An Improved Iterative Water Filling Algorithm in Multiuser DSL Environment

In digital subscriber line system, crosstalk is created among a bundle of twisted copper pairs due to the effect of an electromagnetic coupling. In very high bit rate digital subscriber line system, higher frequencies are used for data transmission. At these higher frequencies crosstalk seriously affects the system performance. The crosstalk from the near end users in upstream data transmission at higher frequency band significantly declines the bit rate of far end users. In order to resolve this ‘Near-Far’ problem the effective spectrum management techniques are used. Iterative water-filling (IWF) is one of the spectrum management techniques in which power from all subcarriers of near end user are reduced in order to remove crosstalk at far end user. IWF algorithm has low complexity but due to inefficient use of bandwidth it does not give optimal result. In this paper a modified IWF algorithm is proposed in which power from only those subcarriers of near end user are reduced which has a worst effect on bit rates of far end users. The power back off from these subcarriers is done by reducing power spectral masks at these subcarriers. The simulation results of the proposed algorithm give significant performance advantage in terms of data rate over the traditional IWF algorithm. These results approach near to the performance of highly complex optimal spectrum management algorithms while maintaining the complexity as that of traditional IWF algorithm.