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

This paper considers a DSL system 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 (possibly after some kind of bit distribution optimization) with a corresponding Quality of Service (QoS) constraint, e.g., to guarantee a certain error probability. The aim of the paper is 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 are obtained from simulations using realistic DSL MIMO channel models recently developed.