Uniform DFT Filter Banks Research Articles

Filter-bank based efficient transmission of Reduced-Guard-Interval OFDM

We propose a new way to structure the digital signal processing for reduced guard-interval (RGI) OFDM optical receivers. The idea is to digitally parallelize the processing over multiple parallel virtual sub-channels, occupying disjoint spectral sub-bands. This concept is well known in the optical or analog sub-carrier domains, but it turns out that it can also be performed efficiently in the digital domain. Here we apply critically sampled uniform analysis and synthesis DFT filter bank signal processing techniques in order to realize a novel hardware efficient variant of RGI OFDM, referred to as Multi-Sub-Band OFDM (MSB-OFDM), reducing by 10% receiver computational complexity, relative to a single-polarization version of the CD pre-equalizer. In addition to being more computationally efficient than a conventional RGI OFDM system, the signal flow architecture of our scheme is amenable to being more readily realized over multiple FPGAs, for experimental demonstrations or flexible prototyping.

Application of uniform DFT filter bank in radar jamming system

The principle of uniform DFT filter bank is presented. Exploiting poly-phase structure, radar jamming system samples the intercepted wideband radar signals through analysis filter bank by different channels and linearly modulates the intercepted radar signal according to the theory of signal and system, then synthesizes the jamming signal through the synthesis filter bank. The method merely requires lower sample frequency, reduces the computational complexity and the data quantity to be processed. The un-ideal filter's influence to the result of signals processing is analyzed by simulating the match filter in radar jamming system.

A hybrid method for the design of oversampled uniform DFT filter banks

Subband adaptive filters have been proposed to speed up the convergence and to lower the computational complexity of time domain adaptive filters. However, subband processing causes signal degradations due to aliasing effects and amplitude distortions. This problem is unavoidable due to further filtering operations in subbands. In this paper, the problem of aliasing effect and amplitude distortion is studied. The prototype filter design problem is formulated as a multi-criteria optimization problem and all the Pareto optima are sought. Since the problem is highly nonlinear and nonsmooth, a new hybrid optimization method is proposed. Different prototype filters are used and their performances are compared. Moreover, the effect of the number of subbands, the oversampling factors and the length of prototype filter are also studied. We find that prototype filters designed via Kaiser or Dolph–Chebyshev window provide the best overall performance. Also, there is a critical oversampling factor beyond which the improvement in performance is not justified. Finally, if the length of the prototype filter increases with the number of subbands, an increase in the subband level will not deteriorate the performance.

Filterbank design for oversampled subband adaptive filtering structures

A simple design procedure for uniform DFT filterbanks used in oversampled subband adaptive filtering structures is presented. The analysis prototype filter is designed with extended bandwidth to obtain fast convergence. The synthesis prototype filter is then optimised to reduce the mean square error. The resulting improvements in the convergence performance are verified through computer simulations.

Simple design of oversampled uniform DFT filter banks with applications to subband acoustic echo cancellation

Subband adaptive filtering, which is the basis of modern acoustic echo cancellation (AEC) systems, is an important application of filter banks in which critical sampling cannot be used in general because of decimation aliasing effects. This leads to the use of oversampling schemes in the filter bank design wherein the perfect-reconstruction (PR) or near PR property is still required. In this work, a simple design technique for uniform DFT filter bank with near PR property is presented for the purpose of subband adaptive filtering. The prototype filter in the proposed filter banks is derived simply by performing an interpolation of a two-channel QMF filter, which can be obtained easily by computation or table look-up. An efficient implementation of the filter banks based on a weighted-overlap-add structure is described that allows flexibility in oversampling. The filter bank design technique presented in this paper is of particular interest in engineering applications, as demonstrated by design examples and experimental results in a real-time subband AEC application.

Design of stable, causal, perfect reconstruction, IIR uniform DFT filter banks

Design procedures for stable, causal and perfect reconstruction IIR parallel uniform DFT filter banks (DFT FBs) are presented. In particular a family of IIR prototype filters is a good candidate for DFT FB, where a tradeoff between frequency selectivity and numerical properties (as measured by the Weyl-Heisenberg frames theory) could be made. Some realizations exhibiting a simple and a massively parallel and modular processing structure making a VLSI implementation very suitable are shown. In addition, some multipliers in the filters (both the analysis and synthesis) could be made; powers or sum of powers of 2, in particular for feedback loops, resulting in a good sensitivity behavior. For these reasons as well as for the use of low order IIR filters (as compared with conventional FIR filters), the overall digital filter bank structure is efficient for high data rate applications. Some design examples are provided.

Design of a family of stable causal perfect-reconstruction IIR uniform DFT filter banks with good numerical properties

A family of stable causal perfect reconstruction (PR) infinite-impulse response (IIR) discrete Fourier transform filter banks is presented, where a tradeoff between frequency selectivity and numerical properties is made. Some multipliers in both the analysis and synthesis filters could be made powers or sums of powers of two, in particular for feedback loops. Moreover, a simple scaling procedure that results in good sensitivity behavior is described. For these reasons, and also for the use of low-order IIR filters, the overall digital filter-bank structure is efficient for high data-rate applications. A design example, including quantization effects, is provided.

Stable, causal, perfect reconstruction, IIR uniform DFT filter banks

A simple design procedure for stable, causal and perfect reconstruction infinite impulse response parallel uniform discrete Fourier transform filter banks (DFT FBs) based on a new polyphase decomposition, the ‘polyphase-oversampled’ FB, is presented. The proposed design results in causal and stable analysis and synthesis filters that are all derived from a single prototype filter, resulting in efficient realisations. A discussion of the FB numerical properties and some design examples are provided.

On the design and realization of a class of uniform single rate FIR DFT filter banks

In this paper we present a computationally efficient realization of single rate uniform FIR filter banks for audio and spectral analysis applications. The channel filters in the analysis bank are represented as modulated versions of a prototype narrowband lowpass FIR filter. Using the IFIR filter design technique [23], [24], this prototype lowpass filter can be designed very efficiently as a cascade of two subfilters. The IFIR filter design is extended for the two-branch realization of uniform filter banks with overlapping channels. A generalized structure is presented which can be used for bothodd andeven stacking arrangements of the channels. The shaping filter structures for the two branches are realized from a single delay line and a single set of filter coefficients, thus conserving the total number of multipliers and delays in the overall realization. The postfilter structure, in conjunction with the Generalized DFT matrices, performs the channel selection. The Generalized DFT matrices are used to provide the necessary modulation for the postfilter coefficients so that the appropriate passbands are selected for each channel of the analysis bank. This leads to a polyphase network realization of the postfilter structure. We derive conditions so that the original input signal can be exactly reconstructed from the channel signals.

Design of uniform DFT filter banks optimized for subband coding of speech

A new approach for designing uniform DFT analysis/synthesis filter banks, optimized for subband coding (SBC) of speech, is presented. A spectral-domain distortion measure, which consists of a weighted sum of error terms due to filtering, rate conversion, and quantization, is derived. The quantization is embedded by means of a statistical model. For the case of 'fine' quantization, a simpler, deterministic distortion function is derived. The optimal filters are designed using an iterative algorithm in which two sets of linear equations are solved in each iteration, aiming at minimizing the distortion function. A 16-kb/s SBC is simulated using a filter bank designed by the new approach, and is found to achieve subjective and objective (SNR) performance similar to that of a conventional QMF-based SBC, with only about half the amount of computation. >

Efficient subband coding of speech with optimized uniform DFT filter banks

Uniform DFT filter banks (FB) offer reduced implementation complexity of subband coders (SBC) as compared with QMF-based SBC. However, because known design techniques aim at minimizing the overall response error of the FB, using either deterministic [V. K. Jain and R. E. Crochiere, Proc. ICASSP 83, 228–231 (1983)] or statistical [A. Dembo and D. Malah, IEEE Trans. Acoust. Speech Signal Process. ASSP-36, 328–341 (1988)] error measures, the performance of DFT-based SBC was found to be subjectively inferior. A new approach is presented for DFT-FB design, which is based on a frequency-doman distortion function in which different weights are applied to the different error components (including interband aliasing and leakage of both signal and quantization noise) thus allowing an optimized design for SBC. The minimization of the proposed distortion function results in two sets of linear equations that are solved iteratively to obtain the optimal analysis and synthesis prototype filters. A 16-band DFT-based SBC operating at 16 kb/s with the designed filters was found in simulations to have subjective and objective performance similar to a QMF-based SBC at the same rate, but with less than half of the computations.