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.

Acquisition of PN Sequences for DS/SS Systems using a truncated sequential probability ratio test

Abstract: An acquisition scheme for a direct sequence spread spectrum signal using the truncated sequential probability ratio test (TSPRT) was studied. Coherent demodulation is assumed. For testing the synchronization, a sliding-correlator linear detector was employed. Since the partial correlation of PN sequences is difficult to characterize by a simple model, the worst case was considered. Linearized bounds of the partial correlation were used for designing the TSPRT. The design parameters of the TSPRT are chosen so that the average sample number (ASN) is approximately minimized while the maximum ASN is always smaller than that for the fixed dwell scheme with similar false alarm and miss probabilities. Some simulation results were obtained and they agree well with analytic results.

Apparatus for transmitting streams of information bits and methods for estimating the most likely sequence sent

Abstract: Embodiments of apparatus are described for transmitting a stream of information bits by sending corresponding signals over a channel in a plurality of signalling slots. A family of multi-dimensional convolutionally coded modulation systems achieves enlarged minimum distance between possible sequences of signal points, reduced number of error events with the minimum distance, acceptable peak-to-average power ratio, reduced number of signal points in each constituent two-dimensional constellation, immunity to rapid carrier phase changes, and reduced complexity, resulting in a reduced error probability when maximum likelihood decoding is used. These advantages are achieved by the construction and by the partitioning into subsets of the multi- dimensional constellation, by the design of convolutional codes using those multi-dimensional subsets, by using a bit converter and a block encoder to convert a multi-dimensional constellation mapping into multiple two-dimensional constellation mappings, and by a simplified decoding technique.

A new complex system identification method and its application to echo canceller fast initialization

Abstract: A method is proposed for estimating the impulse response of a complex system based on its complex input and only the real part of its output. A unique periodic white complex testing sequence is constructed, and it is then sent to the system to be estimated. An important feature of the testing sequence is that its real and imaginary parts are mutually orthogonal, i.e. their cross-correlation is zero. Due to this orthogonality, the effects of the system's real imaginary parts are ideally decoupled. The cross-correlation between the complex testing sequence and the system's real part output yields an accurate estimate of the system's complex impulse response. In applications where the unknown system's impulse response is sparse, it is possible to squeeze it and choose a considerably small period for the sequence to reduce complexity. An effective algorithm for this purpose is presented. The application of this new method to fast training of the Nyquist echo cancellers in data modems is described. It is shown that using these techniques, fast and accurate estimation can be achieved efficiently. >

Linear phase digital filter

Abstract: An improved linear phase digital filter for filtering a data signal, featuring, in one aspect, means for storing samples of the signal on two delay lines which, when cycled, provide pairs of samples whose member sample sequences are oppositely time ordered.