| Summary: | 碩士 === 國立臺灣大學 === 電信工程學研究所 === 93 === The discrete multitone transmission (DMT) has been recognized as one of the most practical technology for high data rate transmission. The IDFT matrix and the DFT matrix
with the size proportional to number of bands are parts of a transmitter and a receiver, respectively. As we know that, IDFT and DFT have only Nlog_2(N) complex multiplications and additions. For many baseband transmission systems such as DSL, the channels and signals are real. Complex conjugation is done at the DMT transmitter to get real signals. In this thesis, we consider DCT based transceivers which involve only real signals and operations. Like DFT systems, DCT based systems also have Nlog_2(N) complexity. Both DFT and DCT based transceivers belong to the class of block transmission scheme where data are sent on a block by block basis and there is no overlapping between blocks. Block transmission suffers from poor frequency response due to short filter length, no longer than block size. Thus, in the presence of narrowband interference (NBI), the performance of both DFT and DCT based systems degrades significantly as many tones will be affected by the NBI.
To improve the frequency response of transceivers, the perfect reconstruction (PR) filter bank transceivers (FBTs), having the advantage of high stopband attenuation, are often proposed as mitigative solutions in past. To reduce the complexity, the cosine modulated filter bank transceiver (CMFBT) have been studied for DSL applications. However, for frequency selective channels, the CMFBT suffers from severe ISI and ICI. In this thesis, we consider the CMFBT that can mitigate the ISI and ICI effects. For both known and unknown channels, the CMFBT problem can be formulated as a SIR optimization problem. The
optimal solution can easily obtained as the eigenvector of a corresponding Rayleigh-Ritz ratio. To further enhance the SIR performance of the CMFBT, an iterative procedure is
proposed for the SIR maximization. Two frequency constraint methods are introduced to preserve the frequency response of the CMFBT over iteration. Simulations show that the
CMFBT with both high SIR and good frequency response can be designed using the proposed methods.
We also verify the performance of our systems in DSL applications. In order to apply the DCT based transceivers and the CMFBTs, we need to design the time domain equalizer
(TEQ) that gives a symmetric target impulse response. A new TEQ design method is proposed for this purpose. For the commonly used 8 DSL loops, the simulation results show that in the absence of NBI, all systems have roughly the same performance whereas in the presence of NBI, the proposed CMFBT has significantly better performance.
In the second part of the thesis, we consider the general solutions of PR block transceivers for unknown multipath channels. We show that under mild assumptions, the a mutually-orthogonal usercode-receiver (AMOUR) is the only solution to such a problem. In other words, there is no transceiver other than the AMOUR that can achieve PR for
unknown multipath channels.
|
|---|
