Showing papers on "Frequency-division multiplexing published in 1985"

Analysis and Simulation of a Digital Mobile Channel Using Orthogonal Frequency Division Multiplexing

Abstract: This paper discusses the analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel. This system uses the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel. When this technique is used with pilot-based correction, the effects of flat Rayleigh fading can be reduced significantly. An improvement in signal-to-interference ratio of 6 dB can be obtained over the bursty Rayleigh channel. In addition, with each subchannel signaling at a low rate, this technique can provide added protection against delay spread. To enhance the behavior of the technique in a heavily frequency-selective environment, interpolated pilots are used. A frequency offset reference scheme is employed for the pilots to improve protection against cochannel interference.

Optical code-multiplex transmission by gold sequences

Abstract: This paper describes a transmission system that uses passive optical multiplexing with gold sequences. The system is composed of an optical fiber network and electrical matched filters, and allows for N + 2 asynchronous stations each with a gold sequence address of length N . We analyze, theoretically, the error probability of the system and verify the results with experimental data. We further show that, in the synchronous case, the maximal error-free multiplexity is, in practice, N + 1 . The features of the System are as follows: 1) The system uses optical multiplexing instead of conventional electrical multiplexing. 2) The number of assignable addresses is large. 3) In the asynchronous case, each station can transmit a code at any time irrespective of other stations' timings.

Signal multiplexing circuit

Abstract: Bidirectional communication of voice and data signals over a two wire telephone line interconnecting several telephone sets with a digital access circuit of a central data and voice communication facility is achieved by a frequency division multiplexing circuit that functions either as a set interface for a telephone or as a line card interface for the access circuit. Data message signals input to the multiplexing circuit are stored in a shift register for subsequent modulation of a carrier signal, but since only one interface may enter a transmission mode at one time transmission priority is assigned by a controller to the interface that first attempts transmission on an inactive line. All other interface then enter a monitor mode to listen but not act on the transmitted message. Transmission errors caused by line noise, or collision transmissions between two or more interfaces are resolved via message transactions between the interfaces only, and retransmission priority is resolved in favor of an interface having the lowest address. Controllable transmit and receive equalizers define analog signal paths in the interfaces and compensate for line losses.

450 Mbit/s optical frequency-division-multiplexing transmission with an 11 GHz channel spacing

Abstract: A 450 Mbit/s 13 km optical frequency-division-multiplexing transmission with an 11 GHz channel spacing was demonstrated at 1.5 μm wavelength to confirm the feasibility of a laser-diode frequency-stabilising circuit and a narrow-channel-spaced optical demultiplexer.

Simultaneous modulation and wavelength multiplexing with a tunable Ti:LiNbO3 directional coupler filter

Abstract: We report a broadly tunable (85 A/V) wavelength-selective Ti: LiNbO3-waveguide directional coupler, with which we demonstrate λ=1.3 μm/λ = 1.55 μm multiplexing while simultaneously modulating the long-wavelength channel.

On The Equivalence of Time-Division and Frequency-Division Multiplexing

Abstract: On the basis of a general sampling formula it is shown that, for a system of n band-limited signals, FDM and band-limited TDM are equivalent in the sense that one can be derived from the other by a simple linear transformation. The transformation matrix is the same as for expanding an arbitrary polyphase system with n phases into its symmetric components. It is further shown that this equivalence also holds for nonideal sampling waveforms as they appear in certain multiplexing and demultiplexing systems used in practice.

Optical fiber communication for local area networks with frequency-division-multiplexing

Abstract: A method and associated system for providing multi-channel transmission of digital and broadband video information in optical fiber communication for local area networks through frequency-division-multiplexing, comprising the steps of generating a plurality of closely spaced optical carrier wave pairs with the optical carrier waves within each optical carrier wave pair having a predetermined separation frequency between one another, assigning each of the plurality of optical carrier wave pairs to a predetermined frequency slot and optically combining the plurality of optical carrier wave pairs to provide a multiplexed optical output wave. Advantageously, in addition to direct detection the plurality of optical carrier wave pairs may be detected by opto-electronic heterodyne detection and/or incoherent optical-heterodyne detection to electronically recover the optical carrier wave pairs.

Apparatus for use in an antenna arrangement

Abstract: A radar includes a rotatable array of antenna elements 11, 12, 13, 14, 15 and 16 which receives pulses reflected by a target. The received signals are mixed with local oscillator signals L01, L02, L03, L04, L05 and L06, the phases of which are controlled by phase shifters, only one of which, 39, is shown. The phase control signal is generated at 19 at the fixed part of the radar, converted into optical form at 20 and colour multiplexed with the local oscillator signal from generator 17 on to a line 24. The signals are passed via an optical rotary joint 26 to the rotating part of the radar where they are demultiplexed and converted into electrical form at 34 and 35. A frequency multiplexing signal generator 21 is also located at the fixed part and generates a fixed frequency signal which is converted into optical form at 22 and passed via the optical rotary joint 26 to a frequency multiplexer 48. This produces a comb of spaced frequencies which are mixed with respective signals from the antenna elements to give a wide bandwidth signal. This is converted into optical form by a laser diode 51 and passed to the fixed part of the radar where it undergoes further processing. The construction of the optical rotary joint, which has several optical lines, is also disclosed.

Automating the power grid: Real-time communication between customers, the electricity grid, and power plants can cut costs for both supplier and user; the technology options are many

Abstract: The benefits that would accrue from real-time monitoring and control of the distribution system are listed. The communication techniques that have been investigated for this purpose are seen as falling into four groups: physically connected media, including wire lines, coaxial cable, and fiber-optic cable; power-line media, including distribution-line carrier communication and power-frequency communications; electromagnetic propagation media, including UHF/VHF radio, AM/VHF radio, and spread-spectrum satellite radio; and common-carrier media, primarily telephone company lines. The advantages and disadvantages of each of these techniques are discussed. To illustrate the various factors involved, the author discusses the automation of the Colorado Springs Department of Utilities.

Frequency-multiplexed acoustooptic architectures and applications

Abstract: The use of frequency multiplexing to increase the utility of acoustooptic correlators is described. Space-integrating and time-integrating architectures are described and specific demodulation and synchronization applications including a novel coarse/fine synchronization technique using these processors are detailed.

Two-Level Multiaccess Schemes for Packet Satellite Systems with Low Duty Factor Terminals

Abstract: A two-level packet satellite network architecture is proposed to provide efficient communications for a large number of low duty factor terminals. At the first level, disjoint subnets of prioritized users employ a minislotted alternating priorities (MSAP) protocol. At the second level, a time division multiple access (TDMA) or frequency division multiple access (FDMA) uplink, and a time division multiplexed (TDM) or frequency division multiplexed (FDM) downlink is assumed, with the satellite regenerating and reformatting the data appropriately. Examples with a large number of terminals show that the two-level schemes provide superior delay performance over single-level methods for wide ranges of throughput.

Frequency multiplexing in an optical system using a Mach-Zehnder waveguide frequency translator

Abstract: A Mach-Zehnder waveguide frequency translator is used to assemble an optical frequency multiplex. The linearity of the process is reported and experimental measurements are compared with theory.

A frequency division multiplexing system designed on the basis of an abrupt filter

Abstract: An FM-FM telemetry system is described analytically. The system is especially suitable for transmitting seismology or magnetotelluric measurements, and it is designed on the basis of an abrupt bandpass filter that permits insertion of more than the usual number of channels in a given telephone band.

Reliability Analysis of a Non-Redundant Repairable Multiplexing Unit

Abstract: This paper analyzes steady-state reliability measures of a modular multiplexing unit. It is based on a Markov model for the failure and repair process. In particular some reliability figures of merit are determined for a subset of the whole communication path set supported by the multiplex. The key point is a procedure for evaluating the probability that a suitable subset of communication paths can be established. The proposed methodology is applied to some examples of common time-division multiplexing units. The results are useful for the dimensioning of communication networks with reliability constraints.

Method and device for information transmission in a digital radio transmission system

Abstract: In known radio communication systems time-division multiplexing, frequency division multiplexing or code division multiplexing or combinations are applied thereof, for message transmission. The NachrichtenubertragungskanaJe in hitherto known radio communication systems, in both directions, that is operated by both the stationary radio station BS to the mobile stations MS as well as in the opposite direction, in the same way. The use of the same transmission method in both directions due to but with the various above-mentioned methods each have different disadvantages in the stationary radio station BS and the mobile stations MS. To avoid the disadvantages occurring in the application of the known multiplex method in a digital radio transmission system for transmitting messages in the direction from the stationary radio station BS to the associated mobile radio stations MS, a broadband multiplexing method and, in the direction from the mobile radio stations MS applied to the stationary radio station BS, a narrow-band multiplex method.

Measurements of the time statistics of FMTV spectra and TV interference into FDM/FM carriers

Abstract: When computing the amount of interference from FMTV signals in satellite systems, it is customary to consider that the only effective TV modulation is the energy dispersal signal (EDS). This leads to a sufficient but highly conservative system design, since for most of the time the wanted demodulated signal may experience interference levels well below that computed using this approach. If the time statistics of the interference can be determined through measurement, then a grade-of-service approach can be taken in which interference can be guaranteed not to exceed a certain level for more than a prescribed fraction of the time. This approach will lead to more efficient use of orbit/spectrum resources as a result of the implementation of less conservative system designs. This paper presents a simulation approach used to ‘measure’ FMTV power spectra with and without EDS and the corresponding interference powers into the basebands of FDM/FM carriers. Time statistics in the form of FMTV spectral masks and FDM baseband interference power time distributions have been derived from the measured data of 1000 off-air TV frames for co-channel TV and standard FDM/FM carrier sets (12 to 1200 channels) deployed by INTELSAT. Sample results are given.