Search

Of the wide palette of 5G features, ultra-wide bandwidth and large-scale antenna configuration are regarded as the essential enabling technology components for millimeter wave (mmWave) communication. Accurate knowledge of delay and angle information of multipath components is essential for many applications in mmWave systems. There is a strong need for a low computation-cost channel estimation algorithm for such systems, where typically adopted far-field and narrowband assumptions might be violated. In this paper, a generic yet novel beamspace uniform circular array (UCA) beamforming algorithm with successive cancellation scheme is proposed to jointly detect the impinging azimuth angle and delay of each multipath component. The proposed algorithm is computationally cheap and it works for ultra-wideband UCA systems in the near-field conditions as well as the traditional narrowband systems in the far-field conditions. Both numerical simulations and experimental validation results are provided to demonstrate the effectiveness and robustness of the proposed algorithm, compared to the state-of-art works. [ABSTRACT FROM AUTHOR]

In this paper, a novel scheme is proposed to optimize the effectiveness of the device-to-device (D2D) enabled vehicular communications (D2D-V), which are underlaid in cellular networks, where the uplink channel allocated to one cellular user (CU) is reused by the multiple D2D-V links. To develop a well-functioning D2D-V system, the sum rate of all D2D-V links is necessary to be maximized, and also the reliability of the co-channel CU to infrastructure has to be guaranteed with the CU interference constraint. Unlike the traditional statical D2D systems, the D2D-V system suffers with high mobility and channel uncertainty. Therefore, the CU interference constraint is formulated as a probabilistic function by the Bernstein approximation, the constraint attempts to address the mobile channel fluctuations. Besides, the tractable approximate constraint is reformulated as two separable structure, this reformulated constraint attempts to determine the near-optimal solutions more efficiently. Since the objective function with a logarithmic form is nonconvex, successive convex approximation is applied to transform the nonconvex problem into the convex problem. The dual decomposition is used to determine the near-optimal solutions. After the problem is reformulated, a distributed robust power control algorithm is proposed to perform the chance-constrained optimization. Numerical simulations are used to evaluate the performance of the proposed scheme. The simulation results show the impacts of system performance when applying the proposed scheme in vehicular environments with high mobility. The proposed optimization schemes are further verified by comparing with the existing methods. [ABSTRACT FROM AUTHOR]

This paper proposes a new algorithm to evaluate the performance of the mobile edge computing system. Specifically, a new metric called computation efficiency is defined as the number of calculated data bits divided by the corresponding energy consumption. In order to compute the required data timely, we combine two schemes, local computing and data offloading, into a joint computation algorithm. An optimization problem is formulated with the objective to maximize the sum of computation efficiency among users with weighting factors. With iterative and gradient descent methods, the problem can be solved efficiently. Simulation results show that the proposed scheme outperforms traditional approaches. In addition, the tradeoff study between local computing and data offloading reveals that when data size is small, local computing plays a more important role, but when the size grows, data offloading becomes preferable. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) is a promising scheme for the fifth generation (5G) of mobile communication systems. In this scheme, transmission to multiple users is performed on the same subchannel using superposition coding and successive interference cancellation. In this paper, we focus on a multi-cell network with two users’ data traffic models, namely elastic and streaming. We exploit the NOMA scheme in order to maximize the download elastic traffic rate at cells, without degrading the download streaming traffic rates. Since elastic traffic rates at different cells are interactive, we maximize the total elastic traffic rates assuming either perfect or partial channel state information available at each base station subject to a target rate for streaming users. Because of the interference due to NOMA as well as the interference among different cells, subchannel assignment and power allocation affect the system performance significantly. For this reason, we propose an iterative algorithm to jointly solve the subchannel assignment and the power allocation problem via the Hungarian algorithm and successive convex approximation, respectively. Finally, our simulation results show the efficiency of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this paper, we propose a generalized channel decoding scheme for nonbinary physical-layer network coding (CD-NC) in two-way relay channels (TWRCs), where two source nodes A and B exchange their nonbinary symbols via a relay. The two sources use the same nonbinary low-density parity-check (LDPC) channel code over the integer ring $\mathbb {Z}_M$ and $M$ -pulse-amplitude modulation, respectively. The existing channel decoding schemes for nonbinary network coding suffer severe rate loss compared with the cut-set bound of TWRC, especially in the low-to-medium signal-to-noise ratio regime. The proposed CD-NC can decrease the rate loss. Our contributions are as follows: 1) We develop a generalized nonbinary sum product algorithm (G-SPA) for CD-NC according to the principle of virtual encoding of the superimposed symbols. Simulation results show that our CD-NC can achieve significant performance gains over the conventional nonbinary network coding for both additive white Gaussian noise and fading channels; and 2) We exploit two-dimensional fast-Fourier-transform-based belief propagation (2-D-FFT-BP) and extended min-sum (EMS) decoding algorithms to reduce the decoding complexity of G-SPA. Simulation results show that the 2-D-FFT-BP has the same performance as G-SPA, while EMS can greatly reduce the decoding complexity of G-SPA at the cost of slight performance degradation. [ABSTRACT FROM AUTHOR]

In this correspondence paper, we study the application of approximate message passing (AMP) algorithm in the signal detection of index modulation (IM) with multiple active resources (antennas or subcarriers). First, for uplink generalized spatial modulation (GSM), AMP detectors in both spatially uncorrelated and correlated channels are proposed. Specifically, an effective method to utilize the activation pattern constraint of GSM signal vector per user in the posterior probability computation of scalar symbol node is derived. Furthermore, a simple while effective damping strategy is introduced in AMP detector to guarantee convergence in correlated channels. Second, for orthogonal frequency division multiplexing with IM in rapidly time-varying channels, the damped AMP detector is further studied. In addition, the convergence of proposed detectors is analyzed by state evolution. Finally, the effectiveness of proposed AMP detectors is verified by simulations. [ABSTRACT FROM AUTHOR]

The hidden terminal problem degrades the uplink system throughput of wireless local area network seriously. In this paper, we propose the optimum allocation (OA) scheme of the location-based virtual sector (VS) method, which solves the hidden terminal problem without massive overheads like request-to-send and clear-to-send (RTS/CTS) packets. The VS method forms sectors virtually to make short-distance mobile terminal (MT) groups using MTs’ location information. In the group, all MTs can sense the transmission of all other MTs. In the proposed method, rough time slot control is implemented for intersector control, which does not need a highly functional centralized controller. The proposal OA scheme of the VS method improves the fairness among MTs by optimizing active periods of VS according to the number of MTs in each VS. By computer simulations, we show that the proposed method can increase the system throughput from the RTS/CTS and improve fairness among MTs even in the condition that positioning error is 1/10 of cell radius. [ABSTRACT FROM AUTHOR]

This paper presents the posterior linearization belief propagation (PLBP) algorithm for cooperative localization in wireless sensor networks with nonlinear measurements. PLBP performs two steps iteratively: linearization and belief propagation. At the linearization step, the nonlinear functions are linearized using statistical linear regression with respect to the current beliefs. This SLR is performed in practice by using sigma-points drawn from the beliefs. In the second step, belief propagation is run on the linearized model. We show by numerical simulations how PLBP can outperform other algorithms in the literature. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a resource management scheme for on-demand video streaming in orthogonal frequency-division multiple access (OFDMA) networks with both time-varying channels and a user's personalized quality requirement. We design a user quality satisfaction model to evaluate the degree of the user quality satisfaction with respect to his/her personalized quality requirement. To perform the dynamic resource management, we propose a joint rate control (RC) associated with the quality adjustment at the application layer and resource allocation (RA) associated with the power allocation and subcarrier assignment at the physical layer. By using the Lyapunov optimization technique, we develop a joint RC and RA (JRCRA) algorithm to maximize the time-averaged quality satisfaction of all users (QSAU). We show that the QSAU achieved by the JRCRA algorithm without any prior knowledge of the channel statistics can arbitrarily attain the optimal QSAU achieved by the algorithm with a complete knowledge of the channel statistics. Simulation results verify the advantages of the proposed JRCRA algorithm. [ABSTRACT FROM PUBLISHER]

In this paper, the downlink of a clustered coordinated multicell multiuser multiple-input multiple-output (MIMO) system is considered, and various low-complexity user scheduling algorithms to maximize the sum rate are proposed. The users' data signals are transmitted cooperatively via the base stations (BSs) of a cluster within the sectorized multicell heterogeneous cellular network. Exhaustive search as the optimal scheduling method is extremely complex, particularly for large numbers of users requesting service. We therefore propose suboptimal scheduling algorithms based on the lower complexity metaheuristic stochastic optimization techniques of simulated annealing (SA) and particle swarm (PS). Moreover, a hybrid algorithm combining the traits of PS and a greedy scheduler is also proposed. The performance and complexity of these algorithms are evaluated for a heterogeneous system model employing different precoding methods. Assessing the algorithms' performance via computer simulations, the effectiveness of the proposed schemes in terms of sum rate is demonstrated, yielding performance very close to that of the exhaustive search at much lower complexity. For each precoding method used in the employed system model, the best corresponding approach to scheduling from our proposed algorithms is determined. [ABSTRACT FROM AUTHOR]

This paper describes an integrated chassis control (ICC) algorithm of differential braking, front/rear traction torque, and active roll moment control. The integrated control algorithm is designed to maximize driving velocity and enhance vehicle lateral stability in cornering. The target longitudinal acceleration is determined based on the driver's intention and vehicle current status to ensure vehicle lateral stability in high-speed maneuvering. An optimization-based control allocation strategy is used to distribute the actuator control inputs optimally under consideration of tire and vehicle limitations. Closed-loop simulations of a driver–vehicle–controller system were conducted to investigate the performance of the proposed control algorithm. The performance of the ICC has been compared with those of individual chassis control systems, such as electronic stability control, four-wheel drive (4WD), and active roll control system. The simulation results show that the proposed ICC algorithm improves the performance in high-speed cornering with respect to driving speed without losing stability, compared with individual chassis control systems. [ABSTRACT FROM PUBLISHER]

This paper proposes an algorithm to control the suspension dynamics with an energy regeneration capability and high conversion efficiency. Central to the concept is the development of a switched-mode rectifier (SMR) that is capable of providing either an equivalent positive or negative damping and alternating between regenerative and motoring modes. Simulation results are presented to demonstrate power flow in regeneration and motoring modes and verify the equivalent damping characteristic and vibration energy harvesting. The studies are conducted on a small-scale proof-of-concept electromagnetic suspension system excited by emulated International Standard Organization (ISO) 8608 road profiles. An autonomous start/stop algorithm is proposed such that autonomously turns on or off the converter. This mechanism mitigates quiescent power consumption of auxiliary integrated circuits (ICs) such as gate drivers and current transducers, therefore increasing the conversion efficiency of the power electronics throughout an ISO standardized variable-speed driving cycle. The autonomous start/stop algorithm is implemented experimentally to demonstrate its feasibility under typical standardized driving cycles. [ABSTRACT FROM PUBLISHER]

This paper describes an integrated speed and steering control driver model for vehicle–driver closed-loop simulation at high-speed maneuvering. In numerous research studies, the performance of vehicle control systems is validated via closed-loop computer simulations due to safety, cost, and repeatability issues. A driver model for the analysis of interactions between vehicle systems and drivers is a significant part of the validation. In particular, in developing a chassis control system, limit-driving characteristics of the actual driver, which mainly affects the performance of the system, has to be taken into consideration. Thus, the proposed driver model is developed to realize the actual driver's driving pattern. A speed control part of the proposed driver model consists of two modules, i.e., the real-time velocity planner and the motion stabilizer. The former plans the desired velocity profile from curvature information on a preview desired path in real time. The latter, i.e., the motion stabilizer, is developed to cope with losing maneuverability through deceleration because there is an obvious limitation to securing stability with velocity profile planning only. On the other hand, a steering control part of the proposed driver model utilizes the yaw-rate gain-based self-adaptation algorithm. An actual driver drives a vehicle without an exact understanding of system dynamics, and the self-adaptation algorithm is adequate for this characteristic accordingly. The proposed driver model has been validated by comparison with an expert driver's driving data, collected on the Korea International Circuit in Yeongam, Korea. [ABSTRACT FROM PUBLISHER]

In cognitive networks, primary and secondary users (PUs and SUs) share the radio resource according to fair regulations. The goal of this paper is to introduce a new method to detect an unfair user (freeloader) that hides its radio signal under the noise floor in the presence of an active (either primary or secondary) user. The performance of the proposed technique is evaluated by theoretical analysis and computer simulations. The probability of detection is expressed, for constant false-alarm rates, as a function of both the active signal power and the background noise variance. The results show the effectiveness of the new monitoring algorithm in several operating cases. [ABSTRACT FROM PUBLISHER]

Intercell interference coordination (ICIC) techniques not only help improve cellular data coverage but allow more efficient use of a valuable wireless spectrum as well. This paper investigates soft frequency reuse (SFR), which is a form of ICIC, for long-term evolution (LTE) systems. By analyzing the throughput of the SFR scheme, we find that classifying cell-edge users and cell-center users is critical. Thus, we develop low-complexity decentralized SFR scheduling algorithms that include optimal user classification and balance throughput and fairness among multiusers. We also propose suboptimal methods to reduce computational complexity. Computer simulation demonstrates that gains of the proposed SFR algorithm can improve the fifth percentile user throughput by 26% while maintaining the same cell average throughput, compared with a non-ICIC system. [ABSTRACT FROM PUBLISHER]

Signal detection algorithms providing likelihood information for coded spatial-multiplexing multiple-input–multiple-output (MIMO) wireless communication systems pose a critical design challenge due to their prohibitively high computational complexity. In this paper, we present a low-complexity soft-output detection algorithm by adopting four implementation-friendly algorithm-level improvements to the fixed-complexity sphere decoder. More specifically, we introduce a reliability-dependent tree expansion approach and an on-demand list-size reduction scheme for low-cost candidate list generation. In terms of performance improvement, we apply an early bit-flipping strategy and utilize the \ell^1-norm distance representation. The algorithm is evaluated by computer simulations performed over Rayleigh flat fading channels and computational complexity analysis. Compared with the soft-output K-Best algorithm, the proposed algorithm saves at least 60% of the computations for detecting 4 \times 4 64-quadrature amplitude modulation (QAM) MIMO signal and, at the same time, provides better detection performance, making it a promising detection scheme for real-life hardware implementation. [ABSTRACT FROM PUBLISHER]

Driving simulators are increasingly being used for driver evaluation and/or education. In this paper, we describe the design and the modeling aspects of a 2-degree-of-freedom (2-DOF) low-cost motion platform allowing the rendering of the longitudinal and yaw movements. This prototype will be used to study various configurations of motion rendering and the impact of these variants on controllability and simulator sickness. The whole motion platform is considered as two coupled systems that are linked mechanically. The first system consists of a motorized rail for the longitudinal movement, which is mounted on top of the second system, which is a motorized turret allowing rotation of the platform. We present the platform mechanics and a number of experimental studies that have been carried out to obtain a characterization of the platform capabilities and frequency responses, as well as to assess platform performance in a classical drive operation. First conclusions and directions of future work are presented. [ABSTRACT FROM PUBLISHER]

The integration of third-generation (3G) cellular networks and IEEE 802.16e networks is an important interworking case within the forthcoming fourth-generation heterogeneous wireless networks. In this paper, we extend the virtual partitioning with preemption technique for admission control in cellular/802.16e interworking and evaluate its performance. First, we describe the mobility scenario between 3G cellular networks and IEEE 802.16e networks in terms of the horizontal (intrasystem) and vertical (intersystem) handoffs that can occur and derive the corresponding handoff rate equations. We then propose admission-control algorithms for connection requests that consider the class of service (i.e., real time or nonreal time) and the type of user (i.e., new or handoff). For the handoff requests, a different priority is assigned to each type of handoff. A joint connection- and packet-level optimization approach is used for quality-of-service (QoS) provisioning. The accuracy of the analytical model is validated via simulations. Numerical results show significant performance improvement. The blocking probabilities for new connection requests can be reduced by 70% when the joint QoS optimization approach is used. [ABSTRACT FROM AUTHOR]

In cognitive radio (CR) networks, secondary users can cooperatively sense the spectrum to detect the presence of primary users. In this paper, we propose a fully distributed and scalable cooperative spectrum-sensing scheme based on recent advances in consensus algorithms. In the proposed scheme, the secondary users can maintain coordination based on only local information exchange without a centralized common receiver. Unlike most of the existing decision rules, such as the OR-rule or the 1-out-of-N rule, we use the consensus of secondary users to make the final decision. Simulation results show that the proposed consensus scheme can have significant lower missing detection probabilities and false alarm probabilities in CR networks. It is also demonstrated that the proposed scheme not only has proven sensitivity in detecting the primary user's presence but also has robustness in choosing a desirable decision threshold. [ABSTRACT FROM AUTHOR]

In this paper, we propose a low-complexity decision-directed channel-estimation scheme, which offers improved performance for space-frequency-block-coded orthogonal frequency-division multiplexing (SFBC-OFDM) systems under doubly selective (i.e., frequency selective and fast fading) channels. First, we propose a square-root-free inverse-QR-decomposition-based groupwise recursive (SIQR-GR) channel-estimation algorithm employing sequences of scaled Givens rotations. The proposed SIQR-GR scheme recursively processes data decisions corresponding to the SFBC groups within each OFDM block to improve system performance under doubly selective channels. Furthermore, the avoidance of square roots and the utilization of scaled Givens rotations ensure that the proposed SIQR-GR scheme is computationally efficient. Second, we derive semi-analytical expressions for the normalized mean square error (NMSE) performance of SIQR-GR and verify the accuracy of the NMSE analysis via numerical simulations. Finally, we provide performance and complexity comparisons between SIQR-GR and previously proposed schemes. These comparisons show an excellent performance-complexity tradeoff achieved by SIQR-GR over the previous solutions under various channel conditions. [ABSTRACT FROM AUTHOR]

In this paper, we propose two simple orthogonal frequency-division multiplexing (OFDM) mean-delay estimation schemes, i.e., a channel impulse response (CIR)-based scheme and a differential scheme, which are applicable for adaptive algorithms including improved channel estimation and fast handover. Instead of time-domain processing which requires additional inverse fast Fourier transform (IFFT), the mean delay can be obtained in the proposed CIR-based scheme using the estimated frequency-domain CIR. When cell-specific preamble sequences are employed, the mean delay can also be estimated without CIR estimation in the proposed differential scheme using cross correlation of differentially correlated received signals, enabling further complexity reduction and performance improvement when the CIR estimation is not sufficiently accurate. The performance of the proposed schemes is verified by computer simulation. [ABSTRACT FROM AUTHOR]

An iterative receiver for a multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system is considered to jointly decode the transmitted bits and estimate the channel state. The receiver consists of a list detector, a turbo decoder, and a channel estimator that is based on the space-alternating generalized expectation-maximization (SAGE) algorithm. This paper proposes a way to improve the convergence of the iterative detection and decoding by using a priori information to also recalculate the candidate list, aside from the log-likelihood ratios (LLRs) of the coded bits. A new list parallel interference cancellation (PlC) detector is derived to approximate an a posteriori probability (APP) algorithm with reduced complexity and minimal losses of performance. Further- more, the organization of spectrally efficient decision-directed (DD) SAGE channel estimation under a constrained number of detector-decoder iterations is optimized by computer simulations, and the SAGE algorithm itself is modified for nonconstant envelope constellations. The list recalculation is shown to improve convergence. It is also shown that the list PlC detector with good initialization outperforms the K-best list sphere detector (LSD) in the case of small list sizes, whereas the complexities of the algorithms are of the same order. Despite the low preamble density and fast-fading channel, the proposed iterative receiver shows robust performance. [ABSTRACT FROM AUTHOR]

This paper presents a modified decorrelated delay lock loop (MD-DLL) for synchronous direct-sequence code-division multiple-access (DS-CDMA) systems under multiuser environments. The structure of the MD-DLL is similar to that of a traditional delay lock loop (T-DLL), aside from the fact that the despreading signals in T-DLL are replaced by a linear combination of all the users' code sequences with various weightings and timing offsets. The basic principles of MD-DLL are given as follows: 1) to use the decorrelating technique of a multiuser detector to remove the multiple-access interference at the on-time code position instant and 2) to choose a proper timing offset for the code sequences to reduce the weighting imbalance between the two arms of the tracking loop and suppress noise enhancement. The proposed MD-DLL scheme solves the tracking bias problems in a decorrelated delay lock loop under a low-signal-to-noise-ratio (SNR) condition. Computer simulations based on Gold code sequences are used to verify the findings. It is shown that MD-DLL achieves a better and stable S-curve with negligible tracking bias, better rms tracking error and mean-time-to-lose-lock performance under high-SNR conditions, and stronger near-far resistance than T-DLL. [ABSTRACT FROM AUTHOR]

In order to improve the performance of multicarrier code division multiple access (MC-CDMA) in the uplink channel, quasi-synchronous MC-CDMA with minimum-mean-square-error (MMSE)-based subcarrier-combining method is effective. However, conventional MMSE methods require a lot of pilot symbols for derivation of optimal weights. In this paper, in order to reduce the number of pilot symbols for uplink MC-CDMA systems, we propose a multistage recursive-least-square (MS-RLS) method for the derivation of the weights for the MMSE subcarrier combining. In the MS-RLS, the received symbols are stored in the buffer memory, and the RLS algorithm is repeatedly performed with a multistage structure by using the same pilot symbols. In this method, the weights and the inverse matrices of correlation matrices of the adjacent subcarriers are utilized for the initial values of the next-stage weight updating. Through computer simulation, we confirm that the performance of MC-CDMA in the uplink channel is improved by using the proposed MS-RLS method, even with short pilot symbols. [ABSTRACT FROM AUTHOR]

A suboptirnum search algorithm that considers the users' power profile in conjunction with a primary stage of polynomial-expanded (PE) linear multiuser detector for mobile uplink is proposed to suppress interference level. The initial stage is improved by mathematical analysis using two new ideas based on the Rayleigh-Ritz and Gershgorin theorems for both synchronous and asynchronous users. The performance of the PE structure is further enhanced by a new suboptimum search algorithm as the second stage. The structure of the search algorithm is based on starting from a point close to the optimum search and performing sequential steps to modify it. The proposed structures of the PE method and the suboptimum search algorithm are well suited together and make them collaboratively work without encountering a high level of complexity, since they use similar information as the correlation matrix. The power profile of the users is also considered in the suboptimum search algorithm, which led to more than a 50% reduction of the complexity, while keeping the performance almost the same. The performance of the final structure is carried out by means of computer simulations, and it has been compared to a partial parallel interference cancellation method with optimized partial coefficients. One of the main features of the structure proposed in this paper is that it performs its operations on the canonical formulation of the system, which makes it highly suitable for a broad range of systems such as multicarrier code division multiple access and multiinput multioutput. [ABSTRACT FROM AUTHOR]

In this paper, a novel preamble structure, including a synchronization field (S-field) and a cell-search field (C-field), is proposed for orthogonal-frequency-division-multiplexing-based cellular systems. An efficient algorithm for downlink synchronization and cell search using the preamble is also proposed. The synchronization and cell-search process includes the initial symbol-timing estimation using continuously or, at least, periodically transmitted downlink signal, the frame detection, the fine symbol-timing estimation, the frequency-offset estimation using the preamble S-field, and the cell identification using the preamble C-field. Performance of each synchronization and cell-search step is analyzed and verified by computer simulation. The overall performance of the synchronization and cell search is then analyzed in terms of the mean acquisition time. It is shown that the proposed preamble with the corresponding synchronization and cell-search algorithm can provide a very robust synchronization and cell-search capability, even in bad cellular environments. [ABSTRACT FROM AUTHOR]

Mobile positioning has drawn significant attention in recent years. Nonline-of-sight (NLOS) propagation error is the dominant error source in mobile positioning. Most previous research in this area has focused on NLOS identification and mitigation. In this paper, we investigate new positioning algorithms to take advantage of the NLOS propagation paths rather than canceling them. Based on a prior information about the NLOS path, a geometrical approach is proposed to estimate mobile location by using two NLOS paths. On top of this, the least-squares (LS)-based position estimation algorithm is developed to take multiple NLOS paths into account, and its performance in terms of root mean-square error (RMSE) is analyzed. A general LS algorithm considering both LOS and NLOS paths is also derived, and the maximum likelihood-based algorithm is presented to jointly estimate the mobile's and scatterers' positions. The Cramer-Rao lower bound on the RMSE is derived for the benchmark of the performance comparison. The performance of the proposed algorithms is evaluated analytically and is done via computer simulations. Numerical results demonstrate that the derived analytical results closely match the simulated results. [ABSTRACT FROM AUTHOR]

It has been well recognized that significant throughput gains can be leveraged in multiuser wireless communication systems by exploiting multiuser diversity with a smart scheduler. This scheduler collects channel state information (CSI) from all users and allocates the resources to the user(s) experiencing favorable channel conditions. However, for a frequency-division-duplex system with a large number of users, how to efficiently collect the required CSI will be a challenging task, especially when the feedback links are of limited capacity. In this paper, we propose a scheduling algorithm to exploit multiuser diversity with possibly imperfect one-bit channel state feedback. The basic idea is to define a threshold λ and let each user report one-bit information to the scheduler about the comparison between its measured channel fading level and λ. Correspondingly, the scheduler uses these feedback bits to classify all users into two sets and assigns the channel to one user belonging to the set experiencing favorable channel conditions. Several implementation schemes are developed by attacking the optimization of λ under different system configurations, covering both the case when the one-bit feedback is perfect and those when the one-bit feedback is imperfect. Computer simulations show that when the user number is large, say, more than ten users, the proposed scheduling supports significantly larger data rate over the round-robin scheduling, while in comparison with the optimum scheduling with complete CSI, the performance loss is limited if the one-bit feedback is of high reliability. In addition, our studies show that we can effectively enhance the robustness against feedback imperfectness by incorporating the feedback reliability into optimization of λ. [ABSTRACT FROM AUTHOR]

Recently, ultra wide-band (UWB) wireless communication technology, which provides high data transmission rates and is capable of linearly trading off between throughput and signal-to-noise ratio (SNR), has drawn much attention for short-range wireless networks. To fully exploit its desirable features and to minimize its interference with coexisting other systems requires knowledge of the SNRs at the receivers. In this paper, we propose an algorithm for estimating the pulse energy-to-noise ratio of an UWB signal through utilization of output samples from a correlator in the receiver and evaluate the performance of the proposed algorithm through computer simulation. A notable feature of the proposed algorithm is that it does not affect the effective throughput because the estimation process does not require any additional specific training signals. [ABSTRACT FROM AUTHOR]

A novel full rate space-time turbo trellis code, referred to as an assembled space-time turbo trellis code (ASTTTC), is presented in this paper. For this scheme, input information binary sequences are first encoded using two parallel concatenated convolutional encoders. The encoder outputs are split into four parallel streams and each of them is modulated by a QPSK modulator. The modulated symbols are assembled by a predefined linear function rather than punctured as in the standard schemes. This results in a lower code rate and a higher coding gain over time-varying fading channels. An extended two-dimensional (2-D) log-MAP (maximum a posteriori probability) decoding algorithm, which simultaneously calculates two a posteriori probabilities (APP), is developed to decode the proposed scheme. Simulation results show that, under the same conditions, the proposed code considerably outperforms the conventional space-time turbo codes over time-varying fading channels. [ABSTRACT FROM AUTHOR]

Resulting from Ph.D. research, a vehicle simulation program is proposed and continuously developed, which allows simulation of the behavior of electric, hybrid, fuel cell, and internal combustion vehicles while driving any reference cycle. The goal of the simulation program is to study power flows in the drivetrains of vehicles and the corresponding component losses, as well as to compare different drivetrain topologies. This comparison can be realized for energy consumption and emissions, as well as for performance (acceleration, range, maximum slope, etc.). The core of this program, consisting of a unique iteration algorithm, will be highlighted in this paper. This algorithm not only allows the calculation of the limits of vehicle acceleration in the function of drivetrain component characteristics, but at the same time is able to develop and evaluate the different power-management strategies of hybrid vehicles, combining combustion engines and electric motors. Furthermore, the comprehensive iteration algorithm is demonstrated to be very efficient in handling any type of working limit for aft components in different types of drivetrains, which results in an accurate and modular vehicle simulation program with high data flexibility. [ABSTRACT FROM AUTHOR]