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2003 Vol. 25, No. 4
Display Method:
Two linear intercarrier interference cancellation techniques in ofdm systems over multipath channels
2003, 25(4): 433-438.
Abstract:
InterCarrier Interference (ICI) is an important, factor degrading the performance of Orthogonal Frequency Division Multiplexing (OFDM) systems. Two linear ICI cancellation techniques, Frequency RAKE (F-RAKE) and frequency equalization (F-FIR), with different length of delay-line, L, are studied in this paper. Assuming that the channel information is known in the receiver and MMSE criterion is adopted for F-FIR, results show that F-RAKE has about 2~5dB Carrier-Interference-Ratio (CIR) achievement than standard receiver in case of L=3. Meanwhile, F-FIR has about 2~7 dB CIR achievement. And the CIR performance gains of the two schemes decrease with increment of L. Also, the computational complexity of F-FIR is L times than that of F-RAKE. Thus, the tradeoff between complexity and performance in the engineering can be reached by selecting the length of delay-line and receiver scheme.
InterCarrier Interference (ICI) is an important, factor degrading the performance of Orthogonal Frequency Division Multiplexing (OFDM) systems. Two linear ICI cancellation techniques, Frequency RAKE (F-RAKE) and frequency equalization (F-FIR), with different length of delay-line, L, are studied in this paper. Assuming that the channel information is known in the receiver and MMSE criterion is adopted for F-FIR, results show that F-RAKE has about 2~5dB Carrier-Interference-Ratio (CIR) achievement than standard receiver in case of L=3. Meanwhile, F-FIR has about 2~7 dB CIR achievement. And the CIR performance gains of the two schemes decrease with increment of L. Also, the computational complexity of F-FIR is L times than that of F-RAKE. Thus, the tradeoff between complexity and performance in the engineering can be reached by selecting the length of delay-line and receiver scheme.
2003, 25(4): 439-446.
Abstract:
As time-variant multipath channels, the time-variant property of MW and SW channels causes the interchannel interfere (ICI) between different subchannels of OFDM-based digital amplitude modulation broadcasting (DAMB) system. In this paper, the OFDM system model is analyzed in MW and SW channels, and ICI due to time-variant channel is formulated. Finally, by computer simulation, the maximum number of the total subcarrier in OFDM system is estimated under the condition that ICI is much smaller compared to signal. This value is very important for the DAMB system.
As time-variant multipath channels, the time-variant property of MW and SW channels causes the interchannel interfere (ICI) between different subchannels of OFDM-based digital amplitude modulation broadcasting (DAMB) system. In this paper, the OFDM system model is analyzed in MW and SW channels, and ICI due to time-variant channel is formulated. Finally, by computer simulation, the maximum number of the total subcarrier in OFDM system is estimated under the condition that ICI is much smaller compared to signal. This value is very important for the DAMB system.
2003, 25(4): 447-452.
Abstract:
In this paper, the status of transcoder buffer is analyzed. The conditions that have to be met by both the encoder and transcoder buffers for preventing the decoder buffer from underftowing or overflowing are derived also. A model of sequence image transcoding is established. A new rate control strategy based on the quantizer optimization is proposed, and the target number of bits firstly on picture layer based on the status of the buffer and the channel rate is allocated. Then the characteristics of the image by the distributed characteristics of the DCT coefficients are denoted and a best quantization parameter for every macroblock in a frame is selected. The experiment shows that this rate control strategy can effectively reduce or avoid the overflow and underflow of the encoder buffer, and the output bit rates tend to stabilization. The Peak Signal-to-Noise Ratio(PSNR) of the reconstructed image is raised.
In this paper, the status of transcoder buffer is analyzed. The conditions that have to be met by both the encoder and transcoder buffers for preventing the decoder buffer from underftowing or overflowing are derived also. A model of sequence image transcoding is established. A new rate control strategy based on the quantizer optimization is proposed, and the target number of bits firstly on picture layer based on the status of the buffer and the channel rate is allocated. Then the characteristics of the image by the distributed characteristics of the DCT coefficients are denoted and a best quantization parameter for every macroblock in a frame is selected. The experiment shows that this rate control strategy can effectively reduce or avoid the overflow and underflow of the encoder buffer, and the output bit rates tend to stabilization. The Peak Signal-to-Noise Ratio(PSNR) of the reconstructed image is raised.
2003, 25(4): 453-459.
Abstract:
In this paper, based on an embedding strategy for watermarking in DWT domain, the influence of characteristics of orthogonal wavelet for the robustness of watermarking and the selection of wavelet bases are mainly investigated. The results show the features like regularity, number of vanishing moments, filter length and the degree of energy collecting in the low frequency subband do not have any important impact on the robustness for watermarking. Meanwhile a significant conclusion that wavelet Haar is the most suitable for digital watermarking is got. Wavelet decomposed levels and watermarking embedding formula are also addressed.
In this paper, based on an embedding strategy for watermarking in DWT domain, the influence of characteristics of orthogonal wavelet for the robustness of watermarking and the selection of wavelet bases are mainly investigated. The results show the features like regularity, number of vanishing moments, filter length and the degree of energy collecting in the low frequency subband do not have any important impact on the robustness for watermarking. Meanwhile a significant conclusion that wavelet Haar is the most suitable for digital watermarking is got. Wavelet decomposed levels and watermarking embedding formula are also addressed.
2003, 25(4): 460-466.
Abstract:
A practical mathematic model of modulation characteristics of Propeller Aircraft (PA) returns in the Low-Resolution Radars (LRR) is proposed in the paper, based on configuration of PA and characteristics of LRR. The model is analyzed and simulated with actual parameters of PA and LRR. Then, modulation characteristics of actual returns from PA in the LRR are analyzed, and modulation limitations from LRR are discussed. Finally, a comparison between the analyzed and simulated results shows the agreement of theoretical model with practical application. Mathematics relationship between modulation of LRR and target configuration is established.
A practical mathematic model of modulation characteristics of Propeller Aircraft (PA) returns in the Low-Resolution Radars (LRR) is proposed in the paper, based on configuration of PA and characteristics of LRR. The model is analyzed and simulated with actual parameters of PA and LRR. Then, modulation characteristics of actual returns from PA in the LRR are analyzed, and modulation limitations from LRR are discussed. Finally, a comparison between the analyzed and simulated results shows the agreement of theoretical model with practical application. Mathematics relationship between modulation of LRR and target configuration is established.
2003, 25(4): 467-472.
Abstract:
Due to the multiplicative nature of the speckle noise in SAR images, for edge detecting of SAR images, few method can be found to detect edges efficiently while depress the speckle noise effects without too much false edges, especially in the low look number SAR image case. In this paper, discussions are presented on the improvement of Touzi ratio edge detect method and maximum likelihood method in the low look number SAR image case, and then an adaptive window technique is introduced into SAR image edge detection. The adaptive windows are applied to the two Constant False Alarm Ratio (CFAR) edge detection algorithms mentioned above and fine improvement has been achieved. The technique is also proper for other SAR image edge detection algorithms.
Due to the multiplicative nature of the speckle noise in SAR images, for edge detecting of SAR images, few method can be found to detect edges efficiently while depress the speckle noise effects without too much false edges, especially in the low look number SAR image case. In this paper, discussions are presented on the improvement of Touzi ratio edge detect method and maximum likelihood method in the low look number SAR image case, and then an adaptive window technique is introduced into SAR image edge detection. The adaptive windows are applied to the two Constant False Alarm Ratio (CFAR) edge detection algorithms mentioned above and fine improvement has been achieved. The technique is also proper for other SAR image edge detection algorithms.
2003, 25(4): 473-478.
Abstract:
This paper points out that a class of chaotic stream ciphers proposed recently is not secure enough, which is based on digital Piecewise Linear Chaotic Maps (PLCM). It has been known that digital PLCMs statistical properties have essential degradation when PLCMs are realized in finite computing precision, and that such degradation is determined by the resolution of the control parameter (i.e., determined by which digital subset the control parameter is in). Hence, for the studied chaotic stream ciphers, the whole key space can be divided into n- 1 sub-spaces with incremental weakness degree, and the weakness of any fixed key cannot be improved by using higher precision. Based on the above fact, a kind of multi-resolution cryptanalysis is presented to attack the chaotic ciphers. When secure key is selected randomly, the key entropy will decrease by 2bit as a whole. Experiments show that this cryptanalysis is feasible and efficient.
This paper points out that a class of chaotic stream ciphers proposed recently is not secure enough, which is based on digital Piecewise Linear Chaotic Maps (PLCM). It has been known that digital PLCMs statistical properties have essential degradation when PLCMs are realized in finite computing precision, and that such degradation is determined by the resolution of the control parameter (i.e., determined by which digital subset the control parameter is in). Hence, for the studied chaotic stream ciphers, the whole key space can be divided into n- 1 sub-spaces with incremental weakness degree, and the weakness of any fixed key cannot be improved by using higher precision. Based on the above fact, a kind of multi-resolution cryptanalysis is presented to attack the chaotic ciphers. When secure key is selected randomly, the key entropy will decrease by 2bit as a whole. Experiments show that this cryptanalysis is feasible and efficient.
2003, 25(4): 479-485.
Abstract:
This paper presents the expressions of three bounds and three ranges on handover performance in CDMA system, and divides the space of handover performance into several parts according to the six expressions. In order to form the basis of the above expressions, this paper then proposes the methods to deduce the outage probability of hard and soft handovers. By simulating the WCDMA(FDD) system, the expressions are proved to be right and it is also concluded that they are more accurate and appropriate to describe the handover performance in a real CDMA system than Viterbis.
This paper presents the expressions of three bounds and three ranges on handover performance in CDMA system, and divides the space of handover performance into several parts according to the six expressions. In order to form the basis of the above expressions, this paper then proposes the methods to deduce the outage probability of hard and soft handovers. By simulating the WCDMA(FDD) system, the expressions are proved to be right and it is also concluded that they are more accurate and appropriate to describe the handover performance in a real CDMA system than Viterbis.
2003, 25(4): 486-494.
Abstract:
A new analytical model for the TCP throughput, considering the packet losses caused by high and bursty errors in wireless links, is proposed. The analysis and numerical simulation prove that this model is exact and simple. And it is shown that channel correlations can result in better performance of TCP over slow fading channels, and the TCP throughput in i.i.d channel is the lower bound.
A new analytical model for the TCP throughput, considering the packet losses caused by high and bursty errors in wireless links, is proposed. The analysis and numerical simulation prove that this model is exact and simple. And it is shown that channel correlations can result in better performance of TCP over slow fading channels, and the TCP throughput in i.i.d channel is the lower bound.
2003, 25(4): 495-502.
Abstract:
This paper presents a sub-optimal data-selected scheme based on chip-matched filter for the multi-user receiver in multi-path CDMA channels, and studies the impact of this scheme on Multiple-Access Interference (MAI) and Inter-Symbol Interference (ISI). Then, the Recursive Least-Square (RLS) blind space-time multi-user detection based on the constrained condition is presented. Finally, the results of the simulations illustrate that the presented method is effective.
This paper presents a sub-optimal data-selected scheme based on chip-matched filter for the multi-user receiver in multi-path CDMA channels, and studies the impact of this scheme on Multiple-Access Interference (MAI) and Inter-Symbol Interference (ISI). Then, the Recursive Least-Square (RLS) blind space-time multi-user detection based on the constrained condition is presented. Finally, the results of the simulations illustrate that the presented method is effective.
2003, 25(4): 503-508.
Abstract:
A Dynamical Reserved Bandwidth Allocation scheme (DRBA) for handoff in multimedia mobile networks is presented to reduce the call dropping probability and improve the bandwidth utilization. The proposed scheme reserves bandwidth for real-time handoff calls and allows non-real-time handoff calls to borrow the over-booked bandwidth from real-time handoff calls when the free bandwidth is deficient. Simulation results show that reduction in dropping probability and increase in bandwidth utilization are obtained in our proposed DRBA scheme. It also provides fair QoS for different types of services.
A Dynamical Reserved Bandwidth Allocation scheme (DRBA) for handoff in multimedia mobile networks is presented to reduce the call dropping probability and improve the bandwidth utilization. The proposed scheme reserves bandwidth for real-time handoff calls and allows non-real-time handoff calls to borrow the over-booked bandwidth from real-time handoff calls when the free bandwidth is deficient. Simulation results show that reduction in dropping probability and increase in bandwidth utilization are obtained in our proposed DRBA scheme. It also provides fair QoS for different types of services.
2003, 25(4): 509-514.
Abstract:
In this paper, the characteristics of two link adaptive algorithms based on Carrier to Interference ratio (C/I) and Packet Error Rate (PER) are discussed. Furthermore, two hybrid algorithms of link adaptation are proposed on the analysis of the existing algorithms. One is named integrated hybrid method, in which PER and C/I are taken as the estimates of channel quality simultaneously. The other that selectively considers C/I or PER as the estimates of channel quality at a time is called selective hybrid method. Simulation results indicate that the integrated hybrid method can achieve the maximum throughputs at an ideal uni-user scenario. While at a multi-user scenario, a few received packets of one user lead to the large variance of PER values, which results in throughput loss. Therefore, at the scenario above, selective hybrid method is superior to other methods in term of network throughputs.
In this paper, the characteristics of two link adaptive algorithms based on Carrier to Interference ratio (C/I) and Packet Error Rate (PER) are discussed. Furthermore, two hybrid algorithms of link adaptation are proposed on the analysis of the existing algorithms. One is named integrated hybrid method, in which PER and C/I are taken as the estimates of channel quality simultaneously. The other that selectively considers C/I or PER as the estimates of channel quality at a time is called selective hybrid method. Simulation results indicate that the integrated hybrid method can achieve the maximum throughputs at an ideal uni-user scenario. While at a multi-user scenario, a few received packets of one user lead to the large variance of PER values, which results in throughput loss. Therefore, at the scenario above, selective hybrid method is superior to other methods in term of network throughputs.
2003, 25(4): 515-521.
Abstract:
In this paper, a distributed packet scheduling algorithm called DHIOS(Distributed Hierarchical Ingress and Output Scheduling) is presented and simulated for an input and output queuing switch whose switch fabric is a shared memory. The distributed packet scheduling algorithm can support variable length packets and guarantee the QoS (Quality of Service) of flows. The simulation on OPNET shows that the distributed packet scheduling algorithm has good performance.
In this paper, a distributed packet scheduling algorithm called DHIOS(Distributed Hierarchical Ingress and Output Scheduling) is presented and simulated for an input and output queuing switch whose switch fabric is a shared memory. The distributed packet scheduling algorithm can support variable length packets and guarantee the QoS (Quality of Service) of flows. The simulation on OPNET shows that the distributed packet scheduling algorithm has good performance.
2003, 25(4): 522-530.
Abstract:
Routing is an important topic in communication network research. But many existing routing mechanisms are awkward to highly dynamic network environment. With a proposed cooperative model of multi-agents based on fuzzy knowledge and a basic algorithm for routing computation, a multiple mobile agents cooperating system is applied to the problem of dynamic network routing. Some key factors of the system are discussed in the context. With the help of a simulative dynamic network and the experiments on it, the performance-overhead characteristic of the system is analyzed and the comparison among some cooperation strategies is made. The results show that the proposed theoretic model and algorithm are suitable to the routing of dynamic network and able to improve the responsibility of the routing system.
Routing is an important topic in communication network research. But many existing routing mechanisms are awkward to highly dynamic network environment. With a proposed cooperative model of multi-agents based on fuzzy knowledge and a basic algorithm for routing computation, a multiple mobile agents cooperating system is applied to the problem of dynamic network routing. Some key factors of the system are discussed in the context. With the help of a simulative dynamic network and the experiments on it, the performance-overhead characteristic of the system is analyzed and the comparison among some cooperation strategies is made. The results show that the proposed theoretic model and algorithm are suitable to the routing of dynamic network and able to improve the responsibility of the routing system.
2003, 25(4): 531-535.
Abstract:
It is one of advanced technologies used in modern radar that control nulls of the beam-pattern when array antenna radiates beams. This paper describes a phase-only conjugate gradient adaptive nulling method and the experimental radar adaptive nulling array processing system based on TMS320C31. Theoretical analysis and experimental results all show that the system is useful and practical.
It is one of advanced technologies used in modern radar that control nulls of the beam-pattern when array antenna radiates beams. This paper describes a phase-only conjugate gradient adaptive nulling method and the experimental radar adaptive nulling array processing system based on TMS320C31. Theoretical analysis and experimental results all show that the system is useful and practical.
2003, 25(4): 536-542.
Abstract:
In this paper a general study of the relation between the performance of shaped beams and beam width and spacing has been done for multiple-beam antennas with array-fed reflectors. Four parameters indicating the performance of shaped beams are first denned. On the basis of these parameters, a mathematical model of beam-shaping is presented which determines the relation between the performance of shaped beams and beam width and spacing and then this model is resolved by using functional analysis theory. Through the discussion of the solution, the mechanism of beam shaping is shown in signal and system way. Then this mechanism and the relation are illustrated by the explanation of the simulation results of a practical example. According to the relation proved above, with given performance parameters, optimum beam width and spacing can be chosen, which correspondingly determine the optimum configuration of the antenna. A very simple formulation for choosing the optimum beam width and spacing is finally obtained, as a result of the discussion in this paper.
In this paper a general study of the relation between the performance of shaped beams and beam width and spacing has been done for multiple-beam antennas with array-fed reflectors. Four parameters indicating the performance of shaped beams are first denned. On the basis of these parameters, a mathematical model of beam-shaping is presented which determines the relation between the performance of shaped beams and beam width and spacing and then this model is resolved by using functional analysis theory. Through the discussion of the solution, the mechanism of beam shaping is shown in signal and system way. Then this mechanism and the relation are illustrated by the explanation of the simulation results of a practical example. According to the relation proved above, with given performance parameters, optimum beam width and spacing can be chosen, which correspondingly determine the optimum configuration of the antenna. A very simple formulation for choosing the optimum beam width and spacing is finally obtained, as a result of the discussion in this paper.
A new kind of interconnect crosstalk model and estimation formula for high-speed integrated circuits
2003, 25(4): 543-550.
Abstract:
In this paper, an interconnect delay estimation model is built up, including the effect of distributed resistance, capacitance and even inductance. Then, on the basis of this model, the respondence of the terminal on the worst condition is analyzed and three-order precise formula to estimate the crosstalk respondence is presented. In the end, a new estimation formula for interconnect crosstalk respondence is derived. Moreover, experimental result is excellent enough to the simulation result of SPICE for practical circuit.
In this paper, an interconnect delay estimation model is built up, including the effect of distributed resistance, capacitance and even inductance. Then, on the basis of this model, the respondence of the terminal on the worst condition is analyzed and three-order precise formula to estimate the crosstalk respondence is presented. In the end, a new estimation formula for interconnect crosstalk respondence is derived. Moreover, experimental result is excellent enough to the simulation result of SPICE for practical circuit.
2003, 25(4): 551-556.
Abstract:
Broadband klystron is one of key devices in radar and communication system. The broadband performances of microwave output circuit play an important role for extending klystrons bandwidth. This paper describes the numerical results of a broadband output circuit-radial coupling multicavity circuit by using 3D electromagnetic field computation program, IS-FEL 3D, which includes the resonance performance, field distribution, mode construction and difference of radial with axial coupling multicavity circuit. The radial coupling multicavity circuit has been designed and manufactured, and the cold measurement shows that 7% bandwidth has been obtained.
Broadband klystron is one of key devices in radar and communication system. The broadband performances of microwave output circuit play an important role for extending klystrons bandwidth. This paper describes the numerical results of a broadband output circuit-radial coupling multicavity circuit by using 3D electromagnetic field computation program, IS-FEL 3D, which includes the resonance performance, field distribution, mode construction and difference of radial with axial coupling multicavity circuit. The radial coupling multicavity circuit has been designed and manufactured, and the cold measurement shows that 7% bandwidth has been obtained.
2003, 25(4): 557-561.
Abstract:
A new method of feature extraction for visual signal is presented in this paper. The signal of the image projection, which is acquired by CCD, is transformed with wavelet. And the zero cross point of transform is located at the center of the image when the scale of wavelet is suitable. The experiment shows that the method possesses stronger robustness for stochastic error disturbance than other methods do.
A new method of feature extraction for visual signal is presented in this paper. The signal of the image projection, which is acquired by CCD, is transformed with wavelet. And the zero cross point of transform is located at the center of the image when the scale of wavelet is suitable. The experiment shows that the method possesses stronger robustness for stochastic error disturbance than other methods do.
2003, 25(4): 562-566.
Abstract:
Multiuser detection in Code-Division Multiple Acess(CDMA) system is an effective method. The Partial Parallel Interference Cancellation(PPIC) detector is considered as an effective yet simple receiver. However, the optimal cancellation level which is controlled by Partial Cancellation Factor(PCF) is usually determined by trial and error, since no theoretical values were reported. A multiuser receiver employing two-stage PPIC based on MMSE criteria is introduced in this paper. Computer simulation shows that the derived PCF is insensitive u the estimation bias of the noise level and the interfering signal power.
Multiuser detection in Code-Division Multiple Acess(CDMA) system is an effective method. The Partial Parallel Interference Cancellation(PPIC) detector is considered as an effective yet simple receiver. However, the optimal cancellation level which is controlled by Partial Cancellation Factor(PCF) is usually determined by trial and error, since no theoretical values were reported. A multiuser receiver employing two-stage PPIC based on MMSE criteria is introduced in this paper. Computer simulation shows that the derived PCF is insensitive u the estimation bias of the noise level and the interfering signal power.
2003, 25(4): 567-572.
Abstract:
At first, in this paper, the feedback mechanisms of downlink channel quality for cdma2000 IxEV-DO/DV, a 3G technical proposal, are described briefly. Then a new feedback control algorithm is presented and integrated with proportional fair scheduling algorithm. The modified scheduling algorithm is studied by analysis and simulation. It is shown that this new algorithm can bring some significant improvements over the ordinary scheduler without feedback control in terms of system throughput, leaving no harm on fairness. In addition, the new algorithm will be helpful to reduce the power consumption of mobile terminals. The fundamental strategy underlying this new algorithm will be useful to other application fields where shared resources are needed to be scheduled.
At first, in this paper, the feedback mechanisms of downlink channel quality for cdma2000 IxEV-DO/DV, a 3G technical proposal, are described briefly. Then a new feedback control algorithm is presented and integrated with proportional fair scheduling algorithm. The modified scheduling algorithm is studied by analysis and simulation. It is shown that this new algorithm can bring some significant improvements over the ordinary scheduler without feedback control in terms of system throughput, leaving no harm on fairness. In addition, the new algorithm will be helpful to reduce the power consumption of mobile terminals. The fundamental strategy underlying this new algorithm will be useful to other application fields where shared resources are needed to be scheduled.
2003, 25(4): 573-576.
Abstract:
For most sequences at very low bit rates, the value of motion compensation data usually is very small, and will all be reduced into zero after DCT and quantization. Alice Yu method(1997) and Zhou method(1998) both are effective to predicting these All-Zero Coefficients (AZC) blocks, but these two methods will, to a large extent, mis-justice and leak out the AZC blocks respectively, especially for complex sequences. In order to overcome these disadvantages, a new method of early predicting AZC blocks is proposed in this paper. In this method, no additional computation is needed and the threshold can be changed with the quantization level. Applying this method to H.2G3 encoder, about 40%-80% blocks of Miss America and News picture sequences can be determined to be AZC blocks before DCT and quantization. It can greatly reduce the encoding computation time and is very useful to the software implementation of H.263 in real-time. In addition, PSNR of decoding sequences is controlled within O.OOOSdB.
For most sequences at very low bit rates, the value of motion compensation data usually is very small, and will all be reduced into zero after DCT and quantization. Alice Yu method(1997) and Zhou method(1998) both are effective to predicting these All-Zero Coefficients (AZC) blocks, but these two methods will, to a large extent, mis-justice and leak out the AZC blocks respectively, especially for complex sequences. In order to overcome these disadvantages, a new method of early predicting AZC blocks is proposed in this paper. In this method, no additional computation is needed and the threshold can be changed with the quantization level. Applying this method to H.2G3 encoder, about 40%-80% blocks of Miss America and News picture sequences can be determined to be AZC blocks before DCT and quantization. It can greatly reduce the encoding computation time and is very useful to the software implementation of H.263 in real-time. In addition, PSNR of decoding sequences is controlled within O.OOOSdB.
