A study of the single-ended loop characterization for special services.

Abstract

The objective of this research is to propose an approach for single-ended loop characterization by which the insertion loss (IL) over a subscriber loop can be estimated to within $\pm$1 dB accuracy based on some measurements from the central office (CO) only. The estimation of transmission loss at 1 kHz is an essential requirement for both basic plain old telephone services (POTS) and special services provided by telephone companies (telcos). The loss at 1 kHz is used as an indication of the quality of the connection. To maintain the quality (loss) of the subscriber loops at a certain level, skilled technicians are conventionally needed to perform two-ended loss measurements at both the customer end and the central office. The latest methods used in the industry require large but unreliable data base. These result in substantial expenses to telephone companies. Our objective is to replace these by an automatic procedure. Estimation of the loop loss based on measurements from the Central Office only is complicated by the fact that the customer's terminal set may be one of a wide variety of terminations and will not, in general, be known to the operating companies. The approach proposed in this thesis is intended for voice band special services for Carrier Serving Area (CSA) loops in digital loop carrier (DLC) systems. The problem is formulated as that of modelling a two port network using single port measurements. The parameters of the model representing the subscriber loop are determined so as to minimize the input impedance error at several frequencies for arbitrary customer's termination. It is shown that using this model for insertion loss estimation results in errors within the required 1dB at 1 kHz. Next, a simple algorithm is proposed to use the same parameters in the model to determine insertion loss at higher voice frequencies. Finally, effect of error in input impedance measurement on loss estimation is studied.