Optimal Spectrum Balancing in multi-user SIMO xDSL networks

When multiple xDSL users coexist in the same network, crosstalk can become a major performance limiting factor, e.g. in so-called near-far scenarios. By employing multiple receiver signals, i.e. by operating in a SIMO (Single Input Multiple Output) rather than the standard SISO (Single Input Single Output) mode, each user can estimate and compensate the crosstalk more efficiently, thereby increasing its performance. In this paper, an algorithm is presented for the optimal allocation of transmit power in these multi-user SIMO networks. Secondly, since transmitters are usually limited to integer bit loadings, an optimal bit allocation algorithm is presented which has the added advantage of being computationally more efficient than the power allocation algorithm. The focus is on multi-tone xDSL systems, where the use of multiple tones allows the transmit spectra to be easily shaped and where near-far scenarios frequently occur when some of the users are serviced from remote terminals. Simulation results show that in these cases an improvement of the data rate of 10% is possible by using existing twisted pairs in SIMO configurations, compared to the standard SISO (Single Input Single Output) configuration.