We propose an efficient open-loop channel estimator for a millimeter-wave (mm-wave) hybrid multiple-input multiple-output (MIMO) system consisting of radio-frequency (RF) beamformers with large ...antenna arrays followed by a baseband MIMO processor. A sparse signal recovery problem exploiting the sparse nature of mm-wave channels is formulated for channel estimation based on the parametric channel model with quantized angles of departures/arrivals (AoDs/AoAs), called the angle grids. The problem is solved by the orthogonal matching pursuit (OMP) algorithm employing a redundant dictionary consisting of array response vectors with finely quantized angle grids. We suggest the use of non-uniformly quantized angle grids and show that such grids reduce the coherence of the redundant dictionary. The lower and upper bounds of the sum-of-squared errors of the proposed OMP-based estimator are derived analytically: the lower bound is derived by considering the oracle estimator that assumes the knowledge of AoDs/AoAs, and the upper bound is derived based on the results of the OMP performance guarantees. The design of training vectors (or sensing matrix) is particularly important in hybrid MIMO systems, because the RF beamformer prevents the use of independent and identically distributed random training vectors, which are popular in compressed sensing. We design training vectors so that the total coherence of the equivalent sensing matrix is minimized for a given RF beamforming matrix, which is assumed to be unitary. It is observed that the estimation accuracy can be improved significantly by randomly permuting the columns of the RF beamforming matrix. The simulation results demonstrate the advantage of the proposed OMP with a redundant dictionary over the existing methods such as the least squares method and the OMP based on the virtual channel model.
Multidrug-resistant Gram-negative bacteria (MDR-GNB) are an emerging public health threat. Accurate estimates of their clinical impact are vital for justifying interventions directed towards ...preventing or managing infections caused by these pathogens. A retrospective observational cohort study was conducted between 1 January 2007 and 31 July 2009, involving subjects with healthcare-associated and nosocomial Gram-negative bacteraemia at two large Singaporean hospitals. Outcomes studied were mortality and length of stay post-onset of bacteraemia in survivors (LOS). There were 675 subjects (301 with MDR-GNB) matching study inclusion criteria. On multivariate analysis, multidrug resistance was not associated with 30-day mortality, but it was independently associated with longer LOS in survivors (coefficient, 0.34; 95% CI, 0.21–0.48; p < 0.001). The excess LOS attributable to multidrug resistance after adjustment for confounders was 6.1 days. Other independent risk factors for higher mortality included male gender, higher APACHE II score, higher Charlson comorbidity index, intensive care unit stay and presence of concomitant pneumonia. Concomitant urinary tract infection and admission to a surgical discipline were associated with lower risk of mortality. Appropriate empirical antibiotic therapy was neither associated with 30-day mortality nor LOS, although the study was not powered to assess this covariate adequately. Our study adds to existing evidence that multidrug resistance per se is not associated with higher mortality when effective antibiotics are used for definitive therapy. However, its association with longer hospitalization justifies the use of control efforts.
In this paper, a Gaussian two-way relay channel, where two source nodes exchange messages with each other through a relay, is considered. We assume that all nodes operate in full-duplex mode and ...there is no direct channel between the source nodes. We propose an achievable scheme composed of nested lattice codes for the uplink and structured binning for the downlink. Unlike conventional nested lattice codes, our codes utilize two different shaping lattices for source nodes based on a three-stage lattice partition chain, which is a key ingredient for producing the best gap-to-capacity results to date. Specifically, for all channel parameters, the achievable rate region of our scheme is within 1/2 bit from the capacity region for each user and its sum rate is within log3/2 bit from the sum capacity. PUBLICATION ABSTRACT
Epidermal growth factor receptor (EGFR) gene amplification and mutations are the most common oncogenic events in glioblastoma (GBM), but the mechanisms by which they promote aggressive tumor growth ...are not well understood. Here, through integrated epigenome and transcriptome analyses of cell lines, genotyped clinical samples, and TCGA data, we show that EGFR mutations remodel the activated enhancer landscape of GBM, promoting tumorigenesis through a SOX9 and FOXG1-dependent transcriptional regulatory network in vitro and in vivo. The most common EGFR mutation, EGFRvIII, sensitizes GBM cells to the BET-bromodomain inhibitor JQ1 in a SOX9, FOXG1-dependent manner. These results identify the role of transcriptional/epigenetic remodeling in EGFR-dependent pathogenesis and suggest a mechanistic basis for epigenetic therapy.
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•Oncogenic EGFRvIII mutation remodels the enhancer landscape in GBM•EGFRvIII induces SOX9 and FOXG1 transcription in GBM•SOX9 and FOXG1 collaborate to activate an oncogenic gene regulatory program•EGFRvIII-dependent transcription sensitizes GBM cells to JQ1
Epidermal growth factor receptor (EGFR) gene amplification and mutations are the most common oncogenic events in glioblastoma (GBM). Through an integrative genomics analysis, Liu et al., identify a role for transcriptional/epigenetic remodeling in EGFR-dependent pathogenesis and suggest a mechanistic basis for epigenetic therapy.
A two-way relay channel (TWRC) in which two terminals T 1 and T 2 exchange orthogonal frequency division multiplexing (OFDM) signals with the help of an amplify-and-forward (AF) relay T 3 is ...considered here, and an efficient technique for allocating powers to N parallel tones of OFDM is developed. A sum rate maximization problem is formulated by replacing the individual power constraints of the conventional sum rate maximization problem, which limit the power of each terminal, with the total power constraint limiting the sum of powers of all terminals. The maximization problem with the total power constraint yields a more efficient power allocation policy than the conventional problem with individual power constraints. It is shown that the closed-form solution of the maximization problem under the total power constraint can be obtained for a single-tone system ( N =1). Based on this result, a two-step suboptimal approach is proposed in which the power is optimally assigned to each tone first, and then at each tone the assigned power is distributed to the three terminals. The proposed method is shown to assign 50% of the total power to relay T 3 irrespective of the channels. It is demonstrated that the proposed method is considerably simpler to implement than the conventional dual-decomposition method (DDM), yet the performance of the former is almost identical to that of the latter.
We consider the design of a uniform circular array (UCA) system under array misalignment over line-of-sight (LoS) channels. UCAs have been considered as useful array structures since their LoS ...channels can be diagonalized without the channel state information at the transmitter (Tx). However, such a characteristic holds only when transceiver arrays are perfectly aligned. To overcome this difficulty, we propose an optimal design method and transceiver architectures for UCA systems under array misalignment that achieve channel capacity without knowledge of misalignment angles. To this end, we first verify that the singular values of the misaligned UCA system are independent of tilting and center-shift and small relative array rotation, but fluctuate with the Radii Product to Distance Ratio (RPDR). Using the result, we present an optimal design method for UCA systems that performs an one-dimensional search for the RPDR to maximize channel capacity, and we show that a simple zero-forcing (ZF) receiver can achieve the maximum channel capacity because of the channel characteristic at the optimal design criteria. Additionally, we propose a low-complexity precoding scheme for UCA systems in which the optimal design criteria cannot be fulfilled. The simulation results demonstrate the validity of the proposed design method and transceiver architectures.
An electronically steerable parasitic array radiator (ESPAR) transmitter, employing one active and one parasitic antenna element, which can simultaneously transmit two orthogonal frequency division ...multiplexing (OFDM) signals with quadrature phase shift keying (QPSK) modulation via spatial multiplexing, is developed. In particular, a minimum mean square error (MMSE) scheme for quantizing the parasitic load impedance is developed to reduce the number of distinct load impedance values that should be realized for spatial multiplexing over ESPAR. To this end, the probability density function of the parasitic load impedance is derived, and the realizable region of the load impedance is analyzed. It is observed that the resistance of the active antenna element should be large enough to transmit OFDM signals. The characteristics of two existing ESPAR antennas with different mutual coupling matrices are examined, and it is observed that the one with the larger active antenna resistance is suitable for OFDM transmission. The bit error rate (BER) and the receive error vector magnitude performances of the proposed ESPAR systems with 6/8-bit quantizers and zero-forcing (ZF) receiver are compared with those of the corresponding ideal multiple-input multiple-output (MIMO) system through computer simulation. The results demonstrate that the performances of the proposed ESPAR with the 8-bit quantizer and the ideal MIMO systems can be almost identical, whereas the proposed ESPAR with the 6-bit quantizer exhibits some performance loss.
This paper considers a multiuser two-way relay channel (MU-TWRC) in which a base-station and a selected mobile-station (MS) among K number of MSs exchange messages during two time slots with the help ...of a half-duplex amplify-and-forward relay. We analyze the performances of a MU-TWRC. The closed-form expressions of the lower bound of the average rates are derived. The asymptotic expressions of the average rates are also analyzed in the limit of large K. Analysis and simulation results indicate that the former matches well to the latter, and the performance of a MU-TWRC can increase as K increases or be bounded to some constant according to the channel conditions.
In this paper, the power-allocation problem is solved in the context of maximizing the energy efficiency (EE) of orthogonal frequency-division multiplexing (OFDM) signaling over a two-way ...amplify-and-forward (AF) relay network with two sources and one relay. The EE is defined as the ratio of the system throughput over the total power consumption incorporating the transmission power, the fixed circuit power, and the dynamic circuit power, which is rate dependent. In the EE maximization (EEM) problem, the efficiency values of the power amplifiers (PAs) of the three terminals can differ from one another. It is shown that EE is a quasi-concave function of the transmission power. Based on this result, we use Dinkelbach's method for fractional programming and propose a two-step allocation (TSA) algorithm to solve the inner loop of Dinkelbach's method. Simulation results demonstrate that the proposed scheme can efficiently maximize the EE.
We study benefits of opportunistic routing in a large wireless ad hoc network by examining how the power, delay, and total throughput scale as the number of source-destination pairs increases up to ...the operating maximum. Our opportunistic routing is novel in a sense that it is massively parallel, i.e., it is performed by many nodes simultaneously to maximize the opportunistic gain while controlling the interuser interference. The scaling behavior of conventional multihop transmission that does not employ opportunistic routing is also examined for comparison. Our main results indicate that our opportunistic routing can exhibit a net improvement in overall power-delay tradeoff over the conventional routing by providing up to a logarithmic boost in the scaling law. Such a gain is possible since the receivers can tolerate more interference due to the increased received signal power provided by the multi user diversity gain, which means that having more simultaneous transmissions is possible.
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