dc.description.abstract |
Discrete Multitone (DMT) modulation is a popular multicarrier technique adopted for wireline
communication, which offers computationally inexpensive channel equalization, based on cyclic
prefix, in addition to bit and power loading. A cyclic prefix is pre-appended in multicarrier
modulated (MCM) techniques, that helps mitigate the inter-symbol interference due to mul-
tipath effect. For channel equalization, a single tap per subcarrier is sufficient to compensate
for the channel distortion in the frequency domain, provided the cyclic prefix length is of the
order of the channel. This formulates a Zero-Forcing frequency domain equalizer, which com-
pensates the channel attenuation with an inverse channel response. However, this method has
the shortcoming of enhancing channel noise, where the channel is of low magnitude, in the
high frequency range. It has been observed through the studies on channel measurements that
most channels display the characteristics similar to that of a lowpass filter. Therefore, the
cyclic prefix (CP) based equalization in MCM techniques enhances channel noise, which in turn
increases the bit error rate and also reduces the post equalization signal-to-noise ratio (SNR).
In this thesis, as a solution to this problem, hybrid DMT modulation techniques, that is the
Uniform and Non-Uniform DMT modulation are proposed and implemented for the DSL and
the power line channels.
The performance analysis of the proposed modulation techniques in the DSL channel and
for the various categories of the power line channel is presented. Since the Non-Uniform and
Uniform modulation techniques are hybrid techniques, and their structures are a combination
of wavelet filter banks and conventional DMT systems, therefore, the effect of inter-channel
crosstalk and its relation with the filter’s order is also investigated. Computational complexity
of the hybrid modulation techniques is also derived, and it is found to be greater than that of the
conventional DMT system. Moreover, different methods are adopted for quantization of channel
noise enhancement. A reconstruction error is derived to ascertain the quantity of channel noise
enhancement in different subbands of the communication channel and also for this purpose,
post equalization SNR is computed. A modified Non-Uniform DMT transceiver was proposed
and implemented for the DSL channel. It is depicted through simulation results that the Non-
Uniform DMT modulation shows some improvement in the post equalization SNR, and its
modified form gives better performance, however at the cost of reduced data rate. The Uniform
DMT modulation technique is proposed with a power-allocation algorithm for different sub-
channels of the DSL and the power line channels. The Uniform DMT modulation performance
evaluation through simulation results shows significant improvement in SNR in comparison with
the conventional DMT system, at the cost of greater computational complexity, for the various
DSL and power line channels. |
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