In this paper, the optimization of cooperative spectrum sensing mechanisms in cognitive radio networks is investigated to improve the sensing efficiency and spectrum utilization. The optimization algorithms and strategies of detection period, detection time and searching time are proposed respectively for channel monitoring and channel searching scenarios. Analysis and simulations show that exploitation of cooperative sensing and proactive sensing can improve the sensing performance and transmitting rate. The proposed sensing mechanisms can increase the system throughput, reduce the sensing latency, and thus enhance the sensing efficacy and agility significantly under the interference constrains of primary signal.

Shortwave communication works with frequency-selective fading channel, of which coherence bandwidth is an important parameter describing the “flat” channel bandwidth to be used by single carrier system. As has been known, increasing the coherence bandwidth can facilitate larger bandwidth system with faster data rate transmission and simplified system with reduced receiver complexity. This paper proposes a method of using narrow beam to concentrate spatially the transmitted signal power on the main path and suppress the undesired multipath signals resulting in delay spread. For realizing the functions motioned above, the adaptive technique is taken to set up and maintain the narrow beam link for the point-to-point communication. The theoretical study shows that the coherence bandwidth can be effectively increased by this method. The calculations are performed for different number of antennas over the mid-range channel and the results confirm this approach.

A new concept of orthogonal matrix pair is presented, which is the extension of orthogonal matrix, and especially the binary orthogonal matrix pair is not restricted by the fact that the order of matrix should be the power of 2. Based on the binary sequence pair with two-level periodic autocorrelation, the binary orthogonal matrix pair and orthogonal sequence pair set are constructed. By interleaved technology, a new class of binary Zero Correlation Zone (ZCZ) sequence pair sets applied to Quasi-Synchronous Code Division Multiple Access (QS-CDMA) is constructed from the binary orthogonal matrix pair or orthogonal matrix and orthogonal sequence pair set. In order to achieve greater energy efficiency and upper theory bound of binary ZCZ sequence pair sets, it is necessary to select appropriate binary sequence pairs with two-level periodic autocorrelation.

In this paper, a new throughput-maximizing transmit beamforming scheme with limited feedback is presented in Multiple-Input Single-Output Orthogonal Frequency Division Multiplexing (MISO-OFDM) systems. By dividing the total subcarriers of an OFDM symbol into a series of clusters, from the codebook the “proper” codeword maximizing the average throughput per subcarrier of the considered cluster is chosen as the BeamForming Vector (BFV) for this one. In low Signal to Noise Ratio (SNR) range, the close-form expression of the optimal BFV is derived. While in high SNR range, since the close-form expression of the optimal BFV is difficult to found, a simple sub-optimal algorithm exploiting the correlation of channel frequency responses at different subcarriers is proposed to reduce the computational complexity of the exhaustive search in the optimal solution. The simulation results show that the proposed algorithm can provide not only higher throughput but also lower bit error rate than other existing schemes.

Hybrid Automatic Retransmission reQuest (HARQ) is an error control method for reliable communications. Combining HARQ with Multiple-Input-Multiple-Output (MIMO) systems using spatial multiplexing can provide reliable high data rate transmission. In this paper, a sequential power allocation method is proposed in MIMO-HARQ systems. Based on channel state information, the receiver searches the optimal power allocation vector and sends its index back to transmitter, with which the transmitter sequentially allocates powers for next retransmission. The proposed method needs less feedback information and can tolerate large feedback delay. Simulation results show that it can significantly improve the BER performance in spatial correlated MIMO channels.

In this paper, a suboptimal user selection method is proposed based on Block Diagonalization (BD). Firstly, an upper-bound of sum-rate capacity is deduced, and is used as the selection criterion of proposed algorithm. Secondly, the upper-bound is used as the adaptive criterion instead of capacity formula, called simplification of the proposed algorithm. Finally, considering the fairness between users, proposed algorithm is combined with Proportional Fair Scheduling (PFS) method. The simulation results show that proposed algorithm almost achieves the performance of the optimal algorithm and the proposed algorithm with PFS can obtain a tradeoff between the system sum-rate capacity gain and fairness.

In this paper, a downlink precoding scheme is proposed for the Quasi-orthogonal Space Time Block Coded Multi-User MIMO (QSTBC-MU-MIMO) system. Based on the SLNR (Signal-to-Leakage-Noise Ratio) maximization, this scheme minimizes the co-channel interference more efficiently by using an iterative optimization approach. It is robust to the number of users in the system. Furthermore, the influence of noise is taken into account, and thus a simple solution of the optimization problem can be achieved by choosing the complex scalars properly. Simulations demonstrate the effectiveness of the proposed scheme.

A non-sufficiently guaranteed handover scheme for multiple services is proposed in this paper. Under this scheme, the channels will be allocated and reserved for the arriving calls to be served when an interval is less than the maximum cell residence time. And when the calls are terminated, the allocation strategy will be adjusted for those associated channels facing the risk of handover failure. At the mean time, the degree of non-sufficient guarantee is adjusted periodically according to real-time performance of the handover calls. Through simulation, the QoSs of the proposed strategy are analyzed under different degrees of non-sufficient guarantee, and the efficiency for multiple services is thus verified. The simulation results show that, the proposed channel allocation strategy (IGH) can significantly reduce the new call blocking probability, at the expense of slight handover failure probability. Therefore, compared with the guaranteed handover scheme, IGH is more suitable for multi-service LEO constellation communication system.

In this article, a universally composable group key exchange ideal function is proposed and realized using witness indistinguishable proof of knowledge with partially isolated party based on the tamper-proof hardware token. Compared with protocols under the CRS model, the group key exchange protocol can greatly reduce the risk of putting all trusts in one place. The protocol is proved to be AKE secure and resistant to the attacks of adaptive adversaries and malicious insiders.

Nowadays, IP networks are suffering many faults and malicious attacks which greatly threaten its security and survivability. So it is an important issue that how to make the IP networks to be more robust under faults and attacks, i.e., to improve their tolerance abilities for both fault and intrusion. However recently, most of the researches focus on only one of them, and decouple the survivability and security each other. According to the trust model in social networks, this paper proposes an efficient fault-tolerant and intrusion-tolerant scheme based on trust relationship for IP networks. This scheme not only borrows the trust rating from the social links, but also qualitatively describes the relationships between the trust rating and the network behavior. Then, this paper analyses the scheme how to tolerate three known malicious behaviors, viz., self-faults, bad mouth attacks and conflict behavior attacks. Finally, the numeric simulation results show that the scheme can detect the malicious nodes fast and accurately and efficiently prevent these malicious behaviors in IP networks.

An algorithm of reliability indexes is proposed in this paper for evaluating the reliability of the distributed tightly-coupled virtual private networks with multi-QoS requirements, which is constructed in the environment of interconnection network. Firstly, according to the requirements of QoS, all routes satisfying the QoS requirements are calculated between the distributed tightly-coupled nodes in the weighted networks. Secondly, the network adjacency matrix is constructed according to these routes, and the disjoint network state set satisfying the QoS requirments is obtained by decomposition transformation and conformity transformation of the adjacency matrix. Finally, the calculation expression of the reliability indexes is obtained according to the disjoint network state set, and then the reliability indexes are accomplished. The whole procedure is realized through algebra or logical algebra calculation, and it is easy to be programmed by computer. The correctness of each key step of the new method is discussed. It is proved by numerical example, experiment and comparison with the results of the traditional algorithm, that the new algorithm reflects relevantly the reliability of the distributed tightly-coupled virtual private networks.

According to the characteristics of tree-topology aggregating traffic of wireless mesh network, this paper proposes a channel assignment strategy based on topology-division. Considering the effect of interference on different links, wireless interference is classified into vertical and horizontal interferences with determinate directions. An algorithm is proposed to divide the network topology into hop-by-hop subtopologies along the vertical interference. A channel assignment strategy for subtopologies is proposed including minimum channels to avoid vertical interference and additional channels to enhance the minimum throughput subtopology. A method is proposed based on channels to partition horizontal interference with channels within a subtopology. The collision domains within a subtopology and network performance bottleneck are analyzed, and the throughput and the order of channels assignment are simulated. The simulation results show that the proposed channel assignment strategy could effectively assure and enhance network throughout, and the method of horizontal interference partitioning outperforms the common channel framework multichannel mechanism defined in 802.11s.

Regional partition packet classification algorithm is one of the most effective algorithms. To solve the unsymmetrical distribution problem of regional partition for packet classification, a heuristic lookup partition algorithm is proposed after analysing the character of rules’ sets. The main research work on the algorithm in this paper includes two parts: the method of lookup partition to ensure the symmetrical distribution of rules, and the construction of decision tree based on the partition found. The time cost of this algorithm is composed by the time for lookup partition and the time for line-search in the partition found. The results of simulation show that the algorithm is not sensitive to the increasement of rules, meanwhile it supports the incremental updating on-line.

Due to the limited energy, small storage room and so on, the traditional network key management scheme is challenged. Based on the transerval design，bivariable polynomial and threshold strategy, a new pairwise key establishment scheme and multi-path key construction strategy suit to clustered wireless sensor network is proposed. By this scheme and transerval design, the nodes in the same cluster can directly construct pair-wise key and the nodes in the different clusters can construct path key based on threshold strategy. Theory and simulation analysis indicate that the new scheme can not only increase the security, connectivity and vulnerability, but also decrease the communication overload and storage cost. The scalability is another good character.

To improve MSE performance in steady-state and convergence rate of blind equalization, a hybrid blind channel equalization algorithm is proposed in this paper. With decision feedback equalizer, the proposed algorithm applies the error item of DD-LMS (Directed Decision-Least Mean Square) for adaptation when decision is reliable, and error item of MCMA (Modified Constant Modulus Algorithm) is applied when decision is unreliable. And the reliable interval of decision is adapted according to the errors of directed-decisions. The proposed algorithm has been simulated with 64QAM signals through severe digital wireless channel, simulation results show that the proposed algorithm has faster convergence rate and better MSE performance in stead-state than MCMA, and brings 2dB advantage when BER is 10^-6.

Multi-view Video Coding (MVC) demands high compression rates, temporal random access, spatial random access, as well as view scalability, which based on inter-view prediction structure. Joint Multi-view Video Coding (JMVC) proposed the fixed view-temporal prediction structure for the standardization MVC, which is difficult to cope with various characteristics of multi-view videos. Considering coding efficiency and random access on, the multi-view coding scheme based on correlation analysis is proposed in this paper, which can dynamically select to the inter-view prediction structure. Experimental results show that the proposed prediction structure can improve coding efficiency and random access.

For protecting directional geometric structure information, a novel basis function called multibandelets is presented in this paper. And then an image compression algorithm is proposed based on the multibandelet transform and Shannon encode. Experiments show that the multibandelets-based compression provides improvements both in visual effects and quantitative analysis, especially for the detail information containing directional geometric structures. The compared methods are multiwavelets, and those of the wavelets and bandelets with the same vanishing moments, respectively.

There are many analysis algorithms for frequency rate of LFM signal, but those algorithms have some drawbacks, such as highly computational complexity, long time for searching, and cross-term in multi-LFM signal. In this paper, a new analysis algorithm of frequency rate of LFM signal is presented based on Biorthogonal Fourier Transform (BFT), the signal is expanded with biorthogonal base function that could be got frequency rate density spectrum of the signal. This algorithm need no searching, and has better performance for detection different frequency rate of multi-LFM signal. This paper derives continual BFT formula and discrete transform formula and discusses its some main characters.

At present, there exist a lot of algorithms of blind separation, among which there are few algorithms focusing on blind separation of digital signals and estimating source number. To solve the problem, this paper proposes a novel algorithm to solve the blind separation problem of BPSK signals. First, according to characteristics of observations, the algorithm to estimate the source number is given in noise circumstance and no noise circumstance. Second, mixing matrix is gotten by using the relation of observations, which is also proved feasible. Finally, the source signals are recovered by permutations and sign changes of their rows, which are allowed in blind separation. It is well shown that the algorithms are excellent and feasible to estimate the mixed matrix and recover source in the last simulation.

Contour detection from natural scenes is a tough task in computer vision. This paper proposes a visual model of contour detection based on compound receptive field. By inducing dis-inhibition mechanism to traditional model that was based on inhibition mechanism, inferences are suppressed while weak edges are preserved, so that the integrity of contour is improved. Experiment results show that this approach can suppress edges due to texture, protect object contour and improve the performance of contour detection from nature scene.

In order to deal with the uncertainties in feature extraction and decision-making, an information fusion algorithm of fault diagnosis is presented based on random set metrics of fuzzy features and evidence reasoning. Firstly, membership functions are used to describe the fault templates in model database and features extracted from sensor observations. Secondly, a random sets model of fuzzy information is introduced to give a likelihood function, which can be transformed into a Basic Probability Assignment (BPA) function. A BPA numerically shows the support degree of the hypotheses that the machine has certain faults under the fuzzy features. The proposed fuzzy feature is not extracted from single observation but from continuous observations. The fusion diagnosis results based on this proposed feature are more accurate than that based on traditional single observation feature. Finally, the diagnosis results of machine rotor show that the proposed method can enhance diagnostic accuracy and reliability.

The Probabilistic Data Association Filter (PDAF) and the Joint Probabilistic Data Association Filter (JPDAF) are theoretically analyzed and their shortages in theory are pointed out. Based on the probability theory, a New Probabilistic Data Association Filter (NPDAF) is proposed, in which a measurement may originate from targets or a clutter, but the sum of the probabilities originating from targets and a clutter is equal to 1. Also in the paper, the mathematical model for data association in target tracking and the realization technique for NPDAF are presented. The　correlative probabilities between a measurement and targets are first computed in the realization technique, then the gain of a tracking filter is modified using the correlative probability. Simulation results show that the performance of NPDAF is better than that of JPDAF in multiple target tracking.

According to biological attention mechanism, a region of interest detection based on visual attention model and evolutionary programming is proposed in this paper. Candidate image regions are segmented with evolutionary programming algorithm. The interest of a region is measured with local saliency produced by visual attention model and global saliency based on evolutionary programming. After wavelet multiscale transform, local saliency in visual attention model is computed by center-surround differences. Under the action of saliency enhancement factors, focus of attention selects region of interest from candidate regions. The experimental results show the proposed approach is closer to human attention mechanism and performs well for object detection and interest measurement.

Mammography is a conventional early detection method for breast cancer. A novel Computer-Aided Diagnosis (CAD) method for the masses is proposed in this paper. Two characteristic models are built up to represent the masses with various backgrounds, and iterative thresholding is carried out to detect the masses in the fatty tissue; however, black-hole detection of wavelet-domain is applied to label the masses in the dense tissue. Filling dilation based on ANFIS controller, Canny detector and the energy field constraint is used to segment the suspicious masses, and MLP-based classifier is applied to suppress the false positives. The experiments validate that the proposed algorithm gets high detection precision, as well as low false positive rate.

This paper presents a multi-frame stepped-frequency signal processing method to detect moving targets, and a Doppler bin alignment method is proposed to compensate the image aliasing caused by moving targets. This method makes use of the relationship of Doppler bins among different sub-frequencies and can realize the velocity compensation of moving targets via the rearrangement of Doppler bins and phase compensation. This algorithm can simultaneously compensate the effects of linear range migration for all moving targets without knowing their unknown velocity. Analysis and simulation results show that this processing can image the range and velocity of moving targets simultaneously with stepped-frequency signals and can be applied easily because of its computational efficiency.

The direction finding cross localization using bistatic MIMO radar system is studied in this paper, and a fast multi-target localization algorithm based on propagator method is proposed. The new method avoids the estimation and SVD (Singular Value Decomposition) of the covariance matrix of the received signals which are the main computational burden in traditional subspace method, and does not need two-dimensional (2-D) spectrum peak searching. Thus, the computational complexity of the proposed algorithm is reduced with the maintenance of good performance for two-dimensional angle estimation. According to the elementary matrix transformation and the tripartite relationship among matrix, the eigenvalue of the matrix and the eigenvector corresponding to the eigenvalue, the estimated parameters of the proposed algorithm are automatically paired with the additional paring computation eliminated. The simulation results demonstrate its effectiveness and robustness.

When using Tomography SAR combined with spatial spectrum estimation to solve layover effect, the number of signals should be estimated in the elevation direction first. The accuracy of number of signals is directly related to the following estimation performance. The conventional Information Theoretic Criteria (ITC) methods are usually influenced by multiplicative noise of the data, consequently, the performance of the estimation decreases. In this paper, a new method, FB-MAPES, is proposed to detect the number of signals. Then the performance of General Minimum Descriplion Length (GMDL) and FB-MAPES is compared via the Monte Carlo simulation. The experimental results confirm the validity of the FB-MAPES method. Moreover, the proposed method is prior to conventional ITC in detecting the number of tomography SAR signals in the elevation direction.

This paper investigates an implementation of Polar Format Algorithm(PFA) in Bistatic SAR imaging based on the principle of Chirp Scaling(CS). PFA realizes data’s Polar Coordinate Transformation by two 1-D interpolations, which is computationally expensive. Based on the linear frequency modulation characteristic of emission signal, the paper uses Chirp Scaling methodology to process data in range dimension, which only includes signal multiplications and FFTs, thereby avoiding interpolation. The chirped and dechirped signals are discussed separately. Compared with interpolation, the results are equivalent, but the method of CS has increased speed significantly. The experimental simulation results with the point target validate the validity of this method.

Based on the current research on bistatic SAR image, a new algorithm to process data of repeated trajectory bistatic spotlight SAR system is proposed. The algorithm first suppress azimuth aliasing with an azimuth preprocess step, and focus image with traditional wavenumber domain algorithm. It is with high focusing accuracy without distortion involved, by which well focused image over large scene can be obtained. The principal of the azimuth preprocess is also suited to deal with other spotlight SAR mode. And a numeric simulation confirms the validity of the algorithm.

To solve the problems of the self-signature interference and the nonuniformity of image background existing in the vehicle-mounted Forward-Looking Ground Penetrating Synthetic Aperture Radar (FLGPSAR) detection system, an adaptive method is proposed to realize interferences suppression and background uniformization based on distance-band partition and iterative operation techniques in the image domain. Parallel processing can be realized via distance-band partition, which can also improve the accuracy of parameters estimation. Parameters can be estimated and updated on line by using the iterative operation technique, and then the interference suppression and background gain uniformization can be adaptively achieved. Experimental results of the real data show that proposed method has a better adaptability to environment and is prone to real-time processing in structure. It can effectively meet the needs of the vehicle-mounted FLGPSAR system for image preprocessing.

A method of interferometric phase estimation based on the robust beamforming is proposed. The method can provide the accurate interferometric phase estimation, by correcting the spatial steering vector and by taking advantage of the coherence information of the neighboring pixels. Theoretical analysis and experimental results show that the method can present the accurate estimation of the interferometric phase even if the coregistration error be close to one pixel. The effectiveness and robustness of the technique is verified by the simulated and real data.

The multi-frequency MIMO radar uses sparse-array to transmit the FMCW signals of multiple carrier frequencies, and an array to receive the echoes. The signal model of multi-frequency MIMO radar is analyzed in this paper. A new method is proposed to resolve velocity ambiguity, using which the least squared estimation of real velocity can be obtained from the ambiguous Doppler shifts corresponding to the different transmit frequencies without transmitting multiple PRF(Pulse Repetition Frequency) signals. Another method for synthetic impulse and aperture processing is presented in this paper. Every range cell after coherent integration is divided equally into N_n parts, which is weighted by the coherent integration results. As a result，the range grating lobes are suppressed greatly and the aperture of transmitting and receiving array is utilized adequately. Finaly, the problem how to choose the system parameters is discussed. The simulation results indicate the validity of the method presented in this paper.

To overcome the “Doppler dispersion” of the wideband radar return, a method of subband implementation for wideband radar clutter suppression and target High Resolution Range Profile (HRRP) enhancement is presented in this paper. The return is decomposed by oversampled DFT modulation filter bank. In every subband the “Doppler dispersion” can be ignored and weighting processing is implemented for multi coherent returns to suppress the clutter and enhance the target return, then the results of all subbands are reconstructed to get the enhanced target HRRP. The derivation of optimal weight vector is on the principle of maximizing the Pearson correlation coefficient between the reconstructed HRRP and the referenced HRRP. The optimal weight vector can not be implemented because it is dependent on the actual target HRRP and the realizable MVDR weight vector can be derived from the optimal weight vector in the case of high SNR. Theory analyzing and simulation results show that the method presented in this paper can suppress the clutter and enhance the target HRRP.

This paper is for the identification from the RCS sequence of the Mid-course missile. On the base of analyzing its motion and electromagnetic scattering characteristic, a new method using RCS magnitude changes with respect to the object gesture angle for inversing the mid-course object’s long-short axis ratio and gesture angle to the line of the radar is presented. Comparing with the traditional ellipse method, the new method overcomes the disadvantage of the necessity for the maximal and minimal RCS value of the object. The experiment results tested by the simulated and darkroom measurement of the representative missile object show the effectiveness of the method.

In order to correctly estimate the variance of noise in iteration, a pure synthesis noise as an image is synchronously iterated with the observation image in de-convolution, and it takes variance of pure noise image as the estimation of the variance of noise in observation image and computes the regularization parameter by the variance. A novel regularization term that can ensure the synchronous changing of the variance of the two noises is proposed in this article. The new regularization term is put into use only in iteration of pure noise image. Under the condition of knowing the variance of noise of image in iteration, this paper established the relationship between the variance of synthetic noise and the regularization parameter, and the relationship was converted to a simple quadratic equation. Experiments confirm that the new algorithm not only better restrains the noise but also avoids the over smoothing. The adaptability of total variation based image restoration is improved.

Based on nonsubsampled Contourlet transform and SAR image statistical property, a SAR image enhancement method is proposed. A speckle noise variance estimate algorithm is given using nonsubsampled Laplace Pyramid decompose, and a wake edge enhancement algorithm using directional local neighborhood is proposed. This paper estimate the speckle variance in each decomposes direction, and the directional local neighborhood statistical is used to distinguish the strong edge, wake edge and noise. The wake edge is enhanced and the speckled noise is restrained. Experiment results show that the method represents better performance compared with NSWT in wake edges information enhancement and speckle reduction.

The electron-optical system of an L-band multi-beam klystron is designed. The 2-D simulation for the system is conducted first and the 3-D simulation is done in succession. Confined-flow uniform magnetic fields focusing system with multi-lenses is adopted and the paraxial beams with perfect characteristic are obtained. Simulation indicates that the beam occupancy rate is about 55%, the beam transmission rate is 100%, the multi-lenses system can modulate the beam equilibrium radius effectively and the uniform magnetic field in gun region can modulate the beam trajectories. The focusing system allows matching beams with the magnetic fields on the cathode range from 0.001 T to 0.01 T and the magnetic fields in main region range from 0.06 T to 0.13 T.

Fast algorithms for solving the 2 order nonlinear diffusion equations in image processing are presented. A linear finite difference scheme incorporating the explicit scheme and the implicit scheme is given. The stability condition of the scheme is also pgivend. Then three fast iteration algorithms including the MultiGrid (MG) method, the Alternative Direction Implicit (ADI) scheme, and the Additive Operators Splitting (AOS) schemes are discussed. Comparison of the three methods show that, the denoising performance is comparative. The MG method is a little better in denoising the smooth regions, while the ADI and the AOS schemes are simpler in realization.

In order to solve the modulation classification problem of detecting illegal or jamming signal in normal communication, a new modulation classification algorithm for the same channel jamming signal is proposed. Firstly, the effects of unknown parameters, such as phase offset and frequency offset, on forth-order cumulant of co-channel signal are analyzed and the related improving methods are presented. Then, the modulation classifications of jamming signal are done by forth-order cumulant as classification features. Simultaneously, its phase offset and frequency offset are estimated. The experiment results show the validity of the proposed algorithm.

A novel method to estimate the parameters of 1/f-type fractal signal is proposed according to characteristics of the wavelet coefficient variance versus scale of 1/f-type fractal signal in white noise, and namely, after the wavelet coefficient variance is simply transformed, the parameter estimation of 1/f-type fractal signal is according with parameter estimation conditions of least square method. The simulation experiment results demonstrate that, this method can effectively estimate parameters of 1/f-type fractal signal such as γ and σ² etc.to extract them from additive white noise.

Because of the multiplicative nature of the speckle noise in SAR images, it is difficult to solve SAR image segmentation problems using general image segmentation technique. A novel SAR image segmentation algorithm based on an artificial immune system is proposed. After extracting texture features from an image and encoding them with real numbers, it determines partitioning of the feature vectors by optimizing the objective function based on clonal operator. The experimental results show that the novel algorithm is feasible and effective for SAR image segmentation.

In this paper, a new signcryption scheme called CPK-SC is proposed based on Combined Public Key (CPK) to resolve the authentication and non-repudiation problem. CPK-SC discards the pairings and solves the restriction that the traditional identity-based signcryption schemes can only deal with fixed length messages by introduction symmetric cryptography algorithm. CPK-SC spends fewer computations and produces shorter ciphertext, which can be widely used in the environment of computation and communication resource constrained, such as mobile ad-hoc network. In the random oracle model, the security of CPK-SC is tightly related to the Decision Diffie-Hellman (DDH) assumption.

A novel Passive Optical Network (PON) model is proposed. By exploiting this architecture, an efficient Quantum Key Distribution (QKD) protocol with Quantum Identity Authentication (QIA) is designed. In this scheme, both the QIA and QKD between optical line terminal and optical network units in this PON are implemented. Also, the QKD is implemented between each two optical network units in the same optical virtual private network with the simple operations of optical line terminal. The security proofs and the proposed experimental scheme show this protocol is feasible and absolutely secure. Quantum virtual private network can be ultimately realized by using the conversation key generated by QKD protocol to encrypt the intra-communication data.

Channel estimation for MIMO-OFDM systems is investigated, and a chain weighted averaging LS channel estimation algorithm is proposed. Based on the FDM circular pilot sequence, the new algorithm obtains a temporal channel estimation using LS algorithm, and improves the estimation performance by weighted averaging. The circular pilot structure and weighted averaging effectively decreases the effect of the carrier edges on the system’s performance. Furthermore, avoiding the inversion of a large matrix, the new algorithm can be easily realized.

To combat fading in wireless channel, an Opportunistic Relaying scheme based on Physical-layer Network Coding (PNC-OR) is proposed, which not only improves the network throughput by network coding ideas, but also achieves the multi-user diversity gain through relay node selection. Focusing on the bi-directional wireless relaying channels, the sum capacity of the destination nodes in the PNC-OR scheme for the quasi-static fading environment is developed. The numerical results show that in contrast to the opportunistic relaying scheme and conventional network coding scheme, PNC-OR scheme achieves higher spectral efficiency.

The Radio Frequency Interference (RFI) makes the most performance degradation for the Synthetic Aperture Imaging (SAI) and the object detection of Stepped-Frequency Ground Penetrating Radar (SFGPR). This paper proposes a random phase-coded method to transform RFI into zero-mean random signal without effect on the object’s echo. Then the RFI can be suppressed easily by a classical average filter. Analysis indicates that the proposed method makes the SFGPR have the same anti-RFI performance as that of noise radar. It keeps the low sidelobe property of SFGPR and can be realized by FFT. Monte Carlo simulation conforms to the theoretic analysis and demonstrates that the proposed method is effective.

The conventional coarse-grained reconfigurable analog circuits have bad flexibility, and the reConfigurable Analog Block (CAB) structure is complicated. In order to solve such problems, a new OTA-based reconfigurable analog circuit is presented in this paper. In this circuit scheme, the complexity of CAB is reduced and the CAB utilization rate is increased. To verify the effectiveness, three examples of analog circuit design (a second-order low pass filter, a second-order high pass filter and a low-pass third-order Butterworth filter) are presented. The experimental results indicate that the proposed circuits is effective and feasible, which make a better balance between circuit resources?and functions.

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The security of the three convertible ring signature schemes proposed by Zhang-Liu-He (2006), Gan-Chen (2004) and Wang-Zhang-Ma(2007) is analyzed, and it is found that these convertible ring signature schemes are susceptible to convertibility attack or non-repudiation attack, i.e., any member in the ring can claim that he is the actual signer or pretend others’ identity to sign message. To guard against the attack, these convertible ring signature schemes are improved, which can make the improved schemes satisfy the security requirements for convertible ring signature.