ISSN:1124-318X    

DOI:10.1002/ett.4460010102

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

年代:1990

数据来源: WILEY

ISSN:1124-318X    

DOI:10.1002/ett.4460010103

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

年代:1990

数据来源: WILEY

ISSN:1124-318X    

DOI:10.1002/ett.4460010104

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis article deals with both the principles of the Green Paper on telecommunications and the current situation of its implementation. It presents the measures necessary for the completion of the Community's internal market and the liberalization of the markets for telecommunications terminal equipment and services. Moreover, it describes the European Commission's initiatives in the field of public procurement and Community‐wide telecommunications infrastructure

ISSN:1124-318X    

DOI:10.1002/ett.4460010105

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn Europe, second generation equipment for mobile telecommunications will operate in the WMHz band as defined by the Groupe Spécial Mobile (GSM) of the European Conference of Posts and Telecommunications (CEPT). By contributing to and complying with these recommendations, Alcatel, in cooperation with Nokia and AEG, has contributed in developing a pan‐European digital Cellular mobile‐Radio system, the ECR900.This system is based on the Intelligent Network (IN) concept. The Alcatel E10 and the System 12 digital switches are compatible IN components and naturally accommodate the ECR900 system.Outside these digital exchanges, specific mobile functions are concentrated at mobile‐radio service control points, built on ALCATEL8300 telecommunication processors.The ECR900 system has already been ordered in France for the GSM Mobile‐Radio network, in the Federal Republic of Germany and in the Net

ISSN:1124-318X    

DOI:10.1002/ett.4460010106

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe interest into PMR trunking systems is due to the increase of spectral efficiency that can be obtained sharing frequencies between more users. The British DTI protocol specification MPT 1327, intended to be used on this kind of systems, has been recently released, and it is now being accepted as a standard on some european countries.This protocol is based on the MPT 1317 signaling format specification, designed to work at frequencies of 50–500 MHz, and for this reason, it presents some problems when working with RF frequencies of 900 MHz and moving vehicles.The problem comes out from the low bit rate used (1200 bit/s, and the block length (64 bit). If we consider a vehicle that is running at a speed of 100 km/h, we will have a mean of two fades into each information block, while the code (BCH 63, 48) has only a good capacity of error detection/correction for single error bursts.The paper, proposes a solution to this problem, that consists on raising the bit rate to 2400 bit/s, using indirect PSK modulation, with coherect demodulation, instead of FFSK with incoherent demodulation, as it is usual. With this method, we obtain the same BER. Added to this bit rate increase, that allows us to lower the mean number of fades into each block to one, we apply time diversity [2], sending two times each block into the forward control channel, and sending also two times each return control channel or traffic channel message. This diversity system can be implemented bitwise, using channel information to select the most likely value of each bit [4], or block to block, using the error detection capabilities of the code [6].The system has been simulated for 900 MHz and 100 km/h, and measured into a laboratory test setup, using a fading simulator.The results show that proposed method gives the same quality working at 900 MHz that the classic approach working at 150 MHz, showing an improvement of 6 dB over the standard approach working at 900 MH

ISSN:1124-318X    

DOI:10.1002/ett.4460010107

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

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper gives an introduction to the use of Hidden Markov Models and Information Theory principles for speech recognition. The use of these techniques has led to powerful large vocabulary speech recognition systems developed in the recent years. The use of Hidden Markov Models for stochastic modeling of speech and the basic modules of a Hidden Markov Model based speech recognition system are explained. It is shown how the speech waveform can be transformed into acoustic features and into prototypes which characterize the acoustic state space of the given speaker. The phonemes of the language can be represented by Hidden Markov Models. The statistical parameters of these Markov models can be obtained during a training session. During recognition the input to the linguistic decoder is the acoustic label string resulting from the speech signal of a spoken sentence. The decoder picks the sentence which maximizes the probability of the word sequence of this sentence if the given label stream is seen. The paper concludes with a more detailed explanation of the acoustic processor of the speech recognition system and some proposed algorithms for its improvement which can lead to a better system performance.

ISSN:1124-318X    

DOI:10.1002/ett.4460010108

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

年代:1990

数据来源: WILEY

摘要:

AbstractThe performances of a Local Area Network (LAN) integrating voice and data are improved changing the 2 register management in the Reserved Virtual Time CSMA protocol adopted for vocal packets, and using a new exponential backoff algorithm for voice, that introduces a maximum backoff time equal to the vocal packet size involved in the retransmission. In addition, a dynamic priority assignment is used between voice and data, that permits to consider a finite number of buffers for data packets.Simulation results are presented to evaluate LAN performances.

ISSN:1124-318X    

DOI:10.1002/ett.4460010109

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

年代:1990

数据来源: WILEY

摘要:

AbstractMultiple site diversity systems are foreseen for earth to satellite paths operating at frequencies above 10 GHz in localities with high rain‐induced attenuation. A recently suggested model for the prediction of diversity performance is properly modified by considering also the stratified type of rain. The modified method uses the assumption of lognormal unconditional distribution of rainfall for the location under consideration. Numerical results are applied to several satellite systems operating in various locations in the United States and Italy. Some useful conclusions are deduce

ISSN:1124-318X    

DOI:10.1002/ett.4460010110

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

年代:1990

数据来源: WILEY

摘要:

AbstractIn order to store digital image data in a pel‐by‐pel representation a huge amount of storage capacity is necessary. For example a DIN A4 page scanned with a resolution of 300 dpi (dots per inch) needs about 1.1 Mbyte storage capacity in binary representation.This paper deals with various methods to compress binary image data. The focus is to discuss their suitability for archiving usual business documents made up of text, graphics and halftone segments.The two‐dimensional CCITT group 4 recommendation is compared with an adaptive prediction algorithm and a Classified Pel‐Pattern (CLAP) method. For the latter a very efficient systematic code is given. The Classified Pel‐Pattern algorithm achieves the best data compression but at the cost of high complexity. Compressing documents scanned with a resolution of 300 dpi the measured compression ratio is between 1.3–2.5 (halftone pictures) and 50 (line art). Considering only text and graphic documents the recommendation of the CCITT is 5–10% worse but complexity is significantly less. However, it is found that this methods show unsatisfactory results applied to half

ISSN:1124-318X    

DOI:10.1002/ett.4460010111

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

年代:1990

数据来源: WILEY