Optimum joint transmit-receive linear processing for vectored DSL transmission with QoS requirements

A digital subscriber line (DSL) system is considered, in which a subset of the twisted-pair copper wires within a bundle can perform a joint processing at both sides of the communication system (e.g., links between central offices and remote terminals or between central offices and private networks). The DSL channel is treated as a multi-input multi-output (MIMO) system over which many substreams are established. It is assumed that the signal constellation to be used at each substream is given with a corresponding quality of service (QoS) constraint, e.g., to guarantee a certain error probability. The aim was to optimally design joint transmit-receive linear processing to satisfy the QoS requirements with minimum transmit power. A novel multi-level water-filling algorithm is proposed to solve the problem very efficiently in practice. Numerical results were obtained from simulations using realistic DSL MIMO channel models recently developed.