Showing papers on "Carrier-to-noise ratio published in 1992"

Brillouin scattering in externally modulated lightwave AM-VSB CATV transmission systems

Abstract: The authors measure the stimulated Brillouin scattering threshold for a CW (continuous wave) laser externally modulated with an AM-VSB (amplitude modulation vestigial sideband) CATV (cable television) signal. The threshold is essentially unchanged from the unmodulated case. For injected powers above the threshold power, substantial degradation of the carrier to noise ratio is seen. >

Impulse noise eliminating circuit for a television receiver

Abstract: A noise eliminating circuit 6, 8 for a television receiver outputs an image signal 10 without noise by detecting and eliminating impulse noise and effecting interpolation for an image signal, in the case where the carrier to noise ratio (C/N) of a received signal is lowered and impulse noise is detected The noise eliminating circuit 6, 8 comprises a noise defecting circuit 8, which detects only the noise component and judges whether the C/N is such that impulse noise is likely to be produced or not When it is judged that there exists impulse noise, a noise reduction circuit 6 detects noise pulses in the image signal and a brightness signal and a chrominance signal of this portion are separately interpolated so that an image signal from which the impulse noise component is removed is produced If impulse noise is not likely to be produced, the noise reduction circuit is rendered inoperative In an alternative, image ratios may be taken into account (figs 14, 15)

Upstream-FDMA/downstream-TDM optical fiber multiaccess network

Abstract: The upstream-frequency-division-multiple access/downstream-time-division multiplexing (UFDMA/DTDM) optical multiaccess network is discussed. The system design for the proposed network is outlined. In this network, superluminescent diodes, which have a wide optical spectrum linewidth, are used as transmitter light sources in the network terminators to avoid optical beat interference. The carrier to noise ratio (CNR) and the dispersion power penalty are calculated to determine the channel capacity. For example, in the 1.5 mu m wavelength region. 800 Mb/s downstream channel capacity and 1.5 Mb/s upstream channel capacity are applicable for 32 network terminators and a 10 km optical fiber. >

Performance evaluation of high level coded modulation over satellite channels

Abstract: The performance of various coded and uncoded bandwidth efficient modulation schemes capable of providing bandwidth efficiency of 2 b/s/Hz over satellite links, is studied. The schemes are: Gray-coded 8-PSK (phase-shift keying), uncoded 8-AMPM, uncoded pi /2 8-AMPM, trellis-coded modulation (TCM) 16-QAM (quadrature-amplitude modulation), pi /4 TCM 16-QAM, and TCM 16-PSK, all bandlimited with roll-off factor alpha =0.5. The satellite high-power traveling wave tube amplifier (TWTA) is assumed to incorporate a soft-limiter-type linearizer in order to obtain the best possible bit error rate (BER) and minimum out of band emission (OBE). Performance, obtained by computer simulation, is expressed as the total carrier-to-noise (CNR) loss for a given BER, which is the sum of the CNR degradation due to the nonlinearities and high-power amplifier backoff. The performances of the various schemes are compared. >

High-track-density flattened magnetooptical disks with low crosstalk

Abstract: The carrier-to-noise ratio (CNR), crosstalk and noise levels have been investigated for flattened and semiflattened magnetooptical disks with narrow track pitches of 1.2 and 1.0 µm. The track pitch of the flattened and semiflattened disks can be reduced to less than the laser spot size under the condition that the laser spots irradiated on the adjacent recording regions overlap each other only on the spiral guiding band. The CNR of 48.3 dB and low crosstalk of less than -36 dB were achieved for the track pitch of 1.2 µm when the domains of 0.76 µm length were recorded. Crosstalk of less than -30 dB was obtained for the track pitch of 1.0 µm with the conventional optical head having an objective lens of 0.53 NA and a 780-nm laser.

Estimating symbol error rate vs. carrier to noise in IQ modulated systems based on digitization of constellation and statistical models

Abstract: Methods used to characterize the degradation of symbol error rate (SER) vs. carrier-to-noise ratio (C/N) performance of several different components of systems that broadcast digital video signals are presented. The techniques are based on repetitively sampling and then digitizing the IQ constellation at baseband. Mathematically different levels of noise calculated relative to the carrier are added to the digitized constellation. Examination of the resulting distributions of noise versus error thresholds allows the estimation of SER vs. C/N in the absence of any error correction in the receiver. The effects of IF bandwidth and transmit and receive filters are also taken into account. The estimated SER vs. C/N can be plotted and compared to the theoretical SER vs. C/N for the modulation format, IF bandwidth, and transmit and receive filters in the system under test. >

A High Power and Low Noise Transmitter AM-VSB Transmission Using Erbium-Doped Fiber Post Amplifier,

Abstract: : Erbium doped fiber amplifiers(EDFAs) with high output power and no distortion degradation are very useful for the amplitude-modulated vestigial-sideband(AM-VSB) transmission systems which require a relatively high received power for a preferred carrier to noise ratio(CNR) and a low distortion (1) (2) A field trial was conducted and feasibility of multi-distribution for trunk lines was confirmed(3) We have developed an erbium doped fiber with a high conversion efficiency of 86 % and a small wavelength dependence In this paper, by using this fiber as a post amplifier, we present a high power and low noise transmitter with monitoring functions for practical use We also show the effectiveness of long-wavelength-pass filters which have a low insertion loss and no need for wavelength tuning unlike band-pass filters