"Telecommunication systems and networks"

Theme of master's work:

Abstract on the theme of master's degree work

"The Research of the PLL for systems of synchronization in the radio frequency channels of telecommunication networks"

Accurate work and careful planning of the systems of synchronization is required not only in order to avoid unacceptable working characteristics, but to damp hidden, expensive and nondescript problems and to decrease the barely visible mutual influencing of networks of a different submission.

To beginning

Purpose and research tasks

The purpose of this master's degree work is researching Phase-Locked Loop for the systems of synchronization of telecommunication networks, also justification and development of analytical and digital model of PLL and experimental model for the analysis and improvement of performance of network of synchronization..

For achievement of the formulated purpose it is necessary to solve the following tasks:

• to analyze functions of networks of synchronization, basic types and methods of synchronization of telecommunication networks;

• to explore PLL on the basis of methods of automatic control theory and digital simulation;

• to realize the experimental assembly of the multilevel system of synchronization.

For understanding of purpose of synchronization fist of all we will give determination to the concept of synchronization.

Synchronization it is the process of adjustment of meaning moments of digital signal for establishment and maintenance of the required temporal relations. Due to synchronization continuity of the passed information is supported and its integrity is provided, I.e. position of the passed code words and their sequence is determined.[1] The basic task of synchronization of digital network consists of that, to guarantee the receipt of the same speed of transmission and reception of information in digital communication networks and avoid appearance of «slipping». All generators set in a digital communication network must be synchronized from one or several leading generators with the near values of frequencies of output oscillation. Synchronization is needed in any digital communication networks.

Network synchronization, at first unknown and considered irrelevant to the operation and performance of telecommunications networks, has played an increasingly important role throughout the evolution of telecommunications, especially since transmission and switching became digital.

The evolution of digital transmission and switching technology for public telephone networks began with isolated digital transmission links between analog switching machines or radio transmission systems. The fact that digital technology was used was transparent to the interfaces. Thus, there was no need to relate the internal clock rate in one system to the internal clock rate of another system.[2]

Even as higher-level multiplexing systems were developed, there was no need (or viable means) to relate the clock rates of higher-rate multiplexed signals with those of lower-rate tributaries. Indeed, transmission equipment based on plesiochronous digital hierarchy (PDH) technology does not need to be synchronized, since a bit justification technique (pulse stuffing) allows multiplexing of asynchronous tributaries with substantial frequency offsets.

Problems began to arise with such asynchronous architecture when digital technology was adopted for switching machines too. Digital switching equipment requires synchronization in order to avoid slips in the elastic input stores. While slips do not significantly affect normal phone conversation, they may be troublesome indeed on some data services.

The introduction of circuit-switched data networks and the integrated services digital network (ISDN), therefore, first yielded the need for more stringent synchronization requirements. As a matter of fact, however, the ongoing spread of synchronous digital hierarchy (SDH) and synchronous optical network (SONET) technology in transmission networks has made synchronization a hot topic in standard bodies in the last few years, as the need for adequate network synchronization facilities has become more and more stringent in order to fully exploit SDH/SONET capabilities.

Beyond SDH/SONET needs, nowadays network synchronization facilities are indeed unanimously considered a profitable network resource, allowing slip-free digital switching, enhancing the performance of transport services based on asynchronous transfer mode (ATM), and serviceable for improving the quality of a variety of other services — ISDN, Global System for Mobile Communications (GSM), and so on.

For this reason, all the major network providers have set up or are now planning national synchronization networks in order to distribute a common timing reference to each node of their telecommunications networks.

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