Efficient Implementation Structure Research Articles

Adaptive digital self-interference cancellation based on fractional order LMS in LFMCW radar

Adaptive digital self-interference cancellation (ADSIC) is a significant method to suppress self-interference and improve the performance of the linear frequency modulated continuous wave (LFMCW) radar. Due to efficient implementation structure, the conventional method based on least mean square (LMS) is widely used, but its performance is not sufficient for LFMCW radar. To achieve a better self-interference cancellation (SIC) result and more optimal radar performance, we present an ADSIC method based on fractional order LMS (FOLMS), which utilizes the multi-path cancellation structure and adaptively updates the weight coefficients of the cancellation system. First, we derive the iterative expression of the weight coefficients by using the fractional order derivative and short-term memory principle. Then, to solve the problem that it is difficult to select the parameters of the proposed method due to the non-stationary characteristics of radar transmitted signals, we construct the performance evaluation model of LFMCW radar, and analyze the relationship between the mean square deviation and the parameters of FOLMS. Finally, the theoretical analysis and simulation results show that the proposed method has a better SIC performance than the conventional methods.

Photo-acoustic tomographic image reconstruction from reduced data using physically inspired regularization

We propose a model-based image reconstruction method for photoacoustic tomography (PAT) involving a novel form of regularization and demonstrate its ability to recover good quality images from significantly reduced size datasets. The regularization is constructed to suit the physical structure of typical PAT images. We construct it by combining second-order derivatives and intensity into a non-convex form to exploit a structural property of PAT images that we observe: in PAT images, high intensities and high second-order derivatives are jointly sparse. The specific form of regularization constructed here is a modification of the form proposed for fluorescence image restoration. This regularization is combined with a data fidelity cost, and the required image is obtained as the minimizer of this cost. As this regularization is non-convex, the efficiency of the minimization method is crucial in obtaining artifact-free reconstructions. We develop a custom minimization method for efficiently handling this non-convex minimization problem. Further, as non-convex minimization requires a large number of iterations and the PAT forward model in the data-fidelity term has to be applied in the iterations, we propose a computational structure for efficient implementation of the forward model with reduced memory requirements. We evaluate the proposed method on both simulated and real measured data sets and compare them with a recent reconstruction method that is based on a well-known fast iterative shrinkage threshold algorithm (FISTA).

Kernelized-Likelihood Ratio Tests for Binary Phase-Shift Keying Signal Detection

In this article, kernelized-likelihood ratio tests (LRTs) for binary phase-shift keying (BPSK) signal detection based on the polynomial kernel function are proposed. Specifically, we kernelize the conventional LRT of BPSK signal detection using the so-called kernel trick, such that the inner product of the conventional LRT is replaced with proper polynomial kernel functions allowing for richer feature space to be deployed in the detection. We also derive computationally efficient recursive implementation structures for the proposed methods, resulting overall in six new detectors. With respect to the noise variance uncertainty (NVU), the proposed detectors can be divided into two general classes, namely i) constant false alarm rate (CFAR) and ii) semi-CFAR (S-CFAR) methods. To facilitate efficient operation under NVU, we also propose a new threshold-setting strategy to adjust the level of the proposed S-CFAR detectors. Additionally, we address the well-known energy detector (ED) under NVU and devise a new fixed-level ED formulation while also obtaining closed-form expressions for its false alarm and detection probabilities. Our extensive simulation results show that the proposed S-CFAR detectors outperform the state-of-the-art BPSK signal detectors with 2.4 dB signal-to-noise ratio (SNR) gain under practical worst-case NVU assumptions, while the performance gain is approximately 5.7 dB without NVU. In the case of the proposed CFAR detectors, the corresponding improvement in detection performance is approximately 1.8 dB.

Towards efficient security policy lookup on many-core network processing platforms

Modern network security devices employ packet classification and pattern matching algorithms to inspect packets. Due to the complexity and heterogeneity of different search data structures, it is difficult for existing algorithms to leverage modern hardware platforms to achieve high performance. This paper presents a Structural Compression (SC) method that optimizes the data structures of both algorithms. It reviews both algorithms under the model of search space decomposition, and homogenizes their search data structures. This approach not only guarantees deterministic lookup speed but also optimizes the data structure for efficient implementation on many-core platforms. The performance evaluation reveals that the homogeneous data structure achieves 10Gbps line-rate 64byte packet classification throughput and multi-Gbps deep inspection speed.

Efficient design of non-uniform cosine modulated filter banks for digital hearing aids

In this paper, efficient and simple designs of non-uniform filter banks for digital hearing aid applications are proposed. Hearing aids should be individually tuned to satisfy the requirements of hearing impaired persons. Cosine modulated filter banks are one popular filter bank having simple design procedure with efficient implementation structure. In the proposed structure for hearing aid, non-uniform subbands are obtained using two methods. The first method is by merging the adjacent channels of a uniform filter bank and the second method, is by using transition filters between two filters with different bandwidths. The advantages of the proposed structure are simple design procedure, less implementation complexity, greater flexibility in tuning the subbands for various types of audiograms and improved performance in terms of matching error.

An input-balanced realization-based structure for efficient implementation of digital IIR filters

Based on an input-balanced state-space realization, this paper derives a novel structure for efficient implementation of digital IIR filters. Such a structure is very similar to a normalized lattice and, for an N th order IIR filter, it possesses 5 N -1 non-trivial multipliers: two multipliers less than in a normalized lattice. Expressions for transfer function sensitivity measures and roundoff noise gain for the proposed structure are derived. Interestingly, it is shown that, when the filter is all-pass, the proposed structure requires 4 N multiplications in order to compute one output sample. Moreover, the corresponding roundoff noise gain is 4 N , much smaller than that of ( N +1) 2 given by the classical minimum roundoff state-space realizations. Results of simulations performed show that the proposed structure outperforms many classical ones in terms of implementation efficiency and robustness against finite-word-length effects.

A Class of Multimode Transmultiplexers Based on the Farrow Structure

This paper introduces multimode transmultiplexers (TMUXs) in which the Farrow structure realizes the polyphase components of general lowpass interpolation/decimation filters. As various lowpass filters are obtained by one set of common Farrow subfilters, only one offline filter design enables us to cover different integer sampling rate conversion (SRC) ratios. A model of general rational SRC is also constructed where the same fixed subfilters perform rational SRC. These two SRC schemes are then used to construct multimode TMUXs. Efficient implementation structures are introduced and different filter design techniques such as minimax and least-squares (LS) are discussed. By means of simulation results, it is shown that the performance of the transmultiplexer (TMUX) depends on the ripples of the filters. With the error vector magnitude (EVM) as the performance metric, the LS method has a superiority over the minimax approach.

A filter design strategy for binary field wavelet transform using the perpendicular constraint

Wavelet decomposition has recently been generalized to binary field in which the arithmetic is performed wholly in GF(2). In order to maintain an invertible binary wavelet transform with multiresolution properties, three constraints are placed on the filters, namely the bandwidth, the perfect reconstruction and the vanishing moment constraints. While these constraints guarantee the existence of the inverse filters, their form is unconstrained and could be signal length dependent. In this paper, we propose to use the perpendicular constraint to relate the forward and inverse filters. With this constraint, it is shown that the form of the inverse filters remains unchanged after the up-sampling operation associated with the wavelet transform. We also explore an efficient implementation structure in the binary filters so as to save memory space and reduce the computational complexity. A detailed comparison with the lifting implementation in the real field wavelet transform is carried out. It is found that the computational complexity of the binary filter is significantly less than that of the real field wavelet kernel.

IWRM concept for the Cuvelai Basin in northern Namibia

This paper presents main findings of a feasibility study for a joint transdisciplinary project to strengthen the implementation of integrated water resources management (IWRM) in the Cuvelai Basin, northern Namibia. The region is characterised by seasonal alterations of droughts and heavy rainfall, mostly saline groundwater and a lack of permanent rivers. Difficult local conditions pose a great challenge for water supply against the background of high population density. Currently, most drinking water of the area is withdrawn from the Kunene River at the Angolan border and transported through a canal and pipeline scheme. However, it is expected that this infrastructure will be put at risk due to increasing water demand on both the Namibian and Angolan side. By integrating social-ecological as well as technical aspects IWRM may be instrumental in mitigating these problems. The aim to identify alternative water sources and create a multi-resource mix will be approached by strengthening the use of endogenous resources alongside with demand-oriented water and land management. Technologies considered have to be adapted to the local situation, not only concerning technological constraints but also concerning social and ecological factors. Furthermore, the implementation of technology must be integrated into the institutional and administrative processes of resource management as well as into the social, economic and ecological conditions of water use. Taking these conditions into account, actions and measures require clear and efficient organisation, implementation and participatory structures. They also call for a combined approach from natural, engineering and social sciences leading to a transdisciplinary research and development process. This paper aims to identify the design and conceptualisation of an IWRM which is adapted to the specific regional conditions.

Efficient Implementation of 2<tex>$times$</tex>Oversampled Exponentially Modulated Filter Banks

This paper studies 2times oversampled exponentially modulated filter banks because they can be a useful solution for various communications signal processing problems. At first, the perfect reconstruction (PR) property of this kind of 2M-channel complex modulated filter bank is proven by using the results of M-channel PR cosine-/sine-modulated filter banks (CMFBs/SMFBs). Then, two efficient implementation structures are developed. The computational complexities of CMFB/SMFB-based and discrete Fourier transform (DFT)-based realizations are practically the same when comparing the required number of multiplications and additions. However, the DFT-based structures can be further simplified by using an intuitive spectral interpretation. This results in the modified filter bank part that requires less arithmetic operations than the original one

Second derivative methods with RK stability

General linear methods are extended to the case in which second derivatives, as well as first derivatives, can be calculated. Methods are constructed of third and fourth order which are A-stable, possess the Runge–Kutta stability property and have a diagonally implicit structure for efficient implementation.

Decimation by non-integer factor in multistandard radio receivers

In many applications it is required to have a system for non-integer sampling rate conversion (SRC), which supports any decimation factor, and provides enough attenuation for aliasing and imaging signal components. A good example case is a software radio receiver, where the ratio of sampling rate just after A/D converter and symbol rate for a supported standard may be a ratio of two large mutually prime numbers. In a digital mobile receiver, it is very important to reduce the power consumption. The power consumption in context of SRC can be reduced by designing a system that has low rate of multiplication and addition operations. This paper introduces a novel non-integer decimation method. The proposed structure is a combination of an FIR filter and a polynomial-based interpolation filter. For the special case based on a cascaded integrator-comb (CIC) filter and simple polynomial-based interpolation filter, the proposed combination has a very efficient implementation structure. The results shown in this paper indicate that the computational complexity and multiplication rate can be reduced compared to the earlier solutions.

Power efficient structure for conversion between arbitrary sampling rates

This work presents a novel efficient method for conversion between arbitrary sampling rates. The method allows arbitrary number of zeros at multiples of both input and output sampling rates, thus it has both good anti-imaging and good anti-aliasing properties. Further, two equivalent efficient implementation structures are presented. The implementation is done either by using the modified Farrow or transposed modified Farrow structure. By choosing one of these two alternatives appropriately, it is possible to shift most of the operations to lower sampling rate.

Efficient Implementation of Nearly Perfect Reconstruction FIR Cosine-Modulated Filterbanks

In this paper, a new fast implementation of nearly perfect reconstruction finite impulse response (FIR) cosine-modulated filterbanks is shown. A new expression for the analysis bank has been developed, and based on it, an efficient implementation structure is obtained for specific prototype filter lengths. The new computationally efficient algorithm can be applied to both the conventional cosine-modulated filterbank and the Koilpillai-Vaidyanathan pseudo-quadrature mirror filterbank. We also show how the implementation cost (measured in multiplications and additions per input sample) is reduced.

A Novel Image Rejection Architecture for Quadrature Radio Receivers

In radio communications, a bandpass-to-lowpass transformation is needed to demodulate the received signal down to baseband. One crucial question in this context is how to effectively attenuate the image band signal. For this purpose, inphase/quadrature (I/Q) signal processing is widely utilized in today's radio receivers. In this paper, a novel structure for obtaining an image-free baseband observation of the received bandpass signal is presented. The starting point is to approximate the needed 90/spl deg/ phase difference between the I and Q branch signals using a simple time delay of one quarter of the carrier cycle. For narrowband signals, this approach can be used directly to attenuate the inherent self-image. By using an interference canceller-type of compensation technique, this concept is here generalized to cover also wideband multichannel signals. Furthermore, a closed-form expression to explicitly characterize the obtainable image attenuation is derived. Efficient implementation structures for digital radios utilizing periodically nonuniform subsampling are presented, and the validity of the proposed approach is further illustrated through simulation and design examples.

MAP harmonic retrieval in Gaussian colored noise with prior information

In this paper we deal with the MAP estimation of the parameters of a single complex sinusoid in Gaussian white and colored noise. We analyze the effects of modeling the frequency and amplitude as random variables, deriving the expressions of the MAP estimators, and we analytically compute the CRB's for a tone with Gaussian frequency and amplitude distributions. Moreover, we explicitly derive closed-form expressions of the optimal estimators in the case of Gaussian and Rayleigh distributed amplitude. In particular, we show that, in the colored noise case, the amplitude information can also help improving the performance of the frequency estimator, and vice versa. We propose an efficient FFT-based implementation structure of the optimal estimators, which can be further simplified when the noise can be modeled as an AR process; besides, when the estimators cannot be expressed in closed form, we propose a simple univariate optimization algorithm in order to compute the estimates. Simulation results are reported, which validate the theoretical results and witness the significant performance improvement that can be achieved embodying the parameter priors into the frequency and amplitude estimators.

A review of cyclically extended single carrier transmission with frequency domain equalization for broadband wireless transmission

In this paper we investigate the concept of cyclically extended single carrier transmission with frequency domain equalization (SC/FDE). We present a detailed mathematical derivation of fast Fourier transform (FFT) based optimum linear receivers, and we describe the signal processing steps of an efficient FDE implementation structure. With a specific system design, where the parameters have been adapted to the IEEE 802.11a and Hiperlan/2 orthogonal frequency division multiplexing (OFDM) based wireless local area network (WLAN) standards in the 5 GHz band, we demonstrate that SC/FDE is a powerful candidate for high speed wireless future applications. Copyright © 2003 AEI.

Quasi-Newton algorithm for adaptive minor component extraction

An adaptive quasi-Newton algorithm is first developed to extract a single minor component corresponding to the smallest eigenvalue of a stationary sample covariance matrix. A deflation technique instead of the commonly used inflation method is then applied to extract the higher-order minor components. The algorithm enjoys the advantage of having a simpler computational complexity and a highly modular and parallel structure for efficient implementation. Simulation results are given to demonstrate the effectiveness of the proposed algorithm for extracting multiple minor components adaptively.

Closed-form design and efficient implementation of generalized maximally flat half-band FIR filters

In this letter, a closed-form expression for the impulse response of the generalized half-band (HB) maximally flat (MF) FIR filters is obtained by solving the linear equations of the MF conditions. Based on the resultant impulse responses, an efficient implementation structure is derived. The dynamic range of the multipliers of the new structure is shown to be greatly reduced in comparison to the one of the direct form impulse response.

The theory and implementation of arbitrary-length linear-phase cosine-modulated filter bank

In this paper, we propose an arbitrary-length linear-phase cosine-modulated filter bank (CMFB). It can be considered as an extension of the existing linear-phase CMFBs to arbitrary length. It is shown that the 2 M-channel arbitrary-length linear-phase CMFB needs to satisfy the same conditions as the conventional M-channel arbitrary-length CMFB does for perfect reconstruction. By using the linear-phase property of a prototype filter, we obtain an efficient implementation structure in which 2×2 lossless lattices are used instead of 2×1 ones in the traditional implementation of the existing linear-phase CMFBs. The total number of the lattices is reduced by half.