Abstract-The orthogonal frequency division multiplexing (OFDM) transceiver has enjoyed great success in many wideband communication systems. It has low complexity and robustness against multipath channels. It is also well-known that the OFDM transceiver has poor frequency characteristics. To get transceivers with better frequency characteristics, filterbank transceivers with overlapping-block transmission are often considered. However these transceivers in general suffer from severe intersymbol interference (ISI) and high complexity. Moreover costly channel dependent post processing techniques are often needed at the receiving end to mitigate ISI. In this paper, we design discrete Fourier transform (DFT) modulated filterbank transceivers for multipath fading channels. The DFT modulated filterbanks are known to have the advantages of low design and implementation cost. Although the proposed transceiver belongs to the class of overlapping-block transmission, the only channel dependent part is a set of one-tap equalizers at the receiver, like the OFDM system. We show that for a fixed set of transmitting or receiving filters, the design problem of maximizing signal-to-interference ratio (SIR) can be formulated into an eigenvector problem. Experiments are carried out for transmission over random multipath channels, and the results show that satisfactory SIR performance can be obtained.
In this paper, we study DFT-bank transceivers with filter length longer than the block size. We show how to optimize the DFT-bank transceiver so that both the intra-band and cross-band interferences are minimized for unknown multipath channels. No costly post processing technique is needed and the only channel dependent part is a set of one-tap equalizers at the receiver. The optimization problem is formulated as a Rayleigh-Ritz ratio whose solution is well-known. Experiments are carried out for transmission over random multipath channels and the results show that satisfactory SIR performance can be obtained.
Discrete MultiTone (DMT) modulation has been widely adopted for wideband transmission over digital subscriber loop (DSL) channels. In the conventional DMT system, the transmitting filters are the DFT filters. DFT filters suffer from poor frequency responses. Hence the resulting transmit signal has a large spectral sidelobe and its power spectral density (PSD) decays at a rate of ½ only. In this paper, we propose a modified DMT scheme with improved transmitting filters. In the proposed system, shaping filters are applied to improve the frequency responses of the transmitting filters. Moreover, an efficient implementation of the proposed system is derived. Experiment shows that for VDSL applications, the proposed system has a very satisfactory spectral efficiency.
The discrete multitone (DMT) transceivers have enjoyed great success in high speed data transmission. It is known that when the cyclic prefix is no shorter than the channel impulse response (CIR), the DMT system is IS1 free. For channels with very long CIR such as DSL loops, a time-domain equalizer (TEQ) is typically added at the receiver to shorten the effective impulse response. This paper proposes a filterbank approach to the design of TEQ for maximizing the bit rate. Moreover we introduce a structure of DMT system with multiple TEQs. The optimal solution for multiple TEQs is given in closed form and it can serve as a theoretical upper bound for all other TEQs. From the multiple TEQ structure, we propose a DMT system with a pair of complex conjugating TEQs. Simulation examples are given to verify the merit of the proposed TEQ.
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