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

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

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

Differential expression of long noncoding RNA in primary and recurrent nasopharyngeal carcinoma

Background. Recent studies suggested that non-protein-coding genes are implicated in the tumorigenic process of nasopharyngeal carcinoma (NPC). In the present study, we aimed to identify the differentially expressed long noncoding RNA (lncRNA) using data available in the public domain. Methods. Microarray data set GSE12452 was reannotated with ncFANs. Real-time quantitative PCR was used to quantify and validate the identified lncRNAs in NPC. Results. In primary NPC, upregulation of lnc-C22orf32-1, lnc-AL355149.1-1, and lnc-ZNF674-1 was observed. High levels of lnc-C22orf32-1 and lnc-AL355149.1-1 were significantly associated with the male patients. In addition, increased expression of lnc-C22orf32-1 and lnc-ZNF674-1 was associated with advanced tumor stages. Recurrent NPC displayed a distinctive lncRNA expression pattern. lnc-BCL2L11-3 was significantly increased in the recurrent NPC tissues. In addition, significant reduction of lnc-AL355149.1-1 and lnc-ZNF674-1 was observed in the recurrent NPC tissues. Conclusions. Our results demonstrated that it is feasible to identify the differentially expressed lncRNA in the microarray dataset by functional reannotation. The association of lncRNA with gender and tumor size implicated that lncRNA possibly plays a part in the pathogenesis of primary NPC. Further, the distinctive lncRNA identified in the recurrent NPC may reveal a distinctive development mechanism underlying tumor recurrence. © 2014 Wei Gao et al.published_or_final_versio

Optimal multi-user MISO solution with application to multi-user orthogonal space division multiplexing

In this paper, we shall show that for a nT-element base station (BS) communicating with M(≤ nT) single-element mobile stations (MS) (or multi-user MISO) orthogonally in the spatial domain, the optimization problem is equivalent to the least squares (LS) problem for an underdetermined linear system. We then prove that the optimal BS antenna weights can be expressed as the pseudo-inverse of the multi-user channel matrix. This solution decomposes the multi-user system into many single-user systems with maximal resultant channel responses. The average of the squared channel response (defined as channel gain) and the inverse of the normalized variance of the squared channel response (defined as diversity order) are derived for performance analysis. It is found that every individual user of the resulting system behaves like a single-user system with nT-M+1 reception diversity. Finally, by applying the solution on a multi-user MIMO antenna system (i.e., with multiple antennas at the MS as well), an iterative approach is proposed to perform multi-user orthogonal space division multiplexing (OSDM) in the downlink.published_or_final_versio