A fault-tolerant network clock regenerator (NCR) will be analyzed, which consists of two digital phase-locked loops (DPLL), and which allows a dynamical configuration control and thus is able to meet CCITT's Recommendations concerning permissible slip rates, frequency inaccuracy, as well as phase jitter and wander. The network synchronization scheme will conform to the master-slave principle, in the course of which the reference clock is derived from a national caesium atomic oscillator as master. The NCR's mentioned before serve as slaves which are equipped with highly precise voltage-controlled crystal oscillators and proportional-integral working DPLL's. The results of a field trial in the long-distance communications network of the "Deutsche Bundespost (FRG)" are given and interpreted by a Random Walk Model which describes the time interval errors appearing. For future digital exchanges, an NCR with intelligent configuration control is introduced, which consists of two microprocessor-controlled digital phase-locked loops (MCDPLL) and which has comparable time stability characteristics as the double-DPLL mentioned above at half the circuit volume. Finally, the dominant advantages are shown which result from synchronizing broad-band services by intelligent NCR techniques.

Synchronization Techniques for Digital Networks

Method and apparatus for synchronizing a clock of a telecommunication switching system. The clock of the telecommunication switching system is supplied, at least at times, with reference clock signals from a plurality of external reference clock sources. Every external reference clock source has a predetermined priority allocated to it. The supplied reference clock signals are checked for clock errors to which individual errors are allocated. For synchronization, the clock accepts an external reference clock signal dependent on the priorities allocated to the reference clock sources and dependent on the clock-error-associated error values. In an initialization, initial error values are allocated to the reference clock sources. In a re-initialization of the system, the synchronization procedure is continued from the current error values that are present at the time of the system outage.

Method and apparatus for the synchronization of a clock means of a telecommunication switching system

A clock circuit of a telecommunication switching system is supplied with reference clock signals from a plurality of external reference clock sources at least from time to time. Each external reference clock source is allocated a predetermined priority. The reference clock signals supplied are checked for clock errors which are allocated individual errors. For its synchronisation, the clock circuit accepts an external reference clock signal in dependence on the priorities allocated to the reference clock sources and on the clock-error-individual error values. During an initial commissioning, initial error values are allocated to the reference clock sources. During a recommissioning of the system, the synchronisation method is continued on the basis of current error values available at the time of system failure.

Method and apparatus for synchronising a clock-circuit of a switching communication system

A cognitive radio (CR) tries to intelligently utilise the idle periods of the primary system (PS) for opportunistic transmission and can improve the overall spectral utilisation. When a signal is transmitted, the authors usually consider the spectral occupancy from all propagation directions and assume circular signal coverage. In this study, they derive the relationship between transmission rate and signal-to-interference ratio statistics in a CR network (CRN) while protecting the rate of the PS to a specified level. Applying this relationship to a CR, they show that the regions for a CR receiver to keep an outage probability and bit error rate, defined as permissible areas, are no longer concentric in shape even in a pure path loss channel. Through detecting which permissible area a CR receiver is located, a new cognitive cycle is developed for rate enhancement. Simulation results show that as compared with a distance-dependent rate-adaptation approach, the system sum-rate increases significantly. These results suggest a new version of CRN with enhanced system capacity.

Rate enhancement for cognitive radios using the relationship between transmission rate and signal-to-interference ratio statistics

This article investigates the correlations between multimedia objects (particularly speech and text) involved in language lectures in order to design an effective presentation mechanism for web-based learning. The cross-media correlations are classified into implicit relations (retrieved by computing) and explicit relations (recorded during the preprocessing stage). The implicit temporal correlation between speech and text is primarily to help to negotiate supplementary lecture navigations like tele-pointer movement, lips-sync movement, and content scrolling. We propose a speech-text alignment framework, using an iterative algorithm based on local alignment, to probe many-to-one temporal correlations, and not the one-to-one only. The proposed framework is a more practical method for analyzing general language lectures, and the algorithm's time complexity conforms to the best-possible computation cost, O(nm), without introducing additional computation. In addition, we have shown the feasibility of creating vivid presentations by exploiting implicit relations and artificially simulating some explicit media. To facilitate the navigation of integrated multimedia documents, we develop several visualization techniques for describing media correlations, including guidelines for speech-text correlations, visible-automatic scrolling, and levels of detail of timeline, to provide intuitive and easy-to-use random access mechanisms. We evaluated the performance of the analysis method and human perceptions of the synchronized presentation. The overall performance of the analysis method is that about 99.5p of the words analyzed are of a temporal error within 0.5 sec and the subjective evaluation result shows that the synchronized presentation is highly acceptable to human beings.

Exploring many-to-one speech-to-text correlation for web-based language learning

N integrated digital network which combines digital transmission and switches can provide efficient and economical paths to carry analog ~ and digital information. Digital networks have been developed for data or voice services, and it is believed that they may be extended in the future to apply to the integrated services digital network (ISDN). Network synchronization is an essential  technique in constructing an integrated digital network. In several countries, the domestic network synchronization systems have either been developed or are under development, These systems employ either the master-slave or mutual synchronization scheme. For the future international digital network, plesiochronous operation is recommended by the CCITT.

H. Fukinuki

Papers

Master-slave synchronization techniques