Showing papers on "Frequency-division multiplexing published in 1989"

Digital sound broadcasting to mobile receivers

Abstract: The authors describe a system that combines the orthogonal frequency-division multiplexing technique and a coding strategy associated with diversity in the frequency domain. The system is suitable for digital broadcasting through a particularly hostile urban radio channel. The general principles of COFDM (coded orthogonal frequency-division multiplexing) are explained, and a detailed representation of the signals and the decoding procedure is given. The performance of the system in the selective Rayleigh channel is presented, and the behavior of the system when the conditions of temporal and frequency coherence of the channel are not fully met (very high-speed reception and abnormally extended channel delay spread) is described. The first implementation of a 4-PSK-COFDM systems has been demonstrated at the WARC-ORB 88 conference in Geneva, validating this concept of digital sound broadcasting. >

Technology and system issues for the WDM-based fiber loop architecture

Abstract: A fiber-optic subscriber loop architecture employing multichannel wavelength-division multiplexing (WDM) techniques is discussed. The architecture, which is called the passive photonic loop (PPL), eliminates the need for outside-plant multiplexing and routing electronics while maintaining complete compatibility with broadband ISDN. An experimental demonstration of the PPL employing 32-channel WDM and a combination of distributed-feedback (DFB) laser and light emitting diode (LED) transmitters is described. A family of alternative PPL implementations is identified. Tradeoffs between these alternatives are explored, and related hardware issues such as wavelength alignment and WDM-component temperature sensitivity are discussed. An economic analysis comparing the PPL with the use of dedicated fiber between the central office and customer premises is presented. The analysis predicts that the PPL can achieve a cost advantage for at least 80 to 90% of the subscribers served in today's network, given DFB-laser and dense-WDM-component cost reductions of approximately one order of magnitude from today's unit-quantity prices. >

Cable televison spread spectrum data transmission apparatus

Abstract: Apparatus for transmitting data spread across at least a portion of the bandwith of a cable television channel comprises a carrier signal oscillator (203), a frequency divider (205), a pseudorandom sequence generator (202) and two exclusive OR gates (207, 210). A first exclusive OR gate (207) serves to spread a data signal across the pseudorandom noise sequence generator (202) having a much higher chip rate than the bit rate of the data signal. The second exclusive OR gate (210) modulates the spread spectrum data signal to a carrier frequency for transmission over the cable television channel. The apparatus may be applied for return path transmission in the 0-30 megahertz band which is highly susceptible to interference noise and provides approximately a 20 dB signal to interference ratio advantage over known data coding and transmission schemes. A microprocessor (201) normally present in a cable television terminal may format data for transmission, control the spread spectrum modulation process and control gain control circuitry for introducing an appropriate power level into the cable plant.

Signal distribution network system

Abstract: A signal distribution cable network system in which frequency division multiplexing is employed to provide a plurality of information channels. A channel allocation controller (CT) allocates free channels on request for the transport of signals from a local signal source (SS1, SS2, SS3) to a signal destination receiver (SR1, SR2, SR3) connected to the network. The local signal source includes a programmable modulator (CFS, VCO, MOD) which is set by the channel controller (CT) to operate at the carrier frequency of the selected channel. The signal level of the signals transmitted by the local signal source is measured in the controller and adjusted to compensate for signal attenuation by a command signal sent by the controlle to the programmable modulator in the local signal source.

Distributed intelligence network using time and frequency multiplexing

Abstract: A distributed intelligence network (10) using time and frequency domain multiplexing. On power-up, each node (20) determines its skew and requests downloading of program code and configuration data. A node claims timeslots by transmitting a packet into an apparently empty timeslot and verifying receipt of its own packet.

Passive optical subscriber loops with multiaccess

Abstract: Deployment of optical fiber in the subscriber loop may eventually lead to a full-scale deployment of the broadband network. A network architecture that can be introduced inexpensively to meet the near-term demand and upgraded smoothly to support future needs is desired. The feasibility of applying multiaccess architectures to subscriber loops is studied, and five architectures for passive optical subscriber loops that meet this need are presented. All of these architectures use a double-star topology and dense wavelength division multiplexing in the downstream direction; however, various topologies and multiaccess techniques are used in the upstream direction. Limitations on node size, frame synchronization, cost, privacy and security, and standards are discussed. >

Optimized decision feedback equalization versus optimized orthogonal frequency division multiplexing, for high-speed data transmission over the local cable network

Abstract: The ideal near-end crosstalk and thermal noise-limited throughput capabilities of uncoded decision feedback equalized (DFE) and orthogonally frequency division multiplexed (OFDM) PAM digital signals transmitted over nonloaded twisted metallic pairs bundled in a multicore transmission cable are determined. Though OFDM has recently loomed as a possible strong competitor among alternatives to DFE for high-speed data transmission over the digital subscriber loop network, it is revealed to be, at best, of marginal value, even if one allows an infinite number of transmission subchannels. >

WDM applications in broadband telecommunication networks

Abstract: Network applications of multichannel wavelength-division multiplexing (WDM) techniques are considered. The photonic technologies that will be critical to future systems using WDM are reviewed. Both interoffice and subscriber loop architectures that utilize the unique properties of WDM to achieve important advantages over more traditional network designs are presented. Several experimental demonstrations that illustrate how these architectures can be realized with currently available components are described. >

Wide-band lightwave distribution system using subcarrier multiplexing

Abstract: A description is given of a bidirectional lightwave distribution system based on subcarrier multiplexing. Eight independent wideband channels (180 Mb/s/channel) are transmitted from the head-end on one 1.3- mu m wavelength laser as frequency-shift-keyed (FSK) subcarriers, between 2.6 and 4.7 GHz. Each receiving node uses a parallel-resonant p-i-n FET receiver, a microwave bandpass filter and a limiter-discriminator demodulator to select and demodulate the appropriate channel. A 45-Mb/s return channel is provided from each node to the head-end on a separate subcarrier frequency. Error-free bidirectional transmission is obtained without penalties from laser nonlinearities, optical reflections or interference, or interchannel interference from closely spaced subcarrier channels. >

Two-stage integrated-optic acoustically tunable optical filter with enhanced sidelobe suppression

Abstract: Demonstrates a two-stage integrated-optic acoustically tunable infra-red optical filter with subnanometre bandwidth and -19 dB sidelobe suppression. This configuration also eliminates the optical frequency shift of one-stage devices.

The coded orthogonal frequency division multiplexing (COFDM) technique, and its application to digital radio broadcasting towards mobile receivers

Abstract: A system which is able to broadcast at high data rates in a selective Rayleigh channel is presented. This technique combines an orthogonal frequency division multiplexing technique and a convolutional coding scheme associated with a Viterbi decoding algorithm. This system is able to benefit from wideband transmission by employing the information contained in all the echoes of the multipath channel while having a very good spectral efficiency and a low computational complexity. The authors present the theoretical principles of the system. They describe the realization of a complete COFDM (coded orthogonal frequency division multiplexing) system, designed within the framework of the DAB (digital audio broadcasting) EUREKA 147 project, which is able to broadcast at 5.6 Mb/s in a bandwidth of 7 MHz. At present, this rate corresponds to 16 high-quality stereophonic programs. Network aspects are pointed out as far as the introduction of a new radio broadcasting service is concerned. >

Two-way CATV system using frequency division multiplexing

Abstract: A two-way CATV system, in which a plurality of communication channels are set simultaneously in an upstream communication line between a plurality of end terminal equipment and a center equipment by using frequency division multiplexing, is disclosed A digital transmultiplexer is arranged at each junction between a trunk line and a branch line for converting a frequency division multiplex signal into a time division multiplex signal Frequency division multiplex signals from the terminal equipment are converted into time division multiplex signals, and then only a time slot corresponding to a frequency slot containing a signal therein is picked up to thereby prevent upstream noises from flowing into the trunk line

Cochlear implant employing frequency-division multiplexing and frequency modulation

Abstract: A cochlear prosthesis composed of a transmitter part which is to be carried exterior to the user's body and a receiver part which is to be implanted in the user, the transmitter and receiver parts being coupled by a radio link provided by implanted receiver coils and external transmitter coils free of any percutaneous connections. In the transmitter part, sound signals are obtained in plurality of channels, and these channels are frequency multiplexed into a composite signal with the aid of a plurality of surface acoustic wave filters, each having a respective passband. In the implanted receiver, the received composite signal is frequency demultiplexed by means of a similar plurality of surface acoustic wave filters each having a respective passband. A further signal is transmitted from the transmitter part to the receiver part via the radio link in order to supply operating power for the circuits in the receiver part, where the further signal is rectified to produce d.c. operating voltages.

A broad-band optical network based on hierarchical multiplexing of wavelengths and RF subcarriers

Abstract: A multiwavelength local-access optical network that is capable of supporting multiple services with diverse requirements is discussed. Integral to the network is an acoustooptic tunable filter, which has the unique capability of selecting multiple, but not necessarily adjacent, wavelengths simultaneously. The use of multiwavelength selectivity, together with subcarrier multiplexing in the electronic domain, suggests simple solutions to many transmission and switching problems in a multiservice setting. An important conclusion is that multiwavelength selectivity can be used to implement many networking functions not easily realized otherwise. >

Edtv recording apparatus

Abstract: Extended definition television (EDTV) signals including a compatible composite wideband signal and a separate helper or extended definition signal are combined, for example, for recording purposes, using frequency multiplexing techniques. The helper signal is applied to a modulator, which produces a suppressed carrier modulated signal, to frequency shift the helper signal to a spectral band above the frequency band occupied by the compatible composite wideband signal. The frequency shifted and wideband signal are then added to form the combined signal.

Observation of coherent interchannel interference in the multiwavelength operation of an acoustooptic filter

Abstract: Wavelength-division multiplexing using acoustically tuned optical filters offers narrow channel spacing, wide tuning range, and the capability for multiple-wavelength switching. It is shown that a coherent source of interference can arise in multiwavelength switching, due to the simultaneous interaction of several acoustic waves with even a single optical channel. Bit-error-rate studies have been performed on an integrated-optic version of the acoustooptic filter and a crosstalk penalty of approximately 2 dB due to dual channel interference has been observed. The theoretical origin of this crosstalk is described and it is shown that a modest relaxation of channel spacing can effectively eliminate and crosstalk penalty. >

Nonlinear distortion due to optical amplifiers in subcarrier-multiplexed lightwave communications systems

Abstract: We show that an optically amplified, subcarrier-modulated lightwave signal suffers both a compression of the optical modulation indices and second-order nonlinear distortion (NLD). Expressions are derived which show that the NLD can seriously degrade performance, unless the lowest subcarrier frequency is larger than several gigahertz. System implications of these effects are discussed.

16-channel optical FDM distribution/transmission experiment utilising multichannel frequency stabiliser and waveguide frequency selection switch

Abstract: A 16-channel, 622 Mbit/s optical FDM distribution/transmission system experiment is demonstrated for a fibre length of 13 km. The feasibility of a multicarrier frequency stabiliser and waveguide frequency selection switch for 5 GHz frequency intervals is verified.

A hybrid lightwave transmission system for subcarrier multiplexed video and digital B-ISDN services in the local loop

Abstract: Lightwave-subcarrier-multiplexed (SCM) transmission systems can provide high-capacity and low-cost delivery of both current and future advanced TV signals. Compatibility of SCM technology with existing baseband digital transmission equipment would eliminate the need for a separate analog distribution network and thereby permit a more graceful evolution to a broadband integrated digital services network (B-ISDN). One version of a hybrid system whereby SCM video and baseband digital signals are simultaneously transmitted by a single laser diode, and the technical issues related to such an implementation are considered. An experiment is discussed in which the three color components of a high-definition TV (HDTV) signal and a baseband 622.08-Mb/s SONET STS-12 rate data signal are transmitted simultaneously by a DFB laser diode via frequency-modulated (FM) subcarriers, over 2 km of a single-mode fiber. >

Frequency division multiplexing of optical fiber sensors using an optical delay loop with a frequency shifter.

Abstract: We propose a new approach for multiplexing a fiber sensor array. The proposed optical systems are interferometers using a low coherent light source. Each input signal imprinted on each sensor can be multiplexed/demultiplexed by using a series of heterodyne carriers with different intermediate frequencies. Intensity or phase modulation has been applied to the sensors in the experimental system, successfully demonstrating the function of our proposed approach. Furthermore, the condition for the proposed system to achieve optimal signal-to-noise ratio is discussed.

Design alternatives of asynchronous WDM star networks

Abstract: Various architectural alternatives for asynchronous wavelength-division multiplexing (WDM) optical local area networks are discussed. Different choices of receiver/transmitter functionality, the number of buffers, and the number of wavelengths are studied and their effect on system performance are analyzed. An analytical solution is introduced to allow a uniform treatment of the various designs within the same modeling framework. The results show the interdependence between the system's hardware complexity and its potential performance. >

Wavelength routing for long haul networks

Abstract: Networks employing wavelength routing, optical amplifiers, and flexible access techniques offer the potential of high reliability and high capacity for telecommunications core network systems. The requirements of these long-haul networks will place high demands on the optical bandwidth and noise performance of optical amplifiers. Network models based on both optical broadband and wavelength selective principles are compared, and a method of equalizing the useful optical bandwidth of amplified routes in wavelength selective networks is presented. Experimental work using commercially available wavelength-division in multiplexing technology, distributed-feedback lasers, and optical amplifiers is described. >

CNR requirements for subcarrier-multiplexed multichannel video FM transmission in optical fibre

Abstract: We clarify the CNR improvement factors applicable to FM video signals provided via satellite links employing energy dispersal waveforms, noting that a CNR of 17.5 dB is required to achieve a weighted SNR of 56 dB for a 525-line C-band NTSC signal with an energy dispersal deviation of 2.5 MHz, accommodated in a 36 MHz satellite transponder channel.

Densely Spaced FDM Optical Coherent System With Near Quantum-Limited Sensitivity and Computer-Controlled Random Access Channel Selection

Abstract: We report the results obtained with a densely spaced FDM coherent optical fiber star network utilizing monolithic frequency-tunable lasers to generate optical signals FSK at 200 Mb/s, which provides an optical receiver sensitivity of 74 photons/bit at a BER of 10-9 and random access channel selection by computer control of the receiver LO laser frequency. The results indicate that this system has the potential to provide a throughput of 2000 Gb/s.

2 Gbit/s subcarrier multiplexed coherent lightwave system

Abstract: The letter reports the combination of a coherent optical link with subcarrier multiplexing to form a phase-modulated coherent lightwave system transmitting at 2 Gbit/s with a receiver sensitivity of −32 dBm.

Channel selection and stabilization technique for a waveguide-type 16-channel frequency selection switch for optical FDM distribution systems

Abstract: A channel selection and stabilization technique for a waveguide-type 16-channel frequency selection switch (FS-SW) was examined at the 1.5- mu m wavelength region. The desired channel could be selected from 16 optical channels with a 5-GHz channel separation. The frequency fluctuation width for the observed short period was 65-250 MHz, and the frequency drift during 30 min was 20-100 MHz. An average crosstalk level of less than -20 dB was successfully achieved in the on state of the FS-SW stabilization. >

Multi-gigabit fiber-optic video distribution network using BPSK microwave subcarriers

Abstract: The design and performance are described of a field-deployable fiber-optic video distribution system using bi-phase-shift-keyed (BPSK) microwave subcarrier multiplexing techniques to provide each subscriber with twenty 107-Mb/s digitized video signals and one 2.04-Mb/s voice/data signal, giving a total transport capacity of 2.144 Gb/s. The microwave subcarrier frequency covers the range from 1.9 GHz to 5.9 GHz. The 21 microwave subcarriers are multiplexed together to intensity modulate a high-speed 1.3- mu m single-mode laser dedicated to each subscriber. Each subscriber station is equipped with a high-frequency p-i-n diode detector followed by microwave receivers. A bit-error rate of 10/sup -9/ is achieved at a laser modulation depth of 5% and a received optical power of -12 dBm. >

Experimental demonstration of multiwavelength optical network with microwave subcarriers

Abstract: The authors use the unique multiwavelength filtering capability of the acousto-optic tunable filter to demonstrate multiple broadband services with only one fixed-wavelength transmitter and receiver per user in the first experimental demonstration of a multiwavelength subcarrier network.