Adaptive Off-Diagonal MIMO Pre-Coder (ODMP) for Downstream DSL Self FEXT Cancellation

This paper introduces a new family of per frequency linear pre-coders, called off-diagonal MIMO pre-coders (ODMP), for discrete multi-tone (DMT) based digital subscriber line (DSL) systems. ODMP target pre-compensation of the off- diagonal self far-end cross talk (FEXT) terms in the downstream DSL-MIMO channel matrix. We derive a low complexity and adaptive ODMP that simultaneously maximizes the Shannon Capacities per tone, experienced by the (non-cooperative) end-users. The updating scheme makes use of the error samples computed in each receiver. No matrix inversion is required in the algorithm which may be used for learning, tracking, and incrementing the ODMP without any disruption of data service. Finite precision simulation results reveal that coding the complex error with 16 bits allows for the algorithm to reach "self-FEXT free" performance after only 150 iterations in the learning phase and 450 iterations in the incrementing phase.