Sumit Jagdish Darak

Low-Complexity Reconfigurable Fast Filter Bank for Multi-Standard Wireless Receivers

This brief presents a new low-complexity reconfigurable fast filter bank (RFFB) for wireless communication applications such as spectrum sensing and channelization. In RFFB, the bandwidth and center frequency of sub-bands can be varied with high frequency resolution without hardware reimplementation. This is achieved with an improved modified frequency transformation-based variable digital filter (MFT-VDF) at the first stage of the proposed multistage implementation. Existing second-order frequency transformation-based low-pass VDFs have limited cutoff frequency range which is approximately 12.5% of the sampling frequency. The proposed low-pass MFT-VDF offers unabridged control over the cutoff frequency on a wide frequency range thereby, improving the cutoff frequency range of existing VDFs. The design example shows that the RFFB is easy to design and offers substantial savings in gate counts over other filter banks.

Efficient Implementation of Reconfigurable Warped Digital Filters With Variable Low-Pass, High-Pass, Bandpass, and Bandstop Responses

In this brief, an efficient implementation of reconfigurable warped digital filter with variable low-pass, high-pass, bandpass, and bandstop responses is presented. The warped filters, obtained by replacing each unit delay of a digital filter with an all-pass filter, are widely used for various audio processing applications. However, warped filters require first-order all-pass transformation to obtain variable low-pass or high-pass responses, and second-order all-pass transformation to obtain variable bandpass or bandstop responses. To overcome this drawback, the proposed method combines the warped filters with the coefficient decimation technique. The proposed architecture provides variable low-pass or high-pass responses with fine control over cut-off frequency and variable bandwidth bandpass or bandstop responses at an arbitrary center frequency without updating the filter coefficients or filter structure. The design example shows that the proposed variable digital filter is simple to design and offers substantial savings in gate counts and power consumption over other approaches.

A reconfigurable filter bank for uniform and non-uniform channelization in multi-standard wireless communication receivers

In a typical multi-standard wireless communication receiver, the channelizer extracts multiple radio channels of distinct bandwidths from a digitized wideband input signal. The complexity of the digital front end of the receiver is dominated by the complexity of the channelizer which operates at the highest sampling rate in the system. Computationally efficient architecture is essential for cost-effective implementation of the channelizer. Reconfigurability is another key requirement in the channelizer to support different communication standards. In this paper, we propose a low complexity reconfigurable filter bank (FB) channelizer based on coefficient decimation, interpolation and frequency masking techniques. Design example shows that the proposed FB offers complexity reduction of 54.8% over modulated perfect reconstruction FB and 10.5% over discrete Fourier transform FB. Furthermore, the proposed FB has an added advantage of dynamic reconfigurability over these FBs.

A Low Complexity Reconfigurable Non-uniform Filter Bank for Channelization in Multi-standard Wireless Communication Receivers

In a typical multi-standard wireless communication receiver, the channelizer must have the capability of extracting multiple channels (frequency bands) of distinct bandwidths corresponding to different communication standards. The channelizer operates at the highest sampling rate in the digital front end of receiver and hence power efficient low complex architecture is required for cost-effective implementation of channelizer. Reconfigurability is another key requirement in the channelizer to support different communication standards. In this paper, we propose a low complexity reconfigurable filter bank (FB) channelizer based on coefficient decimation, interpolation and frequency masking techniques. The proposed FB architecture is capable of extracting channels of distinct (non-uniform) bandwidths from the wideband input signal. Design example shows that the proposed FB offers multiplier complexity reduction of 83% over Per-Channel (PC) approach and 60% over Modulated Perfect Reconstruction FB. The proposed FB when designed as a uniform FB (subbands of equal bandwidths), offers a complexity reduction of 20% over Discrete Fourier Transform FB (DFTFB) and 57% over Goertzel Filter Bank. Furthermore, the proposed FB has an added advantage of dynamic reconfigurability over these FBs. The proposed FB is implemented on Xilinx Virtex 2v3000ff1152-4 FPGA with 16 bit precision. The PC approach and DFTFB are also implemented on the same FPGA with 14 bit precision. The implementation results shows an average slice reduction of 29.14% and power reduction of 46.84% over PC approach, 14.39% and 2.67% over DFTFB.

Low complexity and efficient dynamic spectrum learning and tunable bandwidth access for heterogeneous decentralized cognitive radio networks

This paper deals with the design of the low complexity and efficient dynamic spectrum learning and access (DSLA) scheme for next-generation heterogeneous decentralized Cognitive Radio Networks (CRNs) such as Long Term Evolution-Advanced and 5G. Existing DSLA schemes for decentralized CRNs are focused predominantly on the decision making policies which perform the task of orthogonalization of secondary users to optimum vacant subbands of fixed bandwidth. The focus of this paper is the design of DSLA scheme for decentralized CRNs to support the tunable vacant bandwidth requirements of the secondary users while minimizing the computationally intensive subband switchings. We first propose a new low complexity VDF which is designed by modifying second order frequency transformation and subsequently combining it with the interpolation technique. It is referred to as Interpolation and Modified Frequency Transformation based VDF (IMFT-VDF) and it provides tunable bandpass responses anywhere over Nyquist band with complete control over the bandwidth as well as the center frequency. Second, we propose a tunable decision making policy, ? t _ rand , consisting of learning and access unit, and is designed to take full advantage of exclusive frequency response control offered by IMFT-VDF. The simulation results verify the superiority of the proposed DSLA scheme over the existing DSLA schemes while complexity comparisons indicate total gate count savings from 11% to as high as 87% over various existing schemes. Also, lower number of subband switchings make the proposed scheme power-efficient and suitable for battery-operated cognitive radio terminals. Low complexity variable bandpass filter (VDF) design.Tunable dynamic spectrum learning and access (DSLA) policy for heterogeneous cognitive radio networks (CRNs).System level approach to integrate VDF with the DSLA policy to support tunable bandwidth access in heterogeneous CRNs.Higher spectrum efficiency and lower subband switching cost.

Linear-Phase VDF Design With Unabridged Bandwidth Control Over the Nyquist Band

This brief presents a low-complexity linear-phase variable digital filter (VDF) design with tunable lowpass (LP), highpass (HP), bandpass (BP), and bandstop (BS) responses anywhere over the entire Nyquist band. The spectral-parameter-approximation-based VDFs (SPA-VDFs) was designed using the Farrow structure and has advantages of linear phase, lower group delay, and fewer variable multipliers. However, the total gate count and the dynamic range of filter coefficient values of SPA-VDFs significantly increase with the tunable range of cutoff frequency, which limits their usefulness in emerging signal processing and wireless communication applications. In addition, existing VDFs need to update either filter coefficients or need parallel filter structures to obtain variable LP, HP, BP and BS responses. In this brief, a new VDF design is proposed by deftly integrating SPA-VDF with the modified coefficient decimation method (MCDM), and it will be referred to as SPA-MCDM-VDF. The SPA-MCDM-VDF provides LP, HP, BP, and BS responses with unabridged center frequency and bandwidth control over the entire Nyquist band without the need for hardware reimplementation or coefficient update. The complexity comparisons show that the SPA-MCDM-VDF offers substantial savings in gate count, group delay, and number of variable multiplications over other linear-phase VDFs.

Design of variable linear phase FIR filters based on second order frequency transformations and coefficient decimation

This paper presents the design of a variable linear phase finite impulse response filter based on second order frequency transformations and coefficient decimation. The design of variable digital filters (VDFs) using first and second order frequency transformations have been proposed in literature. The VDF using second order transformation has better cut-off slope characteristics compared to the VDF using first order transformation. However, the former has the drawback of limited range (approximately 25% of the half of the sampling frequency) over which the cut-off frequency, fc, can be varied. It also fails to provide variable lowpass, highpass, bandpass or bandstop responses from a fixed-coefficient lowpass filter using the same architecture. The architecture proposed here overcomes the above mentioned disadvantages using coefficient decimation technique. The design example shows that the range over which fc can be varied is 2.65 times wider in the proposed VDF than the VDF in [7] and for a given frequency range, the proposed VDF offers a total gate count saving of 33% and 41% over the VDF in [11] and [7] respectively. Also, the proposed architecture provides variable lowpass, highpass, bandpass or bandstop responses from a fixed coefficient lowpass filter.

An efficient policy for D2D communications and energy harvesting in cognitive radios: Go Bayesian!

Recently, there has been a surge of interests in paradigms such as device-to-device (D2D) communications and radio frequency energy harvesting (RFEH) to improve the spectrum as well as energy efficiencies of next-generation decentralized cognitive radio networks. However, little attention has been paid to the dual but competing task of subband selection of any desired bandwidth in D2D mode (i.e., opportunistic vacant spectrum access) and RFEH mode as well as need to minimize the subband switching cost (SSC) for an efficient implementation. Taking these factors into account, a new D2D-RFEH policy is proposed. It consists of: 1)Bayesian approach based Tunable Thompson Sampling (TTS) algorithm to learn subband statistics, 2) Subband access scheme employing TTS algorithm for minimizing collisions among the secondary users, and 3) Mode selection scheme. The simulation results, complexity and SSC analysis validate the superiority of the proposed policy over the policies employing frequentist approach based learning algorithms.

Reconfigurable Filter Bank With Complete Control Over Subband Bandwidths for Multistandard Wireless Communication Receivers

This paper presents a design of linear-phase, low-complexity, reconfigurable digital filter bank that offers independent and complete control over the bandwidth as well as the center frequency of all subbands. The proposed filter bank is designed by integrating spectral parameter approximation (SPA) technique with the modified coefficient decimation method (MCDM), referred to as SPA-MCDM-FB. The architectural details, design examples and complexity comparisons show that the SPA-MCDM-FB is easy to design and offers substantial savings in gate count, number of variable multipliers and group delay over other filter banks. Moreover, these savings increase further with the increase in the filter-bank resolution (i.e., number of subbands). The SPA-MCDM-FB is then combined with the upper confidence bound (UCB)-based decision-making algorithm to search the vacant band(s) of any desired bandwidth for spectrum-sensing application in cognitive radio (CR). The simulations results verify that the proposed scheme offers superior performance [i.e., improved utilization of vacant subband(s)] and needs fewer gate counts compared to uniform filter bank and UCB-algorithm-based schemes. Furthermore, the functionality and advantages of the SPA-MCDM-FB are also verified for the channelization operation in CR supporting multiple communication standards.

A new variable digital filter design based on fractional delay

This paper presents a new method for the design of finite impulse response (FIR) filter that provides variable frequency responses. The proposed idea is to replace each unit delay operator in a fixed-coefficient FIR filter with the 2nd order FIR fractional delay (FD) structure and the cutoff frequency, ƒc of the filter is changed by changing the FD value. The change in FD results in change in amplitude and length of an impulse response. This in turn changes ƒc and transition bandwidth (TBW) of an FIR filter. The mathematical relation between cut-off frequency, TBW and FD value D is derived. The design example shows that the proposed method provides very fine control over ƒc.