Roundoff noise minimization in a modified direct-form delta operator IIR structure

Among various direct-form delta operator realized filter structures, the delta transposed direct-form II (δDFIIt) has been shown to produce the lowest roundoff noise gain in finite wordlength implementations. Recent analyses focus on the optimization of the free parameter Δ of the delta operator, with scaling of the structure to prevent arithmetic overflow. This paper proposes a modified δDFIIt second-order section in which the Δs and filter coefficients at different branches are separately scaled to achieve improved roundoff noise gain minimization. Expressions for the filter coefficients are derived, and reduction of roundoff noise gain is verified by numerical examples.published_or_final_versio

An efficient algorithm for downconverting multiple bandpass signals using bandpass sampling

Bandpass sampling is a useful alternative for direct digital downconversion in software radio. It significantly relaxes the analog-to-digital converter (ADC) sampling rate requirement and facilitates the design goal of moving the ADC as close as possible to the antenna. This paper presents a modified interpretation to the graph of allowable sampling frequencies in uniform bandpass sampling. It is shown that the position and guard bands of a downconverted bandpass signal band are highly related to the order of the valid sampling range, called wedge order. An efficient algorithm is then proposed, which significantly reduces the computational load in determining the valid sampling frequencies to downconvert multiple distinct bandpass signals. Conditions for the placement of bandpass signals to utilize a given sampled bandwidth are also discussed.published_or_final_versio

DC stability analysis of high-order, lowpass ΣΔ modulators with distinct unit circle NTF zeros

This paper presents an analytical approach to the investigation of the dc stability of high-order (order > 2), low-pass (LP) ΣΔ modulators with distinct noise transfer function (NTF) zeros on the unit circle. The techniques of state-space diagonalization and decomposition, continuous-time embedding and Poincaré map analysis are combined and extended. It is revealed that high-order ΣΔ modulators can be transformed and decomposed into second- and first-order subsystems. The investigation, coupled with efficient numerical methods, generalizes itself to different types of transition flow and provides theoretical insight into the state trajectory and limit cycle behavior. It is shown that estimation of dc input bounds based solely on the boundary transition flow is inadequate. A procedure utilizing the information from different transition flow assumptions and the discrete nature of a modulator is introduced for locating the stable dc input bounds of practical, discrete-time ΣΔ modulators.published_or_final_versio

A generalized direct-form delta operator-based IIR filter with minimum noise gain and sensitivity

This brief presents the derivation of an arbitrary order delta operator-based direct-form IIR filter with minimum roundoff noise gain and sensitivity. It utilizes the concept of different coupling coefficients at different branch nodes for better noise gain suppression. Two possible structures for realizing the inverse delta operator are considered and procedures for calculating the optimal filter coefficients are given. By means of state-space representation and matrix manipulation, it is also shown that expressions for sensitivity measures of different filter coefficients and their corresponding roundoff noise gain expressions are the same. This enables the simultaneous minimization of sensitivity and noise power for the proposed generalized filter structure.published_or_final_versio

Fast detection of instability in sigma-delta modulators based on unstable embedded limit cycles

As a sequel to a previous study (Wong and Ng) on the nonlinear dynamical behavior of low-pass, high-order (order > 2), single-bit ΣΔ modulators with distinct unit-circle noise transfer function zeros, this paper proposes a novel scheme for the fast detection of unstable operation in these modulators under general time-varying input. The scheme is based on the variation of unstable embedded limit-cycle fixed points (which form the bounds beyond which the modulator becomes unstable) versus modulator input amplitude. Deployment of the detection scheme requires simple analog components with possible simplification. The effectiveness of the scheme is demonstrated with numerical examples. © 2004 IEEE.published_or_final_versio

Improved roundoff noise performance in a direct-form IIR filter using a modified delta operator

Among various direct-form delta operator filters, the delta direct-form II transposed (δDFIIt) has been shown to produce the lowest roundoff noise in finite-word-length implementations. Recent analyses focus on the optimization of the free parameter Δ of the delta operator, with scaling of the structure to prevent arithmetic overflow. This paper proposes a modified δDFIIt second-order section in which the Δs at different branches are separately optimized to further suppress roundoff noise gain. Noise variance plots against pole locations are presented. Closed-form expressions for the optimal filter coefficients are derived and reduction of noise gain is confirmed by numerical examples.published_or_final_versio

Load forecasting by fuzzy neural network in Box-Jenkins models

In this paper, the use of FNN to identify appropriate Box-Jenkins models for the electricity load forecasting in Hong Kong is presented. FNN is found to be suitable to identify the Box-Jenkin model. By such model, we can forecast the load accurately.published_or_final_versio

Spectral reuse for pilot-aided MIMO-OFDM systems over broadcast time dispersive frequency selective fading channels

This paper combines the techniques of multiple-input multiple-output (MIMO) antennas and orthogonal frequency division multiplexing (OFDM) to deliver high-capacity high-data-rate wireless communications over broadcast time dispersive frequency selective fading channels. For broadcast channels, multiple communications can occur at the same frequency subcarrier and time slot from one base station (BS) to many mobile stations (MS). To realize this, we develop a so-called orthogonal space division multiplexing (OSDM) scheme to decompose per-subcarrier channel into many uncoupled single-user spatial modes. In particular, the scheme is modified to improve its robustness to the channel mismatches arising from pilot-aided channel estimation and Doppler spread. Simulation results reveal that following the ESTI HiperLAN II parameters, our proposed scheme can achieve good performance with four simultaneous downlink users at Doppler spread of 40 Hz, which corresponds to mobile moving at speed of 8.5 km/h communicating at 5 GHz. ©2004 IEEE.published_or_final_versio

Investigating the diversity performance of multiuser spatially correlated MIMO broadcast fading channels

This paper's aim is to investigate the diversity performance of spatially correlated multiple-input multiple-output (MIMO) broadcast channels where multiple communications occur simultaneously in the same frequency band and time slot from the base station (BS) to many mobile stations (MS). To deal with a broadcast system, we employ a previously developed orthogonal space division multiplexing (OSDM) method to decompose the channel into many uncoupled single-user systems so that the diversity can be readily characterized by the second-order statistics of the resultant channel coefficients. Simulation results reveal that good performance can still be achieved with correlation as high as 0.4. Most intriguingly, unlike single-user MIMO channels, the diversity is more sensitive to the spatial correlation on the transmitter than receiver sides.published_or_final_versio

Long non-coding RNA deregulation in tongue squamous cell carcinoma

Background. The deregulated tumorigenic long non-coding RNA (lncRNA) has been reported in several malignancies. However, there is still no comprehensive study on tongue squamous cell carcinoma (SCC). Methods. Functional reannotation for the human lncRNA was carried out by ncFANs. Real-time quantitative PCR was used to validate the identified lncRNAs. Results. Using the functional annotation algorithm from ncFANs, 8 differentially expressed lncRNAs were identified. Lnc-PPP2R4-5, lnc-SPRR2D-1, lnc-MAN1A2-1, lnc-FAM46A-1, lnc-MBL2-4:1, and lnc-MBL2-4:3 were upregulated in the microdissected tongue SCC tissues. In comparison, lnc-AL355149.1-1 and lnc-STXBP5-1 showed significant downregulation. High level of lnc-MBL2-4:3 was significantly associated with the node positive tongue SCC patients. Further, patients with advanced T-stage demonstrated a further reduction of lnc-AL355149.1-1 in the tumor tissues. Treatment of tongue SCC cells with 5-fluorouracil and paclitaxel can reserve the expression patterns observed in the tongue SCC tissues. Further, changes of lnc-MBL2-4:3 and lnc-AL355149.1-1 expression levels were noticed in the cisplatin-resistant tongue SCC cells. Conclusions. Our results demonstrated that functional reannotation allows us to identify novel lncRNAs using the existing gene expression array dataset. The association of lncRNA with the T-stage and nodal status of tongue SCC patients suggested that lncRNA deregulation was involved in the pathogenesis of tongue SCC.published_or_final_versio