Abstract: In order to make full utilization of the scarce spectrum resources for Cognitive radio networks, secondary users are expected to exploit the available spec- trum of primary users. However, when there are several spectrum bands available, how to select an appropriate one for the secondary user according to the spectrum quality and the QoS requirements of di®erent kinds of applications is a new challenge. In this paper, we propose a new Au- tomatic distributed spectrum decision (ADSD) method to solve this problem. ADSD considers multiple spectrum characterization parameters, in particular, the primary users' arrival probability, to estimate the quality of the available spectrum bands. A weight auto-generation mech- anism is included to automatically determine the weights of di®erent parameters, thus avoiding the di±culty and ir- rationality when relying on the users to specify the weights directly. In addition, in conjunction with the recon¯g- uration mechanism, ADSD can reduce the rate of spec- trum hando®s by recon¯guring the transmission parame- ters rather than making a new decision for the existing transmission. Simulation results show that without any users' interference, ADSD can automatically select the ap- propriate spectrum for transmission and signi¯cantly im- prove the Cognitive Radio network performance in terms of throughput and the spectrum hando® rate.
Abstract: This paper considers a new bit commit- ment model named Quantum two-prover bit commitment (QTPBC) and its physical realization. In a QTPBC scheme two provers jointly commit a bit to the veri¯er. The two provers can cooperate and communicate between them to decide on a common optimal strategy before the interac- tion with the veri¯er starts, further they are allowed to share quantum entanglement. But once the interaction be- gins, the two provers are physically separated and isolated, and they cannot send both classical and quantum messages to each other any longer. By virtue of rapid progress in single photon detection technology, we construct a quan- tum protocol for QTPBC based on linear code. Detailed analysis shows that our scheme is of unconditional secu- rity, i.e., the computing power of participants and poten- tial eavesdroppers is assumed to be in¯nite. Moreover, the scheme is proven to be able to tolerate errors due to noise in practice.
Abstract: Decentralized tuple space is an e®ective paradigm for distributed collaborative applications since its loose decoupling, availability and °exibility in system's organization. However, there are very few research results on its replication and consistency. This paper presents a decentralized tuple space model to enable tuple update by creating loose update links among decentralized Tuple space nodes. Besides, tuples are grouped with tuple types, the unit of being applied a replication policy, which con- trols the distribution of replicas. The model is simulated by Desmo-J. The experiments show that applying di®er- entiate replication policies used for di®erent purposes is absolutely necessary, because no single policy is suitable under all use patterns.
Abstract: This paper introduced the optimization and deoptimization technologies for Escape analysis in open world. These technologies are used in a novel Es- cape analysis framework that has been implemented in Open runtime platform, Intel's open-source Java virtual machine. We introduced the optimization technologies for synchronization removal and object stack allocation, as well as the runtime deoptimization and compensation work. The deoptimization and compensation technologies are crucial for a practical Escape analysis in open world. We evaluated the runtime e±ciency of the deoptimization and compensation work on benchmarks like SPECjbb2000 and SPECjvm98.
Abstract: Most Topology control (TC) researches in wireless sensor networks focus on speci¯c algorithms. This paper proposes the problem that which criterion should be adopted for the selection of Connectivity type TC and Coverage type TC. By de¯ning \density of events" as the decision criterion, the corresponding threshold values are computed. Simulations indicate that the criteria analyzed are directive and reasonable.
Abstract: According to the complexity of optimal control for the process of falling motion, a method based on parametric control and the enhancing technique is pre- sented. The piece-wise constant value is used to approach the optimal solution of optimal control problem. More- over, the optimal parameters can be calculated by using the common mathematical programming. Numerical re- sults are presented for illustration and experiments are carried out on real robots.
Abstract: Cryptographic protocols are crucial for se- cure communications and networks, distribution systems and electronic commerce. Model checking technique and supporting tool for analyzing cryptographic protocols are discussed. A model checking technique based on logic of algorithm knowledge for cryptographic protocols is pro- posed, which can specify explicitly the intruder model ca- pabilities. The knowledge completeness of intruder abili- ties is proved. An e±cient veri¯cation model generating system is developed based on PDL (Protocols description language) and SPIN/Promela for cryptographic protocols. Some optimization strategies are implemented in the sys- tem to reduce the state explosion complexity, such as par- tial order reduction, syntactic reorder and static analysis. More than ten cryptographic protocols are analyzed and published °aws are rediscovered successfully with the sys- tem. The veri¯cation system can be used as an e±cient and reliable tool for evaluation of the network security.
Abstract: This paper investigated new properties of the ac (alternative current) Stark e®ect of three-level atom system in two-zone Raman-Ramsey interactions. It de- rived the closed-form expressions of ac Stark shift and shift phase. Then with the help of numerical computation, it demonstrated the e®ect of various combinations of laser intensities, initial atomic populations and laser detuning on Stark shift and shift phase. Based on analytical ex- pressions and results of numerical computation the paper provided useful information for determination of the best conditions in reduction of the ac Stark shift.
Abstract: The authors propose a new type of hash iterative structure-the ring-iterative structure with feed- back which is subdivided into the single feedback ring it- eration and the multiple feedback ring iteration, namely SFRI and MFRI. Prove that SFRI is at least equivalent to the MD structure in security, and MFRI is at least equiv- alent to SFRI in security (property 1 makes people incline to believe MFRI is more secure than MD). Analyze the resistance of MFRI, which results from the joint event on message modi¯cation, endless loop on message modi¯ca- tion and incompatibility of the su±cient conditions, to the multi-block di®erential collision attack. Argue the ine®ec- tiveness of the D-way second preimage attack on MFRI. Discuss the time and space expenses of MFRI, and point out the advantage of MFRI over the tree-iterative struc- ture and the zipper-iterative structure.
Abstract: To cope with the roaring complexity of modern SoC designs, system level modeling and simula- tion are recognized as a must to ful¯ll quick architecture exploration and hardware/software co-veri¯cation. A hy- brid system level modeling method for con¯gurable pro- cessor based on Transport triggered architecture (TTA) is presented in this paper. We implemented a cycle-accurate and bit-accurate model at instruction set simulation level using SystemC to achieve fast simulation and a transaction level model for standard IP interface for easy SoC integra- tion. The object oriented modeling technique was used to cope with the change of the architecture con¯guration. As a case study, an enhanced TTA-like processor, Tcore, was designed and plugged into a SoC for system simulation.
Abstract: Stereo matching is the key of reconstruct- ing 3D face model from 2D face images and Barnard's al- gorithm is one of the classical stereo matching algorithms based on feature points. In order to enhance the stability of extracting feature points, reduce computational com- plexity and minimize the e®ect of subjective factors, in this paper, Barnard's algorithm of edge point matching was im- proved from two aspects: edge point sets of left and right face images were extracted with dyadic wavelet transform, rather than comparing gray values of adjacent pixels; on the other hand, edge points in binocular stereo face images were matched under epipolar constraint in parallel binoc- ular stereo matching. Experimental results demonstrate that stability and e±ciency of stereo matching algorithm are both improved.
Abstract: The paper proposes the dynamic path planning method of mobile robot based on improved ge- netic algorithm. Firstly, to ensure the safety of the robot e®ectively, the improved visual graph and the conception of safety coe±cient are presented. Secondly, to avoid the local optimum, the paper replaces the mutation individual with a better individual searched by hill-climbing method. To increase the convergence speed, the paper updates the colony by the rule of the particle swarm optimization. Thirdly, °oat-point coding is proposed in the improved ge- netic algorithm. The ¯tness function includes the length and the total slope of the path in dynamic path planning. Finally, it emulates the dynamic path planning for mobile robot based on improved genetic algorithm. From the re- sults, it can see that the path planning method is viable and e±cient.
Abstract: Fuzzy vault (FV) scheme, proposed by Juels and Sudan, is intended to develop new concepts to bind cryptographic security into biometric authentication to improve security and protect privacy. But FV is vul- nerable to some attacks, such as Attacks via record mul- tiplicity or correlation attacks, Surreptitious key-inversion attack and Blended substitution attacks. In this paper, a novel biometric encryption scheme, named Efficient fuzzy vault (EFV), is developed using pairing-based cryptogra- phy. EFV scheme provides a higher level of security than FV as adopting random points instead of chaff points to re- sist the attacks that FV has difficulty to overcome. In addi- tion, a complete implementation procedure of fingerprint- based EFV, based on the automatic alignment of minutiae converted in polar coordinates using a reference point, is developed. The security analysis and experiment results show that EFV is a promising scheme for biometric en- cryption.
Abstract: A Feature-Index based algorithm that uses similarity information and spatial coherence is presented in the paper. It especially ¯ts to the case that the base image is very large and real-time property is needed. The algo- rithm is divided into four steps: ¯rstly extract features from base image, and establish feature-index table before- hand; then extract corresponding features from sensed im- age and use the feature-index table to match them with those from base image; thirdly, fuse the matching results of Main line pairs (MLPs) and contours; ¯nally, solve the transformation parameters using the intersection points of MLPs and centers of contours and complete registration. The experiment results show that the proposed algorithm is accurate and e®ective.
Abstract: We presented an improved geodesic active contour model for image segmentation. This method com- bines the geodesic active contour model and the tensor voting framework. We added in°uence of tensor voting in the edge-detector function. The proposed model is more sensitive to edges. It can detect weak boundaries of de- sired objects in some images with low contrast. Using this method, we don't have to spend time to ¯nd some suit- able parameter which is necessary in the geodesic active contour model. Numerical results show the e®ectiveness.
Abstract: To improve the position accuracy, a CNS (Celestial navigation system)/pulsar integrated navigation system with clock drift is proposed. In the pulsar navi- gation subsystem, the epoch-di®erence method is adopted to eliminate clock drift, but it induces colored noise. The two-level ¯lter, which is composed of an UKF (Unscented Kalman ¯lter) and an H1 ¯lter in series connected, is proposed for fusing the data from the celestial navigation and pulsar navigation subsystems. The celestial naviga- tion subsystem adopts the UKF because of its good perfor- mance in nonlinear estimation, while the pulsar navigation subsystem utilizes the H1 ¯lter due to its robustness to colored noise. Compared with CNS and two CNS/pulsar integrated navigation methods without two-level ¯lter, the proposed method can provide higher navigation accuracy. Simulation results show that the position estimation ac- curacy of the proposed method can achieve 140m in the presence of clock drift.
Abstract: When an automatic tra±c light system is not working e.g. due to tra±c jam, it is necessary for traf- ¯c police to control the tra±c by gestures. In this paper, the design of a system to synchronize tra±c lights with tra±c police gestures is presented. The gesture data are extracted by ¯xing a 3-axis accelerometer on the back of each hand. Signals obtained from the accelerometers are transformed into arm motion and palm orientation. A hi- erarchical classi¯er is designed to recognize the gestures, in which fuzzy rules are used to enable vague gesture recog- nition. An embedded micro-processor system has been de- veloped for real-time gesture recognition. Wireless mod- ules are used for communication and a digital compass is used to identify the direction, to which a tra±c policeman faces. The integrate system has been tested, and the fea- sibility of the system to synchronize tra±c lights has been demonstrated.
Abstract: Low-rate denial of service (LDoS) attack is a new class of DoS, which exploits TCP's congestion con- trol mechanism. LDoS attack can reduce the throughput of the attacked link by sending low-rate packets in the way of periodic pulse. Because of its low-rate characteristic, it can elude the monitor of traditional detection approach. Most applications in the Internet use TCP protocol, so the dam- age of LDoS attack is not inferior to the traditional °ood type DDoS attack. The characteristics of LDoS attack in frequency domain were analyzed, by adopting digital sig- nal processing technology. The ¯ltering algorithm was de- signed as a Finite impulse response (FIR) ¯lter to eliminate the illegitimate frequencies in frequency domain. Exper- iments result show that 92.88% of LDoS attack energy is ¯ltered, and 19.75% of normal energy is eliminated.
Abstract: This paper focuses on high-speed design of geometric parameters of any given target for Radar cross section (RCS) reduction. The Binary particle swarm op- timization (BPSO) and the Finite-di®erence time-domain (FDTD) method are combined to acquire a given object's optimum geometric parameters that would lead to its min- imal monostatic RCS. To promote the computation speed as well as the computation capacity in a further way, a par- allel FDTD code is imported in this paper. A basic strat- egy to reduce RCS of a canonical target is proposed. As an illustration of the ability of the optimizing method, the al- gorithm is applied to optimize the position and the width of the slot, which may reduce the monostatic RCS. To verify the e®ectiveness of the algorithm, all possible conditions in this problem are simulated and it is well shown that the optimizer could search out the minimal or subminimal solution quickly and e®ectively.
Abstract: An important class of color constant im- age descriptors is based on image derivatives. However, these derivative-based descriptors are sensitive to blurring changes of image, and also lose much color information in uniform regions. Aiming at overcoming these drawbacks, the contributions of this paper are in three-folds: First, by introducing 3D moment invariants, we propose a color constant descriptor in RGB color space, which can char- acterize original image color content. Second, we de¯ne a 2D edge-based color space based on the diagonal-o®set re°ectance model. A novel color constant descriptor in the proposed edge-based color space is presented by using mo- ment invariants. This descriptor can characterize edge im- age with nearly no sensitivity to image blurring. Finally, we combine the aforementioned descriptors to construct the third color constant descriptor, which can describe not only original image color content but also the edge image color feature. The experiments on scene recognition show that all these descriptors have satisfying performance un- der various light sources. Furthermore, all these proposed descriptors are insensitive to image a±ne transformations and blurring changes.
Abstract: The Neighborhood limited empirical mode decomposition (NLEMD) is improved in the local mean computation using re¯ned symmetrical extrema distribu- tion. The images are decomposed into the IMFs using the improved NLEMD. Then, the IMFs are ¯ltered using one adaptive ¯lter to remove the spots making the skin look aging. The adaptive ¯lter is based on the IMFs' local statis- tics, which is estimated using the fast approach. The skin re-tendering algorithm in this paper makes the skin more tender than other approaches without losing the necessary details of the skin.
Abstract: To maximize the spectral e±ciency of a Decode-and-forward (DF) cooperative Orthogonal fre- quency division multiplexing (OFDM) system, we ¯rst pro- pose the optimal power allocation algorithm when per- fect Channel state information (CSI) feedback is available. Since perfect CSI feedback is unrealistic, we further pro- pose a power allocation scheme using limited feedback, where the power allocation vectors for the source and re- lay are limited in two ¯nite power allocation tables respec- tively. In this scheme, the destination chooses the power allocation vectors for the source and relay, and feeds the indices of the vectors back. The power allocation tables are designed by using the Lloyd algorithm. Simulation re- sults show that the perfect CSI feedback power allocation scheme achieves the best performance, and that the per- formance of the limited feedback scheme lies between the perfect CSI scheme and the scheme with no CSI.
Abstract: Network lifetime optimization is a vital and challenging design issue for battery-operated wireless net- works, which guarantee uninterrupted information trans- mission in wireless networks. Fortunately, emerging as a new communication paradigm, cooperation communica- tion provides an e®ective way to share resource among net- work nodes that can be used to extend network lifetime. In this paper, the dynamic resource allocation strategies are introduced to optimize the network lifetime under Qual- ity of service (QoS) constraints for coded cooperative net- works, which consider power control, multi-relays selec- tion and Level of cooperation (LOC) adjustment jointly. An optimization model for minimizing and balancing the energy consumption under QoS constrains is formulated based on a TDMA scenario. When the LOC is constant, the closed form optimal solution is got by Karush-Kuhn- Tucker (KKT) conditions, which results in an optimal re- source allocation strategy. Based on the solution, a sub- optimal scheme is further proposed for a variable LOC. Simulation results show that our schemes can dramatically prolong network lifetime and support higher QoS levels compared with other existing cooperative resource alloca- tion schemes.
Abstract: The Programming language for symmetric cryptographic algorithms (PLSCA) is proposed. The de- tailed speci¯cation of the syntax of PLSCA is presented, and the cipher of IDEA is described using PLSCA as an example. Using PLSCA, the cryptography designers could describe the structure of symmetric cryptographic algo- rithms in a formal way, exchange their ideas and algorithm details, test and analyze the symmetric cryptographic al- gorithms conveniently and rapidly. PLSCA may improve the testing e±ciency of new algorithms. It is adapt to as- sist the design and automatic analysis for symmetric cryp- tographic algorithms, and it may be used as a standard language to submit new algorithms to the evaluation sta®.
Abstract: The upper bounds on lifetime of three dimensional extended Time hopping impulse radio Ultra- wide band (TH-IR UWB) sensor networks are derived us- ing percolation theory arguments. The TH-IR UWB sen- sor network consists of n sensor nodes distributed in a cube of edge length n1=3 according to a Poisson point process of unit intensity. It is shown that for such a static three dimensional extended TH-IR UWB sensor network, the upper bound on the lifetime is of order O(n¡1), while in the ideal case, the upper bound on the lifetime is longer than that of a static network by a factor of n2=3. There- fore sensor nodes moving randomly in the deployment area can improve the upper bound on network lifetime. The re- sults also reveal that the upper bounds on network lifetime decrease with the number of nodes n, thus extended TH- IR UWB sensor networks aren't prone to be employed in large-scale network.
Abstract: Certi¯cateless public key cryptography was introduced to solve the key escrow problem in identity based cryptography while enjoying the most attractive cer- ti¯cateless property. In this paper, we present a secure Certi¯cateless encryption (CLE) scheme with short cipher- text. The ciphertext length is at least jmj-bit (the length of a plaintext) shorter than the existing CLE schemes while retaining similar e±ciency of computation. The new scheme is provably secure against adaptive chosen cipher- text attacks in the random oracle model.
Abstract: In addition to modern digital communica- tion systems, the new coherent modulation-demodulation systems by two classes of the oblique-orthogonal function set-the Chen-Mobius transform-were applied to the com- munication systems. Then the new digital signal commu- nication system performance was simulated by the MATA- LAB and compared with the traditional system by the sys- tems ¯gures of error rate to S=N. Those results showed that the new system has excellent performances to resist the strong noise and interference. Then the system imple- mentation by FPGA was also analyzed in some detail.
Abstract: Secure multiparty computational geome- try is an important ¯eld of Secure multiparty computation (SMC). We ¯rst present an SMC protocol for comput- ing the area of a triangle using symmetric cryptographic method, which is of independent interest in SMC, then use it to solve the point inclusion problem of convex polygon, and further solve the inclusion problem of concave polygon. Compared with existing solutions, these new protocols are much more e±cient. It is proved, by well accepted sim- ulation paradigm, that all the protocols proposed in this paper are secure.
Abstract: The experimentally feasible scheme of re- motely generating continuous variable quantum entangled communication channel based on beam splitters is pro- posed. It is showed that the long-haul quantum communi- cation channel can be established by means of an assisted single-photon entangled state and a pair of single-mode squeezed vacuum states. The degree of entanglement of the desired continuous variable entangled channel is only related with the assisted beam splitter when the other two parallel ones are of the same parameter values. The suc- cess probability of creating maximal entangled channel can be enhanced with the increasing of beam splitter re°ec- tion coe±cients and decreasing of squeezing parameters. Furthermore, the puri¯cation of success probability is dis- cussed for imperfect photo-detectors.
Abstract: This paper considers the Multiple-input- multiple-output (MIMO) systems with periodic feedback under the assumption that the channel state remains quasi- static within a fading block and varies from one block to the next based on Markov random process. It is assumed that the Channel state information (CSI) is perfectly known at the receiver and fed back to the transmitter once every period. Given the feedback-capacity constraint in terms of maximum number of feedback bits per block, the relation- ship between the outage capacity and the feedback rate is analyzed. The analysis shows that the outage capacity is a non-monotonic convex function of the feedback rate and there exists the maximum value of the outage capac- ity. Then, to maximize the outage capacity, the optimal feedback rates are given by numerical results.
Abstract: We develop a cooperative decode-and- forward strategy of distributed Source-Relay network cod- ing for a three-node relay model, in which Relay and Source both send their own messages to Destination. First, we present a cooperative communication protocol to achieve decode-and-forward capacity by leveraging trans- mit rates between Source and Relay and designing dis- tributed Source-Relay network coding accordingly. After- wards, multi-dimension Low-density parity-check (LDPC) code is constructed as a layered structure, where Source LDPC, Relay LDPC, and network LDPC code are organi- cally integrated to realize a distributed design. Our design randomly embeds network-coded message into the layered structure as e®ective extra checks o®ering side informa- tion for both Source and Relay. Based on derivation of the algebraic relationship between constituent codes, a good multi-dimension LDPC code pro¯le is generated. Mean- while, network coding complexity maintains linear to the block length. The coding scheme is demonstrated to ap- proach decode-and-forward capacity and still provides ef- fective spatial diversity.
Abstract: A (k; n) threshold proxy re-signature scheme distributes the re-signature key of the delegatee and the delegator. The re-signing ability to n proxies in a way that any set of k or more honest proxies can col- laborate to re-sign, while any set of k ¡ 1 proxies cannot. We propose two threshold proxy re-signature schemes with trust dealer, which are both proved secure in the standard model. Threshold proxy re-signature schemes are based on the Computational Di±e-Hellman (CDH) problem with- out random oracles. The schemes satisfy the properties of bidirectionality, non-interactivity, multi-use and private proxy. Meanwhile, the re-signature share generation and veri¯cation algorithms are non-interactive and e±cient.
Abstract: A VLSI array synthesizing digital ran- dom sequence algorithm is proposed, and its Application- speci¯c integrated circuit (ASIC) design of the General random number generator (GRNG) which can generate digital random sequence with uniform distribution, expo- nential distribution, Rayleigh distribution and Gaussian distribution is introduced. In this algorithm, the Box- Muller equation is adopted for real-time generating ran- dom number using hardware, and one improved Taus- worthe sequence generating principle is proposed to speed up the generation and improve the signal quality. More- over, the pipelined Coordinate rotation digital computer (CORDIC) mapping algorithm is used to increases the throughput. The proposed GRNG is implemented with SMIC one-poly six-metal 0.18¹m CMOS technology. The ASIC core occupies 1:8 £ 1:8mm2 die area which generates 16-bit or 32-bit samples up to 4¾, the peak throughput of the ASIC is 420 million samples per second, and the peak power dissipation, which includes the power of I/O, is 416mW in active mode, and 106mW in standby mode respectively in typical operation condition.
Abstract: With the advent of Galileo and Chi- nese Compass, GNSS navigation technologies will develop rapidly. However, as the number of navigation satellites in view will increase, the fault probability will rise. This paper calculates the multi-fault risk of multi-constellation satellite navigation system in terms of MOPS. It is high- lighted that the probability of either one-fault or double- faults is higher than integrity requirement. The paper also describes a snap-shot ramose RAIM technology to protect civil aviation users in multiple-fault case. In this condition, a series of FDE calculation is adopted to separate satel- lites in sight into several groups. Therefore the problem will transform into several single-fault case, which current RAIM can solve. Simulation results verify that this tech- nique is proper to solve both single-fault and double-fault problem of civil aviation caused by application of multi- constellation GNSS.
Abstract: To build a wireless active endoscope with external guidance for controllable and interactive GI track diagnosis, a real time system for 3D localization and 3D orientation is necessary. An approach is to enclose a small rectangle permanent magnet in the capsule. The magnetic ¯eld, produced by the rectangle magnet around the body, can be detected by magnetic sensors outside the patient's body. With these sensor data, the 3D localization and 3D orientation parameters can be computed by the nonlinear optimization algorithm based on the mathematic model of the rectangular magnet's magnetic ¯eld. Simulation exper- iments show that the proposed algorithm works e®ectively, and has good accuracy and time e±ciency when the initial guess of the parameters are within some predetermined ranges.
Abstract: | Multi-mode satellite navigation receivers have to endure heavier computation load because of huge increment of visible satellites, in hybrid GPS, GLONASS, Galileo and Compass navigation scenario. To solve these problems, in the paper, two new technologies are presented to decrease computation load: Fast satellite selection algo- rithm (FSS) and Novel weighted least-squared positioning algorithm (NWLS). Di®erent with conventional methods, FSS is based on satellite elevation and azimuth. Firstly, all visible satellites are classi¯ed by elevation, with three sections: low, medium and high elevation. Then, parts of satellites in medium elevation section are excluded through sorting, di®erencing, and ratio of high elevation satellites and low elevation satellites. As to NWLS positioning al- gorithm, ionosphere delay and other error are analyzed separately ¯rstly; then weighted observation matrix is cre- ated according to two kinds error and satellite position. The matrix is employed in receiver position calculation. With satis¯ed positioning accuracy, FSS algorithm is able to decrease computation load by about 20»30%. In conclu- sion, FSS and NWLS algorithm are e±cient and e®ective to decrease load of receiver; they are proper to integrated satellite navigation application scenario.
Abstract: The GPS multipath signal model is given and analyzed. The all phase DFT (apDFT) is proposed as a new spectral analysis way, which makes full use of (2N ¡ 1) samples to do linear transform into N point se- quence called all phase signal. Phase di®erence method is integrated with apDFT to determine the accurate signal frequency through calculating the two phase value for the two sequences' DFT result, i.e. one is from point 1 to point (2N ¡1) and the other is from (N +1) to (3N ¡1) separately. The application of the proposed method on GPS multipath signal estimation is analyzed, which has multiple frequen- cies components. Monte Carlo simulation results based on GPS simulator data show that the apDFT and the integra- tion with phase di®erence method could give the accurate frequency and precise phase estimation in both ideal and noisy environments.
Abstract: A digital polarization agile monopulse de- tector was presented. Detection work°ow, method of virtual polarization synthesizing and method of digital monopulse angle error extraction based on variable polar- ization antenna with linearly polarized subarrays were pro- posed. Polarization agile was realized by utilizing digital controlled phase shifters in multichannel T/R module. The gain of antenna array can be improved and the beamwidth of cross polarization less than ¡15dB can be widened by ap- propriately increasing the number of subarray. The mea- sured results show the availability of the detector and the e®ectiveness of virtual polarization synthesizing and digital monopulse angle error extraction method.
Abstract: A rectangular pulse generator circuit with fast rising and falling edge will be presented in this pa- per. The generator circuit was designed by controlling the quantity of carriers in the middle layer from regulating forward current of the SRD (Step recovery diode), and then indirectly controlling the pulse width. It is based on the principle that large reverse current will °ow through the diode and last for a relatively long time when it is re- verse biased. Experimental results have been analyzed in physical level. They are tallied with theoretical results. The circuit can generate rectangular pulses with rise time about 150ps, fall time about 250ps, amplitude about 10V and pulse width adjustable from 1ns to 10ns in 50 load. The trig jitter is less than 5ps and the amplitude jitter is better than 4%.
Abstract: In this paper, we address the method of subband implementation for wideband radar clutter sup- pression and target High resolution range pro¯le (HRRP) enhancement. The Doppler dispersion is overcome by separate weighting processing in the individual subbands. The optimal weight vectors are obtained by minimizing the Mean square error (MSE) between the reconstructed target HRRP and the actual target HRRP. The MMSE weight vectors require the actual target HRRP as a prior knowledge and cannot be implemented in practice, as a compromise the Minimum variance distortionless response (MVDR) weights are used. Several simulation results are given to illustrate the enhanced performance of target HRRP obtained by the methods proposed in this paper.
Abstract: A novel Folded waveguide (FW) ampli¯er for Traveling-wave tubes (TWT) was investigated. It is formed by adding rectangular grooves periodically to the bends of a normal FW. In order to test its performance, a three-dimensional Particle-in-cell (PIC) code MAGIC was used to simulate the large-signal beam-wave interaction. It proves to be a potential device for producing more than two times higher Continuous wave (CW) power with a much shorter circuit compared to a normal FW. The band per- formance is also good in above 2GHz. Furthermore, the novel FW e®ectively improves the problem that gain of a normal FW decreases at higher working frequencies due to diminishing of interaction impedance. This novel FW therefore promises a high power and miniaturized circuit for millimeter wave TWT.