The Sub-Band Vectoring Technique for Multi-Operator Environments

Self-and alien-far end cross talk (FEXT) disturbances on the same cable severely limit performance in the commonly employed VDSL2 17a (0-17.6 MHz) standard profile. Then, in a multi-operator environment, VDSL2 may be unable to provide the 100 Mbit/s speed required by the European Commission's policy target, unless vectoring is adopted along with a suitable multi-operator vectoring (MOV) technique. Some vendors have recently proposed enlarging the bandwidth up to 35.2 MHz (so-called e-VDSL) as one possible solution to increase 100 Mbit/s coverage. However, as we show in this paper, the bandwidth advantage is illusory, because alien-FEXT practically destroys the envisaged data-rate increase. Therefore, we introduce the sub-band vectoring (SBV) technique as one near optimal practical solution in terms of achievable data rate, as well as incremental for those countries, where the National Regulatory Authority adopts sub-loop unbundling regulations. SBV adopts a novel frequency division multiplexing approach, which imposes one fairness condition to equalize data-rate values and overall bandwidth per operator at variable distances. This paper shows that e-VDSL with SBV is robust, and it can properly work even in the presence of vectoring implementation imperfections. It is further observed that SBV allows up to three co-located operators with e-VDSL to coexist without imposing any of the burdensome coordination limitations of the ideal MOV architecture. Results show that the SBV enables the achieving of up to 210 Mbit/s per user for e-VDSL and up to 620 Mbit/s per user for a bandwidth expanded up to 105.6 MHz with two telecom operators. Finally, we discuss a simple migration strategy towards usage of the G.fast standard based on the adoption of SBV.