| Summary: | 碩士 === 國立清華大學 === 通訊工程研究所 === 89 === Recently, the demand of high-speed broadband data service is urgent and the traditional 56k modem has been inadequate to cope with the need. Discrete multi-tone (DMT) is the key technology, which could provide high-bandwidth services on the existing ordinary copper telephone lines. Lately, a DMT-based technology called asymmetrical digital subscriber line (ADSL), which can provide high-speed downstream data rate up to 8Mbps, and upstream data rate up to 800kbps, has been wildly adopted. Very high bit-rate digital subscriber line (VDSL) is the latest generation of DSL family, which can provide even high downstream data rate up to 54Mbps, and upstream data rate up to 6.4Mbps for residential customers and 2.3~34Mbps data rate for businesses.
Radio frequency interference (RFI) is a newly threatening interference in VDSL transmission systems. To solve this issue, there are some approaches had been proposed, one of them is a digital scheme and work in frequency domain. The main idea of the algorithm is to construct a narrowband RFI signals model and derive a close form with some reasonable assumptions. With the measurements of some unused tones, we can easily solve the model and estimate the RFI signals. While the tone’s number of VDSL transmission systems is small, this algorithm can suppress RFI to a satisfied level. However, in order to increase the system efficiency, some VDSL standards use larger tone’s number and the simulation results show that the previous scheme can’t achieve the required suppression level.
In this thesis, we propose an enhanced RFI suppression scheme has been proposed, which is based on the previous digital RFI cancellation scheme. Through the modification of previous cancellation procedure, the accuracy of the RFI signals model can be raised. Without increasing much computational complexity, proposed scheme can greatly improve the suppression level. Finally, in order to verify how the digital RFI canceller works in a practical system, we set up a simplified DMT-based VDSL transmission environment and implement the RFI scheme on TI the C6201 DSP.
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