Abstract

In this thesis, the last-mile and home-LAN interference problems of VDSL systems are addressed using turbo codes. With regard to the last-mile problem, a bandwidth efficient turbo coding scheme is proposed in which, turbo codes are combined with bandwidth efficient modulation and the soft information is exchanged between the decoder and demodulator in an iterative manner. The scheme is investigated for various values of transmitting power, signal frequencies and numbers of crosstalkers for a targeted BER of 10 -5 . The effects of various code parameters on the performance of VDSL modems are explored. In order to reduce the latency at the receiver end, a pipelined decoding scheme is proposed. Simulation results are presented and compared with that of the 4D Wei-RS scheme. The results show that the choice of turbo codes not only provides a significant coding gain over the standard FEC scheme but also efficiently maximizes the loop length and bit rate at a very low transmitting power in the presence of dominant far-end crosstalk (FEXT). In order to compare the hardware complexity, the proposed and 4D Wei-RS schemes are synthesized using SYNOPSYS with the target technology of Xillinx 4010-3. The Xilinx FPGA statistics of the proposed scheme is compared with that of the 4DWei-RS scheme. To mitigate the effect of home-LAN interference, an iterative soft interference cancellation and decoding technique is proposed in which, the VDSL and home-LAN signals are jointly detected using a soft interference canceller and a soft-in soft-out demodulator combined with a set of turbo decoders.