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Showing papers on "Telecommunications link published in 1989"


Patent
15 Jun 1989
TL;DR: In this article, a communication link manager is proposed for problem determination and recovery of a failing resource on a link segment in a data communication network, where the using node passes link event data to the link manager for analysis.
Abstract: A communication link manager for problem determination and recovery of a failing resource on a communication link segment in a data communication network. When a problem occurs on a link segment, the using node passes link event data to the communication link manager for analysis. The communication link manager interacts with a configuration data base to determine the physical configuration of the failing link segment and the controlling link connection subsystem manager. The communication link manager directs the appropriate link connection subsystem manager to initiate tests of the various link connection components on the link segment under its control. When the failing resource is identified, the communication link manager initiates the appropriate non-disruptive recovery procedure through the link connection subsystem manager and prompts the data link control to restart the line.

90 citations


Patent
19 Sep 1989
TL;DR: In this article, a secure two-way tactical laser communications between a submarine submerged in an ocean and an airborne platform was proposed, where the uplink beam energy was transmitted by the submarine to the airborne receiver, and the signal processor in the submarine receiver decoded the electrical pulses and verified the IFF code to prevent the submarine from responding to a laser beam from an unfriendly source.
Abstract: An arrangement for secure two-way tactical laser communications between a submarine submerged in an ocean and an airborne platform. During an initital acquisition mode, the airborne transceiver sends a downlink pulse-modulated blue-green laser beam to the ocean surface and below using a predetermined IFF code to identify the transceiver to the submarine. In the preferred embodiment the transmit optics spread the beam out into an elongated elliptically-shaped pattern to maximize coverage of the search area. When the downlink beam energy is within range of the submarine, an optical receiver on the submarine detects the beam, filters out the background light with a very narrow-band filter, and converts the light pulses to equivalent electrical pulse. A signal processor in the submarine receiver decodes the electrical pulses and verifies the IFF code to prevent the submarine from responding to a laser beam from an unfriendly source. If the IFF is verified, the submarine laser transceiver transmits a pulse-modulated uplink beam response at the same wavelength, but timed so that the light pulses are time interleaved with the downlink pulses. The uplink beam power is carefully controlled to the minimum power level required by the airborne receiver to recover the uplink beam. As soon as the airborne receiver verifies the uplink IFF code, communications being over the laser link for the duration of time that the airborne platform receiver is within range of the uplink beam. In one embodiment of this invention, both receivers employ a Cesium filled atomic resonance filter (ARF) to separate the blue-green beam from any background light.

80 citations


Patent
Vaughn L. Mower1
20 Nov 1989
TL;DR: In this article, the uplink R.F. carrier signal has a compensated uplink doppler frequency component which equals the inverted and scaled Doppler frequencies of the received downlink carrier.
Abstract: In a communications data link network of the type having a plurality of ground stations and a single moving airborne station, there is provided a doppler frequency compensation circuit in each of the ground stations. The downlink carrier frequency is fixed and continuously broadcast to the receiving ground station which continuously receive the doppler shifted carrier signal. The ground stations are provided with coherent demodulators which provide a coherent I.F. recovered carrier signal that is applied to a scaling phase-locked loop to provide a deviation frequency signal that is applied to an inverting phase-locked loop which provides a pre-compensated uplink R.F. carrier signal. The uplink R.F. carrier signal has a compensated uplink doppler frequency component which equals the inverted and scaled doppler frequency of the received downlink carrier.

54 citations


Journal ArticleDOI
TL;DR: The development of a system for inferring the position of uplink ground stations, using existing domestic satellites, with minimal disruption of normal operation, using the differential time delay of a single uplink signal passing through two adjacent spacecraft.
Abstract: Describes the development of a system for inferring the position of uplink ground stations, using existing domestic satellites, with minimal disruption of normal operation. The system uses the differential time delay of a single uplink signal passing through two adjacent spacecraft to infer the relative position of the uplink transmitter. A system for the measurement of such differential time delays is described. Since this technique alone does not provide an unambiguous determination of uplink transmitter location, the use of an interferometer to resolve such ambiguities is discussed. >

36 citations


Proceedings ArticleDOI
01 May 1989
TL;DR: The authors describe an efficient and robust TDMA frame structure that requires very low overhead for burst demodulation and synchronization while being robust against both fading and carrier frequency offset.
Abstract: The architecture and implementation of a TDMA (time-division multiple access) digital portable communication system using short bursts are considered. The authors describe an efficient and robust TDMA frame structure that requires very low overhead for burst demodulation and synchronization while being robust against both fading and carrier frequency offset. Based on this frame structure, an experimental radio link was implemented, using a hardware architecture that is suitable for digital signal processing and VLSI implementation. Performance results are presented. >

34 citations


Patent
19 Sep 1989
TL;DR: In this article, a method of providing secure tactical communications between a submerged submarine and an airborne platform using a pulse-modulated blue-green laser beam was proposed. But the beam energy was not transmitted to the ground station.
Abstract: A method of providing secure tactical communications between a submerged submarine and an airborne platform using a pulse-modulated blue-green laser beam. During an initial acquisition mode, the airborne transceiver sends out a downlink laser beam to the ocean surface and below using a predetermined IFF code to identify the transceiver to the submarine. In the preferred embodiment the transmit optics spread the beam out into an elongated elliptically-shaped pattern to maximize coverage of the search area. When the downlink beam energy is within range of the submarine, an optical receiver on the submarine detects the beam, filters out the background light with a very narrow-band filter, and converts the light pulses to equivalent electrical pulses. A signal processor in the submarine receiver decodes the electrical pulses and verifies the IFF code to prevent the submarine from responding to a laser beam from an unfriendly source. If the IFF is verified, the submarine laser transceiver transmits a pulse-modulated uplink beam response at the same wavelength, but timed so that the light pulses are time interleaved with the downlink pulses. The uplink beam power is carefully controlled to the minimum power level required by the airborne receiver to recover the uplink beam. As soon as the airborne receiver verifies the uplink IFF code, communications begin over the laser link for the duration of time that the airborne platform receiver is within range of the uplink beam. In one embodiment of this invention, both receivers employ a Cesium filled atomic resonance filter (ARF) to separate the blue-green beam from any background light.

33 citations


Patent
Endo Kazuhito1
28 Jun 1989
TL;DR: In this article, a correlation calculator is used to estimate uplink cross-polarization interference components from the downlink cross polarization cancelling control signals and adjust the angle settings of the 90° and 180° phase shifters with the estimated components.
Abstract: In a satellite communications system, a rotatable 90° phase shifter and a rotatable 180° phase shifter introduce variable phase shifts to a single pilot signal, which is transmitted to the satellite. Downlink cross-polarization interference cancelling control signals are derived from a beacon signal received from the satellite. A pulse sequence is generated to modulate the amplitude of a carrier to produce an ASK signal as the pilot signal. A correlation calculator provides coarse mode interference cancellation by estimating uplink cross-polarization interference components from the downlink cross-polarization cancelling control signals and adjusting the angle settings of the 90° and 180° phase shifters with the estimated components. The pilot signal is transmitted back to the earth and synchronously detected with the pulse sequence to derive a DC signal which represents an uplink cross-polarization interference. A stepwise tracking controller provides fine mode interference cancellation by stepwisely varying the 90° and 180° phase shifters by predetermined amounts an detecting previous and recent values of the synchronously detected DC signal resulting from the stepwise variations, and repeating the stepwise variations until a difference between the previous and recent values is substantially reduced to a minimum.

16 citations


Proceedings ArticleDOI
01 May 1989
TL;DR: It was found that uplink transmission quality lags behind that of the downlink in moderate to heavy cochannel interference environments, but not unmanageably so.
Abstract: Computer simulation results are given for two-way transmission quality resulting from portable radio access. Downlink and uplink performance were examined for a range of frequency reuse factors, propagation models and traffic levels. The effect of traffic on the TDMA (time-division multiple access) uplink is given as a function of occupancy. It was found that uplink transmission quality lags behind that of the downlink in moderate to heavy cochannel interference environments, but not unmanageably so. >

9 citations


Proceedings ArticleDOI
27 Nov 1989
TL;DR: A Monte Carlo simulation of QPSK (quadrature phase shift keying) and offsetQPSK group modems which take into account the effect of the nonlinearity of each ground terminal HPA is described.
Abstract: The authors describe a Monte Carlo simulation of QPSK (quadrature phase shift keying) and offset QPSK group modems which take into account the effect of the nonlinearity of each ground terminal HPA. The effect of uplink fading due to rain, as encountered in satellite links operated in the Ka and Ku bands, is included. Results show that a normalized channel spacing with respect to a symbol rate of 2.5 or greater is required to reduce the effect of adjacent channel interference. At this spacing the performance of the model will still incur a E/sub b//N/sub 0/ (energy per bit/noise density) degradation of about 1.0 dB. In addition, design criteria for major components such as digital subfilter, rate conversion filter, carrier recovery circuits, and quantization are given. >

9 citations


Proceedings ArticleDOI
27 Nov 1989
TL;DR: A centralized, integrated voice/data radio network for indoor fading multipath radio channels is proposed and analyzed and the results are compared with those of Monte Carlo computer simulations.
Abstract: A centralized, integrated voice/data radio network for indoor fading multipath radio channels is proposed and analyzed. It can operate as a stand-alone system or as a cell in a cellular network. The packets of voice and data in the uplink are integrated through a movable-boundary framed-polling protocol to optimize the throughput of the data traffic for a given number of voice terminals. The down link is a simple TDM (time division multiplexing) system. The system dynamically switches between two transmission rates and uses multiple antennas to maximize the throughput in the fading multipath indoor channel. Using three different techniques, the throughput and delay characteristic of the system are analyzed. A simple equation is given to provide an approximate relation between the number of voice users, the data traffic with less than 10-ms delay, and the average transmission rate of the system. The results are compared with those of Monte Carlo computer simulations. >

8 citations


Proceedings ArticleDOI
26 Sep 1989
TL;DR: In this paper, the authors describe the design and fabrication of a self contained satellite beacon tracking system for optical communications, which uses high bandwidth steering mirrors to effectively cancel atmospheric turbulence and mount jitter.
Abstract: This paper describes the design and fabrication of a self contained satellite beacon tracking system for optical communications. This device is installed on a tracking mount and uses high bandwidth steering mirrors to effectively cancel atmospheric turbulence and mount jitter. The steering mirrors are integrated with a 20-cm, unobscured telescope used for receiving the beacon and for transmitting a modulated communications uplink. Satellite range and velocity calculated for its ephemeris are used to offset the transmitted beam from the beacon by as much as 50 microradians to compensate for optical transit time.

Proceedings ArticleDOI
T.J. Sam1
09 Apr 1989
TL;DR: The author outlines the theory and implementation of an uplink power control (UPC) technique for Ku -band VSATs (very small aperture satellite terminals) that saves operational costs by reducing static power margins.
Abstract: The author outlines the theory and implementation of an uplink power control (UPC) technique for Ku -band VSATs (very small aperture satellite terminals). The proposed uplink power control algorithm uses a VSAT outlink signal for a pilot or 'beacon' reference; it requires no extra space segment for power-level monitoring. A control loop holds satellite EIRP (equivalent isotropically radiated power) constant by modifying the earth station EIRP to compensate for uplink rain attenuation. The C/N estimator technique can be extended to low-cost VSAT stations by sampling the I-channel and Q-channel of the PSK (phase-shift keying) data demodulator. Ultimately, UPC saves operational costs by reducing static power margins. >

15 May 1989
TL;DR: In this paper, the X-and S-band system operating noise temperatures of the Deep Space Network (DSN) 70-m antennas are presented for future use in telecommunications link modeling.
Abstract: The X- and S-band system operating noise temperatures of the Deep Space Network (DSN) 70-m antennas are presented. Models of atmosphere and ground noise temperature contributions, as they affect the antenna calibrations, are given for future use in telecommunications link modeling. The measured 70-m antenna network gain/system noise temperature (G/T) performance is presented. Compared with the earlier 64-m antenna network, G/T improvements of from 1.8 dB to 2.5 dB, depending on elevation angle, were achieved. G/T comparisons are made with the DSN/Flight Project Design Handbook and the Voyager telecommunications design control table. Actual Voyager telecommunications link performance is compared with predictions made by TPAP (the Voyager telecommunications prediction and analysis program) and with measured performance of the individual 70-m antennas. A modification in the use of antenna gain, system noise temperature, and atmospheric attenuation in existing telecommunications design control tables is suggested.

Proceedings ArticleDOI
15 Oct 1989
TL;DR: The authors present computer simulation results illustrating the transient as well as the steady-state performance capabilities of the synchronization mechanisms in the presence of satellite and platform motion.
Abstract: A synchronous spread-spectrum communications system utilizing the resources of a nonprocessing satellite transponder is considered. The systemwide time and frequency standard (which is assumed to be maintained by the system master terminal) is transferred to the satellite, and from there it is disseminated and used by all slave terminals in synchronizing their downlink and uplink operations. The downlink and uplink time and frequency tracking processes that must be performed by each system terminal in order to achieve and maintain synchronization are described, analyzed, and evaluated. The mechanism that establishes system time and frequency reference at the satellite is also described. The authors present computer simulation results illustrating the transient as well as the steady-state performance capabilities of the synchronization mechanisms in the presence of satellite and platform motion. >

Proceedings ArticleDOI
11 Jun 1989
TL;DR: Certain design and implementation problems related to space-borne multicarrier (or group) demodulation (MCD) of a large number of low-to-moderate data rate signals relevant to business services exchanged via FDMA (uplink)/TDM (downlink) communication satellites, are discussed.
Abstract: Certain design and implementation problems related to space-borne multicarrier (or group) demodulation (MCD) of a large number of low-to-moderate data rate signals (137 kb/s to 4.369 Mb/s), relevant to business services exchanged via (regenerative) FDMA (uplink)/TDM (downlink) communication satellites, are discussed. Emphasis is given to MCDs utilizing chirp Fourier transform (CFT) processors, displaying an interesting mix of analog and digital signal processing. Mass/DC power budgets for some representative data rates are indicated, and a comparison is made with some alternative MCD technologies. >

Proceedings ArticleDOI
27 Nov 1989
TL;DR: The results of channel-capacity estimation indicate that reasonable channel capacity and availability objectives equal to those for Super IBS are attainable through the use of the uplink and downlink power control incorporated in the outbound link with BPSK/SCPC (binary-phase shift keying/single channel per carrier) transmission.
Abstract: The double-hop VSAT (very small aperture terminal) network was studied with emphasis on its feasibility and networking in the INTELSAT system. The results of channel-capacity estimation indicate that reasonable channel capacity and availability objectives equal to those for Super IBS (INTELSAT business services) are attainable through the use of the uplink and downlink power control incorporated in the outbound link with BPSK/SCPC (binary-phase shift keying/single channel per carrier) transmission. Possible network architectures for various beam configurations were devised, and the accessibility of individual network architectures was analyzed in terms of blocking probability and call setup time. Based on the results of architecture study, an example implementation of VSAT system is shown. Furthermore, experimental results on the developed VSAT system are discussed. The experiment showed that the transmit power control for the outbound SCPC carrier is conducive to meeting stringent performance objectives stipulated for international digital transmissions. >

24 May 1989
TL;DR: In this paper, the authors considered the implementation and performance of power control in a communication satellite system employing a highly elliptical orbit and referred to the EAS/Archimedes land mobile system as studied by the BAe consortium.
Abstract: Considers the implementation and performance of power control in a communication satellite system employing a highly elliptical orbit. In particular, the paper refers to the EAS/Archimedes land mobile system as studied by the BAe consortium. The purpose of power control is to adjust the EIRP from the satellite, ideally for each call, in order to eliminate unnecessary margins from the link. This will allow more efficient use of the satellite power and hence more channels may be provided. In satellite communication systems a power control loop is often used to counteract the effects of fading on the feeder link. This can be implemented by providing a receiver to monitor the downlink signal level, and adjusting the uplink power to give the correct value. The aim of such a system is to ensure that all of the carriers are at the same power level in the transponder. The Fixed Earth Station (FES) must control its total power output (control of each carrier is not required providing that they are all at the same level).

Proceedings ArticleDOI
15 Oct 1989
TL;DR: In this paper, the authors present an approach for determining the required uplink EIRP (effective isotropically radiated power) for each link of an ECCM (electronic counter counter countermeasures) satellite communications network as a function of link and network parameters.
Abstract: The authors present a novel approach for determining the required uplink EIRP (effective isotropically radiated power) for each link of an ECCM (electronic counter countermeasures) satellite communications network as a function of link and network parameters A feature of this analysis is that each link can be assigned a parameter that indicates the fraction of transponder capacity required by that link This approach provides an accurate initial estimate of the required uplink EIRP without performing the complex hardlimiter nonlinearity calculations In addition, this approach provides an insight into the maximum available capacity of the transponder >

Proceedings ArticleDOI
09 Apr 1989
TL;DR: The IBM PS/2s and OS/2 were used to devise a system which allows multiple satellite teleport facilities to be controlled from any computer on the network, and the operation of a group of uplink terminals may be centralized and the problem of control reduced.
Abstract: The IBM PS/2s and OS/2 were used to devise a system which allows multiple satellite teleport facilities to be controlled from any computer on the network. Additional sites may be added to an existing system by the addition of the necessary communications lines, additional site computers, and configuration changes. During operation, an operator at any computer on the network can monitor any uplink site and, with sufficient privilege, assume control of a remote system. Thus the operation of a group of uplink terminals may be centralized and the problem of control reduced. The control software is described in detail. >

01 Jan 1989
TL;DR: In this paper, the authors proposed a multisite throughput calculation method for the downlink of a mobile digital radio link, where multiple transmitter/receiver sites can be used to improve the system throughput.
Abstract: The throughput of a mobile digital radio link can be improved by using multiple transmitter/ receiver sites. The use of multiple sites to improve throughput is not sufficiently addressed in the literature. This paper presents some methods for multisite throughput calculations. Part I of this paper addressed the uplink issue. [l] Here in part 11, the downlink is treated. The downlink channel throughput (from the site to the mobile units) for a single-site system is 1 because the transmissions are scheduled and no conflict occurs. The service area and system throughput are limited for single-site systems. To widen the service area and to increase system throughput on the single-site system without using additional frequency channels, multiple transmitter/ receiver sites can be used. The throughput of a radio channel increases with the number of sites, and is limited only by the traffic density. Throughput and optimal site assignment in the downlink channel are calculated using an iterative method. FM capture is assumed to depend on the received signal level difference between the two strongest signals rather than on the difference between the strongest signal and the collection of all other signals.