Showing papers on "Frequency-division multiplexing published in 1979"

Telephone system in which communication between stations is controlled by computers at each individual station

Abstract: A telephone system is provided which requires no central office. All the stations on the system are interconnected by a single line or cable and each station includes a computer which carries out the necessary switching. Each station is then able to call any other station, or to respond to a call, without requiring any central office. Frequency division multiplexing is used to permit a number of conversations to be carried on simultaneously and two frequencies are assigned to each conversation to permit duplex operation. A page capability is also provided.

Receiver Windowing for FDM MFSK Signals

Abstract: Frequency division multiplexed, orthogonal M -ary FSK modulated signals transmitted over a frequency hopping channel (with one channel use per hop) interfere with each other unless perfectly synchronized in time and frequency with the receiver. In order to maintain the interfering "crosstalk" energy at harmless levels, even in the case of grossly power unbalanced users, the frequency separation between assigned signaling frequencies must be expanded beyond the orthogonal spacing. It is found that the required bandwidth expansion can be significantly reduced by amplitude windowing at the receiver, at a cost of a slight decrease in detectability. This effect is evident through examination of both worst case, single source crosstalk and average, multiple user crosstalk.

The Use of an Optical Power Combiner for Multiplexing Multiple Television Sources in Single-Fiber Optical Systems

Abstract: A theoretical analysis is made of the maximum allowable transmission loss for frequency division multiplexed optical transmission of TV signals using an optical power combiner and intensity modulated multiple light sources. A PIN photodiode detector is assumed and the performance of a configuration using multiple light sources and an optical power combiner is compared to the performance of an electronic power combiner with a single light source. The results show that the maximum allowable transmission loss for 10 TV channels is greater than 25 dB if the modulation factor is 0.8 and the power supplied to the power combiner is 3 mW per light source. Practical optical fiber transmission systems carrying 10 TV channels over distances greater than 5 km therefore appear possible in the not-too-distant future if optical fiber cable with a loss of 5 dB/km is used.

Frequency Domain Storage

Abstract: The main features of a non-volatile, optical storage scheme which has the potential of storing on the order of thousands of data bits in the frequency domain (f) are described. The frequency dimension can be used independently of the two or three spatial dimensions thus creating a three dimensional x,y,f- or a four dimensional holographic storage scheme. This frequency multiplexing method can, in principle, lead to an increase in storage densities of two or three orders of magnitude. The described scheme is based on a method of laser photochemistry which is known as photochemical hole burning (PHB); its limitations lie in the nature of the low temperature photochemistry as will be discussed in some detail.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Multichannel signal processing using acoustooptic techniques

Abstract: The feasibility of acoustooptically processing several different signals simultaneously has been demonstrated using two distinct multiplexing techniques. A four-channel acoustooptical system using frequency multiplexing was successfully used for correlating signals;each channel had a 45-MHz bandwidth and about 45-dB interchannel isolation. A second technique for multiplexing, which uses the angular orientation of acoustic waveforms, was also demonstrated; a minimum of 20-dB channel isolation was measured, and parameters that may limit the number of channels and the channel isolation were identified and measured. Both multiplexing techniques can be used in a memory device for increased data-handling capability.

Multiwavelength Monolithic Integrated Fiber-Optic Terminal

Abstract: The paper presents the Multiwavelength Monolithic Integrated Fiber Optic Terminal (MMIFOT) developed under NASA sponsorship. The program aims to utilize the advantage of optical fiber and integrated optical device technology to achieve parallel transmission of many data channels over the same optical fiber link, and to develop an eight channel wavelength multiplexed fiber optic link that transmits eight bit words in a parallel format at a nominal rate of 20 Mw/s; in the second phase of the program a transmitter/multiplexer chip will be developed. The MMIFOT configuration, the receiver/demultiplexer development, and the waveguide detector development are discussed, concluding that the first phase of the MMIFOT program will culminate in the demonstration of an eight channel receiver/demultiplexer chip with a four channel breadboard multiplexer with the data rate of 20 Mbps per channel with a dynamic range of minimum 20 dB.

Carrier wave communications system - sends frequency multiplexed analog signals and TDM digital signals in parallel

Abstract: The carrier wave communications system sends in parallel analog signals by frequency multiplexing and digital signals by time multiplexing over the same pair of wires or a separate pair in the same cable. To prevent the analog and digital signals overlapping, the digital signal is modulated onto a carrier whose frequency is a multiple of half the bit frequency and sent in the main band as well as the lower band. The overlap in the lower band is suppressed.

Level Division Multiplexing of Service Channels in Multilevel Digital Transmissions

Abstract: Level Division Multiplexing (LDM) is a technique suitable for the addition of supplementary information within multilevel digital transmissions using either amplitude modulation or frequency modulation. Its principle of operation is based on the addition of a supplementary modulation area outside that normally provided for, which does not produce any worsening of the transmission quality of the main information signal. The supplementary information can be added without identifying the frame of the main information signal, but simply by arranging the supplementary information in a frame of its own, which is completely independent of the frame of the main information signal. An example of application (the addition of 4 service channels within the DSA2 system) shows that the LDM technique is particularly suitable for the addition of service channels in PAM/FM digital microwave radio links.

Random Coding Bounds for Noncoherent mFSK Multiple-Access Channels

Abstract: We investigate a time-varying trellis coded multiple-access scheme using noncoherent mFSK signals. Techniques similar to this were originally proposed by Cohen, Heller, and Viterbi[1] and more recently in a mFSK form by Viterbi.[2] In these multiple-access systems van der Muelen[3] Ahlswede[4] Liao[5], Gaarder and Wolf [6], Kasami and Lin[7], Weldon[8] and Wolf[9] have shown that the decoded symbols of one user can be used to reduce the “multiple-access noise” to other users and thus allow for a larger achievable rate region than one would expect with conventional time division multiple-access techniques. In some cases, specific codes were investigated. Peterson and Costello[10] and Chevillat[11] have extended these earlier works to convolutional and trellis codes. In this case the decoder is designed as a “super” Viterbi decoder that regards all transmitter trellis codes combined to form a single “super” trellis encoder.