Search

We propose a semi-closed-form solution to the problem of computing the capacity and optimal signaling for a Gaussian MIMO channel under a joint sum power constraint (SPC) and per-antenna power constraint (PAPC). Existing efficient solutions to this fundamental problem are only applicable to some special cases: multiple-input single-output (MISO) systems, or full column rank MIMO channels with sufficiently high transmit power, or full-rank optimal signaling. For the general case, we present an efficient numerical method to solve the considered problem which does not make any assumptions on the rank of the channel matrix or the maximum transmit power. To achieve this, the considered problem is transformed into an equivalent minimax problem. We then exploit the special structure of the minimax problem to derive a closed-form solution based on a concave-convex procedure (CCP)-like algorithm. Extensive simulation results show that our proposed algorithm outperforms the existing solutions in terms of complexity and generality. [ABSTRACT FROM AUTHOR]

The development to date of the bounds for the outputs of the integrators of second-order sigma-delta modulators has relied on a mixture of theoretical analysis and extensive use of simulation. This paper presents a new approach that analyzes the behavior of such systems, and identifies the external boundaries of the trapping region for the outputs of the integrators. With this approach, it is possible to develop fight results for the standard second-order modulator with constant input, without the need for simulation. This approach is flexible, and can be adapted for other second-order architectures, and gives strong insight into the behavior of these systems. Index Terms - Chaos, nonlinear analysis, sigma-delta.

Universal HBV screening before immunosuppression is prudent and cost effective, even when local HBV prevalence is just 0.3%. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the fundamental problem of computing MIMO capacity under per-antenna power constraint (PAPC). Unlike the sum power constraint counterpart which likely admits water-filling-like solutions, MIMO capacity with PAPC has been largely studied under the framework of generic convex optimization. The two main shortcomings of these approaches are 1) their complexity scales quickly with the problem size, which is not appealing for large-scale antenna systems and/or 2) their convergence properties are sensitive to the problem data. As a starting point, we first consider a single user MIMO scenario and propose two provably-convergent iterative algorithms to find its capacity, the first method based on fixed-point iteration and the other based on alternating optimization and minimax duality. In particular, the two proposed methods can leverage the water-filling algorithm in each iteration and converge faster, compared with current methods. We then extend the proposed solutions to multiuser MIMO systems with dirty paper coding-based transmission strategies. In this regard, capacity regions of Gaussian broadcast channels with PAPC are also computed using closed-form expressions. Numerical results are provided to demonstrate the outperformance of the proposed solutions over existing approaches. [ABSTRACT FROM AUTHOR]

Summary: In this paper, a reconfigurable receiver front‐end for the frequency range of 800 MHz to 2.5 GHz is presented. The radio frequency front‐end is realized in wideband form with reconfigurable baseband filter. The proposed front‐end targets the GSM, WLAN, WCDMA, and GPS standards residing in the aimed frequency range. The necessary specifications for each individual standard have been revisited and recalculated. The interaction of the different standards and their interoperability has been thoroughly investigated and extra specifications derived for the multistandard receiver. The multistandard receiver has been designed, layouted, and simulated in RFCMOS 0.18‐μm process. [ABSTRACT FROM AUTHOR]

This paper proposes an efficient (semi-closed-form) zero-forcing (ZF) precoder design for the weighted sum-rate maximization problem under per-antenna power constraint (PAPC). Existing approaches for this problem are based on either interior-point methods that do not favorably scale with the problem size or subgradient methods that are widely known to converge slowly. To address these shortcomings, our proposed method is derived from three elements: minimax duality, alternating optimization (AO), and successive convex approximation (SCA). Specifically, the minimax duality is invoked to transform the considered problem into an equivalent minimax problem, for which we then recruit AO and SCA to find a saddle point, which enables us to take advantages of closed-form expressions and hence achieve fast convergence rate. Moreover, the complexity of the proposed method scales linearly with the number of users, compared to cubically for the standard interior-point methods. We provide an analytical proof for the convergence of the proposed method and numerical results to demonstrate its superior performance over existing approaches. Our proposed method offers a powerful tool to characterize the achievable rate region of ZF schemes under PAPC for massive multiple-input multiple-output. [ABSTRACT FROM PUBLISHER]

Abstract: In this letter, dual band negative group delay circuit (DBNGDC) utilizing a couple of one quarter guided wave length ( λ g 4) open circuited stubs (OCSs) is presented. The centre frequencies ( f 01,2) are fully controlled with the stub lengths. On the other hand, the target negative group delay (NGD) is obtained using couple of resistors ( R 1,2) that connect each OCS to the main microstrip line. The designed DBNGDC accomplishes 52% size diminution compared with smallest size has ever been achieved before. Moreover, 0.2 and 0.4 GHz zero‐NGD bandwidths (BW) are achieved. [ABSTRACT FROM AUTHOR]

Because of its lack of feedback process and the simplicity of its searching algorithm, conventional selected mapping (CSLM) is an efficient peak-to-average power ratio (PAPR) reduction technique in orthogonal frequency division multiplexing systems compared to the present techniques such as partial transmit sequence and active constellation extension. The requirement for large numbers of inverse fast Fourier transform (IFFT) blocks to provide desired PAPR reduction performance is introduced as the most significant drawback of the CSLM. This paper uses the special structure of an N-point radix-II IFFT in the CSLM and proposes a low complexity method to reduce the redundant calculations with almost the same PAPR reduction, bit-error rate, and power spectral density performances as those of the CSLM. The simulation results show that the computational complexity is reduced by at least 46.8% compared to that of the CSLM with approximately the same PAPR performance. [ABSTRACT FROM AUTHOR]

Modern wireless network operators are consistently looking for improvements in the wireless access infrastructure that minimize size, weight, and power. Therefore, compact multiband RF and wideband RF solutions offer an attractive role in forthcoming fifth generation networks. This paper presents a novel compact wideband RF transmitter architecture that is based upon an undersampled digital predistortion (DPD) methodology. The proposed architecture minimizes the required number of RF/analog components in the system by using RF-DAC-based direct RF sampling at the forward transmitter data path and one undersampled analog-to-digital conversion (ADC) with certain bandpass filters at the DPD sampling receiver path. Extensive experimental results validate that the DPD-enabled RF transmitter bandwidth can be significantly increased using the proposed multirate track-and-hold amplifiers architecture. Experimental tests achieved multiple GHz DPD bandwidths with satisfactory linearization performance via very compact sampling receiver that has one undersampled ADC. Particularly, we evaluated three application scenarios: 1) three-band carrier aggregated LTE signals (each one occupying 20-MHz instantaneous bandwidth), the linearization performance achieved 50-dBc adjacent channel power ratio (ACPR) with more than 1-GHz bandwidth using ADC running at 76.8 and 61.44 MSPS; 2) single-band LTE signal with continuous 100-MHz instantaneous bandwidth, the linearization performance achieved −48-dBc ACPR using 61.44-MSPS ADC; and 3) single-band LTE signal with continuous 20-MHz bandwidth at 4 GHz, the linearization performance achieved −54-dBc ACPR using 61.44-MSPS ADC. [ABSTRACT FROM PUBLISHER]

In this paper, a nonlinear autoregressive with exogenous inputs (NARX) digital pre-distortion scheme to linearize power amplifiers is proposed. The proposed NARX digital pre-distortion gives better accuracy and spectral leakage suppression compared with other commonly used Volterra-based techniques. The stability criterion of the NARX digital pre-distortion is derived from the frequency domain analysis. Simulation is carried out with a 20 MHz single carrier long-term evolution signal and two-carrier long-term evolution signal and instantaneous to average ratio of 6.2 dB at 0.01% complementary cumulative distribution function (CCDF). The results of simulation analysis show a slight improvement in adjacent channel leakage ratio performance with 30% reduction in the number of floating point operations compared with conventional pre-distortion techniques. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of existing and novel behavioral models targeted at the outphasing power amplifier (PA) architecture. A comprehensive comparison of ten modeling strategies is presented in the results. Novel techniques for outphasing PAs, such as vector switched and dual path time series, are also presented for the first time. Investigation of such techniques was driven by the analysis of outphasing operation at minimum output powers, demonstrating the generation of frequency-dependent amplitude and phase deviations, which can be difficult to characterize. The increased robustness was achieved at the cost of additional complexity; for practical implementation, time series coefficient reduction techniques were also evaluated. The results of all modeling approaches are experimentally validated for the wideband operation of an NXP 19-W GaN digital outphasing amplifier module. Considering computational complexity and accuracy for system-level modeling across all presented options, a subset of existing and new models is identified as best suited for modeling outphasing PAs. [ABSTRACT FROM PUBLISHER]

Multistandard 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. [ABSTRACT FROM AUTHOR]

We consider small-cell networks with multiple-antenna transceivers and base stations (BSs) cooperating to jointly design linear precoders to maximize the network energy efficiency, subject to a sum power and per-antenna power constraints at individual BSs, as well as user-specific quality of service (QoS) requirements. Assuming zero-forcing precoding, we formulate the problem of interest as a concave–convex fractional program to which we proposed a centralized optimal solution based on the prevailing Dinkelbach algorithm. To facilitate distributed implementations, we transform the design problem into an equivalent convex program using Charnes–Cooper’s transformation. Then, based on the framework of alternative direction method of multipliers (ADMM), we develop a decentralized algorithm, which is numerically shown to achieve fast convergence. Since BSs are generally power-hungry, it may be more energy-efficient if some BSs can be shut down, while still satisfying the QoS constraints. Toward this end, we investigate the problem of joint precoder design and BS selection, which is a mixed Boolean nonlinear program, and then provide an optimal solution by customizing the branch-and-bound method. For real-time applications, we propose a greedy algorithm which achieves near-optimal performance in polynomial time. Numerical results are provided to demonstrate the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

A joint power splitting and beamforming design for multiuser multiple-input single-output (MISO) systems where receivers have capability of decoding information and harvesting energy simultaneously from received signals is considered. The objective is to maximize the ratio of the achieved utility to the total power consumption subject to harvested power requirements and power budget at a base station (BS). The utility function of interest combines the sum rate and the total harvested power. The design problem is nonconvex, and thus, global optimality is difficult to achieve. To solve this problem locally we first convert the problem into a more tractable form, and then propose an iterative algorithm which is guaranteed to achieve a Karush–Kuhn–Tucker solution. Numerical results are provided to demonstrate the superior performance of the proposed method. [ABSTRACT FROM PUBLISHER]

This letter presents the implementation of RF MEMS-based phase shifter with high power handling capabilities (measured IP3 >63 dBm), high phase, and amplitude linearity (measured rms deviation <±1.56° and ±0.16 dB) for cellular applications. Two phase shifter circuits are designed and tested with steps of ±3° and ±17.5° at 900 MHz to efficiently perform an electronic beam tilt for an eight-element array with more than 0.9° accuracy and up to 10° tilt can be obtained. The measured insertion and return loss for the largest phase state are 1.3 and 13 dB, respectively. For experimental validation, a 3 $\times $ 2 array of angled dipole patch antennas is designed and fabricated and four different scans are successfully measured showing a maximum deviation of ±0.6° only for the scan angle. [ABSTRACT FROM PUBLISHER]

This brief describes and analyzes a technique of increasing a sampling rate in a sigma–delta $(\Sigma\Delta)$ modulator based on a discrete-time description, which is an extension of existing techniques of parallelization. The limitations in the signal-to-noise ratio and the maximum increase of the sampling rate in a digital system are explained, and a structure of a low-pass $\Sigma\Delta$ modulator characterized by a short critical path is used in this brief to validate the technique. An implementation of a modulator shows the increase in the sampling rate from 100 to 400 MHz. [ABSTRACT FROM AUTHOR]

In the last decade, mobile phones and mobile devices using mobile cellular telecommunication network connections have become ubiquitous. In several developed countries, the penetration of such devices has surpassed 100 percent. They facilitate communication and access to large quantities of data without the requirement of a fixed location or connection. Assuming mobile phones usually are in close proximity with the user, their cellular activities and locations are indicative of the user's activities and movements. As such, those cellular devices may be considered as a large scale distributed human activity sensing platform. This paper uses mobile operator telephony data to visualize the regional flows of people across the Republic of Ireland. In addition, the use of modified Markov chains for the ranking of significant regions of interest to mobile subscribers is investigated. Methodology is then presented which demonstrates how the ranking of significant regions of interest may be used to estimate national population, results of which are found to have strong correlation with census data. [ABSTRACT FROM PUBLISHER]

This paper presents a study of linearity in wideband CMOS low noise amplifiers (LNA) and its relationship to power consumption in context of Long Term Evolution (LTE) systems and its future developments. Using proposed figure of merit (FoM) to compare 35 state-of-the-art LNA circuits published over the last decade, the paper explores a dependence between amplifier performance (i.e., combined linearity, noise figure, and gain) and power consumption. In order to satisfy stringent linearity specifications for LTE standard (and its likely successors), the paper predicts that LNA FoM increase in the range of +0.2 dB/mW is expected and will inevitably translate into a significant increase in power consumption--a critical budget planning aspect for handheld devices, active antenna arrays, and base stations operating in small cells. [ABSTRACT FROM AUTHOR]

Despite a number of campaigns conducted in Ireland to increase awareness about appropriate waste management, waste enforcement is still a significant issue. Decisions such as the privatisation of waste collection services and the introduction of new waste charges have contributed to some of the classic waste enforcement issues, like illegal dumping. In addition, the current economic recession affects the resources that local authorities have available to implement enforcement actions. In order to analyse the current situation of waste enforcement in Ireland, a survey was carried out amongst the 34 environmental departments within the Irish local authorities. This paper presents the survey findings. From the results, the principal current waste enforcement issues are extracted and compared with previous studies in the field. In addition, an analysis of the resources employed with regard to technology, personnel, legal prosecutions and best practices is also performed. The technologies and practices used are evaluated for efficiency at reducing the main illegal actions, such as illegal dumping, and compared to international best practices. Finally, the actions carried out by the local authorities in terms of public awareness and environmental education are reviewed. [ABSTRACT FROM PUBLISHER]

A \Sigma\Delta-driven RF switch-mode power amplifier is inherently linear only when it has a two-level output. At the same time, a two-level output generates the largest amount of quantization noise. This brief analyzes the effect of nonequal level spacing in a three-level \Sigma\Delta output and provides a method for shaping the corresponding error noise to regions outside the band of interest. Subsequently, the nonlinearity-shaping property is utilized to obtain an improved two-level drive signal based on three-level \Sigma\Delta modulation. The new binary drive signal is proven to have better adjacent channel leakage ratio and higher coding efficiency than a conventional two-level \Sigma \Delta modulator. In the investigated case, measured coding efficiency improves from 8.9% of the conventional two-level modulator to 21% of the modified two-level modulator. [ABSTRACT FROM AUTHOR]

High power wideband interferers appearing at 20, 15 and 10 MHz away from the mobile RX band edge can now be suppressed by applying feedforward cancellation in the RF domain where the filtering is carried out using a new bandstop resonator. A study is conducted on the design of high selective resonators using power splitters, short-terminated delay lines and no attenuators. A 4-tap resonator is designed and measured showing a 3 dB bandwidth of 11 MHz only, a maximum insertion loss of 3.9 dB and more than 21 dB rejection. The system is tuned to handle interferers at different locations using a voltage control phase shifter. The cancellation performance is tested using two 10 MHz wide LTE modulated signals representing both the desired received signal (−50 dBm) and the interferer (−20 dBm). The power spectrum measurements show more than 45 dB cancellation for the interferers at 20 and 15 MHz, while 20 dB for the interferer at 10 MHz frequency separation leaving the desired signal with less than 5 dB insertion loss and no significant noise is added. [ABSTRACT FROM PUBLISHER]

In this letter, a new pre-distortion technique for power amplifiers in wideband applications is proposed. The proposed pre-distortion technique is based on Nonlinear Autoregressive with Exogenous inputs (NARX). The forward path of the proposed predictive method is based on the memory polynomial. Experimental validation is carried out with 4 carrier WCDMA signal with 20MHz bandwidth and \textPAPR=9.8\ \textdB. The results show significant reduction in the number of coefficients with comparable performance in terms of adjacent channel leakage ratio (ACLR) and error vector magnitude (EVM) to Volterra series techniques. [ABSTRACT FROM PUBLISHER]

This article presents a low-power, high-linearity cascode-type low noise amplifier (LNA) with 36 dB of variable gain for the WIDE Code Division Multiple Access systems. By enhancing the substrate resistance of a common gate transistor along with adopting multiple-gate technique, the linearity is significantly improved. Shunt-current steering is adopted for smooth gain control. Step gain mode is used to further increase the gain control range. The main common source transistor is disabled in attenuation mode, saving unwanted power consumption. Measurements show maximum gain of 12.3 dB with S11 of -19.5 dB, and S22 of -14 dB. The total gain control range is 36 dB. NF is measured as 2 dB and two-tone test shows 9.1 dBm of IIP3. Implemented in 0.13-μm CMOS technology, the LNA consumes only 1.6 mA at maximum gain mode and only 0.2 mA in attenuation mode from 1.2 V supply. Its die size is 0.3 mm2. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1385–1388, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24320 [ABSTRACT FROM AUTHOR]

Software-defined radio requires the combination of software-based signal processing and the enabling hardware components. In this paper, we present an overview of the criteria for such platforms and the current state of development and future trends in this area. This paper will also provide details of a high-performance flexible radio platform called the maynooth adaptable radio system (MARS) that was developed to explore the use of software-defined radio concepts in the provision of infrastructure elements in a telecommunications application, such as mobile phone basestations or multimedia broadcasters. [ABSTRACT FROM AUTHOR]

This paper reports on a load balancing system for an academic department, which can be used as an implementation mechanism for strategic planning. In essence, it consists of weighting each activity within the department and performing workload allocation based on this transparent scheme. The experience to date has been very positive, in terms of achieving strategic change and staff contentment. [ABSTRACT FROM AUTHOR]

A novel method using self-organizing maps to determine the optimum ranges to partition the vector switched Volterra series is presented. Analyzing characteristics of the input signal it is possible to separate different regions of operation. Partitioning of the correction algorithm provides the ability to target regions of different non-linear behavior with separate coefficients. This work is validated with experimentally measured results and shows an adjacent channel power ratio (ACPR) of -49/-50 dBc achieved for a four carrier Wideband Code-Division Multiple Access (WCDMA) signal using a 19 watt digital outphasing amplifier from NXP. [ABSTRACT FROM PUBLISHER]

When a larger than required dimension such as memory depth or order of nonlinearity, is specified during behavioral model extraction, redundant terms can be calculated when determining the weights of the model. Extraction of a behavioral model can therefore benefit from a priori knowledge of the system to be modeled. Conversely if there is a limitation in the hardware required to calculate model outputs a limit can be set for the maximum number of weights to be used. In this letter, an approach is proposed which allows the input delay vector to be reduced to a sparse vector including the delayed samples which are most important in the construction of the power amplifier model. Simulations of behavioral models for experimentally measured data of two different PAs demonstrates the sparse models extracted in this way are as accurate as a full model but have a more compact and as a result more computationally efficient structure. [ABSTRACT FROM PUBLISHER]

Orthogonal frequency division multiplexing (OFDM) has become an indispensable part of waveform generation in wideband digital communication since its first appearance in digital audio broadcasting (DAB) in Europe in 1980s, and it is indeed in use. As has been seen, the OFDM based waveforms work well with time division duplex operation in new radio (NR) systems in 5G systems, supporting delay-sensitive applications, high spectral efficiency, massive multiple input multiple output (MIMO) compatibility, and ever-larger bandwidth signals, which has demonstrated successful commercial implementation for 5G downlinks and uplinks up to 256-QAM modulation schemes. However, the OFDM waveforms suffer from high peak to average power ratio (PAPR), which is not desired by system designers as they want RF power amplifiers (PAs) to operate with high efficiency. Although NR offers some options for maintaining the efficiency and spectral demand, such as cyclic prefix based (CP-OFDM), and discrete Fourier transform spread based (DFT-S-OFDM) schemes, which have limiting effects on PAPR, the PAPR is still as high as 13 dB. This value increases when the bandwidth is increased. Moreover, in LTE-Advance and 5G systems, in order to increase the bandwidth, and data-rate, carrier aggregation technology is used which increases the PAPR the same way that bandwidth increment does; therefore, it is essential to employ PAPR reduction in signal processing stage before passing the signal to PA. In this paper, we investigate the performance of an innovative peak shrinking and interpolation (PSI) technique for reducing peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) based signals at waveform generation stage. The main idea behind the PSI technique is to extract high peaks, scale them down, and interpolate them back into the signal. It is shown that PSI technique is a possible candidate for reducing PAPR without compromising on computational complexity, compatible for existing and future telecommunication systems such as 4G, 5G, and beyond. In this paper, the PSI technique is tested with variety of signals in terms of inverse fast Fourier transform (IFFT) length, type of the signal modulation, and applications. Additional work has been carried out to compare the proposed technique with other promising PAPR reduction techniques. This paper further validates the PSI technique through experimental measurement with a power amplifier (PA) test bench and achieves an adjacent channel power ratio (ACPR) of less than –55 dBc. Results showed improvement in output power of PA versus given input power, and furthermore, the error vector magnitude (EVM) of less than 1 % was achieved when comparing of the signal after and before modification by the PSI technique. [ABSTRACT FROM AUTHOR]

Acute esophageal necrosis (AEN) is a rare condition that impacts the distal esophagus after a vascular insult. In this case report, we describe a patient with multiple comorbid conditions presenting with shock from gastroenteritis who subsequently developed AEN complicated by refractory strictures. [ABSTRACT FROM AUTHOR]

Future wireless networks are planned to service many applications with an Ultra Low-Latency (ULL) requirement. Numerous 6G systems have been proposed including more traditional electro-magnetic (EM) antenna transmissions and optical wireless communications (OWC). For extremely wide-band operation, the traditional approaches require digital pre-distortion and other processing techniques which, in turn, require more computational resources and processing times thus increasing latency. Alternatively, OWC has the potential for extremely wide bandwidths in 6G without the need for as much digital signal processing. In order to realise ULL performance, a minimum number of digital signal processing (DSP) blocks is required, as well as an optimal design of each of these. In this letter, we propose a DSP solution for ULL and peak to average power ratio (PAPR) reduction for OWC systems. Unitary checkerboard precoding - orthogonal frequency division multiplexing (UCP-OFDM) is chosen as the modulation scheme and has been implemented within a single digital block avoiding the use of standard OFDM which would otherwise require multiple digital blocks. Experimentally validated results successfully demonstrate a 2.21184 GSps wireless link at distances of up to 2m in noisy daylight settings. Bit error rates (BER) of 0 at root mean square (RMS) error vector magnitude (EVM) of 4.09% are achieved. A complete digital line-up of an OWC transmitter chain for this work contains only three core blocks and ULL of less than 400 ns.

The ability to automatically detect the location of an elder within their own home is a significant enabler of remote elder supervision and interaction applications. This location information is typically generated via a myriad of sensors throughout the home environment. Even with high sensor redundancy, there are still situations where traditional elder monitoring systems are unable to resolve the location of the elder. This work develops a minimal infrastructure radio-frequency localisation system for long-term elder location tracking. An RFID room-labelling technique is employed and with it, the localisation system developed in this work is shown to exhibit superior performance to more traditional localisation systems in realistic long-term deployments.

As part of an ongoing search for novel molecules with therapeutic potential we examined the mediator release inhibition activity of a number of indanones and their derivatives. The aldol condensation product 18 was approximately twice as potent as disodium cromoglycate as an inhibitor of compound 48/80-stimulated histamine release from rat peritoneal mast cells. The activity of this class of dimeric indanone compound is significantly higher than controls and may represent a new class of mast cell stabilizing agents. Compound 18 has been selected for further biological evaluation of its mast cell stabilization profile.