Design and implementation of multiplier-less tunable 2-D FIR filters using McClellan transformation

This paper proposes new structures for realizing tunable 2-D fan and elliptical filters with different spectral characteristics using McClellan transformation. The 1-D prototype is a variable digital filter obtained from the interpolation of a set of desirable impulse responses and is implemented using the Farrow structure. The coefficients of the sub-filters and the transformation parameters in the Farrow structure are represented in SOPOT, which can be easily implemented as simple shift-and-add operations. Furthermore, the transformation part can be shared between the sub-filters leading to significant saving in hardware complexity. Several design examples are given to demonstrate the effectiveness and feasibility of the proposed approach.published_or_final_versio

The design and multiplier-less realization of software radio receivers with reduced system delay

This paper studies the design and multiplier-less realization of a new software radio receiver (SRR) with reduced system delay. It employs low-delay finite-impulse response (FIR) and digital allpass filters to effectively reduce the system delay of the multistage decimators in SRRs. The optimal least-square and minimax designs of these low-delay FIR and allpass-based filters are formulated as a semidefinite programming (SDP) problem, which allows zero magnitude constraint at ω = π to be incorporated readily as additional linear matrix inequalities (LMIs). By implementing the sampling rate converter (SRC) using a variable digital filter (VDF) immediately after the integer decimators, the needs for an expensive programmable FIR filter in the traditional SRR is avoided. A new method for the optimal minimax design of this VDF-based SRC using SDP is also proposed and compared with traditional weight least squares method. Other implementation issues including the multiplier-less and digital signal processor (DSP) realizations of the SRR and the generation of the clock signal in the SRC are also studied. Design results show that the system delay and implementation complexities (especially in terms of high-speed variable multipliers) of the proposed architecture are considerably reduced as compared with conventional approaches. © 2004 IEEE.published_or_final_versio

On the design and multiplier-less realization of digital IF for software radio receivers with prescribed output accuracy

This paper studies the design and multiplier-less realization of the digital IF in software radio receivers. The new architecture consists of a compensator for compensating the passband droop of the conventional cascaded integrator and comb (CIC) filter. The passband droop is improved by a factor of four and it can be implemented with four additions using the sum-of-powers-of-two (SOPOT) coefficients. The decimation factor of the multistage decimator is also reduced so that its output can be fed directly to the Farrow structure for sample rate conversion (SRC), eliminating the need for another L-band filter for upsampling. By so doing, the programmable FIR filter can be replaced by a half-band filter placed immediately after the Farrow structure. As the coefficients of this half-band filter, the multistage decimators and the subfilters in the Farrow structure are constants, they can be implemented without multiplication using SOPOT coefficients. As a result, apart from the limited number of multipliers required in the Farrow structure, the entire digital IF can be implemented without any multiplications. A random search algorithm is employed to minimize the hardware complexities of the proposed IF subject to a given specification in the frequency domain and prescribed output accuracy, taking into account signal overflow and round-off noise. Design results are given to demonstrate the effectiveness of the proposed method.published_or_final_versio

On the design and multiplierless realization of perfect reconstruction triplet-based FIR filter banks and wavelet bases

This paper proposes new methods for the efficient design and realization of perfect reconstruction (PR) two-channel finite-impulse response (FIR) triplet filter banks (FBs) and wavelet bases. It extends the linear-phase FIR triplet FBs of Ansari et al. to include FIR triplet FBs with lower system delay and a prescribed order of K regularity. The design problem using either the minimax error or least-squares criteria is formulated as a semidefinite programming problem, which is a very flexible framework to incorporate linear and convex quadratic constraints. The K regularity conditions are also expressed as a set of linear equality constraints in the variables to be optimized and they are structurally imposed into the design problem by eliminating the redundant variables. The design method is applicable to linear-phase as well as low-delay triplet FBs. Design examples are given to demonstrate the effectiveness of the proposed method. Furthermore, it was found that the analysis and synthesis filters of the triplet FB have a more symmetric frequency responses. This property is exploited to construct a class of PR M-channel uniform FBs and wavelets with M = 2 L, where L is a positive integer, using a particular tree structure. The filter lengths of the two-channel FBs down the tree are approximately reduced by a factor of two at each level or stage, while the transition bandwidths are successively increased by the same factor. Because of the downsampling operations, the frequency responses of the final analysis filters closely resemble those in a uniform FB with identical transition bandwidth. This triplet-based uniform M-channel FB has very low design complexity and the PR condition and K regularity conditions are structurally imposed. Furthermore, it has considerably lower arithmetic complexity and system delay than conventional tree structure using identical FB at all levels. The multiplierless realization of these FBs using sum-of-power-of-two (SOPOT) coefficients and multiplier block is also studied. © 2004 IEEE.published_or_final_versio

Design of FIR digital filters with prescribed flatness and peak error constraints using second-order cone programming

This paper studies the design of digital finite impulse response (FIR) filters with prescribed flatness and peak design error constraints using second-order cone programming (SOCP). SOCP is a powerful convex optimization method, where linear and convex quadratic inequality constraints can readily be incorporated. It is utilized in this study for the optimal minimax and least squares design of linear-phase and low-delay (LD) FIR filters with prescribed magnitude flatness and peak design error. The proposed approach offers more flexibility than traditional maximally-flat approach for the tradeoff between the approximation error and the degree of design freedom. Using these results, new LD specialized filters such as digital differentiators, Hilbert Transformers, Mth band filters and variable digital filters with prescribed magnitude flatness constraints can also be derived. © 2005 IEEE.published_or_final_versio

Bandwidth-guaranteed multicast in multi-channel multi-interface wireless mesh networks

Proceedings of the IEEE International Conference on Communications, 2009, p. 1-5We consider multi-channel multi-interface wireless mesh networks with a schedule-based MAC protocol, where conflict-free transmission is ensured by requiring links assigned with the same channel and within the mutual interference range of each other to be active at different time slots. When a (point-to-multipoint) multicast call arrives, the call is accepted if a multicast distribution tree can be established for connecting the source node with all the receiving nodes, and with sufficient bandwidth reserved on each link. Otherwise, the call is rejected. To maximize the call acceptance rate, the multicast tree must be constructed judiciously upon each call arrival. Aiming at minimizing the carried load on the most-heavily loaded channel, and maximizing the residual capacity of the most heavily loaded node, an integer linear program (ILP) is formulated for multicast tree construction. Since solving ILP can be time-consuming, an efficient heuristic algorithm is then proposed. We compare the two tree construction algorithms by simulations. We found that both algorithms give comparable call acceptance rate, but the heuristic algorithm requires much shorter running time. ©2009 IEEE.published_or_final_versio

The development, fabrication, and material characterization of polypropylene composites reinforced with carbon nanofiber and hydroxyapatite nanorod hybrid fillers

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Cellular mechanisms involved in intermittent hypoxia-induced heart damage in rat

Poster PresentationBACKGROUND: Obstructive sleep apnoea (OSA), characterised by intermittent hypoxia (IH) during sleep, is increasingly recognised as an independent risk factor of cardiovascular diseases (CVD). OSA has been reported to be associated with changes in the levels of circulating oxidative stress and inflammatory markers as well as dyslipidemia, supporting their mediating roles in cardiovascular pathogenesis. This study aimed to investigate the ...published_or_final_versionThe 17th Medical Research Conference, Department of Medicine, The University of Hong Kong, Hong Kong, 14 January 2012. In Hong Kong Medical Journal, 2012, v. 18 n. 1, suppl. 1, p. 23, abstract no. 2

Suppression of inflammation during adipogenic differentiation in human preadipocytes

INTRODUCTION: Preadipocytes are present in adipose tissues throughout adult life that can differentiate into mature adipocytes in response to environmental factors. However, little is known about the secretory inflammation-associated cytokines / chemokines during adipogenic differentiation. METHODS: Human preadipocytes-subcutaneous (HPA-s) cells were cultured to 80% confluence. From preadipocytes to mature adipocytes, a total of six induction cycles …published_or_final_versio

Polypropylene biocomposites with boron nitride and nanohydroxyapatite reinforcements

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