Showing papers on "Telecommunications link published in 1986"

Power control system for satellite communications

Abstract: A system (20, 22) for compensating for varying attenuation of an uplink signal from a local node to a satellite. The system (20, 22) monitors two beacon signals and the local downlink signal to determine fade. An error signal, indicating the uplink fade, is generated and utilized to adjust the gain of the uplink transmitter (42) to compensate for the fade.

Satellite communications system

Abstract: In communications satellites, the emitted transmission power is directly dependent on the power of the received signal, so that the transmission power of the communications satellite is controlled via the transmission power control of the earth stations. Weather-related signal path attenuation must be taken into account in the respective earth stations. In addition to the evaluation of the beacon signal emitted by the satellite, the carrier signal level of different earth stations is evaluated according to the invention in at least one earth station and the attenuation in the signal path between the individual earth stations and the satellite is inferred, since the downlink attenuation from the satellite to the evaluating earth station is identical for all signals.

Performance of Multibeam Packet Satellite Systems with Conflict Free Scheduling

Abstract: The concept of a multibeam satellite system With on-board processing and memory is studied. In this system multiple slotted ALOHA uplinks carry the traffic to the satellite. Packets are accepted at the satellite, when memory is available, and are routed to their destination zones using a TDM protocol. We present a model which can be used to evaluate a satellite system with conflict-free scheduling, i.e., a system in which several packets can be simultaneously chosen for downlink transmissions, given each earth zone is served by at most one satellite transponder in each slot. We compute the system throughput, packet delays, and buffer overflow probabilities for a general configuration. It is shown that for some configurations the one beam per zone restriction can have a significant effect on the system performance. The presented model can be also used to evaluate satellite systems when this restriction is removed and to evaluate a variety of other satellite systems.

Link switch for a burst-switching communications system

Abstract: This invention provides a high-speed link switch (132) for a distributed-control burst-switching communications system. The switch provides fully integrated voice and data services. A communications system employing the invention includes a plurality of switches interconnected by time-division multiplexed links. In a preferred embodiment, a link switch comprises a central memory (160) coupled with a link-input processor (140), a link-output processor (162), a port-input processor (168), a port-output processor (170), and a memory manager (172). The link switch includes switching intelligence for routing a burst through the switch toward its destination port in the system. A burst is a plurality of bytes which may represent, for example, a block of data or a spurt of voice energy as sensed by silence!voice detectors located at voice ports. Within an outgoing communications link, a burst is transmitted by the switch one byte at a time in an assigned channel of sequential frames of the time-division multiplexed link. A byte is a predetermined number of bits, preferably eight bits, equivalent to the transmission capacity within a channel. The routing intelligence employs dynamic allocation of bursts to channels within communications links such that any channel of a communications link is allocated onlywhen a burst is being transmitted therein and such channel is otherwise available for transmission of another burst. A preassigned terminator character is used to signal the end of a burst, and a data-link escape character-insertion method is employed to distinguish a data character having the terminator's bit configuration from the terminator itself. In an alternate embodiment of the invention, a multiplexer is coupled between the port processors and the external port circuits (178). A link switch as disclosed herein will meet the growing communications needs of the present and foreseeable future.

DSS 13 frequency stability tests performed during May 1985 through March 1986

Abstract: Results of station frequency stability testing performed at DSS 13 (Deep Space Station) during May 1985 through March 1986 are presented. The testing was done on X-band uplink and X- and S-band downlink subsystems as well as on end-to-end systems. The subsystem test data are useful for assessing the frequency stability of various prototype X-band uplink or downlink subsystems for purposes of making design improvements. Information derived from extensive testing at DSS 13 will be useful in the preparation of an X-band Uplink Demonstration Experiment to be conducted at DSS 13, and will also be valuable in the preparations of gravity wave experiments to be conducted at other DSN stations in the future.

A second-generation mobile satellite system

Abstract: A design for a low-user-cost, 9000 channel capacity second generation mobile satellite system (Msat-2) for continental U.S., Alaska and Canada using two geostationary satellites at 90 and 130 deg west longitude, is presented. The increased capacity over the first generation system is obtained by use of a 20 m deployable antenna with an offset-fed antenna configuration, a high-power satellite bus, and by relaxing the north-south stationkeeping requirement to + or - 2 deg and the eclipse capability to 50 percent. Efficient frequency utilization is achieved for uplink and downlink spectra by a 7-frequency reuse scheme with 285 5-kHz channels per subband, and subband reuse of up to four times. Problems of interbeam interference and multipath fading contributed to the choice of a nonoverlapping feed for the Msat-2, and a proper modulation scheme using Gaussian baseband filtered minimum-shift-keying with differential detection.

Testing of 30-GHz low noise receivers

Abstract: NASA-sponsored studies of the growth in communications traffic have indicated that the frequency spectrum allocated to fix-service satellites at the C and Ku bands will reach saturation by the early 1990's. The next higher frequency bands allocated for communications satellties are 27.5 to 30 GHz for the uplink and 17.7 to 20.2 GHz for the downlink. Current plans for developing satellite systems that use these bands include a NASA demonstration satellite (ACTS). One of the components identified as critical to the success of that mission is a 27.5 to 30 GHz satellite receiver. In response to that identification, NASA has sponsored the development of such a receiver to the proof-of-concept (POC) level. Design and fabrication of such POC model receivers was carried out under parallel contracts awarded to LNR Communications, Inc. of Hauppauge, New York and to ITT Defense Communications Division of Nutley, New Jersey. The most significant of the performance goals were a 5 db maximum noise figure, a 2.5 GHz passband, and e0 dB Rf to If gain. Following delivery of hardware from each of the contractors, an in-house test program was undertaken at NASA's Lewis Research Center in order to verify the contractor-reported performance and to provide a comparison of the two receivers under identical test conditions. The present paper reports the results of those tests.

Modeling and equalization of nonlinear bandlimited satellite channels

Abstract: The problem of modeling and equalization of a nonlinear satellite channel is considered. The channel is assumed to be bandlimited and exhibits both amplitude and phase nonlinearities. A discrete time satellite link is modeled under both uplink and downlink white Gaussian noise. Under conditions of practical interest, a simple and computationally efficient design technique for the minimum mean square error linear equalizer is presented. The bit error probability and some numerical results for a binary phase shift keyed (BPSK) system demonstrate that the proposed equalization technique outperforms standard linear receiver structures.

Satellite News Gathering : An Overview

Abstract: This paper begins with a brief history of satellite communication, with particular regard to the early Ku-Band satellites and reviews some of the many experiments conducted by different organizations.

Application of multi-frequency TDMA for satellite communications

Abstract: A Multi-Frequency Time Division Multiple Access (MFTDMA") system has been developed for a thin route satellite communication network which has most o f the desirable features o f both FDMA and TDMA systems. We show that when the network downlink is power limited (with negligible uplink noise) and consists o f mixed earth station sizes with dif ferent rain margin requirements, the MFTDMA" and FDMA systems can have greater throughput capacity compared to TDMA. This improvement depends on the amount o f satellite transponder backoff required to keep the intermodulation e f fec ts small, and is the result o f the TDMA downlink having been sized for the smallest station and largest rain margin. In the case where the earth station must provide circuits to more than one station simultaneously, MFTDMA" is advantageous over FDMA because fewer modems are required.Use of MFTDMA" can lead to lower earth station costs by requiring lower transmitter power compared to TDMA, and fewer modems compared to FDMA. Even though the control algorithim for a MFTDMAm network is somewhat more complicated, a high degree o f flexibility in channel assignment is retained.

Satellite communication network

Abstract: A satellite scrambling communication network uses geographically separated uplinks to provide scrambled video and audio signals and descrambling control data to separated individual subscribers and to separated TV signal distribution systems. The network includes a business control center which provides a master data stream including individual subscriber address and encryption data and uplink channel allocation control data. A first uplink adds to the master data stream supplementary data peculiar to those TV channel distribution systems which will distribute the one or more TV channels from the first uplink. The transmission at the first uplink, in addition to the one ore more TV channels, includes the master data stream and the supplementary data peculiar to the first uplink. There are a plurality of geographically seperated additional satellite communication uplinks, each including means for receiving the master data stream as transmitted from the first uplink via the communication satellite. Each additional satellite communication uplink further includes means for transmitting one or more TV channels, as controlled by the allocation data in the master data stream. Each individual subscriber receiver/decorder is controlled by the master data stream. There are a plurality of geographically separated TV signal distribution systems, each with antenna means for receiving the TV channels from one or more of the uplinks. Each TV signal distribution system is controlled by the supplementary data streams which accompany the one or more TV channels from each of the uplinks.

Development of a Microcomputer-Based Workstation for Analysis of Digital Satellite Links.

Abstract: : The product of this thesis is a comprehensive and integrated software package for the analysis of digital satellite links. The system is designed to run on the IBM PC, and should also run on most compatibles. The system performs three basic classes of functions: satellite orbital analysis, antenna gain pattern plotting, and link analysis. The first class includes the computation of such quantities as velocity, orbital period, and coverage area for satellites in circular and elliptical orbits. The second class is concerned with plotting the gain patterns for horns, helixes, parabolic reflectors, and phased arrays of dipoles. The last class represents the major thrust of the system, and entails computing such items as the G/T figure of merit, received useful power, carrier-to-noise ratio, bit error rate, maximum data rate, and power margin. Inherent within this class are mathematical models for computing the attenuation due to rainfall and atmospheric absorption. The link budget itself appears as a color-coded display with two columns: one for the uplink path, and one for the downlink path. The user also has the capability to change certain key inputs, and then have the system automatically recompute the entire link budget with the modified data. Keywords: computer aided design. (Author)

Switches, lasers and electronically-hopped beam antennas in space - NASA's advanced communications technology satellite

Abstract: The proposed design and operation of the Advanced Communications Technology Satellite (ACTS) are described. The ACTS is a three-axis stabilized spacecraft with an in-orbit weight of 2300 lbs and a beginning-of-life power of 1770 W; it is composed of a 20 GHz 2.2 m downlink antenna, a 30 GHz 3.3 m uplink antenna, a 1 m steerable antenna, and a laser package. The space segment communications payload uses high and low burst rate modes; the operations of these modes are discussed. The components of the laser intersatellite link instrument package are examined. Consideration is given to the ACTS's antennas, RF matrix switch system, and the base band processor. Diagrams of the ACTs systems are presented.

A Dynamic Code Division Multiple Access Algorithm for Time Acquisition of FH-MFSK Satellite Communication Systems

Abstract: A code division multiple-access (CDMA) algorithm is presented for uplink coarse time acquisition for satellite communication systems which use frequency-hopped M-ary FSK signalling with onboard processing The algorithm is based on self-probing, and it allows independent acquisition by large numbers of users on a multiple access basis This new algorithm is extremely fast under light loading conditions when compared to the typical approach Also, it is very efficient compared to perfect preassignment over the full range of loading conditions from light to very heavy loading The algorithm requires minimal processing by one user and no coordinated action by other users, and it is highly resistant to degradation by downlink channel errors or fading The performance is evaluated by analysis and verified through Monte Carlo simulations

Propagation Effects on Communications Satellite Link Performance

Abstract: Prior chapters have focused on descriptions of the propagation factors that can degrade satellite communications links. Gaseous attenuation, hydrometeor attenuation, depolarization, radio noise, scintillation, and other factors were described, and methods for predicting the effects on communications links were presented.

telecommunication system by satellite beams Etroits

Abstract: The invention relates to the field of telecommunications. A telecommunications system including a satellite 91, the earth stations 92, 95 and a network control center 93 uses narrow beams to establish links between earth stations. A signal from any station can be directed to any other station in the system by simply selecting the appropriate carrier frequency for uplink to the satellite. therebetween may thus communicating the various earth stations without performing a demodulation signal, or an active switching circuits in the satellite. Application to long distance telecommunications networks. (CF DRAWING IN BOPI)