Optimization of the per tone noise protection in xDSL systems employing virtual noise

In Digital Subscriber Line (DSL) systems, the concept of Virtual Noise (VN) was introduced to improve the protection against fluctuating crosstalk and to increase link stability. In our previous work, we have presented an algorithm that estimates the VN mask and the initialization signal-to-noise-ratio (SNR) margin from noise measurements. In however, perfect bitswapping was assumed. In practical DSL systems bitswapping might be too slow which makes the link sensitive to sudden noise increases. Hence, the outage probability achieved in can only be realized in slowly changing channels. This paper investigates the optimization of the VN mask and the initialization SNR margin presented in in order to improve the robustness against sudden noise increases in terms of outage probability, especially for modems with slow bitswapping procedures.