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2006 Vol. 28, No. 2
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2006, 28(2): 193-197.
Abstract:
In order to study the impacts of array configuration and channel model parameters including antenna spacing and scattering angle on the channel capacity of a MIMO (Multiple Input Multiple Output) system, a novel method is proposed to explore the channel capacity under flat fading. Fading correlation matrix is constructed based on uniform circular antenna and uniform linear antenna at the receiver side, respectively. And then using the properties of Wishart distribution, closed-form expressions for the upper and lower bounds on the ergodic capacity of N by M MIMO system are presented in detail. The problem of calculating the probability density function of eigenvalues of the fading channel matrix is avoided and the computational complexity is lower in contrast to the previous methods. The novel method also could be generalized to MIMO-OFDM systems with any number of transmit and receive antennas. Computer simulation results show that for small spacing the UCA yields higher channel capacity than ULA. The channel capacity is maximized when the antenna spacing increases to a certain point, and further more, the larger the scattering angle, the quicker the channel capacity converges to its maximum. And at high SNR, the upper and lower bounds on the ergodic capacity are close to its true value.
In order to study the impacts of array configuration and channel model parameters including antenna spacing and scattering angle on the channel capacity of a MIMO (Multiple Input Multiple Output) system, a novel method is proposed to explore the channel capacity under flat fading. Fading correlation matrix is constructed based on uniform circular antenna and uniform linear antenna at the receiver side, respectively. And then using the properties of Wishart distribution, closed-form expressions for the upper and lower bounds on the ergodic capacity of N by M MIMO system are presented in detail. The problem of calculating the probability density function of eigenvalues of the fading channel matrix is avoided and the computational complexity is lower in contrast to the previous methods. The novel method also could be generalized to MIMO-OFDM systems with any number of transmit and receive antennas. Computer simulation results show that for small spacing the UCA yields higher channel capacity than ULA. The channel capacity is maximized when the antenna spacing increases to a certain point, and further more, the larger the scattering angle, the quicker the channel capacity converges to its maximum. And at high SNR, the upper and lower bounds on the ergodic capacity are close to its true value.
2006, 28(2): 198-202.
Abstract:
An approach, which exploits the cyclostationarity of the received signal, to blind channel identification for an OFDM system in frequency selective channel is presented in this paper. First, by utilizing the power distribution of the cyclic autocorrelation function of the received signal, the order of the channel is achieved. Then, the estimated channel is got by identifying its zeros. Finally, simulation results are provided to show that it is superior to the other algorithms.
An approach, which exploits the cyclostationarity of the received signal, to blind channel identification for an OFDM system in frequency selective channel is presented in this paper. First, by utilizing the power distribution of the cyclic autocorrelation function of the received signal, the order of the channel is achieved. Then, the estimated channel is got by identifying its zeros. Finally, simulation results are provided to show that it is superior to the other algorithms.
2006, 28(2): 203-207.
Abstract:
In cellular mobile communication systems, the hybrid Time Difference Of Arrival(TDOA) and the Angle Of Arrival(AOA) location algorithm can reach higher accuracy than traditional TDOA method does. But in NLOS environment, when the measurement error of AOA surpasses a certain value, the location error is still large. This paper proposes an effective location method on the condition that the excessive time delay in NLOS environment is exponential. This method estimates the mean and variances of the excessive time delay based on its statistical property firstly and then reconstructs the TDOA for migrating the influence of the NLOS error. Then use the AOA algorithm as the assistant method. The result of simulation proves its effectiveness in improving the location accuracy than traditional TDOA and TDOA/AOA method in NLOS propagation environment.
In cellular mobile communication systems, the hybrid Time Difference Of Arrival(TDOA) and the Angle Of Arrival(AOA) location algorithm can reach higher accuracy than traditional TDOA method does. But in NLOS environment, when the measurement error of AOA surpasses a certain value, the location error is still large. This paper proposes an effective location method on the condition that the excessive time delay in NLOS environment is exponential. This method estimates the mean and variances of the excessive time delay based on its statistical property firstly and then reconstructs the TDOA for migrating the influence of the NLOS error. Then use the AOA algorithm as the assistant method. The result of simulation proves its effectiveness in improving the location accuracy than traditional TDOA and TDOA/AOA method in NLOS propagation environment.
2006, 28(2): 208-212.
Abstract:
In a multiuser wireless system with multiple antennas, the independence of different users random fading characteristic can be exploited to obtain great gain of multiuser diversity by combining different techniques, such as random beamforming, spatial diversity, antenna selection. The performance of these different multiuser diversity schemes is not the same. This paper gives out the formula of the average throughput and analyzes the performance of some typical multiuser diversity schemes. This paper also compares the effect of number of users and antennas on throughput performance of different multiuser diversity schemes. It will present beneficial reference for the design of practical multiuser system with multiple antennas.
In a multiuser wireless system with multiple antennas, the independence of different users random fading characteristic can be exploited to obtain great gain of multiuser diversity by combining different techniques, such as random beamforming, spatial diversity, antenna selection. The performance of these different multiuser diversity schemes is not the same. This paper gives out the formula of the average throughput and analyzes the performance of some typical multiuser diversity schemes. This paper also compares the effect of number of users and antennas on throughput performance of different multiuser diversity schemes. It will present beneficial reference for the design of practical multiuser system with multiple antennas.
2006, 28(2): 213-216.
Abstract:
Based on the investigation of Multiple-Input Multiple-Output (MIMO) technology and Ultra-Wide Band (UWB) wireless communication systems, a novel MIMO UWB system is proposed, which based on adaptive modulation technique in time varying channel. By using Singular Value Decomposition (SVD) theory and rate quantization methods, the joint time slot average power control algorithm to allocate power and rate is proposed. Simulations indicate that system performance is highly improved by using the power control algorithm.
Based on the investigation of Multiple-Input Multiple-Output (MIMO) technology and Ultra-Wide Band (UWB) wireless communication systems, a novel MIMO UWB system is proposed, which based on adaptive modulation technique in time varying channel. By using Singular Value Decomposition (SVD) theory and rate quantization methods, the joint time slot average power control algorithm to allocate power and rate is proposed. Simulations indicate that system performance is highly improved by using the power control algorithm.
2006, 28(2): 217-222.
Abstract:
Focusing on coherent DS-SS/MPSK system in single path slow fading channel model, this paper analyzes the effect of frequency offset on system performance, and the closed-form Bit Error Rate (BER) expressions are also obtained. Firstly, the Signal Noise Ratio (SNR) characteristic of matched filter despread symbol and the distribution of coherent phase estimation error are derived. Secondly, the exact integration formula of BER for fading channel is presented, moreover, by using the Maclaurin series expansion of MPSK conditional Symbol Error Rate (SER), the simplified BER approximations for BPSK and QPSK are derived over AWGN, Nakagami-m fading and Rayleigh fading channel. Finally, numerial results show that the approximations provide excellent accuracy without loss and can be applied to practical system design and performance evaluation.
Focusing on coherent DS-SS/MPSK system in single path slow fading channel model, this paper analyzes the effect of frequency offset on system performance, and the closed-form Bit Error Rate (BER) expressions are also obtained. Firstly, the Signal Noise Ratio (SNR) characteristic of matched filter despread symbol and the distribution of coherent phase estimation error are derived. Secondly, the exact integration formula of BER for fading channel is presented, moreover, by using the Maclaurin series expansion of MPSK conditional Symbol Error Rate (SER), the simplified BER approximations for BPSK and QPSK are derived over AWGN, Nakagami-m fading and Rayleigh fading channel. Finally, numerial results show that the approximations provide excellent accuracy without loss and can be applied to practical system design and performance evaluation.
2006, 28(2): 223-227.
Abstract:
A new method named Particle Swarm Optimization (PSO) has been proposed by Kennedy and Eberhart (1995) and it can accomplish the same goal as GA in a new and faster way. In this paper a new binary algorithm, which derives from conventional PSO conception and named BEP algorithm, has been proposed. Then the BEP and Binary PSO (BPSO) have been applied to solve the multiuser detection problems in the CDMA system. The simulation results proved that BEP Detector (BEPD) and BPSO Detector (BPSOD) have better capability against error bit and converge more quickly than Conventional Detector (CD) and GA Detector (GAD).
A new method named Particle Swarm Optimization (PSO) has been proposed by Kennedy and Eberhart (1995) and it can accomplish the same goal as GA in a new and faster way. In this paper a new binary algorithm, which derives from conventional PSO conception and named BEP algorithm, has been proposed. Then the BEP and Binary PSO (BPSO) have been applied to solve the multiuser detection problems in the CDMA system. The simulation results proved that BEP Detector (BEPD) and BPSO Detector (BPSOD) have better capability against error bit and converge more quickly than Conventional Detector (CD) and GA Detector (GAD).
2006, 28(2): 228-231.
Abstract:
A new digital PN code tracking loop with a sequential filter is proposed, and an equivalent model of the loops dynamic process is provided to derive the loops nonlinear performance. The performance is also analyzed by computer simulation under Rayleigh fading channel. The results show that this loop has satisfactory performance under fading environments.
A new digital PN code tracking loop with a sequential filter is proposed, and an equivalent model of the loops dynamic process is provided to derive the loops nonlinear performance. The performance is also analyzed by computer simulation under Rayleigh fading channel. The results show that this loop has satisfactory performance under fading environments.
2006, 28(2): 232-236.
Abstract:
This paper presents a novel multiple object segmentation algorithm based on a Bayesian framework. According to the characteristic of the intra-frame and inter-frame (spatial and temporal) information, a representation of Maximization of the A posteriori Probability(MAP) of spatio-temporal label field is proposed. So a minimization of energy function is obtained. The optimization of solution is carried out by Iterated Conditional Mode(ICM) method. The initial segmentation label fields is gotten using vector histogram. The experimental results show that the algorithm is effective to multiple object segmentation with partial occlusion.
This paper presents a novel multiple object segmentation algorithm based on a Bayesian framework. According to the characteristic of the intra-frame and inter-frame (spatial and temporal) information, a representation of Maximization of the A posteriori Probability(MAP) of spatio-temporal label field is proposed. So a minimization of energy function is obtained. The optimization of solution is carried out by Iterated Conditional Mode(ICM) method. The initial segmentation label fields is gotten using vector histogram. The experimental results show that the algorithm is effective to multiple object segmentation with partial occlusion.
2006, 28(2): 237-241.
Abstract:
This paper describes an efficient Motion-Compensated (MC)three dimension wavelet video coding system. In this system, MC temporal analysis is used to remove temporal redundancy. Then an adaptive group of pictures structure according to characteristics of motion can increase the coding efficiency and reduce computational complexity and memory requirement at the same time. Finally, a quadtree-based wavelet image coding method is proposed, which can adapt the property of wavelet image coefficient. The experimental results show that, the coding system is better than other motion-compensated three dimension wavelet video coding methods.
This paper describes an efficient Motion-Compensated (MC)three dimension wavelet video coding system. In this system, MC temporal analysis is used to remove temporal redundancy. Then an adaptive group of pictures structure according to characteristics of motion can increase the coding efficiency and reduce computational complexity and memory requirement at the same time. Finally, a quadtree-based wavelet image coding method is proposed, which can adapt the property of wavelet image coefficient. The experimental results show that, the coding system is better than other motion-compensated three dimension wavelet video coding methods.
2006, 28(2): 242-246.
Abstract:
A syndrome-based type-I Hybrid ARQ (HARQ) is proposed, where Reed-Solomon code is selected to be the FEC subsystem and the error-detection function is embedded ably in the decoding process. Analytical and simulation results of Bit Error Rate (BER) and throughput efficiency of the system show that syndrome-ahead and syndrome-behind structures are suited to short codes and long codes, respectively. By choosing the maximum of retransmission times, a perfect tradeoff can be obtained between the throughput efficiency and the reliability of the system.
A syndrome-based type-I Hybrid ARQ (HARQ) is proposed, where Reed-Solomon code is selected to be the FEC subsystem and the error-detection function is embedded ably in the decoding process. Analytical and simulation results of Bit Error Rate (BER) and throughput efficiency of the system show that syndrome-ahead and syndrome-behind structures are suited to short codes and long codes, respectively. By choosing the maximum of retransmission times, a perfect tradeoff can be obtained between the throughput efficiency and the reliability of the system.
2006, 28(2): 247-251.
Abstract:
This paper proposes a pairing-based group key agreement protocol based on Shims certification-based tripartite key agreement protocol. This protocol adopts a pseudo-random sequence to avoid the unknown key-share attack and the known-key attack. Some attacks described in the literatures are presented, which proved infeasible in the protocol. And this protocol can achieves the forward security and backward security, when a dynamic group performs it.
This paper proposes a pairing-based group key agreement protocol based on Shims certification-based tripartite key agreement protocol. This protocol adopts a pseudo-random sequence to avoid the unknown key-share attack and the known-key attack. Some attacks described in the literatures are presented, which proved infeasible in the protocol. And this protocol can achieves the forward security and backward security, when a dynamic group performs it.
2006, 28(2): 252-256.
Abstract:
Traditional steganographic techniques for JPEG images always suffer from histogram-based attacks because they change the DCT coefficient histogram of the cover image, or from the reduced hiding capacity due to the correction of the change of the histogram. A new steganography preserving the property of the histogram is proposed in this paper. When the secret message is embedded, an adjust_info table is built to memorize the alteration of the histogram. Then the modification direction of the coefficient is adjusted according to the table. In this way, the change of the histogram is compensated and the hiding capacity is not reduced yet. Several experimental results demonstrate that the algorithm can attain a high hiding capacity of 13% (the quality factor is 75). Furthermore the average distortion rate of the general DCT coefficient histograms on stego-images is 0.81%, the maximal distortion rate of the histograms on low frequency coefficients is 3.83% obtained from the stego-images generated by the improved algorithm and the average distortion rate of them is only 1.98%. The property of the histogram is fine changed; therefore, various histogram-based attacks can be effectively resisted and secure steganorgraphy can be insured.
Traditional steganographic techniques for JPEG images always suffer from histogram-based attacks because they change the DCT coefficient histogram of the cover image, or from the reduced hiding capacity due to the correction of the change of the histogram. A new steganography preserving the property of the histogram is proposed in this paper. When the secret message is embedded, an adjust_info table is built to memorize the alteration of the histogram. Then the modification direction of the coefficient is adjusted according to the table. In this way, the change of the histogram is compensated and the hiding capacity is not reduced yet. Several experimental results demonstrate that the algorithm can attain a high hiding capacity of 13% (the quality factor is 75). Furthermore the average distortion rate of the general DCT coefficient histograms on stego-images is 0.81%, the maximal distortion rate of the histograms on low frequency coefficients is 3.83% obtained from the stego-images generated by the improved algorithm and the average distortion rate of them is only 1.98%. The property of the histogram is fine changed; therefore, various histogram-based attacks can be effectively resisted and secure steganorgraphy can be insured.
Performance Analysis of Joint Source-Channel Decoding Based on MS Estimation and Iterative Structure
2006, 28(2): 257-261.
Abstract:
Based on structure of MS estimation soft-bit source decoding and iterative source-controlled channel decoding, this paper deduces the parameter SNR and BER upper bound for above joint source-channel decoding respectively, and gives the factors which determine the improvement of system performance. The result shows the feasibility of joint source-channel decoding algorithm. Also, simulation proves the validity of analysis process.
Based on structure of MS estimation soft-bit source decoding and iterative source-controlled channel decoding, this paper deduces the parameter SNR and BER upper bound for above joint source-channel decoding respectively, and gives the factors which determine the improvement of system performance. The result shows the feasibility of joint source-channel decoding algorithm. Also, simulation proves the validity of analysis process.
2006, 28(2): 262-266.
Abstract:
Fractal modulation based on multiwavelet is proposed and its power density spectrum is calculated and also its bit error ratio under binary data is calculated. Multiwavelet fractal modulation provides more sub-bands and holds more users at each scale and has much higher band efficiency than that with single wavelet. The bit error rate under additive white Gaussian noise channel, Rayleigh channel and multi-path channel is simulated. The systems anti-multi-path fading ability is analyzed by the periodic auto-correlation function of multiwavelets and wavelets. According to the number of the zero point of the periodic auto-correlation function, the capacity can be improved by orthogonal shift and overlapping in time domain.
Fractal modulation based on multiwavelet is proposed and its power density spectrum is calculated and also its bit error ratio under binary data is calculated. Multiwavelet fractal modulation provides more sub-bands and holds more users at each scale and has much higher band efficiency than that with single wavelet. The bit error rate under additive white Gaussian noise channel, Rayleigh channel and multi-path channel is simulated. The systems anti-multi-path fading ability is analyzed by the periodic auto-correlation function of multiwavelets and wavelets. According to the number of the zero point of the periodic auto-correlation function, the capacity can be improved by orthogonal shift and overlapping in time domain.
2006, 28(2): 267-271.
Abstract:
Differential Unitary Space-Time Modulation (DUSTM) based on diagonal signals achieves full antenna diversity without requiring channel estimation. However, its receiver has a computational complexity that grows exponentially with the number of transmit antennas and the data rate. To reduce receiver complexity, a new DUSTM scheme is proposed for systems where the number of transmit antennas is even. The scheme partitions transmit antennas into two groups with equal number of antennas, and diagonal unitary space-time modulation is applied on each group. The differential encoding matrix is constructed so that maximum-likelihood detection of the two diagonal signals can be decoupled, thereby reducing receiver complexity significantly. Theoretical analysis and simulation results show that the proposed scheme preserves full antenna diversity and provides better bit-error rate performance than diagonal signals in some scenarios.
Differential Unitary Space-Time Modulation (DUSTM) based on diagonal signals achieves full antenna diversity without requiring channel estimation. However, its receiver has a computational complexity that grows exponentially with the number of transmit antennas and the data rate. To reduce receiver complexity, a new DUSTM scheme is proposed for systems where the number of transmit antennas is even. The scheme partitions transmit antennas into two groups with equal number of antennas, and diagonal unitary space-time modulation is applied on each group. The differential encoding matrix is constructed so that maximum-likelihood detection of the two diagonal signals can be decoupled, thereby reducing receiver complexity significantly. Theoretical analysis and simulation results show that the proposed scheme preserves full antenna diversity and provides better bit-error rate performance than diagonal signals in some scenarios.
2006, 28(2): 272-276.
Abstract:
In this paper, packet scheduling with average transmit power constraint over Gaussian channels is considered with the objective to minimize the maximum delay constraint. It is proved that the optimal average transmit power is decreased with the maximum delay constraint for non-time-varying schedulers with maximum delay constraint. Then the equivalence between the optimal scheduler for average transmit power and for maximum delay constraint is proved according to the decreasing property. Then, the form of non-time-varying optimal scheduler based on this equivalence is given. The schedulers parameter, which also reflects the performance, is determined under some certain arrival process, with an example of Poisson arrival. A practical design for this scheduler is presented and simulations show that this design can realize the optimal scheduler.
In this paper, packet scheduling with average transmit power constraint over Gaussian channels is considered with the objective to minimize the maximum delay constraint. It is proved that the optimal average transmit power is decreased with the maximum delay constraint for non-time-varying schedulers with maximum delay constraint. Then the equivalence between the optimal scheduler for average transmit power and for maximum delay constraint is proved according to the decreasing property. Then, the form of non-time-varying optimal scheduler based on this equivalence is given. The schedulers parameter, which also reflects the performance, is determined under some certain arrival process, with an example of Poisson arrival. A practical design for this scheduler is presented and simulations show that this design can realize the optimal scheduler.
2006, 28(2): 277-280.
Abstract:
Because of limited bandwidth capacity in Ad hoc networks, multipath transport is appealing technique to satisfy the requirement of QoS services on bandwidth by improve available bandwidth. In this paper, the feasibility of reasonable distribution for minimization of delay is proved theoretically, and an algorithm of Adaptive Traffic Distribution Based on Minimize Delay(ATDBMD) in Ad hoc networks is proposed, aiming at the minimization of delay and delay jitter, to satisfy another requirement of QoS services on delay. Simulation result shows that ATDBMD wins other algorithm in simpleness, quickly adaptability and precisely control.
Because of limited bandwidth capacity in Ad hoc networks, multipath transport is appealing technique to satisfy the requirement of QoS services on bandwidth by improve available bandwidth. In this paper, the feasibility of reasonable distribution for minimization of delay is proved theoretically, and an algorithm of Adaptive Traffic Distribution Based on Minimize Delay(ATDBMD) in Ad hoc networks is proposed, aiming at the minimization of delay and delay jitter, to satisfy another requirement of QoS services on delay. Simulation result shows that ATDBMD wins other algorithm in simpleness, quickly adaptability and precisely control.
2006, 28(2): 281-285.
Abstract:
A Busy Tone and Directional antenna Multiple Access Control Protocol with power control (BT-DMACP) for Mobile Ad hoc NETwork (MANET) is proposed. The special hidden terminal problems and side lobe interference in directional antennas used network are considered. Through RTS/CTS handshake mechanism, directional busy tone signals and the power control method, the directional transmission power of data packets can be adjusted in time. In order to estimation of the maximal interference power supported by receiving node, an adaptive estimation algorithm is presented. Simulation results show that BT-DMACP supports effectively the application of directional antennas and provides higher channel utilization and lower energy consumption.
A Busy Tone and Directional antenna Multiple Access Control Protocol with power control (BT-DMACP) for Mobile Ad hoc NETwork (MANET) is proposed. The special hidden terminal problems and side lobe interference in directional antennas used network are considered. Through RTS/CTS handshake mechanism, directional busy tone signals and the power control method, the directional transmission power of data packets can be adjusted in time. In order to estimation of the maximal interference power supported by receiving node, an adaptive estimation algorithm is presented. Simulation results show that BT-DMACP supports effectively the application of directional antennas and provides higher channel utilization and lower energy consumption.
2006, 28(2): 286-289.
Abstract:
Current centralized restoration schemes are bad match for the increasing of the scale and complexity of networks. A novel distributed network partition scheme is proposed in this paper. A large-scale network can be partitioned into several annular sub-networks with nuclear nodes in this scheme. In each sub-network, distributed manage ment and distributed restoration is adopted. The detailed process of partition is provided and the relevant distributed restoration scheme is given. Finally, this scheme has been implemented through computer simulation, and it was tested on practical optical networks. The simulation results show that this scheme is practicable and effectual.
Current centralized restoration schemes are bad match for the increasing of the scale and complexity of networks. A novel distributed network partition scheme is proposed in this paper. A large-scale network can be partitioned into several annular sub-networks with nuclear nodes in this scheme. In each sub-network, distributed manage ment and distributed restoration is adopted. The detailed process of partition is provided and the relevant distributed restoration scheme is given. Finally, this scheme has been implemented through computer simulation, and it was tested on practical optical networks. The simulation results show that this scheme is practicable and effectual.
2006, 28(2): 290-294.
Abstract:
The evaluation of Internet QoS (Quality of Service) is naturally multi-discipline. This paper examines the Internet QoS evaluation by integrating QoS index with price factor. The multinomial logit model is adopted in this paper, which is used to model the choice behaviour of users. Each service class is modelled as independently competitive entity. The goal of each service class is to maximize its own utility. Through the analysis based on noncooperative game, the conclusion is drawn that the equilibria exist between QoS index and price of each service class, and the numerical results is provided to verify the conclusion.
The evaluation of Internet QoS (Quality of Service) is naturally multi-discipline. This paper examines the Internet QoS evaluation by integrating QoS index with price factor. The multinomial logit model is adopted in this paper, which is used to model the choice behaviour of users. Each service class is modelled as independently competitive entity. The goal of each service class is to maximize its own utility. Through the analysis based on noncooperative game, the conclusion is drawn that the equilibria exist between QoS index and price of each service class, and the numerical results is provided to verify the conclusion.
2006, 28(2): 295-298.
Abstract:
The TRBC (Transmitter and Receiver Based Coding) protocol adopted in CDMA Ad hoc networks is analyzed in this paper, its performance is compared with the traditional TBC (Transmitter Based Coding) and RBC (Receiver Based Coding) protocols. The analysis of numerical results indicates that the performance of TRBC protocol using two levels of encoding and decoding is better than that of RBC protocol, and worse than that of TBC protocol under the environments with enough bandwidth or a small quantity of users. However, its system complexity is also more than that of RBC protocol, and less than that of TBC protocol. Therefore, as a trade-off between performance and system complexity, the TRBC protocol has great significance for the designing of a practical CDMA Ad hoc networks.
The TRBC (Transmitter and Receiver Based Coding) protocol adopted in CDMA Ad hoc networks is analyzed in this paper, its performance is compared with the traditional TBC (Transmitter Based Coding) and RBC (Receiver Based Coding) protocols. The analysis of numerical results indicates that the performance of TRBC protocol using two levels of encoding and decoding is better than that of RBC protocol, and worse than that of TBC protocol under the environments with enough bandwidth or a small quantity of users. However, its system complexity is also more than that of RBC protocol, and less than that of TBC protocol. Therefore, as a trade-off between performance and system complexity, the TRBC protocol has great significance for the designing of a practical CDMA Ad hoc networks.
2006, 28(2): 299-302.
Abstract:
As a cryptography algorithm that can provide non-repudiability, hash chains are widely used in electronic micropayment schemes because of its efficiency. In order to further improve efficiency, multiple hash chains can be simultaneously used to represent different denominations in micropayment. Because of the limitation that hash chain has a limited length, system design has to reduce the overhead when hash chains are re-initialized. A efficient one-time-signature-based construction is proposed which can simultaneously re-initialize multiple hash chains and its intrinsic non-repudiability and flexibility of configuration in re-initialization are analyzed. The application of the construction in multi-denomination micropayment is illustrated. The proposed construction can improve the efficiency of systems with multiple hash chains.
As a cryptography algorithm that can provide non-repudiability, hash chains are widely used in electronic micropayment schemes because of its efficiency. In order to further improve efficiency, multiple hash chains can be simultaneously used to represent different denominations in micropayment. Because of the limitation that hash chain has a limited length, system design has to reduce the overhead when hash chains are re-initialized. A efficient one-time-signature-based construction is proposed which can simultaneously re-initialize multiple hash chains and its intrinsic non-repudiability and flexibility of configuration in re-initialization are analyzed. The application of the construction in multi-denomination micropayment is illustrated. The proposed construction can improve the efficiency of systems with multiple hash chains.
2006, 28(2): 303-306.
Abstract:
Based on Schnorr (Elgamal) signature and (string) oblivious transfer, an enhanced oblivious transfer protocol is proposed which solved the access control problem for an oblivious transfer protocol. The protocol proposed has the property: the only receiver who has the signature issued by the central authority can open the message which he chose; the sender can not decide whether the receiver has the signature or not. That is the identity of the receiver can not be confirmed after the protocol. Under the Decisional Diffie-Hellman(DDH) assumption the proposed scheme has provable security.
Based on Schnorr (Elgamal) signature and (string) oblivious transfer, an enhanced oblivious transfer protocol is proposed which solved the access control problem for an oblivious transfer protocol. The protocol proposed has the property: the only receiver who has the signature issued by the central authority can open the message which he chose; the sender can not decide whether the receiver has the signature or not. That is the identity of the receiver can not be confirmed after the protocol. Under the Decisional Diffie-Hellman(DDH) assumption the proposed scheme has provable security.
2006, 28(2): 307-311.
Abstract:
In perceptual audio coding with low bit rate application, the pre-echo artifact is more distinct, and the effective detection of transient signals is the precondition. Transient intensity is defined in term of the Peak-Mean power Ratio(PMR), accordingly, a novel detecting algorithm of transient signals on time domain is presented while PMR is used as a criterion function. Because of considering the temporal masking effects to set up a threshold and the valid hop size of transient points, this method is very suitable for perceptual audio coding. When compared with the typical perceptual entropy detecting on frequency domain，it has some advantages, such as higher time resolution, more accuracy and simple algorithm.
In perceptual audio coding with low bit rate application, the pre-echo artifact is more distinct, and the effective detection of transient signals is the precondition. Transient intensity is defined in term of the Peak-Mean power Ratio(PMR), accordingly, a novel detecting algorithm of transient signals on time domain is presented while PMR is used as a criterion function. Because of considering the temporal masking effects to set up a threshold and the valid hop size of transient points, this method is very suitable for perceptual audio coding. When compared with the typical perceptual entropy detecting on frequency domain，it has some advantages, such as higher time resolution, more accuracy and simple algorithm.
2006, 28(2): 312-316.
Abstract:
An adaptive bilateral filtering method based on mean shift algorithm is presented. The filter is governed by the kernel width in spatial domain, which controls the spatial extent of nearby data for filtering. Its kernel width in range domain is chosen adaptively by the local characteristic of the signal. It can remove impulsive noise and improve smoothing of non-impulsive noise with edges preserved. Comparisons with Gaussian filter and median filter were made. Applications to spectra signal processing show this method can suppress noises in spectra effectively and reduce the amount of smoothing near spectral lines.
An adaptive bilateral filtering method based on mean shift algorithm is presented. The filter is governed by the kernel width in spatial domain, which controls the spatial extent of nearby data for filtering. Its kernel width in range domain is chosen adaptively by the local characteristic of the signal. It can remove impulsive noise and improve smoothing of non-impulsive noise with edges preserved. Comparisons with Gaussian filter and median filter were made. Applications to spectra signal processing show this method can suppress noises in spectra effectively and reduce the amount of smoothing near spectral lines.
2006, 28(2): 317-321.
Abstract:
A universal real-time platform for a Space-Time Adaptive Processing (STAP) is developed. The platform is composed of multi-DSPs，FPGA and a general-purpose processor. Refined from the Bulk Synchronous Parallel model (BSP) by Valiant(1990), an STAP computation model is brought forward. The model provides a bridge between STAP algorithms and real parallel systems. Moreover, it can be applied to performance evaluation. During the course of development, scalable cluster-organized multi-processors structure is adopted as hardware architecture. And data-block static allocating is taken as the mapping scheme. Afterwards, some optimization methods about communication and programming are introduced. This system can meet the real-time requirement, its scalability is good, and it facilitates the development of similar systems.
A universal real-time platform for a Space-Time Adaptive Processing (STAP) is developed. The platform is composed of multi-DSPs，FPGA and a general-purpose processor. Refined from the Bulk Synchronous Parallel model (BSP) by Valiant(1990), an STAP computation model is brought forward. The model provides a bridge between STAP algorithms and real parallel systems. Moreover, it can be applied to performance evaluation. During the course of development, scalable cluster-organized multi-processors structure is adopted as hardware architecture. And data-block static allocating is taken as the mapping scheme. Afterwards, some optimization methods about communication and programming are introduced. This system can meet the real-time requirement, its scalability is good, and it facilitates the development of similar systems.
2006, 28(2): 322-325.
Abstract:
This paper first summarizes the difficulty in detecting and identifying helicopter, then analysis the spectrum signature of radar echo signal from helicopter, and estimates the width of the spectrum modulated by helicopter blades. The author uses the width of the spectrum and applies the theory of blind number to a rough classification of helicopter and fixed-wing aircraft. The author provides the result of emulation, and the result proves the effectiveness of theoretic analyses and the algorithm of classification.
This paper first summarizes the difficulty in detecting and identifying helicopter, then analysis the spectrum signature of radar echo signal from helicopter, and estimates the width of the spectrum modulated by helicopter blades. The author uses the width of the spectrum and applies the theory of blind number to a rough classification of helicopter and fixed-wing aircraft. The author provides the result of emulation, and the result proves the effectiveness of theoretic analyses and the algorithm of classification.
2006, 28(2): 326-329.
Abstract:
Polarimetric adaptive detection of targets in compound-Gaussian clutter with coherent radar is addressed in the paper. An adaptive polarimetric detection algorithm is presented based upon the Generalized Likelihood Ratio Test (GLRT). The proposed algorithm has the Constant False Alarm Rate (CFAR) property with respect to the texture statistical characterization. A sensitivity analysis shows that the probability of false alarm is only slightly affected by variations in the clutter correlation properties. Resorting to simulation, the performance of the algorithm is analyzed in different cases. The proposed algorithm has an close performance as previously proposed algorithm, but it has less complexity, than the previously proposed one.
Polarimetric adaptive detection of targets in compound-Gaussian clutter with coherent radar is addressed in the paper. An adaptive polarimetric detection algorithm is presented based upon the Generalized Likelihood Ratio Test (GLRT). The proposed algorithm has the Constant False Alarm Rate (CFAR) property with respect to the texture statistical characterization. A sensitivity analysis shows that the probability of false alarm is only slightly affected by variations in the clutter correlation properties. Resorting to simulation, the performance of the algorithm is analyzed in different cases. The proposed algorithm has an close performance as previously proposed algorithm, but it has less complexity, than the previously proposed one.
2006, 28(2): 330-334.
Abstract:
The condition under which the output signals of monopulse radar receiver with two Swerling 4 targets are approximate to the Gaussian distribution has been studied in order to apply the detection and estimation methods of Rayleigh targets to Sweriling 4 targets. First, the probability density function(pdf) of the outputs under multiple Swerling targets are derived; then get the condition, under which the pdf of the outputs is approximate to Gaussian distribution, that the difference between the SNRs of two targets , whose returns power are the biggest among the targets, is not more than 7 dB.
The condition under which the output signals of monopulse radar receiver with two Swerling 4 targets are approximate to the Gaussian distribution has been studied in order to apply the detection and estimation methods of Rayleigh targets to Sweriling 4 targets. First, the probability density function(pdf) of the outputs under multiple Swerling targets are derived; then get the condition, under which the pdf of the outputs is approximate to Gaussian distribution, that the difference between the SNRs of two targets , whose returns power are the biggest among the targets, is not more than 7 dB.
2006, 28(2): 335-339.
Abstract:
The detection problem of dim signal is studied based on mono-frequency or narrowband dual-polarization radar system in this paper. Firstly, the descriptions of Instantaneous Polarization Projection Sequences (IPPS) of signal and noise are presented and statistics of generalized distance between random EM wave and the anticipant signa are derived. Then, utilizing the generalized distance difference of signal and noise to the anticipant signal, a novel detection algorithm is presented through polarization accumulation. In this paper, detect performance of radar system is improved obviously and more than 10dB.
The detection problem of dim signal is studied based on mono-frequency or narrowband dual-polarization radar system in this paper. Firstly, the descriptions of Instantaneous Polarization Projection Sequences (IPPS) of signal and noise are presented and statistics of generalized distance between random EM wave and the anticipant signa are derived. Then, utilizing the generalized distance difference of signal and noise to the anticipant signal, a novel detection algorithm is presented through polarization accumulation. In this paper, detect performance of radar system is improved obviously and more than 10dB.
2006, 28(2): 340-344.
Abstract:
In distributed small satellites-synthetic aperture radar (DSS-SAR), the correlation of echoes is determined by both across-track and along-track baselines which are coupling, and the multi-baseline interferometry is obtained with multi small satellites SAR images. The optimal across-track baseline of DSS-SAR for terrain elevation measurement is more complicatedly determined than that of conventional SAR interferometry. A novel approach is presented in this paper to determine the optimal across-track baseline of DSS-SAR multi-baseline interferometry. On the basis of the statistical characteristics of phase difference of complex SAR image pair, the DSS-SAR interferometric phase estimation Crammer-Rao bound is deduced. The relationship between terrain height accuracy and across-track baseline is presented from the bound. And then the optimal across-track baseline is derived via derivative calculation. Finally, the optimal across-track baseline in different DSS-SAR configuration with three small satellites is calculated and analyzed. It is showed that the optimal baseline of single across-track baseline interferometry according to this paper is in agreement with that from known single satellite SAR interferometry. The result validates the novel approach proposed by this paper.
In distributed small satellites-synthetic aperture radar (DSS-SAR), the correlation of echoes is determined by both across-track and along-track baselines which are coupling, and the multi-baseline interferometry is obtained with multi small satellites SAR images. The optimal across-track baseline of DSS-SAR for terrain elevation measurement is more complicatedly determined than that of conventional SAR interferometry. A novel approach is presented in this paper to determine the optimal across-track baseline of DSS-SAR multi-baseline interferometry. On the basis of the statistical characteristics of phase difference of complex SAR image pair, the DSS-SAR interferometric phase estimation Crammer-Rao bound is deduced. The relationship between terrain height accuracy and across-track baseline is presented from the bound. And then the optimal across-track baseline is derived via derivative calculation. Finally, the optimal across-track baseline in different DSS-SAR configuration with three small satellites is calculated and analyzed. It is showed that the optimal baseline of single across-track baseline interferometry according to this paper is in agreement with that from known single satellite SAR interferometry. The result validates the novel approach proposed by this paper.
2006, 28(2): 345-349.
Abstract:
In this paper, a distributed satellites SAR high resolution imaging method based on spectral synthesis is introduced. In distributed satellites SAR system, the scattering spectrums relative to the same scene acquired by different satellites have spectrum shifts in both range and azimuth directions, when join these shifted spectrums to a wider range and azimuth spectrum, a higher range and azimuth resolution can be acquired. In the processing, InSAR technique can be used to estimate the phase difference of the images. And after phase correction procedure, image combination procedure has been done, a higher resolution image both in range and azimuth direction would be generated. In this paper a theoretical analysis of this method is given, and the simulation results are also provided.
In this paper, a distributed satellites SAR high resolution imaging method based on spectral synthesis is introduced. In distributed satellites SAR system, the scattering spectrums relative to the same scene acquired by different satellites have spectrum shifts in both range and azimuth directions, when join these shifted spectrums to a wider range and azimuth spectrum, a higher range and azimuth resolution can be acquired. In the processing, InSAR technique can be used to estimate the phase difference of the images. And after phase correction procedure, image combination procedure has been done, a higher resolution image both in range and azimuth direction would be generated. In this paper a theoretical analysis of this method is given, and the simulation results are also provided.
2006, 28(2): 350-353.
Abstract:
Based on the study of the 2-dimensional position correlation information among resolution cells of a distributed target, a new method for distributed targets detection in SAR image is proposed. Several forms of the method based on different range measure definitions are proposed and compared with the CFAR detection by simulation and experiment, the results and performance analysis show the validity and advantage of the proposed method. By comparing the detection performance and computation complexity of the three range measure definitions with each other, the optimal one is determined.
Based on the study of the 2-dimensional position correlation information among resolution cells of a distributed target, a new method for distributed targets detection in SAR image is proposed. Several forms of the method based on different range measure definitions are proposed and compared with the CFAR detection by simulation and experiment, the results and performance analysis show the validity and advantage of the proposed method. By comparing the detection performance and computation complexity of the three range measure definitions with each other, the optimal one is determined.
2006, 28(2): 354-357.
Abstract:
Chaotic FM signal is similar to random signal. It has good Electronic Counter-Counter Measure (ECCM) capabilities. In this paper, chaotic FM signal is used to improve the ECCM capabilities of imaging radar. A kind of chaotic series was generated using n-Way Bernoulli map. The signals modulated by this kind of series have ideal auto-correlation property. High resolution image can be achieved using these signals. However, the waveform is very hard to estimate. In this paper, the chaotic FM signal model is discussed, and point target imaging is simulated. The simulation result shows that ideal point target image can be achieved using chaotic FM signal, which has good prospects to be applied in imaging radar system.
Chaotic FM signal is similar to random signal. It has good Electronic Counter-Counter Measure (ECCM) capabilities. In this paper, chaotic FM signal is used to improve the ECCM capabilities of imaging radar. A kind of chaotic series was generated using n-Way Bernoulli map. The signals modulated by this kind of series have ideal auto-correlation property. High resolution image can be achieved using these signals. However, the waveform is very hard to estimate. In this paper, the chaotic FM signal model is discussed, and point target imaging is simulated. The simulation result shows that ideal point target image can be achieved using chaotic FM signal, which has good prospects to be applied in imaging radar system.
2006, 28(2): 358-361.
Abstract:
In this paper, based on the theory of the Block Adaptive Vector Quantization (BAVQ) algorithm, a variable-rate algorithm is proposed. In order to reduce the encoding computation complexity of the improved BAVQ algorithm, a fast VQ search algorithm and a look-up table to found quantizer control (threshold) are used. Using this improved algorithm to compress SAR raw data, a higher encoding efficiency is achieved and the SNR does not decrease in evidence. The decompressed images reserve most of details on the images resulted from raw data.
In this paper, based on the theory of the Block Adaptive Vector Quantization (BAVQ) algorithm, a variable-rate algorithm is proposed. In order to reduce the encoding computation complexity of the improved BAVQ algorithm, a fast VQ search algorithm and a look-up table to found quantizer control (threshold) are used. Using this improved algorithm to compress SAR raw data, a higher encoding efficiency is achieved and the SNR does not decrease in evidence. The decompressed images reserve most of details on the images resulted from raw data.
2006, 28(2): 362-366.
Abstract:
Parameter estimation of radar target scatterer plays an important role in the process of target characteristics analysis and target recognition. Based on the GTD(Geometrical Theory of Diffraction) parametric model, this paper presents a novel method which can synthetically apply the multi-band measurements in frequency domain and effectively estimate the parameters of scatterers, including location, amplitude and scattering type. The numeric results indicate that the method can effectively mine the information hidden in the model and hold the ability of supper-resolution, which provides a new way to ultra-wide-band signal processing of radar.
Parameter estimation of radar target scatterer plays an important role in the process of target characteristics analysis and target recognition. Based on the GTD(Geometrical Theory of Diffraction) parametric model, this paper presents a novel method which can synthetically apply the multi-band measurements in frequency domain and effectively estimate the parameters of scatterers, including location, amplitude and scattering type. The numeric results indicate that the method can effectively mine the information hidden in the model and hold the ability of supper-resolution, which provides a new way to ultra-wide-band signal processing of radar.
2006, 28(2): 367-371.
Abstract:
In the field of image processing, the segmentation of moving object in video sequences is a hot research topic in recent years. In this paper, a novel method of moving object segmentation based on spatiotemporal Markov Random Field(MRE) is proposed. Firstly, two observations and two initial labels are derived from the three successive images with the same method in the first scheme. Secondly, the AND-label is obtained with the AND-operation on the two initial labels. Finally, the image segmented with the color clustering algorithm is regarded as prior knowledge, with which the corresponding Gibbs energy function is redefined, and the maximum a posteriori estimator, which is determined by using the iterated conditional mode algorithm, is employed to get optimized labels. The new MRF model contributes to the weakening of the noise and to the elimination of the covered-uncovered background and to the recovery of the uniform moving regions.
In the field of image processing, the segmentation of moving object in video sequences is a hot research topic in recent years. In this paper, a novel method of moving object segmentation based on spatiotemporal Markov Random Field(MRE) is proposed. Firstly, two observations and two initial labels are derived from the three successive images with the same method in the first scheme. Secondly, the AND-label is obtained with the AND-operation on the two initial labels. Finally, the image segmented with the color clustering algorithm is regarded as prior knowledge, with which the corresponding Gibbs energy function is redefined, and the maximum a posteriori estimator, which is determined by using the iterated conditional mode algorithm, is employed to get optimized labels. The new MRF model contributes to the weakening of the noise and to the elimination of the covered-uncovered background and to the recovery of the uniform moving regions.
2006, 28(2): 372-375.
Abstract:
Self impedance,mutual impedance and coupling of antennas are crying out for engineering application，but they can not be easily accurately calculated. The scheme that combines variational principles and the FDTD is presented in this paper to calculate the mutual impedance of wire antennas and the coupling coefficients. Numerical results obtained here have a good agreement with that from FEKO and NEC, which validate the accuracy and efficiency of this method.
Self impedance,mutual impedance and coupling of antennas are crying out for engineering application，but they can not be easily accurately calculated. The scheme that combines variational principles and the FDTD is presented in this paper to calculate the mutual impedance of wire antennas and the coupling coefficients. Numerical results obtained here have a good agreement with that from FEKO and NEC, which validate the accuracy and efficiency of this method.
2006, 28(2): 376-379.
Abstract:
In this paper, it is proven that the divergence relationship of electric-field and magnetic-field is non-zero even in charge-free regions, when the electric-field and magnetic-field are calculated with Alternating Direction Implicit Finite-Difference Time-Domain (ADI-FDTD) method, and the concrete expression of the divergence relationship is derived. Based on the non-zero divergence relationship, the ADI-FDTD which is unconditionally stable is combined with the Reduced Finite-Difference Time-Domain(R-FDTD). In the proposed method (ADI/R-FDTD), the merit of ADI-FDTD, e.g. increasing time step size and decreasing calculation time, is kept, at the same time, the memory requirement is reduced by 1/3(3-D) or 2/5(2-D) of the memory requirement of ADI-FDTD. Compare to the ADI/R-FDTD based on regular zero divergence relationship, the proposed algorithm is more stable when lager time step size is used. Wave propagation in 2-D free space and the scattered field of a 1-D Frequency Selective Surface(FSS) is simulated by the proposed hybrid method. Compared with ADI-FDTD，perfect agreement of numerical results indicates that ADI/R-FDTD method is correct and efficient.
In this paper, it is proven that the divergence relationship of electric-field and magnetic-field is non-zero even in charge-free regions, when the electric-field and magnetic-field are calculated with Alternating Direction Implicit Finite-Difference Time-Domain (ADI-FDTD) method, and the concrete expression of the divergence relationship is derived. Based on the non-zero divergence relationship, the ADI-FDTD which is unconditionally stable is combined with the Reduced Finite-Difference Time-Domain(R-FDTD). In the proposed method (ADI/R-FDTD), the merit of ADI-FDTD, e.g. increasing time step size and decreasing calculation time, is kept, at the same time, the memory requirement is reduced by 1/3(3-D) or 2/5(2-D) of the memory requirement of ADI-FDTD. Compare to the ADI/R-FDTD based on regular zero divergence relationship, the proposed algorithm is more stable when lager time step size is used. Wave propagation in 2-D free space and the scattered field of a 1-D Frequency Selective Surface(FSS) is simulated by the proposed hybrid method. Compared with ADI-FDTD，perfect agreement of numerical results indicates that ADI/R-FDTD method is correct and efficient.
2006, 28(2): 380-384.
Abstract:
This paper implements firstly an adiabatic flip-flop whose energy and information can both be recovered using the 2N-2N2P logic circuit structure. And then by means of calculating error and correcting deviation, this paper presents a stable adiabatic non-integer division circuit of energy-information-recovery. Finally, the above designed circuits are verified by computer simulation.
This paper implements firstly an adiabatic flip-flop whose energy and information can both be recovered using the 2N-2N2P logic circuit structure. And then by means of calculating error and correcting deviation, this paper presents a stable adiabatic non-integer division circuit of energy-information-recovery. Finally, the above designed circuits are verified by computer simulation.
