Measurement and verification of the impact of electromagnetic interference from household appliances on digital subscriber loop systems

We propose a verification method to assess the impact of electromagnetic interference (EMI) from household appliances on multicarrier, fixed quality, variable bit rate asymmetric digital subscriber line (ADSL) systems. Measurements of the interference waveforms from selected appliances and evaluation of their amplitude probability distributions (APDs) were made over the ADSL1 spectrum. Statistical fitting analysis on the APDs revealed that these interferences are well modelled by non-Gaussian α-stable distributions. A computer simulation program for ADSL1 transceivers was developed to estimate the achievable bit rate over standardised loops affected by these interferences. The strength of the simulated α-stable noise was calibrated through actual measurements of the coupled EMI using a cable qualifier. It was observed that a co-located household appliance can increase the noise floor on the twisted pair by several dBs. Simulation results and real-time measurements using an Internet speedometer showed that the bit-rate degradations vary widely depending on the types of appliances and could be as high as 25%. The results obtained quantify and reinforce the conclusion that the current unshielded ADSL1 infrastructure is susceptible to EMI threats from certain household appliances. The proposed verification methodology can be readily adapted to other DSL systems affected by EMI.