Frequency Response Masking Research Articles

Design of Pipelined IIR Filters Using Two-Stage Frequency-Response Masking Technique

A pipelined, high-speed infinite impulse response (IIR) filter based on the frequency-response masking (FRM) technique has been proposed by Johansson and Wanhammar. In their method, the bandedge shaping filters are a pair of IIR power complementary filters whose ${z}$ -transform functions are functions of ${z} ^{M}$ and the masking filters are linear phase finite impulse response (FIR) filters. The IIR bandedge shaping filters have $M$ delays in the feedback loop and can be pipelined by ${M}$ stages. In this brief, we present a two-stage FRM method for reducing the number of multipliers of the pipelined IIR filter proposed by Johansson and Wanhammar for a given magnitude response specification and a given number of pipeline stages in the feedback loop. In our design, all the subfilters are optimized jointly. We show that our two-stage masking design requires fewer multipliers if the number of pipeline stages in the feedback loop is larger than four.

Optimal Design of Multiplier-Less Non-uniform Channel Filters with Successive Approximation of Vectors

Applications such as software-defined radio (SDR) receivers utilize channel filters to isolate the individual frequency bands of different communication standards present in a wideband input signal. Low complexity and sharp transition width are the two important design constraints of channel filters in SDR receivers. Frequency response masking (FRM) with the multiplier-less design is an effective approach for designing sharp filters with low complexity. This paper presents an optimal design for multiplier-less implementation of FRM-based non-uniform channel filters. In the proposed design, multiplier-less channel filters are realized basing upon decomposing their impulse response values in generalized bit planes. This decomposition is based on a vector successive approximation technique in which impulse responses are successively approximated using a dictionary of vectors. The resulting coefficients of channel filters belong to signed sums of powers of two form. The proposed channel filter designs are simulated using MATLAB R2017b, and the results have been compared with the existing ones in order to signify the effectiveness of the proposed design. The simulations show that the proposed channel filter design has low complexity (number of adders) and the design time is considerably low.

Modeling and Simulation of Frequency Response Masking FIR Filter Bank using Approximate Multiplier for Hearing Aid Application

The tremendous increase in the use of portable electronic devices is due to the development in the fields of signal processing and electronic technology. These battery operated devices needs reduction in power consumption with increased performance and long battery life. Since CMOS technology scaling fast approaches its physical limit of minimum supply voltage and smaller feature size, the hardware designer has to opt for new multiplier architectures for achieving low power and high speed performance. This paper proposes an area and power efficient approximate multiplier architecture. The error metrics are estimated to verify its performance advantage over other approximate multipliers. Using Frequency Response masking approach, a 6-band non-uniform digital FIR filter bank is developed using approximate multiplier for hearing aid application. Audiogram matching is done with audiograms of two different types of hearing losses and the matching error is computed. Simulation results show that the audiogram matching error falls within +/- 4 dB range.

The Design of Low-Power 16-Band Nonuniform Filter Bank for Hearing Aids.

A computationally efficient, low-power (107.6 μW@1.1V), small core area (2.82[Formula: see text]@0.35 μm), 16-band nonuniformly spaced digital filter bank with stop-band attenuation of more than 60dB is designed and implemented for hearing aid applications using a 0.35 μm CMOS process. The low computational complexity of the filter bank is achieved using a frequency response masking technique with multiple band-edge shaping filters. The proposed filter bank yields significant improvements in both power consumption and group delay. By coefficient sharing scheme, the implementation of such a filter bank requires only three multipliers.

Design of a Power-Efficient Low-Complexity Reconfigurable Non-maximally Decimated Filter Bank for High-Resolution Wideband Channels

In this paper, two reconfigurable architectures based on frequency-response masking (FRM) and non-maximally decimated filter bank system are proposed. The proposed methods are suitable for sharp wideband channelizers. The basic FRM structure consists of an interpolated modal filter and its masking filters. In both the proposed methods, the masking filters are synthesized by means of reconfigurable non-maximally decimated polyphase filter bank system. The second proposed method also exploits the LTI property of the FRM filter. The methods are beneficial when the number of bandwidths to be realized is large. The effective reduction in the multipliers and adders helps in reducing the hardware size. Both the methods are found to reduce the number of operations per second and hence the power consumption, when compared to the existing methods.

Removal of Baseline Wander Noise in ECG Signal Using Asymmetrical Frequency-Response Masking Bandpass Filters.

FIR filter is one of the best choices for ECG signal processing because of its linear phase property. With frequency response masking (FRM) technique, the multipliers needed to implement FIR filter can be reduced dramatically. This paper proposes an architecture for asymmetrical bandpass FIR filter based on the FRM technique. The optimum interpolation factor for the filter is derived and the design procedure for all the sub-filters is given. A design example is included to illustrate the effectiveness of the proposed filter for ECG signal processing. It shows that the filter can fulfill the design objectives with 70.3% less multipliers comparing to the conventional FIR synthesizing technique.

An Alternating Variable Technique for the Constrained Minimax Design of Frequency-Response-Masking Filters

The frequency-response-masking (FRM) technique is one of the most efficient approaches to the design of narrow transition band FIR filters. The constrained minimax design of linear-phase FRM FIR filters in the frequency domain is considered in this paper. The corresponding optimization problem is a nonconvex one. To deal with the nonconvex design problem and improve the FRM filter performance, we propose an algorithm to alternately optimize different subsets of the design variables by fixing the remaining ones. In this way, the nonconvex optimization problem is converted into a series of linear programming subproblems defined on different frequency bands, which are then solved alternately and iteratively. Moreover, the new algorithm converges to a better FRM filter than those obtained by several competitive methods and is flexible to incorporate linear constraints in the design. Several design examples are provided to demonstrate the advantages of the proposed algorithm.

Improved FRM-based maximally decimated filter bank with NTB for software radio channelizer

Software radio channelizer is employed in the multi-standard wireless communication for extracting individual channels from the wideband input signal. Frequency response masking (FRM) finite impulse response (FIR) filters are used in software radio channelizer for reducing the computational complexity of the maximally decimated filter bank (MDFB) with narrow transition band (NTB). In this paper, we present an approach to design two well-known classes of efficient digital filters, namely the interpolated and full FRM FIR filters. In the proposed MDFB, the FRM is used to obtain flexible transition band and low complexity. The proposed improved FRM-based MDFB with NTB can be directly applied to high sampling rate software radio channelizer. We show the FRM filter examples for single carrier orthogonal frequency division multiplexing (SC-OFDM) modulator and wideband digital receiver (WDR). The simulation results indicate that the improved FRM-based MDFB with NTB is correct. Design examples with complexity comparison are presented to demonstrate the complexity improvement of the proposed FRM-based MDFB with NTB.

Low complexity reconfigurable channelizers using non-uniform filter banks

A Software Defined Radio (SDR) channelizer needs reconfigurable sharp filter banks with low implementation complexity. In this paper, the design of non-uniform Modified Discrete Fourier Transform filter bank (MDFT FB) is proposed to be used in SDR channelizer. The frequency response masking technique is used to design the prototype filter which gives sharp filters with lower hardware complexity, compared to the finite impulse response filters. The canonic signed digit (CSD) representation is used in the design, to convert the continuous filter coefficients into discrete coefficients. Multi-objective artificial bee colony algorithm is utilized to improve the performance degradation when the CSD represented filter coefficients are used. Further, the shift inclusive differential technique with common sub-expression elimination is used to reduce the number of adders. Xilinx ISE is used to verify the hardware requirement, for the implementation of the non-uniform MDFT FB. Hence low complexity reconfigurable SDR channelizers using non-uniform MDFT FB is proposed in this paper.

Efficient uniform digital filter bank with linear phase and FRM technique for hearing aids

This paper attempts to present an uniform digital filter bank based on linear phase FIR and IIR filters applied for Frequency Response Masking (FRM) technique in hearing aid applications.In the proposed filter bank, nine uniformly spaced sub-bands are formed with the help of half band filters and masking filters. These nine channel FIR filter bank is realized using an interpolated half band linear phase FIR filter and an appropriate number of masking FIR filters. The nine channel IIR filter bank is realized using an interpolated half band approximately linear phase IIR filter and an appropriate number of masking filters. The proposed approximately linear phase IIR half band filter bank is compared with filter bank based on linear phase FIR half band filters in terms of area, power, memory and number of gates needed for implementation. The experiment was carried on various hearing loss cases and the results obtained from these tests proves that, the proposed filter bank achieved the required matching between audiograms and magnitude response of the filter bank at very reasonable range with less computational complexity.

Unified FRM‐based complex modulated filter bank structure with low complexity

Software defined radios typically employ digital filter banks (FBs) for channelisation. Frequency response masking (FRM) approach is used to reduce the computational complexity of the complex modulated FB with narrow transition band. A unified FRM-based complex modulated FB structure is proposed to design sharp filters with arbitrary passband bandwidth. The proposed unified FRM-based complex modulated FB structure with low complexity is suitable for different even-stacked or odd-stacked, maximally decimated or non-maximally decimated structures. It also can be directly applied to high sampling rate systems. It is shown that the proposed unified FRM-based complex modulated FB structure can obtain the improvement of the computational complexity compared with the other methods.

A Unified Approach to the Design of Interpolated and Frequency-Response-Masking FIR Filters

We present a unified approach to the design of two well-known classes of computationally efficient digital filters, namely the interpolated and frequency-response-masking (FRM) FIR filters, that are optimized in minimax sense. The highly nonconvex minimax designs of these filters are carried out by jointly optimizing the subfilters involved using a convex-concave procedure (CCP) that yields an iterative and converging process where each iteration involves a convex problem of minimizing a linear function subject to convex quadratic constraints. We present an analysis to explain why CCP is well-suited for the design problems at hand. We also show that the CCP-based design framework is flexible to allow extension to the design of FRM filters that simultaneously promotes sparsity of the filter coefficients to reduce implementation complexity. Design examples with comparisons are presented to demonstrate the performance of the proposed design methods.

Reconfigurable Farrow Structure-Based FRM Filters for Wireless Communication Systems

Recent trends in mobile technology are toward supporting multi-standard communication systems on the same device. This requires their design to be based on some kind of reconfigurable techniques. Also, in cognitive applications, intelligent bandwidth allocation for efficient spectrum utilization requires altering the bandwidth within the same communication channel. Digital filters with non-uniform and varying bandwidths can be used to channelize different frequencies. Efficient designs of such filters are proposed in this paper. Frequency response masking (FRM)-based design is used, where the masking filters can be tuned to a desired set of frequencies by using a variable bandwidth (VBW) digital filter, configured as Farrow structure. For each of the chosen bandwidth, a corresponding masking filter response can be obtained, using the Farrow structure. A novel extension of FRM is proposed in this paper, using two approaches, to realize more than one sharp filter response from the same prototype linear-phase low-pass filter. In both approaches, the masking filters of the FRM filter are realized using Farrow structure. In the first approach, only a set of two Farrow structure filters are required to realize all the required channels. The channel selection is then carried out by varying a single parameter on each of the two masking filters. In the second approach, every channel is realized using a set of two Farrow structure filters and the channel is selected by means of hardware switching techniques. In addition to reconfigurability, hardware implementation complexity of Farrow structure-based VBW is lower compared to the direct FIR filter structure when designed for large set of bandwidths.

On the Implementation of Time-Multiplexed Frequency-Response Masking Filters

The complexity of narrow transition band FIR filters is high and can be reduced by using frequency-response masking (FRM) techniques. These techniques use a combination of periodic model filters and, possibly periodic, masking filters. Time-multiplexing is in general beneficial since only rarely does the technology bound maximum obtainable clock frequency and the application determined required sample rate correspond. Therefore, architectures for time-multiplexed FRM filters that benefit from the inherent sparsity of the periodic filters are introduced in this paper. We show that FRM filters not only reduce the number of multipliers needed, but also have benefits in terms of memory usage. Despite the total amount of samples to be stored is larger for FRM, it results in fewer memory resources needed in FPGAs and more energy efficient memory schemes in ASICs. In total, the power consumption is significantly reduced compared with a single-stage implementation. Furthermore, we show that the choice of the interpolation factor that gives the least complexity for the periodic model filter and subsequent masking filter(s) is a function of the time-multiplexing factor, meaning that the minimum number of multipliers not always corresponds to the minimum number of multiplications. Both single-port and dual-port memories are considered, and the involved tradeoff in number of multipliers and memory complexity is illustrated. The results show that, for FPGA implementation, the power reduction ranges from 23% to 68% for the considered examples.

Design of FRM-based MDFT filter banks in the canonic signed digit space using modified meta-heuristic algorithms

An optimal totally multiplier-less sharp transition width Modified Discrete Fourier Transform (MDFT) filter bank is proposed in this work. Since, here, the aim is to design a low complexity sharp transition width MDFT filter bank, the filters of the filter bank are designed using Frequency Response Masking technique to reduce the number of multipliers and hence the complexity. To replace multipliers with adders and shifters, the filter coefficients are converted into the Canonic Signed Digit space. In order to reduce the number of adders and shifters in the multiplier-less implementation, restricted number of non-zero bits is used in the conversion. This may degrade the performances of the MDFT filter bank. The performances are improved using modified meta-heuristic algorithms. A new hybrid algorithm which combines the qualities of Harmony Search Algorithm and Gravitational Search Algorithm is proposed in this work to optimise the performance of the MDFT filter bank.

A Novel Approach to Design Low-Cost Two-Stage Frequency-Response Masking Filters

The multistage frequency-response masking (FRM) technique is widely used to reduce the complexity of a filter when the transition bandwidth is extremely small. In this brief, a real generalized two-stage FRM filter without any constraint on the subfilters or the interpolation factors was proposed. New principles and equations were deduced to determine the design parameters. The subfilters were then jointly optimized using nonlinear optimization. Experiential results show that when the proposed algorithm obtains different solutions with the conventional algorithm, the solution of the proposed approach is better with less number of filter coefficients and sometimes with lower delay as well than the conventional two-stage FRM, which can lead to a reduced hardware cost in applications.

A novel channelized FB architecture with narrow transition bandwidth based on CEM FRM

The two key requirements of channelized filter bank in the design of a digital receiver are low computational complexity and reconfigurability. Modulated discrete Fourier transform (MDFT) filter bank permits sub-channel with linear phase characteristics and provides high degree of computational efficiency. However, with sub-channel exhibiting narrow transition bandwidth in MDFT filter bank, the length of the prototype filter becomes long prohibitively, which can reduce the computational efficiency. It is well known that the frequency response masking (FRM) provides an attractive technique for the realization of digital filters with very narrow transition bandwidth. In this paper, the FRM digital filter design technique and another important technique named complex-exponential modulation (CEM) are exploited and applied to the design of a novel cascaded channelized filter bank to realize selective sub-channel with very narrow transition bandwidth. A simulation is provided to illustrate the design of the proposed CEM filter bank. It is shown that the resulting filter bank entails less computational complexity substantially and reduces multiplier resource consumption comparing to the conventional MDFT filter bank.

Design of multiplier-less sharp non-uniform cosine modulated filter banks for efficient channelizers in software defined radio

Forthcoming software defined radios require filter banks which satisfy stringent specifications efficiently with low implementation complexity. Cosine modulated filter banks (CMFB) have simple and efficient design procedure. The different wireless standards have different channel spacing or bandwidths and hence demand non-uniform decomposition of subbands. The non-uniform CMFB can be obtained from a uniform CMFB in a simple and efficient approach by merging the adjacent channels of the uniform CMFB. Very narrow transition width filters with low complexity can be achieved using frequency response masking (FRM) filter as prototype filter. The complexity is further reduced by the multiplier-less realization of filter banks in which the least number of signed power of two (SPT) terms is achieved by representing the filter coefficients using canonic signed digit (CSD) representation and then optimizing using suitable modified meta-heuristic algorithms. Hybrid meta-heuristic algorithms are used in this paper. A hybrid algorithm combines the qualities of two meta-heuristic algorithms and results in improved performances with low implementation complexity. Highly frequency selective filter banks characterized by small passband ripple, narrow transition width and high stopband attenuation with non-uniform decomposition of subbands can be designed with least the implementation complexity, using this approach. A digital channelizer can be designed for SDR implementations, using the proposed approach. In this paper, the non-uniform CMFB is designed for various existing wireless standards.

Combined FRM and GDFT filter bank designs for improved nonuniform DSA channelisation

AbstractMultistandard channelisation for base stations is a big application of generalised discrete Fourier transform modulated filter banks (GDFT‐FBs) in digital communications. For technologies such as software‐defined radio and cognitive radio, nonuniform channelisers must be used if frequency bands are shared by different standards. However, GDFT‐FB‐based nonuniform channelisers can suffer from high filter orders when applied to wideband input signals. In this paper, various combinations of GDFT‐FB with the frequency response masking technique are proposed and evaluated for both uniform and nonuniform channelisation applications. Results show that the proposed techniques achieve savings in both the number of filter coefficients and the number of operations per input sample. Copyright © 2015 John Wiley & Sons, Ltd.

Design of low complexity sharp MDFT filter banks with perfect reconstruction using hybrid harmony-gravitational search algorithm

The design of low complexity sharp transition width Modified Discrete Fourier Transform (MDFT) filter bank with perfect reconstruction (PR) is proposed in this work. The current trends in technology require high data rates and speedy processing along with reduced power consumption, implementation complexity and chip area. Filters with sharp transition width are required for various applications in wireless communication. Frequency response masking (FRM) technique is used to reduce the implementation complexity of sharp MDFT filter banks with PR. Further, to reduce the implementation complexity, the continuous coefficients of the filters in the MDFT filter banks are represented in discrete space using canonic signed digit (CSD). The multipliers in the filters are replaced by shifters and adders. The number of non-zero bits is reduced in the conversion process to minimize the number of adders and shifters required for the filter implementation. Hence the performances of the MDFT filter bank with PR may degrade. In this work, the performances of the MDFT filter banks with PR are improved using a hybrid Harmony-Gravitational search algorithm.