HomeChair: Georgios B. Giannakis, University of Virginia, USA
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Kambiz C Zangi, Ericsson Inc. (U.S.A.)
David R Koilpillai, Ericsson Inc. (U.S.A.)
For cellular software radio receivers, this paper presents acomputationally efficient algorithm for extractingindividual radio channels from the output of the wideband A/D converter. In a software radio, the extraction of individual channels from the output of the wideband A/D converter is by far the most computationally demanding task; hence,it is very important to devise computationally efficient algorithms for this task. Our algorithm is obtained by modifying the DFT filter bank structure that is well known in the multi-rate signal processing literature. We show that the complexity of the proposed algorithm is significantly less(2X-50X) than the complexity of the conventional channelizers.
ic982329.pdf (From Postscript)
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Anna Scaglione, University of Rome, La Sapienza (Italy)
Georgios B. Giannakis, University of Virginia (U.S.A.)
Sergio Barbarossa, University of Rome, La Sapienza (Italy)
Transmitter redundancy introduced using FIR filterbank precoders offers a unifying framework for single-and multi-user transmissions. With minimal rate reduction, FIR filterbank transmitters with trailing zeros allow for perfect (in the absence of noise) equalization of FIR channels with FIR zero-forcing equalizer filterbanks, irrespective of the input color and the channel zero locations. Exploiting input diversity, blind channel estimators, block synchronizers, and direct self-recovering equalizing filterbanks are derived in this paper. The resulting algorithms are computationally simple, require small data sizes, can be implemented online, and remain consistent (after appropriate modifications) even at low SNR colored noise. Simulations illustrate applications to multi-carrier modulations through channels with deep fades, and superior performance relative to CMA and existing outputdiversity techniques relying on multiple antennas and fractional sampling.
ic981475.pdf (From Postscript) TOP
Xueming Lin, New Jersey Institute of Technology (U.S.A.)
Ali N. Akansu, New Jersey Institute of Technology (U.S.A.)
A novel nonmaximally decimated multirate filterbank structure is proposed for blind identification of communication channels.This structure is shown to be very similar to a form proposed earlier in the literature. It is presented that the proposed blind channel identification algorithm is not sensitive to the characteristics of unknown channel, including mixed phase and zeros on the unit circle. An optimal minimum mean square error based linear equalizer using the blind channel identification scheme is investigated. It is shown that the proposed system outperforms the existing zero-forcing blind equalization algorithms in literature. It can simultaneously cancel the intersymbol interference (ISI) and suppress the noise enhancement. The reconstructed signal to noise ratio is maximized by the proposed algorithm. Simulation results show the superior performance and robustness of the proposed blind identification and equalization scheme.
ic982539.pdf (From Postscript) TOP
Ufuk Tureli, University of Virginia (U.S.A.)
Hui Liu, University of Virginia (U.S.A.)
In OFDM communications, the loss of orthogonality due to carrier offset must be compensated before DFT-based demodulation can be performed. In this paper, we present a high accuracy blind carrier offset estimation algorithm and a blind channel equalizer which exploit the intrinsic structure information of OFDM signals. The latter method allows the receiver to perform coherent demodulation in changing environments without the overhead required for additional pilots.
ic981656.pdf (From Postscript) TOP
J. Nicholas Laneman, MIT (U.S.A.)
Gregory W. Wornell, MIT (U.S.A.)
The problem of equalization for spread-response precoding systems based on minimum mean-square error (MMSE) estimates of the fading channel coefficients is considered. These systems are attractive, low complexity alternatives to the combination of interleaving and error-control coding for achieving time diversity in fading environments. To make the performance of these systems robust to channel estimation errors, we derive the linear equalizer at the receiver that maximizes the effective signal-to-noise-and-interference ratio (SNIR) subject to uncertainty in the channel measurements. We examine the bit-error rate performance and develop fixed and dynamic solutions to the associated problem of optimal power allocation between the data transmissions and channel measurements. The effectiveness of these algorithms is demonstrated through measurements obtained from an indoor wireless setting.
ic981677.pdf (From Postscript) TOP
An-Yeu Wu, National Central University (Taiwan)
Tsun-Shan Chan, National Central University (Taiwan)
The discrete multitone (DMT) modulation/demodulation scheme is the standard transmission technique in the application of asymmetric digital subscriber lines (ADSL). Although the DMT can achieve higher data rate compared with other modulation/demodulation schemes, its computational complexity is too high for cost-efficient implementations. For example, it requires 512-point IFFT/FFT as the modulation/demodulation kernel. The large block size results in heavy computational load in running programmable DSP processors. It also makes the VLSI implementation not feasible. In this paper, we derive the parallel lattice structure for the IFFT/FFT based on the time-recursive approach. The resulting architectures are regular, modular, and without global communications so that they are very suitable for VLSI implementation. Also, the proposed structure requires only 11% number of multipliers and 9% number of adders compared with the direct implementation approach.
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Arthur J Redfern, Georgia Institute of Technology (U.S.A.)
G. Tong Zhou, Georgia Institute of Technology (U.S.A.)
Orthogonal Frequency Division Multiplexing (OFDM) has become increasingly popular due to its potential applications in digital audio broadcasting, digital terrestrial TV broadcasting, and satellite communication. A notable drawback of OFDM systems is their sensitivity to nonlinear distortion. For maximum power efficiency, amplifiers and transmitters of modern communication systems often operate near their saturation regions which leads to nonlinear distortion. In this paper, we use the special property that the transmitted OFDM symbols are asymptotically white Gaussian to derive an algorithm that identifies the nonlinear channel. A nonlinear equalizer is built to compensate for the undesired nonlinearities. Simulation results show that the nonlinear equalizer outperforms its linear counterpart when nonlinear distortion is present.
ic981810.pdf (From Postscript) TOP
Josep Sala-Alvarez, UPC (Spain)
Alba Pages-Zamora, UPC (Spain)
Sergio Calvo, UPC (Spain)
Josep Prat, UPC (Spain)
A description of the signal processing stage of an on-board integrated VLSI multi-carrier demodulator at the demultiplexer level is presented in this paper, along with a description of the optimization procedure that has been developed for the signal processing functions. The varying adjacent carrier interference and channel noise distribution are modeled to provide the best performing demultiplexing scheme under the given carrier distribution with minimum complexity.
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