically according to the energies of the subband waveforms. The TDHS technique is included as a pre-and post-processors to the SBC. By exploiting the periodic nature of the voiced speech, the scheme compresses and Later expands the frequency range of the input waveform. Though at the expense of pitch calculations and some overhead multiplication, the TDHS reduces the processing requirements of SRC by a factor of two. Forward error correcting codes are also included to improve the robustness of the speech coder to channel coders.

Apparatus for generating sequences of digital signals

Abstract: Apparatus is described for generating a sequence of digital signals xk and/or a sequence of digital signals yk, k = 1, 2, ..., such that yk = Σj≧0 fjxk-j, in which the yk signals are a sequence in a given modulation code. In one arrangement, the signals yk are chosen to be congruent to coset representatives specified in accordance with a modulation code, a plurality of code constellations are used, and at least one constellation include both a point with a positive sum of coordinates and one with a negative sum of coordinates.