ISSN:1124-318X    

DOI:10.1002/ett.4460070102

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

年代:1996

数据来源: WILEY

摘要:

AbstractThe characteristics of timing signals at the output of autonomous and slave clocks are thoroughly investigated: first, a mathematical model of timing signals is introduced, then models for describing autonomous and slave clocks are presented whereby an analysis of their behaviour in a synchronization network is carried out. Further, two commonly used measurement configurations are described in order to identify the measurement set‐ups more useful for telecommunication applications; the most frequently used quantities for characterizing time and frequency stability are introduced and deeply investigated. Finally, the stability quantities behaviour both for autonomous and slave clocks is studied, with the aim at providing synchronization network designers with powerful tools for network planning and for assessing network performanc

ISSN:1124-318X    

DOI:10.1002/ett.4460070103

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

年代:1996

数据来源: WILEY

摘要:

AbstractThere are numerous synchronization methodologies available for consideration in solving the problem of network synchronization in digital communication networks [1, 2]. They include: independent clocks, pulse stuffing, elastic stores, master‐slave hierarchical, time reference distribution, mutual synchronization, etc. This paper considers the network synchronization performance achievable using the method of mutual clock synchronization observed first by Christiaan Huygens in 1665 [3]. Network synchronization performance metrics studied include: nodal timing accuracy, timing jitter, slip rate, time interval between slips, probability of loss of synchronization. These metrics are shown to depend upon the distance (range) between clocks, ranging error, clock stability, nodal phase error processing bandwidth, data rate, signal‐to‐noise ratio and network connectivity. In this regard, the mutual synchronization performance achievable with long wavelength biological rhythms and electric power system rhythms is compared with the performance achievable using short wavelength rhythms required in wideband and broadband digital communications networks. The results are further applied to the problem of synchronizing a satellite communications network. When intrasatellite communication crosslinks (links between satellites in the same orbital plane) are used in a constellation of communication satellites, it is shown that the maximum data rate, the network connectivity and the constellation altitude drive the achievable network synchronization performance; the latter is set by technological limitations due to clock frequency stability, the maximum range between satellites and the minimum ranging error achievable by the ranging system. In this sense, low Earth orbits (LEO) are preferred over geosynchronous (GEO)Earth orbits. The theory is also applied to the Teledesic and Iridium net

ISSN:1124-318X    

DOI:10.1002/ett.4460070104

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

年代:1996

数据来源: WILEY

摘要:

AbstractNetwork synchronization has gained increasing attention since the introduction of the Synchronous Digital Hierarchy (SDH), as network synchronization performance due to the SDH‐internal bit rate adaptation technique have a major impact on the phase transfer characteristic of SDH‐based networks. Excessive jitter or wander may result in bit errors or frame slips within digital exchanges. This paper discusses the requirements with respect to SDH Equipment Clocks (SEC), which are the basis for improved network synchronization. Two parameters have a significant impact on the phase error generated by the clock: the oscillator performance and the phase detector characteristic. This paper proposes a synthesizer‐based PLL structure employing a fixed frequency highly stable oscillator. A novel approach for an all‐digital phase detector provides enhanced resolution, thereby reducing the phase error. Analytical and simulation results demonstrate the feasibility of this a

ISSN:1124-318X    

DOI:10.1002/ett.4460070105

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

年代:1996

数据来源: WILEY

摘要:

AbstractSDH networks require synchronous clocking in order to minimize network wander and jitter. In practice, the clocks in SDH networks are not ideal and thus are not all perfectly synchronous. The operation of SDH networks with non‐ideal clocks results in undesirable wander and jitter effects. Two different philosophies are being used to minimize these undesirable synchronization effects in SDH networks. In Europe, where it is difficult to tighten clock specifications due to the multinational synchronization environment, desynchronizer designs are made more robust. In North America, where Synchronous Optical Network (SONET) is used, the specifications of both the clocks and the synchronization distribution are being tightened. Even with these different approaches, non‐ideal synchronization effects still exist in SDH networks. In particular, the STM‐N. AU, and TU overhead bytes cause gapped pointer effects when traditional fixed threshold pointer processors are used. Another type of pointer processor, a uniform pointer processor, can remove the gapped pointer effects caused by the STM‐N, AU, and TU overhead bytes. Additionally, a compensating desynchronizer may be used to remove the gapped effects caused by the VC overhead bytes. If these gapped effects are not removed. then they cause jitter and wander in a reconstructed PDH signal. This paper focuses on the case where the SDH network clocks have fixed frequency offsets. An El‐rate (2048 kbit/s) payload, which is transported over a network consisting of SDH and PDH islands, is used to show the effects of this non‐ideal clocking in SDH networks. In theory, clock frequency differences in SDH networks are accommodated by the pointer processor mechanism without slips (i.e. losing or repeating data). In practice, non‐ideal synchronization may stil

ISSN:1124-318X    

DOI:10.1002/ett.4460070106

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

年代:1996

数据来源: WILEY

摘要:

AbstractAn imperfect clock timing recovery in receivers of modern communication systems degrades the performance of synchronization loops and, hence, the overall system reliability and data transmission quality. In this paper, the phase‐locked loop (PLL) for the carrier recovery and the delay‐locked loop (DLL) for the clock timing recovery of the pseudonoise (PN) code in direct‐sequence spread‐spectrum systems are analyzed regarding the impacts of imperfect oscillators (including phase noise and a frequency offset between transmitter and receiver) and channel noise on the mean exit time. The optimal design considerations to achieve a maximum mean exit time for second‐order synchronization loops can be used to find the required oscillator stability,Le., the maximum tolerable frequency offset and oscillator ph

ISSN:1124-318X    

DOI:10.1002/ett.4460070107

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

年代:1996

数据来源: WILEY

摘要:

AbstractA new concept of asynchronous multiplexing of digital signals has been recently proposed by authors. The concept is based on a new format called “Transition Place Coding” (TPC). In this paper the TPC principle has been outlined and the transmission efficiency, the jitter and the error multiplication of the TPC format are analyzed in details. It is shown that the TPC format can be used as an optical line code. Two modifications of the TPC format are presented: a format without transition bit (TPC1) and a format with sliding frame (TPC2). An extensive analysis of the above mentioned characteristics of both TPC1 and TPC2 format was performed. A new asynchronous time‐division multiplexing method based on the TPC formats has been proposed and analyzed with emphasis on an adaptive multiplexing. The TPC multiplex is verified by a computer simulation and by several experimental realizations. Finally, a comprehensive comparison of the TPC multiplex is performed and conditions where their applications appear most desirable are defined. It is shown that the TPC multiplex is attractive for optical fibre communica

ISSN:1124-318X    

DOI:10.1002/ett.4460070108

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

年代:1996

数据来源: WILEY

摘要:

AbstractAn application to HF radio links of the constant false alarm rate synchronization method based on both preamble detection and over sampling at the receiver is proposed and discussed. The method provides both frame and bit synchronization: the former is achieved by correlating the received samples with a reference preamble pattern; the latter by over sampling the incoming signal. A closed form expression of the probability of miss is derived for the general case and a statistical analysis of the synchronization method applied to HF transmissions is carried out on a simulation basis. Several curves which show the distributions of probability of miss for different propagation conditions and different fade margins are included. Inspection of these results shows that the reliability of the synchronization method has to be improved through the introduction of a suitable synchronization strategy involving a certain number of pre‐alarm state

ISSN:1124-318X    

DOI:10.1002/ett.4460070109

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

年代:1996

数据来源: WILEY

摘要:

AbstractFollowing the mainstream applied economic literature on the production structure of the telecommunications (TLC) carriers, the paper provides an econometric estimation of theoveralleffects of the adoption of optical systems in junction and trunk network on the aggregatelong‐runcosts of the existing TLC European carriers. The analysis uses data from 16 European carriers over the 1980–'92 period. The optical systems are shown to have significantly reduced the costs of the European carriers. Firms operating non‐rural and high density areas have benefited especially from the adoption of optical systems. In addition, the efficiency gain related to fibre optic lines turns out to be cumul

ISSN:1124-318X    

DOI:10.1002/ett.4460070110

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

年代:1996

数据来源: WILEY

摘要:

AbstractFull photonic packet switching fabrics require memories, which are not available today in the optical domain: therefore, an alternative is the use of optical buffers based on fibers used as delay lines. This letter reports the optimised implementation of such a buffer operated in a multi‐wavelength regime and accessed by fast optical gates. The buffer operating principles and two different implementation structures are first briefly presented. Then differential delays and influence on bit error rate performance are discussed on the basis of test results within a 4 × 4 photonic packet switching matrix handling ATM cells at 2.488 Gbit/s. The results demonstrate that fiber delay lines are a simple, potentially cost‐effective solution to implement buffering within highspeed photonic packet switching systems, adopting current optical techno

ISSN:1124-318X    

DOI:10.1002/ett.4460070111

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

年代:1996

数据来源: WILEY