Alignment Scheme Research Articles

Joint Optimization of Power Consumption and Transmission Delay in a Cache-Enabled C-RAN

In this letter, we consider a cache-enabled cloud radio access network with single-antenna base stations and single-antenna mobile users. Each base station can access the central processor of the network via a separate backhaul link with limited capacity. We utilize the interference alignment scheme as the transmission strategy between base stations and users. By assuming a block transmission scheme, we define a related data transmission delay. We derive the transmission delay and network power consumption. At last, we solve the problem of joint optimization of data transmission delay and network power consumption using DC programming algorithm. In our numerical results, we investigate the trade-off between delay and power consumption, and compare the results with those of a prior work that does not take the transmission delay into account in its optimization problem.

Prediction of Unsteady Developed Tip Vortex Cavitation and Its Effect on the Induced Hull Pressures

Reducing the on-board noise and fluctuating pressures on the ship hull has been challenging and represent added value research tasks in the maritime industry. Among the possible sources for the unpalatable vibrations on the hull, propeller-induced pressures have been one of the main causes due to the inherent rotational motion of propeller and its proximity to the hull. In previous work, a boundary element method, which solves for the diffraction potentials on the ship hull due to the propeller, has been used to determine the propeller induced hull pressures. The flow around the propeller was evaluated via a panel method which solves in time for the propeller loading, trailing wake, and the sheet cavities. In this article, the propeller panel method is extended so that it also solves for the shape of developed tip vortex cavities, the effects of which are also included in the evaluation of the hull pressures. The employed unsteady wake alignment scheme is first applied, in the absence of cavitation, to investigate the propeller performance in non-axisymmetric inflow, such as the inclined-shaft flow or the flow behind an upstream body. In the latter case, the propeller panel method is coupled with a Reynolds-Averaged Navier–Stokes (RANS) solver to determine the effective wake at the propeller plane. The results, including the propeller induced hull pressures, are compared with those measured in the experiments as well as with those from RANS, where the propeller is also simulated as a solid boundary. Then the methods are applied in the cases where partial cavities and developed tip vortex cavities coexist. The predicted cavity patterns, the developed tip vortex trajectories, and the propeller-induced hull pressures are compared with those measured in the experiments.

Partial Interference Alignment Scheme for Three-Tier Downlink Heterogeneous Networks

The introduction of the relay in heterogeneous networks (HetNets) can enhance cell-edge signals, but it will also bring coexistence of multiple interference which is composed of co-tier, cross-tier and cross time slot (caused by the half-duplex mode of the relay) interference, resulting in the ineffectiveness of the existing interference alignment (IA) schemes. To solve the above problem, the partial IA scheme, which achieves IA in the case of limited antennas by rationally designing the order and method of eliminating interference, is proposed in this paper. First, we align the interference from other base stations (BSs) into the interference space generated by pico BS to reduce the interference dimension of the relay, and then solve the interference between BSs and users by null space and concatenated precoding schemes. Furthermore, the feasibility condition of antenna configuration is analyzed. The simulation results show that the proposed scheme is superior to the traditional IA scheme in sum rate, and the performance of the proposed scheme is further improved as the relay transmission power increases.

Interference Alignment for MIMO Downlink Heterogeneous Networks

In this paper, we investigate the interference alignment schemes for the downlink of a heterogeneous network (HetNet), where the macro base station (BS) can serve arbitrary number of macro users. Furthermore, the number of data streams for macro users and pico users can be different. Firstly, we propose a basic grouping method aided interference alignment (IA) scheme and derive the transmit and receiver beamforming matrices in a closed-form expression. Furthermore, for the case where the number of antennas at pico BS is equal to the number of antennas at each user, we propose an advanced generalized eigenvalue decomposition (GEVD) based grouping method aided IA scheme which can reduce the number of transmit antennas required at the pico BS compared to the basic grouping method aided IA scheme. Moreover, we also derive the maximum total achievable degrees of freedom (DoF) for each scheme. In addition, it can be proved that the maximum total achievable DoF of the GEVD based grouping method aided IA scheme is higher than or equal to that of the basic grouping method aided IA scheme for the same configuration.

天文望远镜无偏消旋镜装调方案设计及验证

天文望远镜无偏消旋镜装调方案设计及验证

Fully-/Partially-Connected Hybrid Beamforming Architectures for mmWave MU-MIMO

Hybrid digital analog (HDA) beamforming has attracted considerable attention in practical implementation of millimeter wave (mmWave) multiuser multiple-input multiple-output (MU-MIMO) systems due to the low power consumption with respect to its fully digital baseband counterpart. The implementation cost, performance, and power efficiency of HDA beamforming depends on the level of connectivity and reconfigurability of the analog beamforming network. In this paper, we investigate the performance of two typical architectures that can be regarded as extreme cases, namely, the fully-connected (FC) and the one-stream-per-subarray (OSPS) architectures. In the FC architecture each RF antenna port is connected to all antenna elements of the array, while in the OSPS architecture the RF antenna ports are connected to disjoint subarrays. We jointly consider the initial beam acquisition and data communication phases, such that the latter takes place by using the beam direction information obtained by the former. We use the state-of-the-art beam alignment (BA) scheme previously proposed by the authors and consider a family of MU-MIMO precoding schemes well adapted to the beam information extracted from the BA phase. We also evaluate the power efficiency of the two HDA architectures taking into account the power dissipation at different hardware components as well as the power backoff under typical power amplifier constraints. Numerical results show that the two architectures achieve similar sum spectral efficiency, while the OSPS architecture is advantageous with respect to the FC case in terms of hardware complexity and power efficiency, at the sole cost of a slightly longer BA time-to-acquisition due to its reduced beam angle resolution.

Exploiting the Vulnerability of Relative Data Alignment in Phasor Data Concentrators to Time Synchronization Attacks

In this paper, we formulate an attack on the relative data alignment scheme used by Phasor Data Concentrators (PDCs) to aggregate and stream phasor measurements. This attack leverages the specification governing the PDC functionality in a Wide Area Measurement System (WAMS). Using a Phasor Measurement Unit (PMU) as an attack surface, an adversary injects an attack vector in the PMU timing to manipulate the PDC functionality and force it to drop phasors received from benign PMUs. We expose the PDC relative data alignment scheme to this attack, formulate the attack surface and vector selection as a Linear Program (LP), and demonstrate the impact of this attack on system observability. Our experimental results on standard IEEE test systems demonstrate the attack semantics and impact. In addition, we present the attack in a case study using hardware-in-the-loop co-simulation environment. The outcome of these tests validate the vulnerability of the PDC aggregation scheme to this attack and its significance in targeting system observability.

Deep Learning-Based Stair Segmentation and Behavioral Cloning for Autonomous Stair Climbing

Mobile robots are widely used in the surveillance industry, for military and industrial applications. In order to carry out surveillance tasks like urban search and rescue operation, the ability to traverse stairs is of immense significance. This paper presents a deep learning-based approach for semantic segmentation of stairs, behavioral cloning for stair alignment, and a novel mechanical design for an autonomous stair climbing robot. The main objective is to solve the problem of locomotion over staircases with the proposed implementation. Alignment of a robot with stairs in an image is a traditional problem, and the most recent approaches are centered around hand-crafted texture-based Gabor filters and stair detection techniques. However, we could arrive at a more scalable and robust pipeline for alignment schemes. The proposed deep learning technique eliminates the need for manual tuning of parameters of the edge detector, the Hough accumulator and PID constants. The empirical results and architecture of stair alignment pipeline are demonstrated in this paper.

Secure Retrospective Interference Alignment

In this paper, the K-user interference channel with secrecy constraints is considered with delayed channel state information at transmitters (CSIT). We propose a novel secure retrospective interference alignment scheme in which the transmitters carefully mix information symbols with artificial noises to ensure confidentiality. Achieving positive secure degrees of freedom (SDoF) is challenging due to the delayed nature of CSIT, and the distributed nature of the transmitters. Our scheme works over two phases: Phase one, in which each transmitter sends information symbols mixed with artificial noises, and repeats such transmission over multiple rounds. In the next phase, each transmitter uses the delayed CSIT of the previous phase and sends a function of the net interference and artificial noises (generated in previous phase), which is simultaneously useful for all receivers. These phases are designed to ensure the decodability of the desired messages while satisfying the secrecy constraints. We present our achievable scheme for three models, namely: (1) K-user interference channel with confidential messages (IC-CM), and we show that SDoF is achievable; (2) K-user interference channel with an external eavesdropper (IC-EE); and (3) K-user IC with confidential messages and an external eavesdropper (IC-CM-EE). We show that for the K-user IC-EE, SDoF is achievable, and for the K-user IC-CM-EE, is achievable. To the best of our knowledge, this is the first result on the K-user interference channel with secrecy constrained models and delayed CSIT that achieves an SDoF which scales with , square-root of number of users.

A low-complexity permutation alignment method for frequency-domain blind source separation

Frequency-domain blind source separation is an effective way to separate the signals from convolutive mixtures. The independence component analysis (ICA) is commonly employed to separate signals in each frequency bin, resulting in the well-known permutation problem. To resolve this problem, we present a low-complexity permutation alignment method based on the inter-frequency dependence of signal power ratio. A bin-wise permutation alignment is first carried out across all the frequency bins by measuring the correlation between the current frequency bin and the previous one, but only the permutation with a high confidence is fixed. The permutation with low confidence is then determined by maximizing the correlation between the current frequency bin and a local centroid, which is calculated from a set of determined frequency bins with high confidence. By so doing, the permutation for most frequency bins is aligned without iterations. Finally, a clustering algorithm with centroids is adopted to achieve the fine global optimization in the fullband with only a few iterations. Experiment results show that the proposed method achieves a comparable performance with the state-of-the-art permutation alignment schemes, but the new method achieves a significant computational saving.

On the Secure Degrees of Freedom of Two-Way 2 × 2 × 2 MIMO Interference Channel

We investigate the secure degrees of freedom (SDoF) for the two-way $2\times 2\times 2$ MIMO interference channel (IC) under three wiretap models, i.e., the confidential messages (CM) model, the untrusted relays (UR) model, and the combined CM and UR (CM-UR) model. For the general case of arbitrary antenna configuration under each wiretap model, we derive the upper bound on SDoF with Markov chain and secrecy constraints, and obtain the achievability schemes with designed interference neutralization, cooperative jamming, and interference alignment schemes. To gain insight on these bounds, we further consider the special case where each user node has $M$ antennas and each relay node has $N$ antennas, and highlight the modification process when achieving the maximum SDoF. For such special case, we show that the optimum SDoF of the CM model is achieved in the regimes $M\ge N$ and $M ; and for the UR model and CM-UR model, the optimum SDoF is achieved in the regimes $N\le ({M}/{2})$ , $N > 2M$ , and $N=M$ .

Research on Polar-region Coarse Alignment Algorithm Based on Grid System

Due to the convergence of meridians in polar regions, the geography-based northern-azimuth mechanics arrangement has problems such as increase of error and computational overflow in polar navigation, and the traditional compass alignment scheme is unable to operate normally. In this paper, the problem in polar navigation is solved by using the mechanics arrangement scheme, and a simulated analysis has been carried out on the application of compass alignment in high latitudes through static data, which verifies that it is unable to operate normally at the pole. Then compass alignment has been replaced by anti-sloshing coarse alignment and a simulated verification has been conducted on its correctness. After that, the latitude increment method is used to convert the sports car data at low-latitude regions to high-latitude regions and carry out a semi-physical simulation, which further verifies the correctness of the grid inertial navigation and the coarse alignment method in anti-sloshing polar region.

Relocation schemes of picks with cutting, coupling and group cuts on shearer cutting drums

The possibilities of increasing the efficiency of separating coal from the massif by improving the pick alignment schemes of shearer cutting drums are considered. Given the existing structural limitations of the radial extension of the picks and the thickness of the cuts, an increase in efficiency is achieved by using combined series-group schemes for arranging picks, including energy-efficient cutting, paired and group with a larger cross-sectional area of the cuts and, therefore, with a larger particle size of the separated coal fragments, reduced dust yield and specific energy consumption.

Near Optimal Coded Data Shuffling for Distributed Learning

Data shuffling between distributed cluster of nodes is one of the critical steps in implementing large-scale learning algorithms. Randomly shuffling the data-set among a cluster of workers allows different nodes to obtain fresh data assignments at each learning epoch. This process has been shown to provide improvements in the learning process (via testing and training error). However, the statistical benefits of distributed data shuffling come at the cost of extra communication overhead from the master node to worker nodes, and can act as one of the major bottlenecks in the overall time for computation. There has been significant recent interest in devising approaches to minimize this communication overhead. One approach is to provision for extra storage at the computing nodes. The other emerging approach is to leverage coded communication to minimize the overall communication overhead. The focus of this work is to understand the fundamental tradeoff between the amount of storage and the communication overhead for distributed data shuffling. In this paper, we first present an information theoretic formulation for the data shuffling problem, accounting for the underlying problem parameters (number of workers, $K$ , number of data points, $N$ , and available storage, and $S$ per node). We then present an information theoretic lower bound on the communication overhead for data shuffling as a function of these parameters. We next present a novel coded communication scheme and show that the resulting communication overhead of the proposed scheme is within a multiplicative factor of at most $\frac {K}{K-1}$ from the lower bound (which is upper bounded by 2 for $K\geq 2$ ). Furthermore, we present new results towards closing this gap through a novel coded communication scheme, which we call the aligned coded shuffling. This scheme is inspired by the ideas of coded shuffling and interference alignment. In particular, we show that the aligned scheme achieves the optimal storage vs communication trade-off for $K , and further reduces the maximum multiplicative gap down to $\frac {K-\frac {1}{3}}{K-1}$ , for $K\geq 5$ .

Combined High-Resolution Optical Tweezers and Multicolor Single-Molecule Fluorescence with an Automated Single-Molecule Assembly Line.

We present an instrument that combines high-resolution optical tweezers and multicolor confocal fluorescence spectroscopy along with automated single-molecule assembly. The multicolor allows the simultaneous observation of multiple molecules or multiple degrees of freedom, which allows, for example, the observation of multiple proteins simultaneously within a complex. The instrument incorporates three fluorescence excitation lasers, with a reliable alignment scheme, which will allow three independent fluorescent probe or FRET measurements and also increases flexibility in the choice of fluorescent molecules. We demonstrate the ability to simultaneously measure angstrom-scale changes in tether extension and fluorescence signals. Simultaneous tweezers and fluorescence measurement are particularly challenging because of fluorophore photobleaching, even more so if multiple fluorophores are to be measured. Therefore, (1) fluorescence excitation and detection is interlaced with time-shared dual optical traps. (2) We investigated the photostability of common fluorophores. The mean number of photons emitted before bleaching was unaffected by the trap laser and decreased only slightly with increasing excitation laser intensity. Surprisingly, we found that Cy5 outperforms other commonly used fluorophores by more than fivefold. (3) We devised computer-controlled automation, which conserves fluorophore lifetime by quickly detecting fluorophore-labeled molecule binding, turning off lasers, and moving to add the next fluorophore-labeled component. The single-molecule assembly line enables the precise assembly of multimolecule complexes while preserving fluorophores.

On the Feasibility of Interference Alignment With Finite Channel Extensions for MIMO Interference Broadcast Channels With Common Messages

In this paper, we analyze the feasibility of interference alignment (IA) schemes with $T$ finite channel extensions for multi-input–multi-output (MIMO) interference broadcast channel (IBC) with common messages, where each base station transmits one common single data stream to all users within its cell. We investigate necessary conditions of feasibility of the IA schemes for this network in three different scenarios, i.e., with no channel extensions ( $T=1$ ), with $T$ ( $T\ge 2$ ) channel extensions for a positive measure of channel coefficients, and with $T$ ( $T \ge 2$ ) dependent channel extensions. These necessary conditions impose constraints on system configurations, e.g., the number of users, the number of antennas, the number of cells, and the number of channel extensions, which must be satisfied when the IA schemes are feasible, and also implicitly provide constraints on the upper bound of degrees of freedom (DoF) with finite channel extensions.

Space‐frequency signal alignment for optimal DoF in multi‐carrier MIMO‐NOMA systems

In the process of maximising the utilisation of spatial and radio resources, interference is the major factor limiting the system capacity. In this Letter, a novel multi-carrier signal alignment (MCSA) scheme based on diagonal-block channel matrix is first proposed, to mitigate the interference in downlink multi-input multi-output non-orthogonal multiple access (MIMO-NOMA) cellular networks. The maximum degree of freedom (DoF) can be achieved by the iterative design of MCSA. Simulation results show the effectiveness and superiority of the proposed MCSA scheme in improving the sum-rate and DoF, by fully using multiple antennas and multiple carriers.

Metro gauge inspection system based on mobile laser scanning technology

Detecting metro gauge is very important for the safe operation of the subway. In this study, we design a low-cost metro tunnel mobile scanning system (MDS-TJ-1), which integrates a laser profile scanner with an inertial measure unit and an odometer to provide positioning and attitude parameters of the trajectory. The Lagrange interpolation is used to accomplish the time unification of different sensors. A dynamic alignment scheme for profile scanner is proposed based on the designed plane reflector target with high reflectivity. The error accumulation of the odometer is corrected by recognising the tunnel longitudinal joints, and finish the multi-source data fusion. The horizontal ray method is developed to process the metro gauge inspection. The experiment results show that the alignment accuracy of scanner is within 8 mm, the inner coincidence of the point cloud is within 3 cm, and the average error of the gauge inspection is 7.8 mm.

Entangled-photon decision maker

The competitive multi-armed bandit (CMAB) problem is related to social issues such as maximizing total social benefits while preserving equality among individuals by overcoming conflicts between individual decisions, which could seriously decrease social benefits. The study described herein provides experimental evidence that entangled photons physically resolve the CMAB in the 2-arms 2-players case, maximizing the social rewards while ensuring equality. Moreover, we demonstrated that deception, or outperforming the other player by receiving a greater reward, cannot be accomplished in a polarization-entangled-photon-based system, while deception is achievable in systems based on classical polarization-correlated photons with fixed polarizations. Besides, random polarization-correlated photons have been studied numerically and shown to ensure equality between players and deception prevention as well, although the CMAB maximum performance is reduced as compared with entangled photon experiments. Autonomous alignment schemes for polarization bases were also experimentally demonstrated based only on decision conflict information observed by an individual without communications between players. This study paves a way for collective decision making in uncertain dynamically changing environments based on entangled quantum states, a crucial step toward utilizing quantum systems for intelligent functionalities.

Numeric estimation of resource requirements for a practical polarization-frame alignment scheme for quantum key distribution (QKD)

Abstract Owing to physical orientations and birefringence effects, practical quantum information protocols utilizing optical polarization need to handle misalignment between preparation and measurement reference frames. For any such capable system, an important question is how many resources – for example, measured single photons – are needed to reliably achieve alignment precision sufficient for the desired quantum protocol. Here, we study the performance of a polarization-frame alignment scheme used in prior laboratory and field quantum key distribution (QKD) experiments by performing Monte Carlo numerical simulations. The scheme utilizes, to the extent possible, the same single-photon-level signals and measurements as for the QKD protocol being supported. Even with detector noise and imperfect sources, our analysis shows that only a small fraction of resources from the overall signal – a few hundred photon detections, in total – are required for good performance, restoring the state to better than 99% of its original quality.