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We extended the density-gradient (DG) model to include a second-order quantum correction (SOQC) term. The DG model has been widely used as a device simulation model capable of simulating quantum effects in efficient way. However, when only the first order quantum correction term is considered in the DG model, it is difficult to accurately describe device characteristics such as carrier density or potential fluctuation in the narrow region due to discrete charges such as dopants and interface traps. Thus, we extended the DG model to the SOQC, implemented it as a three-dimensional (3D) simulator, and compared the simulation results for sub-10-nm devices, which have a single point charge, in the DG model and the 3D Schrödinger–Poisson (SP) solver. Through this, we identified that the DG extended to SOQC well reproduces the SP simulation results in terms of both capacitance–voltage (C–V) and local fluctuation in electron density.

In this paper, we consider a signal-level maximum likelihood detection for multiple-input multiple-output filter-bank multicarrier-quadrature amplitude modulation (MIMO FBMC-QAM) system with two prototype filters. Under high-frequency selective channels, the conventional symbol-level maximum likelihood detection suffers from degraded bit error rate performances because it cannot utilize the oversampling characteristics of the signal-level. However, due to intrinsic interference and high computational complexity, a maximum likelihood detection cannot be applied directly to the signal-level. To solve this problem, we propose a signal-level maximum likelihood detection based on partial candidates. Utilizing the diagonal dominant characteristics of effective channels, the proposed signal-level maximum likelihood detection can reduce the effect of intrinsic interference with practical computational complexity. Moreover, a region ordering algorithm based on Euclidean distance can improve the efficiency of the proposed signal-level maximum likelihood detection. Simulation results show that the proposed signal-level maximum likelihood detection can outperform the bit error rate performance of the conventional symbol-level maximum likelihood detection.

We consider the residual interference problem for a filter bank-based multicarrier with quadrature amplitude modulation under multipath fading channels. In order to handle this problem, we propose a layered detection algorithm based on interference cancellation (IC). In proposed algorithm, we define two thresholds, a selection threshold and a region threshold for efficient IC. According to the selection threshold, we decide whether to apply IC or not, and configure a successive detection region based on the region threshold. Simulation results show that the proposed algorithm provides almost the same bit error rate performance as the orthogonal frequency division multiplexing and the criteria for the proposed thresholds are reasonable.

This paper describes the feasibility of software-defined demodulator of DVB-T2 standard using the scalable DSP processor. This paper focuses mainly on the DVB-T2 receiver design and implementation of four major software blocks of the demodulator: FFTs, channel estimator, multi-level de-interleavers and rotated QAM soft-demapper. In particular, 2K-point FFT function is analyzed and mapped on the scalable architecture of coarse-grained reconfigurable array (CGRA) processors resulting 51dB signal to quantization noise ratio (SQNR) performance. The computational burden of frequency interpolator and frequency/cell deinterleavers are greatly reduced with specially designed intrinsics, 30% and 85%, respectively, from the original implementation. The softdemapper for rotated QAM constellation becomes feasible with the latest 1D-MMSE decorrelation method though it is still the most expensive function covering 40% of DTG106 mode. By implementing full chain demodulation software including abovementioned four major functions, it is demonstrated that the software-defined DVB-T2 demodulator is realizable with software on two scalable CGRA processors running at 300MHz.

In downlink multiuser multiple-input multiple-output (MIMO) systems, system performance highly depends on the reliability of downlink channel state information (CSI) at the base station (BS). In frequency division duplexing, the most practical solution is to have downlink CSI from the users fed back to the BS. Most work on this feedback design has assumed independent block fading channels. However, this paper proposes a new differential feedback scheme using the observation that the channel realizations are usually temporally correlated. The sum-rate loss assuming differential feedback is analyzed for a system with the number of users K equal to the number of transmit antennas M. When K >; M, a user selection algorithm based on an approximated signal-to-interference plus noise ratio (SINR) estimation is proposed. In simulation results, the proposed differential feedback scheme increases the sum-rate compared to previous differential feedback schemes. Moreover, the proposed user selection algorithm outperforms semi-orthogonal user selection in the moderate signal-to-noise ratio (SNR) region, despite requiring less feedback information. In low mobility channels, utilizing the channels' time correlation during quantization is shown to play a bigger role in determining sum-rate performance than multiuser diversity for most SNR regimes when a practical number of users is considered.

New waveform design is one of the prominent 5G research directions which aims to increase spectrum efficiency and replace conventional cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM) in 4G LTE systems. In particular, filter bank multi-carrier system (FBMC) is recognized as a promising post-OFDM candidate. Like other candidates, it sacrifices subcarrier orthogonality for improved spectrum confinement. In this paper, we show that a QAM based FBMC (QAM-FBMC) space-time block code (STBC) system can achieve close to CP-OFDM performance with a linear receiver only, settling the conventional perception of the necessity of non-linear equalizers in FBMC to support multiple-input multiple-output. The contribution of this paper is two-fold: (1) in terms of complexity and error rates performance our proposed QAM-FBMC system outperforms conventional OQAM-FBMC scheme; (2) a performance lower bound is shown numerically that QAM-FBMC attains close to CP-OFDM error rates.

Over the last decade, tremendous gains, leading to near-capacity achieving performance, have been shown for a variety of communication systems through the application of the turbo principle, i.e., the exchange of extrinsic information between constituent algorithms for tasks such as channel decoding, equalization, and multiple-input-multiple-output (MIMO) detection. In this paper, we study the practical application of such an iterative detection and decoding (IDD) framework to underwater acoustic communications. We explore complexity and performance tradeoffs of a variety of turbo equalization (TEQ)-based receiver architectures. First, we elaborate on two popular but suboptimal turbo equalization techniques: a channel-estimate-based minimum mean-square error TEQ (CE-based MMSE-TEQ) and a direct-adaptive TEQ (DA-TEQ). We study the behavior of both TEQ approaches in the presence of channel estimation errors and adaptive filter adjustment errors. We confirm that after a sufficient number of iterations, the performance gap between these two TEQ algorithms becomes small. Next, we demonstrate that an underwater receiver architecture built upon the least mean squares (LMS) DA-TEQ technique can leverage and dramatically improve the performance of the conventional implementation based on the decision-feedback equalizer at a feasible complexity. To maintain performance gains over time-varying channels, the slow convergence speed of the LMS algorithm has been improved via two methods: 1) repeating the weight update for the same set of data with decreasing step size and 2) reducing the dimensionality of the equalizer by capturing sparse channel structure. This receiver architecture was used to process collected data from the SPACE 08 experiment (Martha's Vineyard, MA). Receiver performance for different modulation orders, channel codes, and hydrophone configurations is examined at a variety of distance, up to 1 km from the transmitters. Experimental results show great promise for this approach, as data rates in excess of 15 kb/s could readily be achieved without error.

However, polymer resin basedporous supports typically have a wide distribution of pore di-ameters, ranging from micropores ( 50 nm). A large portion of the catalytic groups can be sup-ported within micropores under these circumstances, leadingto serious diffusion limitations. Another problem is that theloosely cross-linked polymeric frameworks can easily swell inmany organic solvents. This swelling can lead to the closing ofpore mouths under reaction conditions with organic solvents.In addition, water (H

This paper proposes new algorithms to improve the bit error rate (BER) and data rate of link-adaptive multiple-input-multiple-output (MIMO) systems with ordered successive interference cancellation (OSIC) receivers in a multiuser environment. The proposed algorithms are as follows: (1) the power adaptation (power allocation-equal rate) scheme; (2) the rate adaptation (equal power-adaptive modulation) scheme; and (3) the power and rate adaptation (power allocation-adaptive modulation) scheme. Additionally, as the OSIC receiver is exploited in the proposed algorithms, the detection order of each user's receiver is considered since the performance of the system using it is seriously affected by the detection order. Finally, the proposed algorithms are executed to minimize the BER or to maximize the data rate of the system by simultaneously considering link adaptation techniques and the detection order of the OSIC receiver.

In this correspondence, we propose a blind carrier phase synchronization algorithm for high-order M-ary quadrature amplitude modulation-orthogonal frequency division multiplexing (M-QAM-OFDM) systems, which can effectively recover residual frequency offset (RFO) in the presence of intercarrier interference (ICI). The proposed algorithm performs frequency and phase synchronization by using post-fast Fourier transform (FFT) demodulated signals without the aid of reference signals (e.g., pilots, guard intervals, and virtual carriers), and is simple to implement. By analyzing its open-loop characteristics, we show that the proposed algorithm is superior to the conventional decision-directed (DD) scheme for high-order M-QAM-OFDM systems.

Owing to frequency diversity gain and simplicity, a chip interleaved multi-carrier code division multiple access (MC-CDMA) system has been considered in a multi-cell environment, and combining it with multiple input multiple output (MIMO) schemes offers high spectral efficiency. In spite of the advantages, the system is highly affected by inter code interferences. To control them, this letter analyzes the asymptotic performance of a MIMO MC-CDMA system with a symbol level MMSE receiver in a multi-cell environment and presents an appropriate multiplexed code ratio satisfying a required error rate.

As a promising candidate to replace cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM), a new quadrature amplitude modulation filter-bank multi-carrier (QAM-FBMC) has been proposed for enabling spectral efficiency increase and spectrum confinement while keeping near orthogonality. QAM transmission can combat intrinsic interference of conventional offset-QAM (OQAM)-FBMC, which is main bottleneck in channel estimator and multiple antenna transceiver design. Compared to existing single filter based QAM-FBMC, the new QAM-FBMC has more optimization freedom in multiple prototype filters to increase self signal-to-interference ratio (SIR). In this paper, the possibility of per-tone multiple input multiple output (MIMO) reception in the new QAM-FBMC system is exploited. Our MIMO receiver is constructed with per-tone MIMO equalization in oversampled signal domain and its soft-demapper in symbol domain. Not only the separate log likelihood ratio (LLR) calculation per stream but also joint LLR calculation (i.e., soft maximum likelihood (ML) detection) is implemented with pre-processing. Simulation results show that the per-tone MIMO reception in QAM-FBMC is comparable to that of CP-OFDM.

Multiple filter-banks enable QAM transmission and reception in filter-bank multi-carrier (FBMC) systems. In this paper, we propose a new method to design a set of simultaneously used base filters for QAM-FBMC by optimizing the trade-off between spectrum confinement and self-interference. The increased freedom in multiple base filter designs brings merits of a tailor-made spectrum confinement and desirable bit error performance simultaneously. Simulations results show the superiority of the proposed QAM-FBMC systems to other post-OFDM waveform candidates.

Recently, as asynchronous heterogeneous network scenario becoming one of the key features for next generation wireless communications, superior spectrum confinement as well as higher spectral efficiency compared to cyclic prefixed orthogonal frequency division multiplexing (CP-OFDM) has been taken into consideration for future radio access technologies. In this paper, we propose a new quadrature amplitude modulation based filter-bank multi-carrier (QAM-FBMC) system that provides with an inherent spectral efficiency gain against CP-OFDM, which comes from reduction of the redundancies such as cyclic prefix (CP) and guard-band, while keeping the symbol rate same as in CP-less OFDM. We propose a new transceiver structure consisting of at least two different filter-bank bases at both transmitter and receiver sides. Practical algorithms including channel estimation and equalization to mitigate multi-path fading channel without CP are proposed. Various evaluation results show that the proposed system performs comparable to the CP-OFDM system even without CP and guard-band reduction is also available from the well-confined spectrum.

This paper proposes a new detection ordering scheme, which minimizes average error rate of the MIMO system with per antenna rate control. This paper shows an optimal scheme minimizing average error rate expressed by the Q function, and simplifies the optimal scheme by using the minimum equivalent SINR scaled by modulation indices, based on approximated error rate. In spite of reduced complexity, the simplified scheme demonstrates the almost same performance as the optimal scheme. Owing to the diversity of detection ordering, the proposed scheme has over 2 dB higher SNR gain at the BER of 10 -3 than the existing ordering schemes in balanced array size systems.