Pedro Amo-López

An efficient and simple method for designing prototype filters for cosine-modulated pseudo-QMF banks

We present a new method to design prototype filters for conventional cosine-modulated pseudo-quadrature mirror filter (QMF) banks. This method is based on windowing, and sets the 3-dB cutoff frequency of the filter obtained at /spl pi//2M. In this way, the filter bank performance can be significantly improved compared to other existing design methods.

On the Use of Discrete Cosine Transforms for Multicarrier Communications

In this correspondence, the conditions to use any kind of discrete cosine transform (DCT) for multicarrier data transmission are derived. The symmetric convolution-multiplication property of each DCT implies that when symmetric convolution is performed in the time domain, an element-by-element multiplication is performed in the corresponding discrete trigonometric domain. Therefore, appending symmetric redundancy (as prefix and suffix) into each data symbol to be transmitted, and also enforcing symmetry for the equivalent channel impulse response, the linear convolution performed in the transmission channel becomes a symmetric convolution in those samples of interest. Furthermore, the channel equalization can be carried out by means of a bank of scalars in the corresponding discrete cosine transform domain. The expressions for obtaining the value of each scalar corresponding to these one-tap per subcarrier equalizers are presented. This study is completed with several computer simulations in mobile broadband wireless communication scenarios, considering the presence of carrier frequency offset (CFO). The obtained results indicate that the proposed systems outperform the standardized ones based on the DFT.

Alternating Analysis and Synthesis Filters

Cruz-Roldan, F., Amo-Lopez, P., Mart??n-Mart??n, P., and Lopez-Ferreras, F., Alternating Analysis and Synthesis Filters: A New Pseudo-QMF Bank, Digital Signal Processing11 (2001) 329?345The process of designing a prototype filter for a pseudo quadrature mirror filter (QMF) cosine-modulated bank can require the optimization of a highly nonlinear cost function to obtain its coefficients or the calculation of a spectral factor of a valid 2Mth band filter. This article presents a new method for designing pseudo-QMF banks in which none of the aforementioned procedures are required. To obtain the coefficients of the prototype filter we can use any technique which enables us to design linear-phase Type I or Type II FIR filters. The result is a system in which amplitude distortion is very low, there is no phase distortion at all, and aliasing is slightly higher than the stopband attenuation of the prototype filter obtained. Several examples are included.

Design of Two-Dimensional Optical Alignment Signals Robust to Diffractive Effects

Mask alignment is one of the most critical processes in photolithography. Prior to the shadow projection, the alignment between the lithographic mask and the silicon wafer is needed. In contact and proximity photolithography, a method to achieve the alignment with submicron or even nanometer resolution consists of superimposing two identical 2-D zero reference codes and registering the optical output signal. In order to increase the resolution of the system, the size of the code must be reduced and the diffractive effects become strong. The signal is then degraded and the precision of the alignment is reduced. In this paper, the effect of the diffraction in 2-D codes is analyzed, the degradation of the signal is characterized and its effect is modelled by means of a simple and fast computing parameter. Finally, we propose a genetic algorithm to optimize this parameter and design 2-D codes robust to diffractive effects. We propose the use of these codes to increase the resolution of alignment systems.

Arbitrary-length spectral factor applied to the design of pseudo-QMF cosine-modulated filter banks

The main advantage of pseudoquadrature mirror filter cosine modulated filter banks with a spectral factor of a 2Mth band filter is that the optimization stage can be avoided when designing the prototype filter. However, these filter banks are constrained by the condition that the order of the prototype filter has to be an integer multiple of the M-number of channels in the bank. In this paper, we set the conditions that must be imposed to cosine-modulation phase factors so as to cancel the most significant terms of aliasing using a prototype filter of arbitrary length. An example is included to confirm the validity of the theory.

Enhanced Spectral Method for T-Wave Alternans analysis

The T-wave alternans or ventricular alternans have been closely linked to electrical instability in the heart. Recent studies have demonstrated that T-wave alternans occurence is related with ventricular arrhythmias. So, T-wave alternans detection may help in the diagnostic of heart diseases and sudden cardiac death. TWA consist of a beat to beat alternation of the ST-T complex, and this alternation can be in order of muV. The noise is a critical factor to be considered as it can mask the T-wave alternans when its magnitude is close to the alternan wave. Therefore, T-wave alternans detection techniques are very dependent on the relationship between noise and alternance power. Among the T-wave alternans detection methods, the spectral method is widely used. In this work, a modified version of the spectral method algorithm is presented. The proposed method increases the alternance significance with regard to the noise in the spectral domain. Experimental study, carried out in this work, shows that this new approach yields better performance in a noisy environment.

Assessment of NPR MDFT filter banks for subband coding and data transmission

Nearly perfect reconstruction (N-PR) modified discrete Fourier Transform (MDFT) filter banks (FBs) have been widely applied to signal coding and their use for data transmission in multicarrier communications has also been addressed in the literature. However, comparison and assessment of the performance of alternative designs for uniform N-PR MDFT-based systems is hampered by the lack of explicit formulas for easily calculating their expected performance. In this sense, this work introduces a unified formulation which can be used for the three different kinds of uniform N-PR MDFT filter banks which have been described in the literature. We demonstrate that the relationship between output and input signals is identical for all of them when a filter bank (FB) configuration is considered. From this expression, amplitude distortion and aliasing errors can be measured. With respect to filter bank multicarrier (FBMC) systems, two new measures that bound the maximum level of intercarrier and intersymbol interferences are defined.

Pseudo-QMF filter banks for audio signals subband coding

Pseudo-QMF banks in which there is no optimization involved in order to obtain the prototype filter used in the cosine modulation are an advance that simplifies the system design. In this paper, three filter bank design methods that satisfy this requirement-all of them employ any conventional designing technique-are proposed. These filter banks do not introduce phase distortion, their aliasing is comparable to the stopband gain of the prototype filter and amplitude distortion can be really minimized. The differences among them are prototype filter specifications and the initial phase factor election. When the prototype filters are appropriately designed, the total error on the reconstructed output signal is reduced. An example where an audio signal is the input signal is included.

Discrete cosine transform Type-IV-based multicarrier modulators in frequency offset channels

Carrier frequency offset (CFO) is one of the main drawbacks of multicarrier modulation based on the discrete Fourier transform (DFT). To solve the above problem, several researchers have proposed the use of discrete trigonometric transforms. In this paper, we analyze the intercarrier interference and the bit-error probability in discrete cosine transform type-IV even (DCT4e)-based multicarrier systems under the presence of carrier frequency offset (CFO). The parameters which are involved in the design are established, and the expressions for both prefix and suffix to be appended into each data symbol to be transmitted are shown. Several computer simulations indicate that the proposed systems outperform the standardized ones based on the discrete Fourier transform (DFT) under the presence of CFO.