Abstract:Explaining the causes of unsatisfiability of the Boolean formulas has many real applications in various fields. The minimum unsatisfiable subformulas can provide most accurate explanations for the causes of infeasibility in many application fields such as the automatic circuits' synthesis. Therefore, two best algorithms of extracting the minimum unsatisfiable subformulas, respectively called the branch-and-bound algorithm and greedy genetic algorithm, were integrated into the automatic synthesis tool of decoding circuits. Adopting the standard encoding circuits in communication fields as the benchmarks, the study compared and analyzed the two algorithms. The experimental results show that the greedy genetic algorithm outperforms the branch-and-bound algorithm on runtime and removed clauses per second. The results also show that the unsatisfiable subformulas play an important role in the process of synthesizing automatically the decoding circuits.

Abstract:In 3D-IC (three dimensional-integrated circuit) technology based 3D SRAM(three-dimensional static random access memory), a large number of TSVs (through silicon vias) have been implemented in circuits. The manufacturing process of TSV is not mature，which makes TSVs more prone to open defects and brings new challenges to the 3D SRAM test. The existing method of TSV test can find out where the faults are, but it needs extra specific circuit to implement, which increases both the area overhead and its design complexity. In consideration of what was discussed above, a new idea to detect the open defects of TSV based on a test algorithm was proposed. It proved to be an effective method to detect the open defects of TSV in 3D SRAM using BIST(built-in self test) without any extra overhead. Results show that the proposed method has no functional problem with the algorithm and it can realize the purpose of TSV open fault detection.

Abstract:With the ever-increasing design complexity in the processor micro-architecture, performance analysis becomes more and more important in the research and design of processors. Performance models are used widely in the performance analysis, which are more suitable for the design space exploration in the early stage. When used in microarchitecture optimizations, the accuracy and the speed of performance models are the limiting factors. Therefore, a performance analysis method based on counters was proposed. In this method, the RTL register transfer level code of a processor core was used as a baseline, and a specialized performance monitor unit was added to collect the events needed by the micro-architecture analysis and optimization. Then the collected events were sent to a result analyzer, where the factors affecting the performance were obtained. By a dopting the method, we analyzed what affects the performance in running SPEC CPU2000 benchmarks on FPGA(field-programmable gate array) prototyping, and optimized the micro-architecture of processor core according to the analysis results. The performance of the optimized processor core is improved obviously.

Abstract:The 3D SRAM (three-dimensional static random access memory) will take the place of 2D SRAM (two-dimensional static random access memory), and will be widely used in high performance microprocessor. However, 3D SRAM still suffers from the dangers of soft error. A novel 3D SRAM soft error analysis platform was designed for studying the soft error characteristic of 3D SRAM. The soft error characteristic of the designed 3D SRAM and the original 2D SRAM were analyzed by using our designed platform. It is found that 3D SRAM and 2D SRAM have the same upset cross section, but the soft error of 3D SRAM is more serious than that of 2D SRAM, which makes it difficult to harden 3D SRAM by using error correction codes technologies. At the static test mode, the upset sensitive nodes were only distributed in the memory array of both 3D SRAM and 2D SRAM. It indicates that the logic circuit can’t induce soft error at static test mode.

Abstract:The packet processing performance of the general multi-core architecture is plagued by many factors, including high packet IO cost, multi-core share memory and process scheduling competition, TLB entries failure rate, etc. Therefore, a TABM (thread affinity for buffer management mechanism) based on multi-core network packet processing system, which is oriented to high-speed packet forwarding application was proposed and completed on network dedicated co-processing engine. The TABM adopts thread affinity scheduling strategy with no interrupt, sends each packet data and descriptor which contains control and buffer address information to several successive shared buffers according to the corresponding thread ID, and organizes the packets and descriptors which processed in the same thread in the form of a chain. The packet forwarding performance was tested on the basis of general multi-core and field-programmable gate array platform. The experimental data show that the average packet forwarding performance is promoted by about 12.4% and the IO cost and the TLB entries failure rate are reduced by adopting the TABM. 

Abstract:LLC (last level Cache) plays an important role in multi-core systems. A shared LLC management scheme with fine granularity, low latency and simple hardware complexity was proposed. The performance goal was translated into eviction probabilities of each core. Then, a victim core, which was near the current core and had higher eviction probability was chosen to provide the victim block for replacement. In this way, LLC was dynamically partitioned among all cores at finer granularity of Cache blocks. This proposal is more flexible than traditional way-partitioning scheme. In addition, the combination of location information and eviction probability improves the locality between Cache resources and the corresponding cores, which can reduce the Cache access latency. The proposed scheme requires only little additional hardware changes to traditional Cache structure. Results on M5 simulator suggest that the performance can improve from 6.8% to 22.7% when comparing with the related works. 

Abstract:A multi-level arbitration based on resource reservation in optical network-on-chip was proposed. The fast and high efficiency arbitration scheme divided the network into multi-stages. With the design of multi priority queues in every node, arbiters provided differential transmissions for different kinds of flows. The arbiter also presented the transmit bund resource reservation scheme to fairly reserve time slots for all nodes, thus achieving the throughput of 100%. The fast arbitration channels were proposed and designed to degrade the arbitration period, and the packet transmitting delay was reduced. The simulation results show that, with the multi-level arbitration based on resource reservation, all nodes are allocated with almost equal service under various patterns. This scheme improves throughput by 17% when compared with FeatherWeight under the self-similar traffic pattern, and eliminats arbitration delay by 15% to 2-pass arbitration, incurring total power overhead by 5%.

Abstract:In order to reduce the consumers’ costs of renting resources in cloud computing system, a random integer linear programming model and a method for memory reservation were presented on the basis of cost constraints. Combined with the memory resource price of the reservation plan and the on-demand plan, the random cost function which consists of costs and total amount of resources constraints was designed. Aimed at minimizing the expected value of the cost function, the optimal amount of memory reserved was obtained on the basis of the probability distribution of memory consumption. The experiments show that the cost of renting recourses by utilizing this method is less than the cost of renting recourses by adopting reservation plan, on-demand plan and other similar methods.

Abstract:Architectural solutions of on-chip Cache fault tolerance are considered as effective means for high persistent failure probabilities. However, less fault injection tools for on-chip Caches are available. Therefore, the CacheFI, a fault injection tool based on the full-system simulator Simics was proposed. A separate mechanism of the fault generation and injection was employed. Fault generation consists of stochastic distribution control, failure patterns and explosive timing. Fault injection was designed to focus on the requirement of repeatability and modularity. According to the experiments based on Simics and 15 benchmarks from SPEC CPU2000, it evaluates typical micro-architectural fault mechanisms, such as Buddy, MAEP(matching access and error pattern) etc. by injecting Cache faults with CacheFI. Consequently, it presents the weakness and issues of these typical mechanisms.

Abstract:To the applications with irregular accessing memory, if the overhead of accessing memory for a given application is much greater than that of computation, it will make the helper thread lag behind the main thread. Hereby, an improved helper thread prefetching model by adding control parameters was proposed. The gradient descent algorithm is one of the most popular machine learning algorithms, which was adopted to determine the optimal control parameters. The amount of the memory access tasks was controlled by the control parameters effectively, which makes the helper thread be finished ahead of the main thread. The experiment results show that the speedup of system performance is achieved by 1.1 times to 1.5 times.

Abstract:Aimed at the problem which Mars can rarefy atmospheric dynamic errors that caused by seasonal variations and diurnal changes during Mars areobraking, the orbital dynamic equation including aerodynamic force was established. Through the research of aerodynamic parameter calculation method applied to rarefied flow, the effect of dynamic errors on aerodynamic force and aerobrake result was analyzed. In consideration of the application in Mars exploration, the characteristics of aerodynamic and orbit during Mars aerobraking were simulated under the condition that the atmospheric dynamic errors exist. To assure the safety of spacecraft and the aerobraking duration, the corridor of aerobraking and the requirement of navigation were proposed. The result can be a reference for the aerobraking implementation of future Chinese Mars exploration.

Abstract:Attitude control system requires special working environment, so it is hard to actualize on the ground, which has brought a certain reliability risk to satellite. According to the characteristics of micro/nano-satellite, a set of semi-physical simulation system for attitude determination and control was designed and implemented. A digital model simulated the satellite attitude and orbit motion, a sensor model generated the measured data, an actuator model generated the control torque, a sensor simulator realized the communication protocol and finally this system realized the whole simulation of attitude control system. The system can be connected in the satellite control system loop to assess software and hardware of the attitude control system, and to verify the performance of the algorithm. The system was applied to validate the attitude control system of TianTuo-3 in ground simulation. The comparison with the on-orbit test data shows that the design of system is reasonable and the result of simulation is credible.

Abstract:Albatrosses use a flight manoeuvre which is called the dynamic soaring, to gain energy from horizontal wind gradient so as to travel for a very long journey and the period almost goes on without making stopovers or flapping their wings. Dynamic soaring is considered a promising technique which can be widely applied to UAV (unmanned aerial vehicle) for extending mission capabilities. The EOM (equation of motion) of a small UAV in the gradient wind field was derived and simplified in the airpath frame of axes based on the flight dynamics. According to the theorem of kinetic energy and mechanical energy variation with respect to the noninertial frame of reference respectively, the energygain mechanism during dynamic soaring was analyzed by using the simplified EOM. The differential flatness method was employed to solve loiter pattern and travel pattern trajectories for the objective function of minimum average change rate of control inputs. The analysis result indicates that the upwind climb and downwind dive is the basic energygain ways of dynamic soaring. The optimal results show that the control inputs are smoothed，even the staged constant inputs to make the actual control simpler. In the optimization of loiter pattern，when the wind gradient is treated as a decision variable, the optimization process finds the optimal wind gradient in the range of ［0，0.5 s^-1］ for the objective function. While in the optimization of travel pattern, the value of the objective function is monotonically decreasing in the same range. 

Abstract:A three-dimensional IGC (integrated guidance and control) approach based on fuzzy disturbance observer was proposed to take advantage of the coupling between the centroid motion, and the attitude motion, and of the uncertainties of a hypersonic vehicle in dive phase as well. An IGC model that can be applied to bank-to-turn control strategy was proposed according to the dynamic equations of the vehicle and the line-of-sight relative motion between the vehicle and the target. The uncertainties in the model were compensated by utilizing the fuzzy disturbance observer, and then an IGC approach was developed by using the block dynamic surface backstepping control method. The states of the closedloop system were proved to be uniformly ultimately bounded by adopting proper Lyapunov functions. Simulations show that the IGC method is robust to the uncertainties and satisfies the required performance. 

Abstract:An advanced genetic algorithm was used to make an optimization analysis on the solar thermal propulsion system condenser parameters for reducing the mass of system. Considering the sunlight collection efficiency and the mass of condenser as the optimization objective function, a mathematical model of condenser work was established and several related simulation researches were carried out. The simulation results show that the advanced genetic algorithm can be effectively used in the optimization analysis of the sunlight collection efficiency and the condenser mass.

Abstract:According to the trajectory tracking problem of hypersonic glide vehicle under great deviation conditions, a new adaptive tracking guidance method in the injection phase was put forward based on the adaptively revised weighting matrix. The main control mode and standard trajectory characteristics were analyzed. The simplified longitudinal motion equations were linearized near the standard trajectory. An improved adaptive tracking guidance method was designed by introducing the error term in linear quadratic performance index. The simulation results of CAV-H indicate that this method can achieve a great performance in adaptive tracking guidance in the injection phase, and has a good robustness to the initial and process deviation.

Abstract:In order to analyze the multi-body flow characteristics and the aerodynamic interference characteristics for the sub-munitions in different bays under sequential separation, the three-dimensional unsteady flow field of the cluster munition under two types of sequential separation and single separation style was simulated with the use of the unstructured dynamic mesh method, based on the governing equations of fluid dynamics and rigid body motion equations of 6DOF (degree of freedom). The variation of the flow characteristics and the aerodynamic interference characteristics of sub-munitions in different separation styles was shown and the interaction process of aerodynamic interference between the sub-munitions in different separation stages was revealed as the results. Numerical simulation results show that the flow characteristics become more complicated and the aerodynamic separation parameters of the rear sub-munition become lower than that of the front sub-munition because of the shock wave interaction between the sub-munitions in the process of sequential separation. During the short sequential separation, the interference from the front sub-munition to the rear sub-munition is more severe so that the security of the separation between the sub-munitions is affected.

Abstract:A coupling method was presented to deal with the heating problems of hypersonic vehicles in rarefied flow. The DSMC (direct simulation Monte Carlo) method was combined with the heat conduction equation by introducing the Newton cooling law. An efficient loose coupling procedure which can calculate the aerodynamic heat and structure heating of vehicle configuration was designed to simulate the temperature distribution of thermal protection systems. After taking the blunted cone as an example to validate the DSMC code, a numerical experiment was conducted to simulate the structure temperature and heat flux distribution characteristics of the X37B orbital vehicle shape in cruise state. The results show that the presented coupling method can simulate the aerodynamic heating process of a hypersonic vehicle in rarefied flow, and can provide technical support for the design of rarefied-flow hypersonic vehicles in terms of thermal protection systems and aerodynamic heating characteristics analysis.

Abstract:A SAR platform location method which utilizes the high-precision scene matching of SAR images and optical reference images was proposed. According to that the projections of SAR platform and object point in SAR image centerline are collinear, some points on the centerline were equably engaged as control points in the proposal method, and then the spatial position was obtained by matching with optical reference image. The equation of the projection line on the local horizon of centerline was estimated with the points. The projection point position of the SAR platform on the horizontal plane was calculated by making use of the straight line and slant-range-altitude information, as well as the spatial position of the platform. Considering the difference between boresight and squint imaging mode, rough rectifying methods were respectively proposed according to the two modes to improve the matching precision. The impact of different errors on location precision was also analyzed and the precision estimation formulas were derived. Both simulation and real data test results show high accuracy and precision of the proposed method, thus bringing forth good practical value for engineering.

Abstract:For the observability of inertial sensor misalignments in inertial platform self-calibration problem, the effects of the system model and platform coordinate frame on observability were analyzed. Based on different system dynamic models and measurement vectors, four system models were built. The observability of inertial sensors misalignments in different models with different definitions of platform coordinate frame was investigated. The theory conclusions and simulation results show that the system is observable only in two conditions: the system measurement models are built up with platform angles and accelerometer triad outputs, the system dynamic model is built up with platform angles and the platform coordinate frame should be defined with the benchmark hexahedron of platform; the system measurement models are built up only with accelerometers triad outputs, the system dynamic models are built up with platform attitude or misalignment models and the platform coordinate frame should be defined with the accelerometer sensor axes. 

Abstract:Neural network model is powerful in problem modelling. But the traditional back propagating algorithm can only execute batch supervised learning, and its time expense is very high. According to these problems, a novel incremental neural network model and the corresponding clustering algorithm were put forward. This model was supported by biological evidences, and it was built on the foundation of novel neuron’s activation function and the synapse adjusting function. Based on this, an adaptive incremental clustering algorithm was put forward, in which mechanisms such as “winner-take-all” were introduced. As a result, “catastrophic forgetting” problem was successfully solved in the incremental clustering process. Experiment results on classic datasets show that this algorithm’s performance is comparable with traditional clustering models such as K-means. Especially, its time and space expenses on incremental tasks are much lower than traditional clustering models.

Abstract:In order to explore the application of deep learning theory in the problem of motion compensated frame interpolation, a DCNN (deep convolutional neural network) built with convolutional blocks and deconvolutional blocks was proposed. The proposed DCNN is capable of processing input images with different resolutions and preserving finegrained image details. The temporal coherent image sequences were used to construct the training sample and the stochastic gradient descent method was adopted to train the designed DCNN. Qualitative and quantitative experiments show that the trained DCNN obtains better interpolated images than the traditional approach in two testing images sequences.

Abstract:BOC（binary offset carrier）modulation will be widely used in satellite navigation systems. The data and pilot channel of GPS L1C signal was modulated with the BOC (1, 1) and the TMBOC (time-multiplex binary offset carrier) modulation. The discrimination curve of TMBOC modulated signal was characterized with bias when using CCRW (code correlation reference wave) technique. In order to eliminate the tracking bias, an unbiased multipath mitigation technique was proposed. The novel technique generated two categories of local wave for the BOC (1, 1) and BOC (6,1) modulated component respectively, and its discrimination output was zero when there was no code phase bias. The technique can obtain unbiased tracking and a better accuracy because of the better utilization of BOC (6, 1) signal component.

Abstract:The analysis of code tracking accuracy for CCRW（code correlation reference waveform）from the literature is mainly on the assumption for the infinite channel bandwidth and the simulation that how the gate width parameters affect the code tracking accuracy. Therefore, the analytical expression of code tracking accuracy was derived. The effect of signal channel bandwidth on CCRW tracking accuracy was analyzed and verified. The analysis shows that the code tracking accuracy with unlimited channel bandwidth can be improved by reducing the width of the gate wave, but there is an optimal value of the gate width in the bandlimited condition. The research results can be used to guide CCRW algorithm design for GNSS receivers．

Abstract:The inter-satellite optical communication system consists of acquisition, pointing and tracking technology; the acquisition technology, which is the premise and guarantee for normal work. The principle of acquisition, key technology and engineering implementation under scanning stare mode were studied in detail. A method for combination of the coarse fine pointing of spiral sine was presented. Numerical simulation results for the scanning process prove that the proposed method has smaller missing scanning area, higher acquisition probability and shorter acquisition time when compared with the traditional single coarse scanning. The coarse fine scanning type is a new method for inter-satellite communication. The proposed method has an important significance in providing a new method for inter-satellite laser communication.

Abstract:High-order scheme has advantages in the simulations of complex flow for its good behavior of preserving high spatial resolution with lower cost than the second order methods. WCNS-E-5(weighted compact nonlinear scheme) was applied in the simulations of thermo-chemical nonequilibrium flow around a cylinder with the freestream velocity from 5 km/s to 5.7 km/s. The distribution of correct flow field parameter was acquired, the pressure and heat flux on the surface agreed well with the experimental data. WCNS-E-5 also exhibited better performance on the grid convergence of heat flux than the second order MUSCL scheme. Results show that the present attempt to combine high order scheme with the calculations of stiff chemically reacting flow is basically successful, and it has established a good foundation for the further study.

Abstract:It is widely recognized that the shaft distance errors have vital effect on the accuracy and performance of anti-backlash gear transmission system. However，the essential mechanism and property is still undiscovered. Based on the contact constrained dynamics model of anti-backlash gear transmission system，the rigid-flexible coupling dynamics model of anti-backlash gear transmission system was established by adopting the ADAM/ Flex. Then，the rigid-flexible coupling dynamics simulation was carried out to study the vibration and frequency characteristics of the anti-backlash gear transmission system with different shaft distance errors. It is discovered that the spring torque，contact force and the friction torque will increase with the decrease of shaft distance，which will hamper the normal motion of the active gear and reduce the magnitude of rotation speed of the fixed shaft ; the main frequency of the main shaft will decrease with the increase of shaft distance，and the decrease will be sharper when the shaft distance is a little more larger than the standard centre distance. These discoveries will be helpful in the design and assembly of anti-backlash system.

Abstract:Several potential failure modes may occur when mechanical components fail, and they have several correlation in some way. For that the conditions of times of load action have an impact on the reliability of mechanical components. Thus it is necessary to take all the failure modes and times of load action into account when analyzing the mechanical reliability sensitivity. Combining the order statistic theory to study the influence of times of load action on the reliability and sensitivity calculation, and applying the probabilistic perturbation method, the research built a reliability calculation model of mechanical components with multiple failure modes and times of load action modes using the stress-strength interference mode. The calculating formulas of reliability sensitivity with respect to the mean and variance of random variables were derived with the gradient method. According to the result of the torque axis reliability sensitivity analysis, the curves of reliabilities and sensitivities can be obtained, and the production can be very useful if it is extended to correlated area of machine sensitivity design.

Abstract:The fault data of ships′ mechanical system are usually not well recorded during operation and maintenance activities, and are typically incomplete and inaccurate. For such incomplete data, fault trend was justified by graphical representation. On this basis, historical fault data was analyzed using homogeneous Poisson process, non-homogeneous Poisson process and geometric process respectively. Numerical results show that the fault of geometric process is minimized, and the future fault intensity can be predicted.

Abstract:In order to improve the antijamming performance of global navigation satellite system receivers, a method based on the complex ANF(adaptive notch filter) was proposed to suppress narrow band interference on digital base band. The ANF was constructed by a series of the first order IIR notch filters, and the frequency parameters of all filters were updated with adaptive algorithm to detect jamming and to suppress it in real time. Simulation results show that the present method is able to suppress the jamming effectively and quickly, and the capability of signal acquisition is enhanced under condition of jamming. Moreover, a better performance than a conditional real ANF is achieved in simulation.