I. Introduction
In a multi-user digital subscriber line (DSL) environment, performance degradation can be caused by near end crosstalk (NEXT) and far end crosstalk (FEXT) [1], [2] and by intercarrier crosstalk, which limits the data rate and service reach. Frequency division duplexing can be used to avoid NEXT, while various block processing techniques can be applied at the receivers for FEXT supression. This can be achieved by deploying crosstalk cancellers (for upstream) or crosstalk pre-compensators (for downstream) at the central office (CO) or DSL access multiplexers (DSLAMs), as shown in Fig. 1, depending on whether the channel state information (CSI) is available after reception or before transmission respectively. Dynamic spectrum management (DSM) in DSL aims to maximise performance by spectrum optimization and joint signal processing through co-ordination (via co-location) of modems in the DSLAM [3]. Further, synchronization of the DSLAMs to a common clock [3] eliminates intercarrier crosstalk.
Multi-user DSL binder with crosstalk canceller.