Browsing by Author "Akkarakaran, S"

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Discrete multitone modulation with principal component filter banks
(2002-10-01)
Vaidyanathan, PP
;
Lin, YP
;
Akkarakaran, S
;
Phoong, SM
;
電控工程研究所
Discrete multitone (DMT) modulation is an attractive method for communication over a nonflat channel with possibly colored noise. The uniform discrete Fourier transforn (DFT) filter bank and cosine modulated filter bank have in the past been used in this system because of low complexity. We show in this paper that principal component filter banks (PCFB) which are known to be optimal for data compression and denoising applications, are also optimal for a number of criteria in DMT modulation communication. For example, the PCFB of the effective channel noise power spectrum (noise psd weighted by the inverse of the channel gain) is optimal for DMT modulation in the sense of maximizing bit rate for fixed power and error probabilities. We also establish an optimality property of the PCFB when scalar prefilters and postfilters are used around the channel. The difference between the PCFB and a traditional filter bank such as the brickwall filter bank or DFT filter bank is significant for effective power spectra which depart considerably from monotonicity. The twisted pair channel with its bridged taps, next and fext noises, and AM interference, therefore appears to be a good candidate for the application of a PCFB. This will be demonstrated with the help of numerical results for the case of the ADSL channel.
On the duality of optimal DMT systems and biorthogonal subband coders
(2000)
Lin, YP
;
Vaidyanathan, PP
;
Akkarakaran, S
;
Phoong, SM
;
電控工程研究所
The discrete multitone modulation (DMT) systems have been widely used in various applications. The DMT system can be considered as a dual of a subband coder, obtained by using the synthesis bank as the transmitter and analysis bank as the receiver. In designing optimal subband coders, the objective is to minimize output quantization noise, whereas in the problem of designing optimal DMT system, the objective function to be minimized is the transmitted power. In this paper we will show that the design of optimal DMT systems can be formulated as a hypothetical design problem of optimal subband coders. The solution of optimal DMT system can be obtained using existing design methods for optimal biorthogonal subband coders.