@inproceedings{40873, abstract = {{In this paper we analyze a turbo equalization scheme that combines maximum a posteriori probability (MAP) equalization and turbo decoding. Our aim is to optimize the turbo equalizer in order to approach the information capacity limit for channels with severe inter-symbol interference (ISI). For this purpose, we perform an extensive search for turbo codes that give an SNR-BER performance closest to the channel information capacity limit. Our results show that the optimized turbo equalizer can approach the information capacity limit to within 0.7 dB. We also optimize the turbo equalizer in terms of the minimum number of required turbo decoding iterations. Our results show that a turbo decoder within a turbo equalization loop requires only a small number of iterations. Finally, our analysis reveals that when there are turbo codes with similar extrinsic information transfer characteristics, the computational complexity can be reduced by choosing the code with the smallest constraint length with no loss in SNR-BER performance.}}, author = {{Trajkovic, Vladimir D. and Fu, Minyue and Schreier, Peter J.}}, booktitle = {{Proc.\ Australasian Telecomm. Netw.\ Applic.\ Conf.}}, pages = {{480–484}}, title = {{{Near-capacity turbo equalization using optimized turbo codes}}}, doi = {{10.1109/ATNAC.2007.4665276}}, year = {{2007}}, } @inproceedings{40874, abstract = {{We consider the assessment of multivariate association between two complex random vectors. For complex data, there are three types of correlation coefficients, which account for rotational, reflectional, and total (i.e., rotational and reflectional) dependencies. We define and analyze these three types for different correlation coefficients, based on two popular correlation analysis techniques: canonical correlation analysis and multivariate linear regression (also known as half-canonical correlation analysis).}}, author = {{Schreier, Peter J.}}, booktitle = {{Proc. 41st\ Asilomar Conf.\ Signals Syst.\ Computers}}, pages = {{577–581}}, title = {{{Correlation Coefficients for Complex Random Vectors}}}, doi = {{10.1109/ACSSC.2007.4487279}}, year = {{2007}}, } @inproceedings{40877, author = {{García-Naya, J. A. and Fernández-Caramés, T. M. and Pérez-Iglesias, H. J. and González-López, M. and Castedo, L. and Ramírez, D. and Santamaría, I. and Pérez, J. and Vía, J. and Torres-Royo, J. M.}}, booktitle = {{Proc. IST Mobile $&$ Wireless Comms. Summit}}, title = {{{Performance of STBC transmissions with real data}}}, doi = {{10.1109/ISTMWC.2007.4299296}}, year = {{2007}}, } @inproceedings{40875, author = {{Wahlberg, Patrik and Schreier, Peter J.}}, booktitle = {{Proc. 41st\ Asilomar Conf.\ Signals Syst.\ Computers}}, pages = {{1093–1097}}, title = {{{Frequency-domain properties of locally stationary improper second-order stochastic processes}}}, doi = {{10.1109/ACSSC.2007.4487391}}, year = {{2007}}, } @article{40878, author = {{Ping, Li and Guo, Qinghua and Tong, Jun}}, journal = {{IEEE Wireless Comm.}}, number = {{3}}, pages = {{18–24}}, title = {{{The OFDM-IDMA approach to wireless communication systems}}}, doi = {{10.1109/MWC.2007.386608}}, volume = {{14}}, year = {{2007}}, } @inproceedings{40876, author = {{Trajkovic, Vladimir D. and Fu, Minyue and Schreier, Peter J.}}, booktitle = {{Proc. 4th\ Int.\ Symp.\ Wireless Comm.\ Syst.}}, pages = {{153–157}}, title = {{{Turbo Equalization With Irregular Turbo Codes}}}, doi = {{10.1109/ISWCS.2007.4392320}}, year = {{2007}}, } @inproceedings{40881, abstract = {{Wigner’s theorem states that there exists no bilinear time-frequency distribution (TFD) that has correct marginals and is nonnegative everywhere. This means that any attempt to interpret a bilinear TFD as an energy or power distribution must be fraught with problems. In this paper, an alternative perspective is proposed, which allows a local interpretation at a point in the time-frequency plane. This approach is based on analyzing the properties of a chirping ellipse that, at a given time instant, gives the best local approximation of the signal from a given frequency. This chirping ellipse is described in terms of its mean shape, orientation, and direction of polarization (counterclockwise or clockwise). A time-frequency coherence measures the quality of the approximation that this ellipse presents. The ellipse parameters and the time-frequency coherence can be expressed in terms of the Rihaczek TFD}}, author = {{Schreier, Peter J.}}, booktitle = {{Proc.\ IEEE Int.\ Conf.\ Acoustics, Speech and Signal Process.}}, pages = {{1133–1136}}, title = {{{A New Interpretation of Bilinear Time-Frequency Distributions}}}, doi = {{10.1109/ICASSP.2007.366884}}, volume = {{3}}, year = {{2007}}, } @inproceedings{40880, abstract = {{We analyze the spectral measure and complementary spectral measure for strongly harmonizable cyclostationary and almost cyclostationary multidimensional complex improper processes. We show that the off-diagonal components of the spectral measure are absolutely continuous with respect to the diagonal component, which is a generalization of a result for scalar processes. For scalar almost cyclostationary processes, we derive representation formulas for the complementary spectral measure and the off-diagonal components of the spectral measure, in terms of the diagonal component of the spectral measure. These results are similar to the cyclostationary case, with some modifications concerning the off-diagonal components of the complementary spectral measure.}}, author = {{Wahlberg, Patrik and Schreier, Peter J.}}, booktitle = {{Proc.\ IEEE Int.\ Symp.\ Inform.\ Theory}}, pages = {{971–975}}, title = {{{Spectra of multidimensional complex improper (almost) cyclostationary processes}}}, doi = {{10.1109/ISIT.2007.4557350}}, year = {{2007}}, } @article{40879, author = {{Spurbeck, Mark S. and Schreier, Peter J.}}, journal = {{Signal Process.}}, number = {{6}}, pages = {{1179–1187}}, publisher = {{Elsevier North-Holland, Inc.}}, title = {{{Causal Wiener filter banks for periodically correlated time series}}}, doi = {{10.1016/j.sigpro.2006.10.008}}, volume = {{87}}, year = {{2007}}, } @inproceedings{40887, abstract = {{In this paper, a new second-order statistics (SOS) based method for blind decoding of orthogonal space time block coded (OSTBC) systems with only one receive antenna is proposed. To avoid the in- herent ambiguities of this problem, the spatial correlation matrix of the source signals must be non-white and known at the receiver. In practice, this can be achieved by a number of simple linear preco- ding techniques at the transmitter side. More specifically, it is shown in the paper that if the source correlation matrix has different eigen- values, then the decoding process can be formulated as the problem of maximizing the sum of a set of weighted variances of the signal estimates. Exploiting the special structure of OSTBCs, this problem can be reduced to a principal component analysis (PCA) problem, which allows us to derive computationally efficient batch and adap- tive blind decoding algorithms. The algorithm works for any OSTBC (including the popular Alamouti code) with a single receive antenna. Some simulation results are presented to demonstrate the potential of the proposed procedure.}}, author = {{Vía, J. and Santamaría, I. and Pérez, J. and Ramírez, D.}}, booktitle = {{Proc.\ IEEE Int.\ Conf.\ Acoustics, Speech and Signal Process.}}, title = {{{Blind decoding of MISO-OSTBC systems based on principal component analysis}}}, doi = {{10.1109/ICASSP.2006.1661026}}, year = {{2006}}, } @article{40892, abstract = {{Based on the additive white quantization noise model, linear transform coders are derived for Gaussian sources corrupted by noise. There are two alternative design objectives: minimizing the trace of the error correlation matrix and thus minimizing the mean-squared error, or minimizing the determinant of the error correlation matrix and thus maximizing information rate. It is shown that a solution to both problems is to first transform the noisy observations into canonical coordinates, quantize and apply a Wiener filter in this coordinate system, and then transform the result back to the original coordinates. Canonical coordinates are uncorrelated, and quantization and Wiener filtering are applied to each component independently. The type of canonical coordinate system depends on the design objective: Quantization in half-canonical coordinates minimizes the mean-squared error and quantization in full-canonical coordinates maximizes information rate. Finally, it is also demonstrated in this paper that majorization is the fundamental principle underlying proofs of optimal transform coding.}}, author = {{Schreier, Peter J. and Scharf, Louis L.}}, journal = {{{IEEE} {T}rans.\ {S}ignal\ {P}rocess.}}, number = {{1}}, pages = {{235–243}}, title = {{{Canonical coordinates for transform coding of noisy sources}}}, doi = {{10.1109/TSP.2005.861085}}, volume = {{54}}, year = {{2006}}, } @article{40891, abstract = {{In this paper, we present an unequal power allocation technique to increase the throughput of code-division multiple-access (CDMA) systems with chip-level interleavers. Performance is optimized, respectively, based on received and transmitted power allocation. Linear programming and power matching techniques are developed to provide solutions to systems with a very large number of users. Various numerical results are provided to demonstrate the efficiency of the proposed techniques and to examine the impact of system parameters, such as iteration number and interleaver length. We also show that with some very simple forward error correction codes, such as repetition codes or convolutional codes, the proposed scheme can achieve throughput reasonably close to that predicted by theoretical limit in multiple access channels.}}, author = {{Liu, Lihai and Tong, Jun and Ping, Li}}, journal = {{IEEE J.\ Select.\ Areas Comm.}}, number = {{1}}, pages = {{141–150}}, title = {{{Analysis and optimization of CDMA systems with chip-level interleavers}}}, doi = {{10.1109/JSAC.2005.858896}}, volume = {{24}}, year = {{2006}}, } @inproceedings{40888, abstract = {{A complex random vector is called improper if it is correlated with its complex conjugate. In this paper, we present a generalized likelihood ratio test (GLRT) for impropriety. This test is compelling because it displays the right invariances: The proposed GLR is invariant to linear transformations on the data, including rotation and scaling, just as propriety is preserved by linear transformations. Because canonical correlations make up a complete, or maximal, set of invariants for the Hermitian and complementary covariance matrices under linear transformations, the GLR can be shown to be a function of the squared canonical correlations between the data and its complex conjugate. This validates our intuition that the internal coordinate system should not matter for this hypothesis test}}, author = {{Schreier, Peter J. and Scharf, Louis L. and Hanssen, Alfred}}, booktitle = {{Proc.\ IEEE Int.\ Conf.\ Acoustics, Speech and Signal Process.}}, pages = {{796–799}}, title = {{{A Statistical Test for Impropriety of Complex Random Signals}}}, doi = {{10.1109/ICASSP.2006.1660774}}, volume = {{3}}, year = {{2006}}, } @article{40890, abstract = {{A new suboptimal algorithm for detection of constant modulus signals in multiple-input multiple-output (MIMO) channels is presented. The deviation of the solution from the desired constant modulus property is used as a penalty or regularization term in the conventional least squares cost function, and an iterative reweighted least squares (IRWLS) procedure is used to minimize the regularized functional.}}, author = {{Ramírez, D. and Santamaría, I.}}, journal = {{Electr. Lett.}}, number = {{3}}, pages = {{184–186}}, title = {{{Regularised approach to detection of constant modulus signals in MIMO channels}}}, doi = {{10.1049/el:20063870}}, volume = {{42}}, year = {{2006}}, } @inproceedings{40889, abstract = {{Clipping is applied to superposition coding systems to reduce the peak-to-average power ratio (PAPR) of the transmitted signal. The performance limit is investigated through evaluating the mutual information driven by the induced peak-power-limited input signals. It is shown that the channel capacity can be approached by clipped superposition coding systems. To alleviate the performance degradation due to clipping noises, we develop a soft compensation algorithm that is combined with soft-input-soft-output (SISO) decoding algorithms in an iterative manner. Simulation results show that with the proposed algorithm, most performance loss can be recovered.}}, author = {{Tong, Jun and Ping, Li}}, booktitle = {{6th\ Int.\ Symp.\ Turbo Codes & Rel.\ Top.}}, pages = {{1–6}}, title = {{{Iterative decoding of superposition coding}}}, year = {{2006}}, } @inproceedings{40883, abstract = {{We develop a causal filter bank implementation of the cyclic Wiener filter for periodically correlated (PC, or cyclostationary) time series. By converting the PC time series into a vector-valued wide-sense stationary (WSS) time series, we may utilize the existing literature on factorization of spectral density matrices. However, because PC analytic and equivalent baseband signals are generally improper, spectral factorization algorithms must be modified for the improper case. Then, given the spectral density matrix for the equivalent WSS vector process, a causal cyclic Wiener filter can be implemented as a multirate filter bank or an equivalent polyphase structure.}}, author = {{Spurbeck, Mark S. and Schreier, Peter J. and Scharf, Louis L.}}, booktitle = {{Proc. 40th\ Asilomar Conf.\ Signals Syst.\ Computers}}, pages = {{1425–1429}}, title = {{{Causal cyclic Wiener filtering}}}, doi = {{10.1109/ACSSC.2006.354993}}, year = {{2006}}, } @inproceedings{40884, abstract = {{Hardware platforms and testbeds are an essential tool to evaluate, in realistic scenarios, the performance of Multiple-Input-Multiple-Ouput (MIMO) systems. In this work we present a simple and easily reconfigurable $2 \times 2$ MIMO testbed for the rapid prototyping of the signal processing baseband functions. The signal generation module consists of a host PC equipped with a board that contains two high performance 100 MHz DACs and a 1 GB memory module that allows the transmission of extremely large frames of data. At the receiver side, we use another host PC equipped with two 105 MHz ADCs, another 1 GB memory module and a trigger that starts the acquisition process when the presence of signal is detected. The platform has been designed to operate at the ISM band of 2.4 GHz with a RF bandwidth of 20 MHz. In order to minimize the number of DAC and ADC circuits, signals are generated and acquired at an IF of 15 MHz. Upconversion to RF is performed with two RF vectorial signal generators (Agilent E4438C) and downconversion with two specific circuits designed from commercial components. Transmitter and receiver signal processing functions are implemented off-line in Matlab. To illustrate the performance and capabilities of the platform, we present the results of two experiments of a $2 \times 2$ MIMO transmission with Alamouti coding.}}, author = {{Ramírez, D. and Santamaría, I. and Pérez, J. and Vía, J. and Tazón, A. and Garcia-Naya, J. A. and Fernandez-Carames, T. M. and Lopez, M. Gonzalez and Iglesias, H. J. Pérez and Castedo, L.}}, booktitle = {{Proc. Int. Symp. on Wireless Comm. Systems}}, title = {{{A flexible testbed for the rapid prototyping of MIMO baseband modules}}}, doi = {{10.1109/ISWCS.2006.4362407}}, year = {{2006}}, } @article{40882, abstract = {{Even though higher-order spectral analysis is by now a mature field, complex signals are still not routinely used, as they are in second-order analysis. The reason is the complexity of the complex case: nth order moment functions of a complex signal can be defined in 2 n different ways, depending on the placement of complex conjugate operators. It is demonstrated that only a few of these different moments are required for a complete nth order description. Properties of nth order moments and spectra with different conjugation patterns are investigated. For the special case of analytic signals, it is shown how spectra with different conjugation patterns provide different information about the signal. Both energy and power signals and deterministic and stochastic signals are discussed. A major focus lies on extending results from continuous-time signals to their sampled versions. Such an extension is not straightforward due to a phenomenon called higher-order or dimension-reduction aliasing. It is demonstrated why spectra of sampled nonstationary signals may suffer from dimension-reduction aliasing unless they are sufficiently oversampled.}}, author = {{Schreier, Peter J. and Scharf, Louis L.}}, journal = {{Signal Process.}}, number = {{11}}, pages = {{3321–3333}}, title = {{{Higher-order spectral analysis of complex signals}}}, doi = {{10.1016/j.sigpro.2006.02.027}}, volume = {{86}}, year = {{2006}}, } @article{40885, abstract = {{A complex random vector is called improper if it is correlated with its complex conjugate. We present a hypothesis test for impropriety based on a generalized likelihood ratio (GLR). This GLR is invariant to linear transformations on the data, including rotation and scaling, because propriety is preserved by linear transformations. More specifically, we show that the GLR is a function of the squared canonical correlations between the data and their complex conjugate. These canonical correlations make up a complete, or maximal, set of invariants for the Hermitian and complementary covariance matrices under linear, but not widely linear, transformation}}, author = {{Schreier, Peter J. and Scharf, Louis L. and Hanssen, Alfred}}, journal = {{IEEE Signal Process.\ Lett.}}, number = {{7}}, pages = {{433–436}}, title = {{{A generalized likelihood ratio test for impropriety of complex signals}}}, doi = {{10.1109/LSP.2006.871858}}, volume = {{13}}, year = {{2006}}, } @inproceedings{40886, abstract = {{This paper presents a peak-power-limited superposition coding scheme based on clipping. A low-complexity soft compensation algorithm (SCA) for combating the clipping effect is investigated. It can be easily combined with soft-input soft-output (SISO) decoding algorithms in an iterative manner. Various numerical results show that the SCA can effectively mitigate the performance loss due to clipping.}}, author = {{Tong, Jun and Ping, Li and Ma, Xiao}}, booktitle = {{Proc.\ IEEE Int.\ Conf.\ Comm.}}, pages = {{1718–1723}}, title = {{{Superposition coding with peak-power limitation}}}, doi = {{10.1109/ICC.2006.254967}}, volume = {{4}}, year = {{2006}}, }