Codex Corporation

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

Circuit and method of switching between redundant clocks for a phase lock loop

Abstract: A phase lock loop monitors the frequency of redundant input clock signals (REFCLK₁AND REFCLK₂) and switches back and forth therebetween should one or the other become invalid. Thus, the PLL may continue normal operation even with a failure of one input clock signal. If both the input clock signals fail, an internal reference signal (RC_CLK) maintains the PLL at a nominal operating frequency until one of the input clock signals is restored whereby the loop can quickly re-establish phase lock. To determined validity, the input clock signals are sampled and stored by the reference signal in a predetermined manner. The input clock signal is valid if the samples of the input clock signal each have the same logic state after the sampling period; otherwise, the input clock signal is invalid if the samples of the input clock signal have at least one different logic state after the sampling period.

Coset codes for partial response channels; or, coset codes with spectral nulls

Abstract: Known coset codes are adapted for use on partial response channels or to generate signals with spectral nulls. By using coset precoding and running digital sum feedback, any desired tradeoff can be achieved between the power and spectra of the relevant sequences, up to the optimum tradeoff possible. A fundamental theorem specifying this optimum tradeoff is given. A maximum-likelihood-sequence-estimation (MLSE) decoder for the original code may be used for the adapted code, and such a decoder then attains the minimum squared distance of the original code. These methods sometimes generate codes with greater minimum squared distance than that of the original code; this distance can be attained by augmented decoders, although such decoders inherently require long decoding delays and may be subjected to quasi-catastrophic error propagation. The authors conclude that, at least for sequences supporting large numbers of bits per symbol, coset codes can be adapted to achieve effectively the same performance and complexity on partial response channels, or for sequences with spectral nulls, as they do in the ordinary memoryless case. >

Corrections to 'The LMS algorithm with delayed coefficient adaptation'

Abstract: The analysis in an earlier paper (see Trans. Acoust. Speech and Signal Processing, vol.37, no.9, p.1397-405, 1989) is improved by correcting an error in the derivation of the system equation. After the correction, the system equation is modified, and thus, so are the related analytical results. >

Givens rotation based least squares lattice and related algorithms

Abstract: The author presents a general and systematic approach for deriving new LS (least squares) estimation algorithms that are based solely on Givens rotations. In particular, this approach is used to derive efficient Givens-rotation-based LS lattice algorithms-the Givens-lattice algorithms. By exploiting the relationship between the Givens algorithms and the recursive modified Gram-Schmidt algorithm, it is shown that the time and order update of any order-recursive LS estimation algorithm can be realized by employing only Givens rotations. Applying this general conclusion to LS estimation of time-series signals results in the Givens-lattice algorithms. Two Givens-lattice algorithms, one with square roots and the other without, are presented. It is shown that the Givens-lattice algorithms are computationally more efficient than the fast QR algorithm of Cioffi (1987). The derivation of other Givens rotation-based LS estimation algorithms and their systolic array implementations are discussed. >

Line probing modem

Abstract: A modem for receiving data sent from a remote device over a communication channel by using a single carrier modulated signal, the modem including a receiver for receiving the modulated signal and for receiving a line probing signal sent by the remote device over the channel, the receiver being capable of receiving the modulated signal over any one of a plurality of frequency bands; a line probing processor for measuring characteristics of the channel based upon the received line probing signal; and a selector for selecting one of the plurality of frequency bands, said selection being based upon the measured characteristics of the channel, said selected frequency band to be used for receiving the modulated signal from the remote device.