Bobin Yao

DOD and DOA Estimation in Bistatic Non-Uniform Multiple-Input Multiple-Output Radar Systems

This letter investigates the joint estimation of the direction of departure (DOD) and direction of arrival (DOA) for multi-input multi-output (MIMO) radar systems. A novel estimation method based on non-uniform array configuration is proposed and the practical identifiability of the corresponding parameter is analyzed. The key idea is to use the Doppler diversity to construct a virtual MIMO array. Through the theoretical proof, we demonstrate that the proposed method can provide much stronger parameter identifiability than the conventional ones, and also can improve the parameter estimation performance. Numerical simulations verify the effectiveness of the proposed algorithm.

Destination Assisted Secret Wireless Communication With Cooperative Helpers

This letter investigates a novel two-stage cooperative scheme to secure the communication system with one source, one destination and multiple helpers. Herein, the source mixes the confidential messages with the interferences transmitted by the helpers and destination. Since the helpers and destination serve to suppress interferences, the destination can acquire an interference-free signal, however the eavesdropper is still confused. This scheme can achieve positive secrecy rate even when the eavesdroppers channel is much better than the legitimate link, and only requires local channel state information (CSI) and a few parameters of the main link. An efficient sub-optimal algorithm for the majorization of system parameters is proposed to avoid global search and the practical case without eavesdroppers CSI is also considered. Simulation results demonstrate the effectiveness of the proposed scheme and algorithm.

Control of two-phase flow in microfluidics using out-of-phase electroconvective streaming

We propose herein to make use of rotating electric fields for achieving flexible control on the hydrodynamic behavior of two miscible co-flowing water solutions in straight microchannels, in the context of a new manipulation tool for stratified liquid contents of microfluidic systems. Our theoretical analysis indicates that, while fluids of distinct electrical conductivities and identical permittivity are parallel pumped into the mainchannel, a circularly traveling field, as emitted from a four-phase electrode array surrounding the channel sidewalls, can direct the deflection of diffusing phase interface between the side-by-side miscible electrolyte streams asynchronously at half of the interfacial relaxation frequency, where the co-field electrorotational torque becomes most appreciable. An immediate application of the out-of-phase electroconvective streaming is that time required for electrolyte mixing is reduced because the area of two-phase contact interface is dramatically enlarged, and a serial comb...

Simulation Analysis of Rectifying Microfluidic Mixing with Field-Effect-Tunable Electrothermal Induced Flow

We report herein field‐effect control on in‐phase electrothermal streaming from a theoretical point of view, a phenomenon termed “alternating‐current electrothermal‐flow field effect transistor” (ACET‐FFET), in the context of a new technology for handing analytes in microfluidics. Field‐effect control through a gate terminal endows ACET‐FFET the ability to generate arbitrary symmetry breaking in the transverse vortex flow pattern, which makes it attractive for mixing microfluidic samples. A computational model is developed to study the feasibility of this new microfluidic device design for micromixing. The influence of various parameters on developing an efficient mixer is investigated, and an integrated layout of discrete electrode array is suggested for achieving high‐throughput mixing. Our physical demonstration with field‐effect electrothermal flow control using a simple electrode structure proves invaluable for designing active micromixers for modern micro total analytical system.

On the Bipolar DC Flow Field-Effect-Transistor for Multifunctional Sample Handing in Microfluidics: A Theoretical Analysis under the Debye–Huckel Limit

We present herein a novel method of bipolar field-effect control on DC electroosmosis (DCEO) from a physical point of view, in the context of an intelligent and robust operation tool for stratified laminar streams in microscale systems. In this unique design of the DC flow field-effect-transistor (DC-FFET), a pair of face-to-face external gate terminals are imposed with opposite gate-voltage polarities. Diffuse-charge dynamics induces heteropolar Debye screening charge within the diffuse double layer adjacent to the face-to-face oppositely-polarized gates, respectively. A background electric field is applied across the source-drain terminal and forces the face-to-face counterionic charge of reversed polarities into induced-charge electroosmotic (ICEO) vortex flow in the lateral direction. The chaotic turbulence of the transverse ICEO whirlpool interacts actively with the conventional plug flow of DCEO, giving rise to twisted streamlines for simultaneous DCEO pumping and ICEO mixing of fluid samples along the channel length direction. A mathematical model in thin-layer approximation and the low-voltage limit is subsequently established to test the feasibility of the bipolar DC-FFET configuration in electrokinetic manipulation of fluids at the micrometer dimension. According to our simulation analysis, an integrated device design with two sets of side-by-side, but upside-down gate electrode pair exhibits outstanding performance in electroconvective pumping and mixing even without any externally-applied pressure difference. Moreover, a paradigm of a microdevice for fully electrokinetics-driven analyte treatment is established with an array of reversed bipolar gate-terminal pairs arranged on top of the dielectric membrane along the channel length direction, from which we can obtain almost a perfect liquid mixture by using a smaller magnitude of gate voltages for causing less detrimental effects at a small Dukhin number. Sustained by theoretical analysis, our physical demonstration on bipolar field-effect flow control for the microfluidic device of dual functionalities in simultaneous electroconvective pumping and mixing holds great potential in the development of fully-automated liquid-phase actuators in modern microfluidic systems.

Distributed Angle Estimation by Multiple Frequencies Synthetic Array in Wireless Sensor Localization System

In this paper, we address the problem of distributed angle estimation in wireless sensor localization system. Given that the practical limitations on size and cost, i.e., anchor node cannot equip a complicated antenna or antenna array, we devise an alternative measure based on a fixed-spacing two-antenna equipment. Through the multiple frequencies tuning, a virtual non-uniform linear array, called multiple frequencies synthetic array (MFSA), can be rebuilt independently at each sensor node. We first provide in theory the angle unambiguity conditions for such virtual array and then propose two different algorithms to achieve the distributed angle of departure (AOD) estimation. The first algorithm is based on the spectral searching technique, which is an improved version of the conventional rank reduction estimator (RARE) and has the same performance but less computational complexity. To further alleviate the computational burden at sensor node end, we convert the above angle estimation into a congruence problem and provide another closed-form solution based on Chinese remainder theorem (CRT). We also derive the Cramer-Rao bound for the MFSA and demonstrate theoretically that the latter algorithm from the perspective of cumulative circular distance is suboptimal when compared with the former one. Numerical examples are provided to show the validity of the proposed algorithms and the corresponding conclusions.

Joint AOD and CFO estimation in wireless sensor networks localization system

Self-localization system of wireless sensor networks based on angle of departure (AOD) is studied in this paper. In AOD model, anchor node with multi-antenna transmits orthogonal pilot signals to sensor node with single antenna, which entitles the sensor node to function as equipping multi-antenna. Given that the limited number of antenna at anchor nodes will result in degree of freedom (DOF) deficiency at sensor node when dealing with more multipath components (MPC), we adopt a novel method without requiring extra antennas. The proposed algorithm simultaneously includes the oscillator mismatch between anchor node and sensor node, i.e., carrier frequency offset (CFO). With the aid of anchors movement and CFO, the equivalent antenna array at sensor node is expended by synthetic aperture procedure to a much larger one, which subsequently improve the estimation ability to MPCs. In addition, the close-form solutions of CFO and AOD are also derived. The effectiveness and performance of proposed algorithm are demonstrated by numerical simulations.

Angle of departure aided sensor localization technique under multipath environment

A new angle of departure (AOD) aided distributed localization approach for wireless sensor node is proposed in this paper. An L-shaped antenna array is arranged on anchor node end and the ground single antenna sensor node conduct its own line of sight AOD estimation for self-localization. Considering the limited degree of freedom provided by the anchor node can not guarantee a successful recognition to the LOS signal component in multipath environment, we adopt the minimum redundancy configuration. Via the intrinsic character of wireless channel, the maximum degree of freedom through performing two-dimension joint difference co-array operation can be obtained at sensor node end. Therefore, the sensor node can identify the LOS signal component in a very high probability with a rebuild degree of freedom increased virtual array. The validity of proposed methods are verified by numerical examples.

AOD estimation in WSN localization system with synthetic aperture technique

Angel of departure (AOD) based distributed localization scheme in wireless sensor networks allows the single antenna sensor node to estimate its own AOD information by an equivalent antenna array for further position calculation. However, the condition that the number of antennas at the multi-antenna agent/anchor node should be larger than the number of multipath signal components (MPCs) constrains its actual application. In this paper, we provide a more practical approach to achieve AOD information estimation under multipath environment. Given that the sensor node can not identify the line of sight (LOS) signal component due to the insufficient degree of freedom, which is determined by the above limiting condition, we introduce a synthetic aperture technique with the aid of a fast moving multi-antenna agent/anchor node. This operation greatly enlarges the degree of freedom of the equivalent antenna array constructed at sensor node end but without requiring other extra physical antennas equipped at agent/anchor node or sensor node end, which means that it relaxes the limiting condition. Therefore, the AOD information of LOS signal component can be estimated and extracted successfully in complex multipath environment. Theoretical analysis proves the effectiveness of our proposed synthetic aperture technique and numerical simulations show great performance improvement.

Weighted Subspace Fitting for Two-Dimension DOA Estimation in Massive MIMO Systems

Massive multiple-input multiple-output system can enable multi-stream transmission for high spectrum efficiency, which is a key technology in future 5G cellular networks. In this paper, we degenerate a direction of arrival (DOA) related 2-D weighted subspace fitting function into two independent parameterized 1-D versions. Based on this, we develop a novel 2-D DOA estimation algorithm, which can be utilized to assist in performing downlink precoding. Furthermore, we also make an analysis on the computational complexity and the theoretical Cramér–Rao lower bound. The direct merits are as follows: the proposed algorithm includes only once polynomial rooting and also does not require angle paring, hence it is of computational efficiency; in addition, compared with some existing algorithms, it can achieve higher 2-D angle estimating accuracy. A series of Monte Carlo simulations are subsequently carried out, which demonstrate the effectiveness of the proposed algorithm.