Chapter 9. Spectral Compatibility of DSL Systems

   


9.1 The Loop Plant Environment

9.2 Crosstalk in the Loop Plant

9.2.1 Near-end Crosstalk Model

9.2.2 Far-end Crosstalk Model

9.3 NEXT vs. FEXT

9.3.1 Channel Capacities in the Presence of NEXT and FEXT

9.4 The "Primary" DSL Signal Spectra

9.4.1 ISDN

9.4.2 HDSL

9.4.3 Symmetric DSL Technologies

9.4.4 ADSL and RADSL

9.4.5 T1 AMI

9.5 Computation of Spectral Compatibility

9.6 Spectral Compatibility of DSL Systems

9.6.1 ISDN

9.6.2 HDSL

9.6.3 SDSL

9.6.4 ADSL

9.6.5 T1 AMI

9.7 Summary

One of the driving elements of DSL technologies is to use the same cables that provide plain old telephone service (POTS) to customers for providing high-bit rate digital services to the end users. However, the key difference from analog voices services is that the bandwidths used in DSLs are significantly greater than that of the analog voice channel. In the cable, these wide- band signals crosstalk into other wire pairs in the same cable and may cause interference into their corresponding signals. Hence, crosstalk is one of the key impairments that limit the performance of digital subscriber line systems.

Spectral compatibility is the quantification of the level of disturbance that one DSL system has on other systems deployed in the same cable. A clear understanding of the interactions that the different types of systems have on each other in the cable is the foundation for managing the deployment of DSL systems for maintaining a specified quality of service.

In the mass deployment of digital subscriber line services, we can expect the cable to be filled with many different types of signal spectra. Given the wide variety of signals in the cable, there can be a wide range of interference between the different systems and a set of rules or guidelines are needed to manage the deployment of these systems to assure that a minimum quality of service. These rules or deployment guidelines is called spectrum management . The rules of spectrum management are based on a working knowledge of the spectral compatibility of the various DSL systems and an agreement on a desired quality of service.

This chapter presents an overview of the spectral compatibility fundamentals and demonstrates the effects that different DSL services deployed in the loop plant have upon each other. Included are discussions on the loop plant environment, cable characteristics, near-end crosstalk and far-end crosstalk, a comparison of key selected DSL spectra, and the compatibility of these spectra with others in the cable. The next chapter describes spectrum management, which is based on the principles described here.


   
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DSL Advances
DSL Advances
ISBN: 0130938106
EAN: 2147483647
Year: 2002
Pages: 154

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