Digital signal

About: Digital signal is a research topic. Over the lifetime, 44213 publications have been published within this topic receiving 345279 citations.

Adaptive pre-distortion apparatus for linearizing an amplifier output within a data transmission system

Abstract: An adaptive apparatus for compensating the non-linear distorting action of an amplifier in a transmission system. I-channel and Q-channel memories store a plurality of digital pre-distortion correction values. The memories are addressed using a predetermined number of significant bits of an incoming, original information signal to retrieve I-channel and Q-channel pre-distortion correction values. The I-channel and Q-channel pre-distortion correction values are combined, digitally, with I-channel and Q-channel components of the original information signal to pre-distort the original information signal. The pre-distorted signal, in real format, is supplied to the amplifier, and a feed-back sample signal is coupled-off of the output of the amplifier. A comparison is made between the original information signal and the feed-back sample signal in digital format and in the complex domain (I/Q). In response to the comparison, the pre-distortion correction values (I/Q) in the memory means are modified.

Frequency conversion method

Abstract: The method provides a frequency conversion or translation. A periodic input signal is converted into a lower frequency output signal by under-sampling with a sample signal. The frequency of the sample signal is provided by means of a digital direct synthesiser which is clocked by a clock signal taken from the input signal. The clock signal has a frequency proportional to that of the input signal. Preferably the direct synthesiser is programmed such that it acts as a frequency divider with a dividing factor which is not a whole number. The direct synthesiser (DS) may generate an oscillator signal from which a pulse shaper generates the sample signal. The method may be used for measuring high frequency input signals.

Method and device for selecting data in a communication network

Abstract: The invention relates to a method of selecting data of a compressed digital signal comprising a plurality of levels of spatial granularity of data, in a communication network comprising at least two communication apparatuses connected together by the network, the digital signal being available at least at one, so-called first, of the communication apparatuses, the data being adapted to be transmitted from the first apparatus to the other, so-called second, communication apparatus, and that data being sufficient to reconstitute a spatial part of the signal termed region of interest which is specified at the second apparatus, characterized in that the method comprises the following steps: determining (S 76 ; S 78 ; S 80 ) at least one level of spatial granularity of data as a function of the region of interest and of the structure and organization of the data in the signal; selecting (S 77 ; S 79 ; S 81 ) data for each determined level of granularity as a function of the region of interest and of the structure and organization of the data in the signal.

System of very-long-distance digital transmission by optical fiber with compensation for distortions at reception

Abstract: A system for very-long-distance transmission of a digital signal between a transmitter station and a receiver station, wherein the transmitter and receiver stations are connected by a monomode optical fiber with negative chromatic dispersion at the operating wavelength of the system, having a length of at least one thousand kilometers. The receiver station comprises device to compensate for the distortions due to the non-linear effects and to the chromatic dispersion introduced by the transmission line, the compensation device carrying out a positive chromatic dispersion of the received signal, the amplitude of the positive chromatic dispersion being a function notably of the amplitude of the negative chromatic dispersion induced by the optical fiber as well as of the mean on-line optical power of the signal transmitted on the optical fiber.

Hand-held data capture system with interchangable modules including autofocusing data file reader using the slope of the image signal to determine focus

Abstract: The present invention provides a novel hand-held data capture system with interchangeable modules including an autofocusing data file image reader. Several exemplary modules having various features are described. For example the invention teaches an apparatus and method for providing an interchangeable RF module, an interchangeable reflected image reader, two exemplary interchangeable non-scanning laser illuminated bar code reader/RF modules, and three exemplary interchangeable long range CCD reader/RF modules. Also disclosed for the described modular system are noise filtering means, a solid state laser illumination system, signal processing means, and filter, exposure control, and depth of field control means. An exemplary autofocusing system adjusts the lens to a position where the intensity change with respect to time or with respect to position is maximized. A novel focusing system employs several signal processing algorithms, including a method whereby the maximum slope of the intensity of the image signal with respect to time or with respect to position is determined. Mathematical operations may be performed by a high performance digital signal coprocessor.