Multiuser detection for digital subscriber line applications

The Internet has created a huge demand for high speed data communication unforeseen just years ago. Digital Subscriber Line (DSL) is one system to provide high data rate. This thesis explores some degradation that a DSL system using Discrete Multitone (DMT) will experience.; One degradation is crosstalk from other communication systems using the same bandwidth. The optimal maximum likelihood multiuser detector for this scenario will be discussed. We will introduce a metric to determine when the detection is possible and present Tone-Zeroing as a method to increase this metric. However, the optimal detector is too complex to implement. A suboptimal detector that does multiuser detection via soft interference cancellation using iterative decoding is proposed. The soft interference canceler (SIC) is able to reduce the effect of the crosstalk. A block maximum likelihood soft interference canceler is able to further drive the bit error rates to acceptable level with the aid of error control codes.; Channel coding is another way to increase the metric. A decoding algorithm that combines the iterative SIC and the channel decoding is presented. It will be shown that the SIC with channel codes is able to reduce the crosstalk, although it does not perform as well as SIC with Tone-Zeroing. The effect of interleaving together with Reed-Solomon codes is explored.; Besides crosstalk, insufficient cyclic prefix length can introduce distortion at the DMT receiver. A precoder is introduced that will remove the distortion at the expense of energy increase at the transmitter.; Energy and bit loading algorithms that take the power spectrum density constraints into account are listed. These algorithms ensure that the system adheres to design specification and further ensures that different DSL receivers co-exist harmoniously.; Finally, the feasibility of using discrete wavelet transform for multicarrier system (MCM) is examined. Distortion at the receiver due to loss of orthogonality after the signals pass through the channel makes it unsuitable for use in MCM.