Digital signal

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

Automatic protection apparatus for span lines employed in high speed digital systems

Abstract: An automatic span line switch for high speed communication lines is disclosed. The apparatus employs an alarm interface unit which is coupled to a service line terminal in order to detect a line failure mode. Upon detection of such a mode, the system operates to modify the parity bit content of the transmitted digital signal in order to provide a unique code to be transmitted to a remote office connected to a near office and indicative of a span line failure. The apparatus automatically proceeds to switch the failed transmission line to a back-up protection line to enable the near location to communicate with the remote location via the back-up line. All control signals transmitted between the locations are implemented by means of unique codes which are generated by purposely modifying the parity bit content in each successive frame of the transmitted digital signal. The system further describes a priority system for preferentially switching higher priority service lines when multiple failures occur. Various other techniques such as manual operation are disclosed to enable manual switching of protection lines during system operation.

System for recognizing bar code information

Abstract: A system for recognizing bar code information having a plurality of bar codes. One of bar codes is constituted as an index code in a different manner from the other bar codes constituted as numerical codes. These bar codes are scanned sequentially and converted into corresponding parallel digital signals. Code scanning directions are discriminated with reference to the parallel digital signal corresponding to the index code. A plurality of registers adapted to memorize each parallel digital signal are triggered in forward and reverse sequences, when the scanning directions are discriminated to be forward and reverse, respectively.

Direct digital FM waveform generator for radar systems

Abstract: A linear FM waveform generator employs direct digital synthesis and includes a digital linear FM signal generator, a digital-analog converter, and a sampler means. The linear FM waveform generator includes a frequency slope register coupled to a first stage integrator which in turn is coupled to a second stage integrator, all of which operate off a system clock. The output signal from the second stage integrator represents phase as a quadratic function of time. A stored sine look-up table is referenced to generate an output digital signal representing amplitude as a function of time. The output digital signal is converted to an analog linear FM waveform which in turn is coupled to a sampler that includes a step recovery diode and a fast switch. The sampler aperture is sufficiently small that the sampler output linear FM waveform includes base and higher harmonic spectra with amplitude attenuation small enough to enable a third or higher harmonic spectra to be used for generation of the output linear FM waveform. The sampler output is filtered to pass a higher harmonic spectra which is directly coupled to output multiplication and filter circuitry.

Generation of optical OFDM signals using 21.4 GS/s real time digital signal processing.

Abstract: We demonstrate a field programmable gate array (FPGA) based optical orthogonal frequency division multiplexing (OFDM) transmitter implementing real time digital signal processing at a sample rate of 214 GS/s The QPSK-OFDM signal is generated using an 8 bit, 128 point inverse fast Fourier transform (IFFT) core, performing one transform per clock cycle at a clock speed of 1672 MHz and can be deployed with either a direct-detection or a coherent receiver The hardware design and the main digital signal processing functions are described, and we show that the main performance limitation is due to the low (4-bit) resolution of the digital-to-analog converter (DAC) and the 8-bit resolution of the IFFT core used We analyze the back-to-back performance of the transmitter generating an 836 Gb/s optical single sideband (SSB) OFDM signal using digital up-conversion, suitable for direct-detection Additionally, we use the device to transmit 836 Gb/s SSB OFDM signals over 200 km of uncompensated standard single mode fiber achieving an overall BER<10(-3)

Method for preventing copying of digital video disks

Abstract: A method for securely storing analog or digital data on a data storage medium. An analog information signal is combined with a noise signal. The composite noise and information signal is encrypted with a key which is derived from the noise signal. The encrypted composite signal is compressed and then recorded on the data storage medium along with an encrypted value of the key. The storage medium data is read, decompressed, and decrypted using a decryption key derived from the stored encrypted key. The data is then converted to an analog signal and combined with a noise correction signal derived from said key to eliminate the noise signal added to the analog information signal before storing the signal on the data storage medium.