Showing papers on "Frequency-division multiplexing published in 1992"

WDM-based local lightwave networks. I. Single-hop systems

Abstract: An overview of emerging all-optical networks is given. The characteristics and alternative architectures for single-hop systems are discussed. The characteristics of lightwave technology that facilitate the design of wavelength-division-multiplexing (WDM) networks are reviewed, and it is explained how WDM local networks can be built based on the single-hop and multihop approaches. Various categories of single-hop systems are discussed: experimental systems, systems based on no pretransmission coordination, and systems based on pretransmission coordination, which also require a separate control channel. A simple classification for single-hop systems is provided. >

10 GHz spacing optical frequency division multiplexer based on arrayed-waveguide grating

Abstract: 11 channel optical-frequency-division multiplexing with a 10 GHz channel spacing is achieved with an arrayed-waveguide grating consisting of SiO2–GeO2/SiO2 waveguides on a silicon substrate.

OFDM for data communication over mobile radio FM channels. II. Performance improvement

Abstract: For pt.I see ibid., vol.39, no.5, p.783-93 (1991). The performance of an orthogonal frequency-division multiplexing (OFDM)/frequency modulation (FM) system for data communication over Rayleigh-fading mobile radio channels was analyzed in pt.I. The effects of forward error correction, switching diversity, automatic gain control (AGC), and squelch are studied. It is shown that OFDM/FM works well with switching diversity because OFDM can average out the transients created by switching between antennas. It is also found that the independent error assumption can be used to predict the distribution of the number of errors in a word. The use of squelch produced a small (about 1 dB) performance improvement, whereas the use of AGC provided negligible improvement. >

Channel capacity optimization of chirp-limited dense WDM/WDMA systems using OOK/FSK modulation and optical filters

Abstract: Frequency chirp in semiconductor lasers that are directly modulated through carrier injection not only induces dispersion in long-haul single-mode fiber communication systems, but also causes energy loss and signal distortion when frequency selective elements such as Fabry-Perot filters are present. This effect is significant for high-bit-rate channels in a dense wavelength-division-multiplexed system in a LAN/MAN environment which requires narrow-band filters to suppress crosstalk from adjacent channels. A simulation approach is used to determine the channel capacity in the presence of chirp and crosstalk. The results show that a minimal channel spacing of less than 37 and 10 GHz with each channel operating at 2 Gb/s using OOK and FSK, respectively, can be achieved by a dense wavelength division multiple access system. It is also shown that this system performance can be optimized through adjusting various parameters of the laser and the filter. >

Apparatus and method for optimal frequency planning in frequency division multiplexing transmissions

Abstract: A method and apparatus for operating a frequency division multiplexing (FDM) transmitter within a common communication channel is disclosed. The carrier frequency for each separate channel is adjusted for minimizing intermodulation interference. The system randomly allocates each separate channel within the available bandwidth to provide an initial set of separate channel allocation and corresponding carrier frequencies. Thereafter carrier to intermodulation ratio (C/IM) on each channel is measured and the worst channel with the lowest carrier to intermodulation ratio (C/IM) is removed. The system then repeatedly inserts a channel in available unoccupied bandwidth to produce the largest minimum carrier to intermodulation ratio (C/IM). The deletion and insertion continues until no improvement in minimum carrier to intermodulation ratio (C/IM) can be achieved for said random allocation of separate channels. The selected set of separate channel allocations is further fine-tuned by deleting the worst channel with minimum carrier to intermodulation ratio (C/IM) and deleting one other channel from said separate channel allocations to provide a particular dual channel deletion. The system then repeatedly inserts two channels in available unoccupied bandwidth which produces the largest minimum carrier to intermodulation ratio (C/IM). The system continues on dual deletion and insertion until no improvement in minimum carrier to intermodulation ratio (C/IM) can be achieved for said random allocation of separate channels. The carrier frequencies are then tuned according to said set of separate channel allocation.

Spatiotemporal frequency multiplex heterodyne interferometry

Abstract: To have the advantages of both spatial and temporal heterodyne techniques and to make efficient use of the limited spatiotemporal frequency bandwidth of image detection systems, we propose a technique of spatiotemporal heterodyne interferometry using both spatial and temporal carrier frequencies. By means of spatiotemporal frequency multiplexing, the technique permits the simultaneous recording of multiple-phase objects on a single space–time interferogram.

Optical frequency division multiplexing transmission system

Abstract: An optical frequency division multiplexing transmission system for sending a large volume of information by a single optical fiber is disclosed. Each of an optical frequency division multiplexing transmitter equipment and an optical frequency division multiplexing receiver equipment has an optical filter having a periodic optical transmission characteristic therein. Each optical filter is stabilized with an absolutely-stabilized standard optical frequency. Each optical signal frequency is stabilized to a periodic transmission characteristic of the optical filter arranged in the optical frequency division multiplexing transmitter equipment, and each local frequency to a periodic transmission characteristic of the optical filter arranged in the optical frequency division multiplexing receiver equipment. Even in the case where no optical signal is applied to the optical frequency division multiplexing receiver equipment due to such causes as a fault of the transmission optical source or the breakage of an optical fiber, the local optical source frequency continues to be controlled in stable fashion.

An efficient multilevel coherent optical system: M-4Q-QAM

Abstract: A coherent multilevel transmission system based on the modulation of all the optical field degrees of freedom (the four quadratures of the optical field) is presented. The transmitted symbols are represented in the space of the field quadratures by a square lattice of points, so that both the transmitter and the decision devices can be easily implemented. The proposed modulation formats allow high spectral efficiency systems to be designed without paying a great sensitivity penalty with respect to binary systems. For this reason the proposed modulation format seems promising for application in densely spaced very-high-capacity FISM networks and in high-speed data transmission in parallel computers. >

A digital modulation method for terrestrial digital TV broadcasting using trellis coded OFDM and its performance

Abstract: OFDM (orthogonal frequency division multiplexing) is regarded as an excellent digital modulation method for various future digital broadcasting systems, including digital audio broadcasting (DAB). The scope of applications of the OFDM can be further expanded by combining it with TCM (trellis coded modulation). This TCM-OFDM system can transmit a much larger number of data than conventional OFDM, causing almost no degradation of bit error rate performance within the same frequency bandwidth. The concept of the TCM-OFDM system for terrestrial digital TV broadcasting and a system configuration that needs no carrier recovery at the receiver and gives simulation results of the bit error rate performances under various receiving conditions are described. >

Diversity communication method of time-division, time-compressed multiplexing telephone signal for mobile communication system

Abstract: In a mobile communication system in which signals are temporally compressed into time slots of a frame structure, a composite signal such as a telephone signal or data signal is hybrid-modulated using the same radio carrier wave, whereby diversity transmission/reception are available. The telephone signal is frequency-modulated using a single time slot of a single radio communication channel which has been allocated between a mobile transceiver and a radio base station. The frequency-modulated signal is again amplitude-modulated by the same telephone signal so that diversity transmission/reception is available.

Digital signal processing in communications satellite payloads

Abstract: Satellite on-board digital signal processing (DSP) offers the potential for significantly improved performance in certain satellite communications system scenarios in terms of system capacity and link quality. On-board DSP functions include digital beamforming, frequency multiplexing and demultiplexing, interference suppression, signal level control and, in a regenerative system, modems. The authors review the status of DSP in communications satellite payloads, focusing on the system advantages, some basic algorithms, and application specific IC implementation issues. As a specific illustrative example an advanced land mobile system is described which features digital beamforming and associated digital signal processing to achieve significant gains in power efficiency (and hence capacity), frequency reuse and flexibility to response to changing traffic scenarios.< >

Spatial Resolution and Data Addressing of Frequency Domain Optical Storage Materials in the Near IR Regime

Abstract: This paper reports recent advances in the study of Frequency domain optical storage (FDOS) based on the photochemical hole-burning (PHB) method. New PHB systems are introduced which operate in the near IR regime and are suitable for the use of semiconductor lasers. Furthermore experiments to determine the spatial resolution of the method are presented. Future applications will also be discussed.

Duplex transmitter configuration for bit-error-free optical FDM cross-connect system

Abstract: A cross-connect bit rate of 156 Mb/s was achieved without loss of a bit by the duplex transmitter using two DBR lasers and an optical LiNbO/sub 3/ switch with a switching speed of 4 GHz. The bit-error-free operation was experimentally verified by observing eye patterns. The proposed optical cross-connect scheme supports cross-connect bit rates up to 2 Gb/s if a 4-Gb/s switching device is employed. Only widely tunable lasers are needed to construct the optical cross-connect system utilizing the duplex transmitter, and the stringent requirements of frequency switching speed for lasers can be eliminated. >

Spatiotemporal frequency-multiplex heterodyne interferometry

Abstract: To gain the advantages of both spatial and temporal heterodyne techniques, and to make efficient use of the limited spatio-temporal frequency bandwidth of image detection systems, we propose a novel technique of spatio-temporal heterodyne interferometry using both spatial and temporal carrier frequencies. By means of spatio-temporal frequency multiplexing, the technique enables simultaneous recording of multiple phase objects on a single space-time interferogram.

Adaptive crosstalk cancellation in dense wavelength division multiplexing networks

Abstract: The LMS algorithm is proposed to cancel received linear crosstalk in dense wavelength division multiplexing (WDM) networks. Analysis and simulations show that with the addition of a few photodetectors, channel spacing requirements are reduced by over 50%. Simulations using a demodulator with Gaussian bandpass characteristics show that a 2.5 dB signal-to-crosstalk ratio is increased to over 35 dB.

Combined multiresolution source coding and modulation for digital broadcast of HDTV

Abstract: A practical end-to-end all-digital multiresolution system is demonstrated that employs joint source-channel coding and modulation in order to achieve efficient broadcast of digital HDTV. The threshold effect plaguing single resolution systems is softened by a stepwise graceful degradation. This can be used to increase the coverage and robustness of the digital broadcast system. This approach is seen as an alternative to traditional single resolution digital transmission systems which are not designed for broadcast situations, and which suffer from the threshold effect. This paper highlights the benefits of using an embedded multiresolution modulation constellation over a modulation scheme that resorts to time or frequency multiplexing of the broadcast resolutions. Besides showing coding results and simulations of transmission effects, the paper discusses the trade-offs between low and high resolution coverage.

Frequency multiplexed data from detector array

Abstract: A two-dimensional imaging system employs a multiplicity of radiation sensors disposed in an array of rows and columns In order to couple signals from each of the sensors from an inaccessible location to an accessible location for processing of the sensor signals to produce an image of a subject viewed by the sensors, a fiber optic link employing both frequency multiplexing and frequency modulation of sensor data connects the sensor array with the signal processing equipment In each column of the array, the sensors produce electrical signals which are coupled via a multiplexer to modulate the frequency of a voltage-controlled oscillator A plurality of oscillators are provided for the concurrent generation of frequency-modulated signals which are then summed together to produce a composite signal The composite signal is transmitted via a fiber-optic link to the signal processing equipment wherein the composite signal is demodulated and the frequency contributions of the various sensors are identified A bank of phase-locked loops may be employed to extract the various frequency components of the composite signal

Advanced technology for fiber optic subscriber systems

Abstract: Key issues in handling optical frequencies for broadband communication services and constructing optical frequency-division multiplexing (OFDM) systems are discussed. The configuration of OFDM transmission systems, their use of multichannel frequency stabilization, multiplexer/demultiplexer, tunable filters, and common amplification systems, and the effects of optical-fiber nonlinearities of OFDM systems are described. The applicability of OFDM to various kinds of telecommunication networks, such as high-capacity end-to-end transmission, information distribution, multinode networks and subscriber systems of both transfer and access networks is discussed. >

Frequency multiplexing of remote all-fiber Michelson interferometers with lead insensitivity

Abstract: A scheme to frequency multiplex a group of sensors based on all-fiber Michelson interferometers is presented. Lead insensibility is obtained by using the two fiber leads of the configuration as an extra Michelson interferometer whose differential phase is kept constant by active compensation. Topics concerning the system design, sensor sensitivity, and crosstalk between sensors are investigated. Experimental and numerical computational results are presented. >

Communication method and network using optical fibers with frequency multiplexing

Abstract: The emission frequencies (F(1) . . . F(2P)) used for simultaneous communications form a stack extending from a fixed based frequency (F(0)) to a top of stack frequency (F(2P-1), F(2-P)). At the beginning of each call, the emission frequency (F(2P-1)) used for the call is at the top of the stack. During the call, said emission frequency is maintained by being servo-controlled to a predetermined spectrum distance (DF) beyond a lower support frequency (F(2P-2)) providing such a frequency can be detected. When such a frequency cannot be detected, the emission frequency is shifted progressively towards the base frequency. The invention is particularly applicable to communications between the peripherals of computer systems.

A frequency stabilization arrangement for dense wavelength division multiplexing systems

Abstract: A frequency stabilization scheme using a tunable twin-guide (TTG) laser diode and a Bragg grating filter on a passive waveguide is proposed. This arrangement is fully compatible with the technologies of monolithic integrated optics. The concept was tested in a hybrid assembly. The frequency drift at laser temperature was 820 MHz/ degrees C and the tuning rate at output power was 310 MHz/mW. >

Subcarrier multiplexing in optical communication networks

Abstract: The bandwidth capability of optical communication networks continues to increase. Optical fibres have low attenuation windows of many thousands of gigahertz and individual optical sources can now be modulated at rates well above 20 GHz. This is much faster than the switching rates of the electronic components needed to achieve multiplexing in applications such as time division multiplexing (TDM). Subcarrier multiplexing, which uses analogue intensity modulation of optical sources with readily available microwave components, can provide an elegant method of using the optical bandwidth and is capable of graceful evolution for future networks.

Optical-fiber data-word transmission system for use with microcomputer controller

Abstract: Experiments were carried out on a new type of data word transmission system employing a GI glass fiber. A frequency division multiplexed scheme was employed because of simple circuit configuration and low cost. Parallel data consisting of multiple frequency signals occupy separate frequencies in a specified frequency domain. The frequency domain used for the parallel data transmission system is described. A square wave frequency modulation (SWFM) scheme was used. Since the SWFM scheme enables the transmission system to be constructed very simply, a data word is easily recovered from the received SWFM signal by using a 4-b parallel data detector. For applying the new system to the industrial field, a Z80 data processor was built into the receiver to process the data words and to output the instructions to the associated external devices. This optical fiber transmission system has high reliability against electromagnetic interference. >

1.244-Gb/s 32-channel transmission using a shelf-mounted continuous-phase FSK optical heterodyne system

Abstract: A total capacity of 40 Gb/s is achieved using a shelf-mounted continuous-phase frequency-shift-keying (CPFSK) optical heterodyne frequency-division-multiplexing (FDM) transmission system with 32 optical channels and a bit-rate of 1.244-Gb/s per channel. For achieving a stable bit-error-rate (BER) characteristics with high-sensitivity, narrow-linewidth laser diodes, a channel-spacing stabilization circuit, and an optical tuner are developed. The obtained sensitivity at a BER of 10/sup -9/ for fiber transmission over 121 km ranges from -45.1 to -44.2 dBm, which is 9.8-10.7 dB lower than the shot-noise-limited sensitivity. The crosstalk penalty is suppressed to within 0.1 dB. The developed system has feasibility achieving a distribution system which can distribute more than 250 HDTV (high definition television) signals or 1250 current-standard TV signals to about 8000 subscribers 10 km from the office, or a 40-Gb/s trunk-line system with a fiber span of more than 50 km. >

Power limitations due to four-wave mixing effects in frequency division multiplexed coherent systems using cascaded optical amplifiers

Abstract: The impact of four-wave-mixing (FWM) effects on phase modulated coherent multichannel systems is investigated numerically for long-haul communications systems using optical amplifiers. Assuming ideal amplifiers spaced at 100 km and compensation of fiber dispersion at the receiver end, the performances of a 2.5-Gb/s 15-channel system are compared for conventional and dispersion-shifted fibers. For 1 mW per channel and 12.5-GHz channel separation, FWM leads to a channel averaged power penalty of 3.3 dB (up to 7 dB in particular channels) after 800 km in a conventional fiber, and 8 dB after only 300 km in the dispersion-shifted fiber. As expected, an increase of channel separation from 12.5 to to 37.5 GHz leads to improved system performance for both types of fibers. The improvement is, however, limited by modulation instability occurring in the individual channels so that for very large channel separations a better system performance is achieved using dispersion-shifted fibers. >

Frequency division multiplexing of fiber-optic gyroscopes

Abstract: The principle of operation of a 2-D frequency-division-multiplexed fiber-optic gyroscope (FDM-FOG) system is presented under the assumption that the two gyro signals do not interfere with each other. The theory is expanded to include the residual cross-interference effect, which may be minimized by proper choice of modulation depths or frequencies. A 2-D FDM-FOG system is realized with a noise equivalent rotation rate of 0.23 degrees /h (0.25 Hz NEB). >

A testbed for DECT physical- and medium access-layer

Abstract: The next generation of cordless telephones in Europe will conform to the DECT (Digital European Cordless Telecommunications) standard. This standard makes a change from today's analog FDMA (Frequency Domain Multiple Access) transmission to the fully digital FDM/TDD/TDMA (Frequency Domain Multiplex/Time Domain Duplex/Time Domain Multiple Access) system. Also, channels will be assigned dynamically at request of the mobile. For the performance of this transmission and access method under indoor conditions no experimental results have been published. Only a few computer simulations of system behavior have been carried out. The authors have set up a testbed for (i) verification of the DECT standard's physical- and medium access-layer specifications, (ii) testing of DECT equipment under typical indoor conditions, and (iii) finding the limitations of a DECT link for indoor and outdoor applications especially in a slightly dispersive radio channel. They present the principle of the DECT testbed, its practical realisation and a few illustrative measurement examples. >

Video image distributer in passenger moving

Abstract: PURPOSE: To provide a video image distributer in a passenger mobile body with a thin and long structure such as an aircraft and a train in which a multi- channel video signal is distributed efficiently to each passenger seat. CONSTITUTION: A head end section 1 provides an output of an electric signal relating to a video signal and subjected to frequency multiplexing. An optical amplifier section 3 applies optical amplification to an optical signal converted by an E/O section 2. An optical signal from the optical amplifier section 3 is sent through one optical fiber transmission line, to which plural optical taps 4 1 -4 n of unequal distribution used to branch part of the optical power of the optical signal on its way are connected in cascade and an optical branching device 6 of equal-distribution to branch the optical power at a final point is connected. Plural O/E sections 5 1 -5 n , 5 o1 -5 om receive the branched optical signals from the optical fiber transmission line and convert the signals into electric signals. Passenger video image reception terminal equipments 7 1 -7 p are connected electrically to the O/E sections 5 1 -5 n , 5 o1 -5 om to receive the electric signal from the O/E sections 5 1 -5 n , 5 o1 -5 om . COPYRIGHT: (C)1994,JPO

Detection scheme of coherence multiplexed sensor signals by using optical loop incorporating frequency shifter

Abstract: A detection scheme of coherence multiplexed sensor signals by using an optical loop incorporating a frequency shifter is proposed and demonstrated. The sensor signals are frequency-multiplexed, and consequently, the numbers of the receiving interferometers and the photodetectors can be reduced.