Physically-Based Realizable Modeling and Network Synthesis of Subscriber Loops Utilized in DSL Technology

Performance analysis of Digital Subscriber Line (DSL) technologies, which are implemented on existing telephone subscriber loops, is of vital importance to DSL service providers. This type of analysis requires accurate prediction of the local loop structure and precise identification of the cable parameters. These cables are the main components of the loop and are typically comprised of multi-conductor twisted pair type currently being used on existing telephone subscriber loops. This system identification problem was investigated through the application of single port measurements, with preference being placed on measurements taken from the service provider's end of the loop under investigation. Once the cabling system has been identified, the performance analysis of the loop was obtained through simulation.

Accurate modeling is an important aspect of any system identification solution; therefore, the modeling of the twisted pair cables was thoroughly investigated in this research. Early modeling attempts of twisted pair cabling systems for use with (DSL) technology has not been vigorously investigated due to the difficulty in obtaining wideband physical data necessary for the task as well as the limitations of simulators to accurately model the skin effects of the conductors. Models are developed in this research that produce a wideband representation of the twisted pair cables through the use of the data measured in high frequency spectra.

The twisted-pair cable models were then applied to the system identification problem through a de-embedding type approach. The identification process accurately characterizes the sections of the subscriber loop closest to the measurements node, and these identified sections were then modeled and de-embedded from the system measurement in a layer removing, or "peeling", type process. After each identified section was de-embedded from the system measurement, the process was repeated until the entire system was identified.

Upon completion of the system identification process, the resulting system model was simulated between the central office (CO) and resulting identified customer nodes for the evaluation of performance analysis. The performance analysis allows the providers to identify points where the DSL technology is feasible, and where so, the rates of the data transfer to the nodes that can be expected.