Showing papers on "Telecommunications link published in 1975"
01 Aug 1975
TL;DR: In this paper, a tracking-mode network is included in the timing-circuit configuration to overcome the source of error due to satellite motion, which can be large compared to noise in the system, and steady state conditions are reached after about 4.5 s and the ultimate timing accuracy is limited only by uplink and downlink signal-to-noise ratios.
Abstract: Synchronisation of earth stations to a switching satellite in the tracking mode is examined in detail. After completion of the fine-search mode, a timing error may exist due to satellite motion, which can be large compared to noise in the system. To overcome this source of error, a tracking-mode network is included in the timing-circuit configuration. By applying a small correction voltage to the voltage-controlled oscillator (v.c.o.) at all times, an offset frequency shift occurs, which can be used to eliminate the timing error due to constant-velocity satellite motion. Both p.s.k. and f.s.k. synchronisation-burst implementations are considered. It is shown that steady-state conditions are reached after about 4.5 s and the ultimate timing accuracy is limited only by uplink and downlink signal-to-noise ratios.
3 citations
01 Jan 1975
TL;DR: In this paper, the authors examined the problem of synchronisation of ground stations to the synchronisation window of a switching satellite and showed that the timing error between a synchronisation burst and the synchronization window can be represented by an error-detection characteristic.
Abstract: An analysis is presented which examines the problem of synchronisation of ground stations to the synchronisation window of a switching satellite. The physical model considered includes the effects of uplink space delay and attenuation, uplink noise, motion of the satellite, downlink space delay and attenuation and downlink noise. Assuming the use of either p.s.k. or f.s.k. synchronisation bursts and a coherent receiver in the ground station, it is shown that the timing error between the synchronisation burst and the synchronisation window can be represented by an error-detection characteristic. This characteristic provides an error voltage which can be used by the ground station to adjust the frequency of a voltage-controlled oscillator (v.c.o.) and thus reduce the timing error. The analysis shows that repeated transmission of synchronisation bursts and adjustments of the v.c.o. leads, in a convergent series of steps, to reduced timing errors. The final timing error thus depends only on uplink and downlink signal/noise ratios and satellite motion.
3 citations
17 Dec 1975
TL;DR: From extensive computer simulations it is concluded that with relatively little degradation 20 unsynchronized 16 kbps satellite users can be packed into a 500 kHz uplink bandwidth that is shared with terrestrial LOS allocations.
Abstract: : The problem of efficiently packing many mobile user signals into the available UHF uplink bandwidth of an advanced communications satellite is considered. The basic approach is FDMA with QPSK modulated data streams individually modified by spectral shaping using data windows. From extensive computer simulations it is concluded that with relatively little degradation 20 unsynchronized 16 kbps satellite users can be packed into a 500 kHz uplink bandwidth that is shared with terrestrial LOS allocations. Alternatively, 7 unsynchronized 2400 bps users can occupy a 25 kHz bandwidth. Signal strengths may vary by as much as 10 to 15 dB at the satellite without the need for transmitter power control.
3 citations
01 Jul 1975
TL;DR: In this article, the development of CO2 laser systems for space-to-space applications is discussed with the completion of a 300 Mpbs data relay receiver and its modification into a transceiver.
Abstract: Projections of the growth of earth-sensing systems for the latter half of the 1980's show a data transmission requirement of 300 Mbps and above Mission constraints and objectives lead to the conclusion that the most efficient technique to return the data from the sensing satellite to a ground station is through a geosynchronous data relay satellite Of the two links that are involved (sensing satellite to relay satellite and relay satellite to ground), a laser system is most attractive for the space-to-space link The development of CO2 laser systems for space-to-space applications is discussed with the completion of a 300 Mpbs data relay receiver and its modification into a transceiver The technology and state-of-the-art of such systems are described in detail
2 citations
TL;DR: In this article, the performance of a number of modulation and speech processing techniques that have been considered for single voice channel per carrier transmissions via satellite is analyzed, and the analysis basically determines the operating point for the satellite transponder which minimizes the required Earth terminal G/T.
Abstract: This paper analyzes the performance of a number of modulation and speech processing techniques that have been considered for single voice channel per carrier transmissions via satellite. This transmission mode is applicable to demand assignment systems, which make possible the most efficient loading of the satellite transponder in applications where the traffic at individual Earth terminals is not sufficient to justify a substantial number of dedicated channels. The analysis basically determines the operating point for the satellite transponder which minimizes the required Earth terminal G/T. The fraction of the total link noise allocated to uplink noise is treated as a parameter, so that the cost of improving G/T may be traded against the cost of providing increased Earth terminal transmitter power. Both analog and digital modulation techniques are considered, together with various practical combinations of syllabic companding, voice-actuated carriers, and error-correcting codes. The results are presented in general analytic form, applicable to any modulation technique for which carrier-to-noise density ratio, channel width, and guardband width may be specified. Curves showing required G/T as a function of the total number of voice channels per transponder are also presented for the above-mentioned signal processing techniques, assuming "CCIR/CITT type" speech quality and transponder EIRP and bandwidth typical of current domestic satellite configurations.
1 citations