摘要:

AbstractThis paper describes the construction of the control centre for the satellites DFS Kopernikus and TVSAT of the German PTT Administration (DBP Telekom), with emphasis on the implemented technical solutions for monitoring and control. The space and ground segments of the two satellite systems are briefly described in relation to the TT&C operations carried out at the control centre.

ISSN:0737-2884    

DOI:10.1002/sat.4600090202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe satellite communications industry has seen the emergence of VSAT (very small aperture terminal) systems with the promise of high growth in the next decade. The system design of the VSAT ground station has generally followed traditional satellite communication system design, namely featuring data transmission using QPSK (quadrature phase shift keying) or BPSK (binary phase shift keying) and 50 per cent raised cosine shaping filters with quasilinear transmission. Transmitter power is strictly limited and is at a premium for the VSAT transmitter which usually consists of a non‐linear solid‐state power amplifier (SSPA). Consequently it is important to operate the SSPA so that the maximum power is obtained, which means that the SSPA should be operated close to its saturation point. In so doing considerable distortion can be introduced, which leads to intersymbol interference (ISI) in the receiver and an associated degradation in error rate. Although constant envelope BPSK or QPSK solves the intersymbol interference problem and enables operation at the saturating point of the SSPA, the sinx/xspectral shape has unacceptable sidelobe levels.This paper gives results of a search for a pulse shaping filter characteristic that is bandlimited and yet has improved performance over the traditional root 50 per cent cosine roll‐off filter when used in a VSAT ground station with a SSPA. The performance improvement due to improved shaping filtering is maintained over a range of output levels of the SSPA.Performance evaluation results using computer simulation are pres

ISSN:0737-2884    

DOI:10.1002/sat.4600090203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe paper establishes practical formulae in order to determine the depointing angle for a geostationary satellite antenna. Both satellite attitude and station‐keeping errors are considered. The attitude control and station‐keeping specifications give the amplitude of the angular motion of the satellite about its centre of mass and the amplitude of the displacement of the satellite with respect to its nominal position, respectively. The effects of these angular motions and displacements on the aiming of the satellite antenna are analysed. A set of formulae is derived which permits the calculation of the overall satellite antenna depointing angle. These formulae can be used for the estimation of the satellite antenna gain loss or interference contribution at a given location on the Ea

ISSN:0737-2884    

DOI:10.1002/sat.4600090204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractFor satellite communications systems which use frequencies above 10 GHz, rain and clouds attenuate signals severely, leading to an increase in bit error rate (BER) in digital links. This may be coped with by using two or more receivers on the ground, spaced far enough apart to avoid simultaneous rain outages. In this paper, a BER‐minimizing decision processor is derived for two receivers and QPSK modulation. In particular, it is applied to a linear attenuating transmission channel adding independent white Gaussian noise. It is found that gains of nearly 3 dB compared to a switched system are possible in down‐link limited ca

ISSN:0737-2884    

DOI:10.1002/sat.4600090205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA geometric propagation model is developed for simulating the reception of direct sequence pseudonoise (DSPN) satellite signals by a directional or omni antenna in the dense scatterer mobile environment. The model is first validated for narrowband signals by a direct comparison of both simulated cumulative signal strength statistics and simulated diffuse Doppler spectra with classical theory. The model is then used to predict fading statistics for DSPN signaling, either with omni or directional antennas. As expected, the mitigation of fading is closely related to the ratio of DSPN chip duration to delay spread of the scatterer medium for both the omni and directional antennas.

ISSN:0737-2884    

DOI:10.1002/sat.4600090206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractAdapted packet speech interpolation (APSI) is presented as an evolution of digital speech interpolation (DSI) techniques. The inherent overload penalties of DSI are mitigated by the use of an overload strategy which distributes the penalties uniformly across all active speech sources. A novel use of linear delta modulation (LDM) allows the system to re‐encode the input sources at various rates depending upon the total offered load to the system. The subjective performance of hardware is discussed. Two models of silence and talk‐spurt behaviour (called activity) of speech are presented: an analytic model for single speakers obtained by the application of renewal theory, and a simulation model obtained from the analytic mo

ISSN:0737-2884    

DOI:10.1002/sat.4600090207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA theoretical and experimental study of Doppler correction strategies for elliptical orbit satellite communications is presented. Exact analytical expressions for Doppler shift and elevation angle as a function of perigee time of the ground‐station are also presented. It is shown that for a 63° inclined Molnya orbit and a U.K. observer, the Doppler shift remains below about ± 10 ppm and the Doppler rate below about 6 × 10−4ppm/s. Various strategies for continuous Doppler correction of the on‐board oscillators are reviewed or proposed. These include a closed loop ground–satellite system and an on‐board programmable correction approach. Two detailed theoretical and experimental studies of on‐board encoded Doppler correction distribution systems are presented in the context of the UK CERS/TSAT mobile communications experiment. A frequency lock system which requires the distribution of only one signal and a phase‐lock system requiring a master reference and the time‐variant code word are described. Numerical values for a 1·5 GHz carrier are presented throughout but can be scaled t

ISSN:0737-2884    

DOI:10.1002/sat.4600090208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

ISSN:0737-2884    

DOI:10.1002/sat.4600090201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY