Frequency-Domain Equalization in Single-Carrier Transmission: Filter Bank Approach
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Research Article Frequency-Domain Equalization in Single-Carrier Transmission: Filter Bank Approach Yuan Yang,1 Tero Ihalainen,1 Mika Rinne,2 and Markku Renfors1 1 Institute 2 Nokia
of Communications Engineering, Tampere University of Technology, P.O. Box 553, 33101 Tampere, Finland Research Center, P. O. Box 407, Helsinki 00045, Finland
Received 12 January 2006; Revised 24 August 2006; Accepted 14 October 2006 Recommended by Yuan-Pei Lin This paper investigates the use of complex-modulated oversampled filter banks (FBs) for frequency-domain equalization (FDE) in single-carrier systems. The key aspect is mildly frequency-selective subband processing instead of a simple complex gain factor per subband. Two alternative low-complexity linear equalizer structures with MSE criterion are considered for subband-wise equalization: a complex FIR filter structure and a cascade of a linear-phase FIR filter and an allpass filter. The simulation results indicate that in a broadband wireless channel the performance of the studied FB-FDE structures, with modest number of subbands, reaches or exceeds the performance of the widely used FFT-FDE system with cyclic prefix. Furthermore, FB-FDE can perform a significant part of the baseband channel selection filtering. It is thus observed that fractionally spaced processing provides significant performance benefit, with a similar complexity to the symbol-rate system, when the baseband filtering is included. In addition, FB-FDE effectively suppresses narrowband interference present in the signal band. Copyright © 2007 Yuan Yang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Future wireless communications must provide ever increasing data transmission rates to satisfy the growing demands of wireless networking. As symbol-rates increase, the intersymbol interference, caused by the bandlimited time-dispersive channel, distorts the transmitted signal even more. The difficulty of channel equalization in single-carrier broadband systems is thus regarded as a major challenge to highrate transmission over mobile radio channels. Single-carrier time-domain equalization has become impractical because of the high computational complexity of needed transversal filters with a high number of taps to cover the maximum delay spread of the channel [1]. This has lead to extensive research on spread spectrum techniques and multicarrier modulation. On the other hand, single-carrier transmission has the benefit, especially for uplink, of a very simple transmitter architecture, which avoids, to a large extent, the peakto-average power ratio problems of multicarrier and CDMA techniques. In recent years, the idea of single-carrier transmission in broadband wireless communications has been revived through the application of frequency-domain equalizers, which have clearly lower implementation complexity than time-domain equa
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