Performance of a dual sensor based interference cancellation scheme for downstream DSL

The use of common-mode (CM) sensor as an interference-alone reference is a viable technique to mitigate an external interference that couples into the useful differential-mode (DM) signal. In this paper, we derive performance bounds on a joint CM-DM based dual sensor interference cancellation scheme in frequency domain and investigate the impact of the CM sensor parameters on the performance of the downstream DSL system under different scenarios of external interference. We derive a tight lower bound on the capacity using parameters available in real time, and show that the optimal capacity can be achieved with a single CM sensor even in the presence of multiple interference under certain conditions on coupling transfer functions. By considering a minimum-mean square (MMSE) based canceler scheme, we derive closed form expressions on the noise variance at the output of the canceler in terms of system parameters of the CM and DM sensors. We show that the canceler can achieve the interference-free performance in various types of external interference provided a higher interference to noise ratio at the CM sensor. Measurement results from a VDSL CPE and computer simulations are presented to demonstrate the performance of the considered canceler scheme.