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Showing papers on "Telecommunications link published in 1979"


Journal ArticleDOI
TL;DR: An analytical solution to the problem of modeling bandpass nonlinear channels and evaluating the performance of digital communication systems operating on them is presented and basic advantages are the generality it offers to the analysis and the fact that it allows accurate evaluation of the error probability in a short computer time.
Abstract: An analytical solution to the problem of modeling bandpass nonlinear channels and evaluating the performance of digital communication systems operating on them is presented. A method based on a Volterra series representation of the overall channel is first proposed, which allows one to extend to nonlinearities with memory the well-known concepts of complex envelope of bandpass signals and low-pass equivalent of bandpass linear systems. The general results previously mentioned are then applied to digital satellite communication systems operating over nonlinear channels. The effect of a nonlinear amplifier located in the satellite is considered, in combination with that of transmitting and receiving filters located in the Earth stations. In addition, both uplink and downlink noise are taken into account. Basic advantages of this approach are the generality it offers to the analysis and the fact that it allows accurate evaluation of the error probability in a short computer time.

293 citations


Patent
12 Apr 1979
TL;DR: In this article, a multiple access, time division multiplex, satellite communications systemn which the uplink and downlink frequencies are the same is considered, where the outgoing information (be it data, encoded data or digitized samples of the voice frequency signals) are assembled into a sequence of pulses to be transmitted as a burst in the time slot assigned to that particular earth station.
Abstract: A multiple-access, time-division multiplex, satellite communications systemn which the uplink and downlink frequencies are the same. In each ground station, the outgoing information (be it data, encoded data or digitized samples of the voice frequency signals) are assembled into a sequence of pulses to be transmitted as a burst in the time slot assigned to that particular earth station. If there are n ground stations in the system, n≧2, then the duration of each ground station sequence is, on the average, 1/2n times the duration of a complete frame or epoch, because for half of the epoch the satellite is in the receiving mode and the other half of the epoch the satellite is in the transmitting mode.

12 citations


01 Jan 1979
TL;DR: In this article, a time synchronization experiment was performed between two ground stations located in the northern and in the central part of Italy, with the uplink carrier at 18 GHz and the downlink at 12 GHz.
Abstract: A time synchronization experiment was performed between two ground stations located in the northern and in the central part of Italy. The rf communication channels used are in the SHF region, with the uplink carrier at 18 GHz and the downlink at 12 GHz. One way and two way techniques were evaluated. Two modes of operation were tested in the two way technique: sequential, time multiplexed, signal transmission on the same communication channel; and simultaneous transmission using separate communication channel. In the sequential mode of operation, range and doppler measurements provided by the timing signals were used to account for the satellite motion. A low cost, versatile, time transfer unit (TTU) was designed, to generate the timing signals and the functions (RF carrier and receiver switching, time tagging of the data, etc.) required to perform automatic time synchronization and data acquisition with a minimum of external components.

5 citations


01 Jan 1979
TL;DR: In this paper, a dual mode traveling wave tube (TWT) equipped with a highly efficient depressed collector is proposed for the downlink amplifier in a 30/20 GHz communications' satellite, and the overall efficiency of such a tube is inferred from a parametric study and from experimental data on multistaged depressed collectors.
Abstract: The rapid growth of communication traffic (voice, data, and video) requires the development of additional frequency bands before the 1990's. The frequencies currently in use for satellite communications at 6/4 GHz are crowded and demands for 14/12 GHz systems are increasing. Projections are that these bands will be filled to capacity by the late 1980's. The next higher frequency band allocated for satellite communications is at 30/20 GHz. For interrelated reasons of efficiency, power level, and system reliability criteria, a candidate for the downlink amplifier in a 30/20 GHz communications' satellite is a dual mode traveling wave tube (TWT) equipped with a highly efficient depressed collector. A summary is given of the analyses which determine the TWT design requirements. The overall efficiency of such a tube is then inferred from a parametric study and from experimental data on multistaged depressed collectors. The expected TWT efficiency at 4 dB below output saturation is 24 percent in the high mode and 22 percent in the low mode.

3 citations


Proceedings Article
01 Jan 1979
TL;DR: The objective of this paper is to analyze the performance degradation of this 'Mismatched Viterbi Receiver' due to the uplink noise and memory truncation, and to understand how the time and phase synchronization errors influence the performance.
Abstract: This paper presents an analysis of a satellite communication system using a Viterbi receiver Here we have a bandlimited nonlinear channel where both uplink and downlink are taken into account as well as the effect of Intersymbol Interference, phase and time synchronization errors In order that ISI can be combatted effectively, we use a Viterbi demodulator which is designed for the satellite channel when there is no uplink noise The Viterbi demodulator for the channels with large memory is too complex to be implemented To reduce the complexity, a Viterbi demodulator with memory shorter than the true channel memory is used The objective of this paper is to analyze the performance degradation of this 'Mismatched Viterbi Receiver' due to the uplink noise and memory truncation, and to understand how the time and phase synchronization errors influence the performance

2 citations


01 Jan 1979
TL;DR: In this paper, a time synchronization experiment was performed between two ground stations located in the northern and in the central part of Italy, with the uplink carrier at 18 GHz and the downlink at 12 GHz.
Abstract: A time synchronization experiment was performed between two ground stations located in the northern and in the central part of Italy. The rf communication channels used are in the SHF region, with the uplink carrier at 18 GHz and the downlink at 12 GHz. One way and two way techniques were evaluated. Two modes of operation were tested in the two way technique: sequential, time multiplexed, signal transmission on the same communication channel; and simultaneous transmission using separate communication channel. In the sequential mode of operation, range and doppler measurements provided by the timing signals were used to account for the satellite motion. A low cost, versatile, time transfer unit (TTU) was designed, to generate the timing signals and the functions (RF carrier and receiver switching, time tagging of the data, etc.) required to perform automatic time synchronization and data acquisition with a minimum of external components.

1 citations


Journal ArticleDOI
TL;DR: When the VPCs combination/VPDs division ratios are controlled according to the criterion maximizing the sum of uplink/downlink rain margins, both efficient on-board RF power utilization and regenerative effect enhancement can be accomplished remarkably.
Abstract: The effects on CNR improvements are described for a K -band PCM-TDMA regenerative satellite relay system, using a multihorn antenna, whose horn powers are combined/divided with variable power combiners (VPCs)/dividers (VPDs). In conclusion, when the VPCs combination/VPDs division ratios are controlled according to the criterion maximizing the sum of uplink/downlink rain margins, both efficient on-board RF power utilization and regenerative effect enhancement can be accomplished remarkably.

Proceedings ArticleDOI
27 Mar 1979
TL;DR: This paper discusses the development of the MPM Inductive Communication System and significant design considerations along with operational data are presented.
Abstract: The Morgantown People Mover (MPM), located at Morgantown, West Virginia, uses low and medium frequency inductive communications for the wayside-to-vehicle (uplink) and vehicle-to-wayside (downlink) communication links. The system has six uplink and one downlink tones in the low frequency (6-50 kHz) range used to communicate speed, switch, calibration, and stop commands and the collision avoidance "safe to proceed" signal, also downlink switch verification. In the medium frequency range (90 - 130 kHz) uplink (command) and downlink (status) digital data are transmitted using two-tone FSK messages. The vehicle interfaces with inductive loops in the guideway surface which range from ten to one thousand feet in length and are driven through feedlines of up to several thousand feed in length. This paper discusses the development of the MPM Inductive Communication System. Included is a brief history of the Morgantown People Mover and an overview of the Inductive Communications System presently in use. Each subsystem is discussed and significant design considerations along with operational data are presented. Emphasis is placed on our experience with this mode of communications.

Proceedings ArticleDOI
P. Christopher1
18 Jun 1979