ISSN:0737-2884    

DOI:10.1002/sat.4600020202

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe International Maritime Satellite Organization (INMARSAT) is the world's only commercial satellite system providing mobile communications. This article describes the system and the services which are provided through it to the worldwide shipping and offshore industries. It provides some background on the establishment of the system and why maritime nations looked to satellites as the way to effect a dramatic improvement in maritime communications. The article discusses some of the research and development now being carried out which is expected to lead to the provision of new services, including aeronautical communications via satellite. Also mentioned is the role to be played by INMARSAT in the Future Global Maritime Distress and Safety System, now being developed by the International Maritime Organization for introduction in 1990. New services, such as these, and greatly expanded capacity are to be provided by INMARSAT in its second generation system, consisting of a new series of satellites for launch from 1988.

ISSN:0737-2884    

DOI:10.1002/sat.4600020203

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

年代:1984

数据来源: WILEY

摘要:

AbstractNotwithstanding the additional spectrum allocations of the 1979 World Administrative Radio Conference (WARC '79) and the ever‐increasing sophistication of spacecraft antennas which allow more intensive spectrum reuse, saturation of the 6/4 and 14/11 GHz bands is foreseeable by the late‐1990s.The next available frequency bands at 30/20 GHz were allocated at WARC '71, when knowledge of propagation phenomena and their effect on satellite communications systems performance was fragmentary. During the past 8 years, numerous experimental programmes have led to the acquisition of more precise information about hydrometeor‐induced propagation disturbances. Analysis of the data reveals that even with corrective means such as diversity and coding, service reliability of satellite communications systems with up‐links at 30 GHz and down‐links at 20 GHz could not reach 99.99 per cent as currently available at the lower frequencies and could be 98.0 per cent, or lower, in certain parts of the world. Since the conventionally proposed use of the 30/20 GHz bands does not lead to optimal solutions, alternative approaches are needed.An approach which would involve a revision of the spectrum allocations at 30/20 GHz is proposed. Placingbothup‐ and down‐links around 20 GHz and redistributing the spectrum available at 20 GHz would prevent the intrinsic imbalance of the up‐ and down‐links with consequent higher reliability, reduced earth‐station transmitter power, reduced construction and operational costs, and simplification of the spacecraft transponders and antenna design.The use of frequencies around 30 GHz could be postponed until the 20 GHz bands became saturated. When the 30 GHz bands would eventually be used, there would be no imbalance of

ISSN:0737-2884    

DOI:10.1002/sat.4600020204

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe importance of weight and power estimates and methods for obtaining them are discussed. A method sufficiently accurate for system and launch vehicle planning is developed. It starts from operational requirements such as numbers of transponders, lifetime, eclipse service, radio frequency powers and certain general technology factors such as the performance of batteries and solar cells, and calculates the array power and the masses of the payload and primary power systems. Using these results, and differentiating between spinning and body stabilized satellites, the results of regression analyses on many communication satellites are then used to ascertain the weights of the other subsystems. Simple orbital mechanics are used to determine the weights of propellants, apogee motor, etc., to arrive at a final mass estimate. This estimate should be accurate to between 5 and 10 per cent if reliable input data are available.

ISSN:0737-2884    

DOI:10.1002/sat.4600020205

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

年代:1984

数据来源: WILEY

摘要:

AbstractThis paper describes a method of measuring the frequency response of a digital radio link given the received (modulated) message signal, suitable for the incremental commissioning and in‐service monitoring of links in a QPSK/TDMA system. The method applies least squares estimation techniques to samples of the I and Q baseband components in order to derive a linear equivalent model for the channel. Results obtained by computer simulation of an INTELSAT V channel demonstrate that the method can provide a better basis for linear equalization of a non‐linear channel than the frequency response measurements provided by conventional techniques. A mathematical formulation and an implementation overview are also gi

ISSN:0737-2884    

DOI:10.1002/sat.4600020206

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe principles of operation and several types of surface acoustic wave devices are reviewed. One device, the interdigital transducer device, can accomplish matched filtering for complex bandwidth‐efficient phase modulations. Data speeds in excess of 120 Mb/s are accomplished with existing thin film lithography. Filters are cheap and small, and show little mismatch to the desired response. A number of receiver designs are proposed that are based on these filters. A bank‐of‐matched‐filters approach seems superior to the Viterbi algorithm at high

ISSN:0737-2884    

DOI:10.1002/sat.4600020207

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

年代:1984

数据来源: WILEY

摘要:

AbstractData taken from real satellite channels point to the fact that such non‐Gaussian behaviour as burst noise exists. Since the probability density function (p.d.f.) which minimizes the Fisher information (If) subject to the given variance of noise is Gaussian, performance can be improved by taking into account the non‐Gaussian nature of the actual noise p.d.f. To achieve the higher efficiency, a modem, which consists of a maximum likelihood sequence detector (MLSD) implemented by an adaptive Viterbi algorithm (VA), is introduced in this paper. The new form of the algorithm, based on them‐interval polynomial approximation (MIPA) method, which adjusts the operation of the VA decoder to ensure its robustness to changing and/or non‐Gaussian noise conditions, leads to an improvement of the error probability in operation of the receiver. In contrast to coding techniques, this improvement through digital signal processing is not obtained at the expense of bandwidth expansion. Monte Carlo simulation results involving bit error rate (BER) support theoretical conc

ISSN:0737-2884    

DOI:10.1002/sat.4600020208

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

年代:1984

数据来源: WILEY

ISSN:0737-2884    

DOI:10.1002/sat.4600020209

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

年代:1984

数据来源: WILEY

ISSN:0737-2884    

DOI:10.1002/sat.4600020213

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

年代:1984

数据来源: WILEY

ISSN:0737-2884    

DOI:10.1002/sat.4600020215

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

年代:1984

数据来源: WILEY