Evolutionary computation is a field of simulating evolution on a computer.Both aspects of it ,the problem solving aspect and the aspect of modeling natural evolution,are important.Simulating evolution on a computer re...Evolutionary computation is a field of simulating evolution on a computer.Both aspects of it ,the problem solving aspect and the aspect of modeling natural evolution,are important.Simulating evolution on a computer results in stochastic optimization techniques that can outperform classical methods of optimization when applied to difficult real-world problems.There are currently four main avenues of research in simulated evolution:genetic algorithms,evolutionary programming,evolution strategies,and genetic programming.This paper presents a brief overview of thd field on evolutionary computation,including some theoretical issues,adaptive mechanisms,improvements,constrained optimizqtion,constrained satisfaction,evolutionary neural networks,evolutionary fuzzy systems,hardware evolution,evolutionary robotics,parallel evolutionary computation,and co-evolutionary models.The applications of evolutionary computation for optimizing system and intelligent information processing in telecommunications are also introduced.展开更多
NP hard problems have appeared in many areas. In this article, it is discussed how to solve this kind of problems using artificial neural network— Hopfield/Tank model, especially the Travelling Salesman Problem (TSP...NP hard problems have appeared in many areas. In this article, it is discussed how to solve this kind of problems using artificial neural network— Hopfield/Tank model, especially the Travelling Salesman Problem (TSP). At first, a stability analysis shows the conditions of the model to converge to the vertices of the hypercube and its relation with the parameters. And then, a HT model for solving TSP is formulated. Some theorems are given to analyze the influence of parameter D on the three subspaces of the connection matrix in which D is set to zero. Based on these analyses, a dynamic analysis of the model is given and a set of parameters′ rules are established. It is indicated that, if the parameters are selected according to these rules, the final solutions are optimal or near optimal. However, the initial noise would have some influences on the final solutions. According to these theories, a 'damping' optimal method is proposed which can not only guarantee the final solutions are high quality, but also weaken the influence of the initial noise. On the other hand, many kinds of modified HT models are summarized and a more simple and effective model is given. Compared with some traditional and modern methods for solving TSP, the performance of our method is very good. Linking with the practice, some applications are exploited. Our method has also been used for programming the posts route of some city in China. Finally, a theoretical analysis is given for com munication network routing problem using HT model. Liu Rong Born in October 1966. He received the Engineering Ph.D in Beijing University Posts and Telecommunications in April 1994.展开更多
The paper deals with a new VQ+DPCM+DCT algorithm based on Self-Organizing Feature Maps(SOFM) algorithm for image coding. In addition. a Frequency sensitive SOFM (FSOFM) has been also devel-oped. Simulation results sh...The paper deals with a new VQ+DPCM+DCT algorithm based on Self-Organizing Feature Maps(SOFM) algorithm for image coding. In addition. a Frequency sensitive SOFM (FSOFM) has been also devel-oped. Simulation results show that a very good visual quality of the coded image at 0.252 bits/pixel is obtained.展开更多
Because it has the advantages of high sensitivity, and it is easy to demodulate and convenient to select in FDM system, the coherent optical fiber communication system is much suitable to be used in long distance opt...Because it has the advantages of high sensitivity, and it is easy to demodulate and convenient to select in FDM system, the coherent optical fiber communication system is much suitable to be used in long distance optical communication systems and in optical fiber WANs. There are two major patterns in coherent optical fiber communication: heterodyne and homodyne. Compared with the heterodyne scheme, the homodyne optical fiber communication system has the following advantages: (1) The sensitivity of the homodyne receiver is higher than that of the heterodyne receiver. As we know, the PSK homodyne optical fiber communication system has the highest sensitivity in coherent optical fiber communication systems. So it is much suitable to be used in long distance optical communication systems or in FDM systems. (2) Because the homodyne receiver only uses the baseband to demodulate the transmitted signals, it occupies much narrower frequency domain than the heterodyne receiver does, which makes it more suitable to be used in multichannel systems. (3) The demodulation pattern used in homodyne receiver is much easier than that used in the heterodyne receiver, since it only needs the baseband demodulation. Usually we construct a homodyne receiver with an optical phase locked loop (OPLL). The research of the OPLL began at 1960′s and the study of the homodyne receiver has been made gradually. In 1984, the first homodyne optical fiber communication system was demonstrated in BTRL, in which the signal laser and the local laser were all 1.5 μm He Ne gas lasers, and the OPLL used was a balanced one. In 1989, L.G.Kazovsky demonstrated experimentally a homodyne receiver in Bellcore using two 1.3 μm Nd:YAG lasers as the signal laser and the local laser and also using a balanced OPLL. Because the linewidth of the normal semiconductor laser is too large and its frequency stability is much poorer, it is very difficult to construct a homodyne receiver with the semiconductor lasers. At the end of 1989, the first Dissertation completed Jul. 1992homodyne optical fiber communication system using two 1.5 μm external cavity semiconductor lasers as the signal laser and the local laser, respectively, was finished in AT&T Bell Lab by J. M. Kahn, in which the OPLL was also a balanced one. In China, the research of the homodyne optical fiber communication system was funded by the National Seventh Five Year Program and by the National Natural Science Foundation. The difficulties to construct a homodyne optical fiber communication system are listed as follows: (1) In homodyne communication systems, the signal laser′s frequency should be stable to avoid the penalty of the receiver′s BER and the crosstalk to other channels in a FDM system, and the local laser could be tuned widely and easily to cover all the signal lasers′ frequency domain. Both the signal laser and the local laser should be narrow in linewidth to decrease the influence of the laser′s phase noise on the BER of the receiver. (2) The modulation pattern used should be studied and chosen carefully because the requirements of different kinds of modulation on the laser, the receiver and the channel are different. (3) Since the construction of the linear OPLL (the balanced) and the nonlinear OPLL (the Costas OPLL, or the Decision Driven OPLL) are rather different, their requirements on the linewidths of the lasers are different too, we should study the theory and the construction of the OPLL carefully to select the suitable scheme to realize. (4) In a multichannel system (such as a FDM system), the influence of crosstalk between channels on the homodyne system should be researched carefully. The technology used to stabilize the channel interval should also be studied. In this thesis, the homodyne optical fiber communication system has been theoretically analyzed, the technical difficulties of constructing the system have been studied. Several kinds of external cavity semiconductor laser have been researched experimentally. Compared展开更多
The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a ...The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a few communication laboratories around the world to the field demonstration stage. This is mainly because of the possibility of receiver sensitivity improvement reaching 10～20 dB, that of frequency division multiplexing (FDM) with very fine frequency separation and the possibility of using electronic equalization network to compensate for the effect of optical pulse dispersion in the Single Mode Fiber (SMF). The author of the dissertation has engaged in the study on COFCSs since 1987. Undergoing 3 years of hard work, the finished research work includes two parts: Part I is the study on heterodyne COFCSs and their key components; Part II is the study on two branch phase diversity COFCS and its components. In the first part, using the Lamb′s semi classical theory and the model of vector field, the effects of various kinds of parameters, such as cavity detuning, cavity′s Q factor and the transverse magnetic field strength, on the intramode beat frequency tuning characteristics are analyzed. On the basis of the theoretical analysis, the equipment of 1 523 nm He Ne Stabilized Transverse Zeeman Lasee (STZL) with high frequency stability and certain continuous single frequency tuning range, has been established domestically for the first time. With the development of long waveband semi conductor laser diodes fabricated domestically, the author mainly deals with the long waveband COFCSs using semiconductor laser diodes as transmitter and local oscillator. To counter the poor spectrum characteristics of the conventional double heterojunction semi conductor laser diodes, the characteristics of 1.5 um InGaAsP GRINROD External Cavity Semi conductor Lasers (ECSL) in the case of strong and weak feedback conditions, is experimentally studied. Then the GRINROD Dissertation completed Apr.1991ECSLs with complete closed and compact structure are developed. Using this kind of lasers and other components made domestically, the long waveband large deviation FSK heterodyne single filter/ envelope detection systems and small deviation FSK heterodyne single filter/delay line frequency discriminator detection system are achieved for the first time. In those experiments, the frequency modulation characteristics, line width, single frequency continuous tuning range and frequency stability of the GRINROD ECSL are measured by means of IF spectrum. Meanwhile, the IF receiving circuits are optimized for obtaining stable transmission properties. The main research achievements in part II are the theoretical analysis of the diversity COFCSs. Firstly, the Bit Error Rate (BER) performance of two branch homodyne phase diversity ASK, DPSK and two branch homodyne phase polarization DPSK receivers are analyzed by means of characteristic function model. In the analysis, the effects of pre and post detection filters on the system performance are especially studied. Secondly, the impacts of the phase noise, shot noise, polarization mismatch and imbalance of branch circuits on the two branch homodyne phase diversity ASK receiver, and that of modulation frequency deviation on FSK receiver are analyzed in terms of Gaussian approximation. Lastly, an improved all fiber 90 degree optical hybrid is fabricated. Utilizing the hybrid and 1.5 um InGaAsP GRINROD and grating ECSLs, a low IF, two branch phase diversity FSK coherent optical fiber transmission system is experimented for the first time in China. Guan Kejian Born in Jan. 1963. He received his Ph. D degree in Apr. 1991, in Radio Engineering, Beijing Uni versity of Posts and Telecommunications.展开更多
So far, the problem of the harmonic retrieval with quadratic phase coupling in mixed noises has not been resolved well. For this reason, this paper, based on the third , forth order cumulants and Hilbert transform, ...So far, the problem of the harmonic retrieval with quadratic phase coupling in mixed noises has not been resolved well. For this reason, this paper, based on the third , forth order cumulants and Hilbert transform, proposes a new method named HBTFCH SVD TLS.The method can realize harmonic retrieval in mixed noises even when the harmonic signal includes the components of quadratic phase coupling.Simulation results show the effectiveness of the method.展开更多
Now, the problem of modeling MPEG 1 video traffic still needs studying further. Based on the analysis of statistical characteristics of this kind of traffic, this paper presents a new traffic model. Simulation result...Now, the problem of modeling MPEG 1 video traffic still needs studying further. Based on the analysis of statistical characteristics of this kind of traffic, this paper presents a new traffic model. Simulation results show that the proposed model can reflect the statistical characteristics of the real MPEG 1 video traffic well.展开更多
In packet switched communication networks, traffic between any source destination (SD) pair is expected to be transmitted over multiple paths. In this paper, we focus on the problem how to optimally distribute the l...In packet switched communication networks, traffic between any source destination (SD) pair is expected to be transmitted over multiple paths. In this paper, we focus on the problem how to optimally distribute the load on a set of paths so that the overall network performance is maximized. This problem is first formulated as a nonlinear programming problem and then we propose a neural network (NN) to solve it. The NN architecture is discussed in detail. At last, we verify the effectiveness of our approach by applying it to a specific network model. The experimental results demonstrate that our method can yield optimal solutions with good stability.展开更多
Performance of high speed coherent optical communication systems has been investigated. A novel frequency tracking/locking automatical fre quency control (clock frequency tracking AFC, CFT AFC) scheme has been pre...Performance of high speed coherent optical communication systems has been investigated. A novel frequency tracking/locking automatical fre quency control (clock frequency tracking AFC, CFT AFC) scheme has been presented. The first Gb/s speed coherent optical communication system of China (1.1 Gb/s FSK optical communication system) has been achieved. The achievements of this paper are as follows: (1) Performance of coherent optical communication system has been investigated. A set of expressions are deduced. In the expressions, the effects of the LD line width, waveform of modulation signal, the signal phase jitter, intersymbol interference (ISI) and various kinds of noises are comprehensively included for the first time. (2) The jitter performance of coherent optical communication system is analyzed for the first time. The timing jitter theory of coherent optical communication system is achieved. (3) A novel frequency tracking/locking automatic frequency control (clock frequency tracking AFC, CFT AFC) scheme is presented. The scheme has three advantages compared with other AFC schemes: (a) frequency tracking/locking may be achieved efficiently; (b) timing clock may be extracted efficiently; and (c) the circuitry is simpler and steadier. (4) Performance of phase diversity (PD) optical communication systems is analyzed. The BER expressions of PD systems modulated under various kinds of signal waveforms are presented. The power penalties of PD systems resulted from signal phase jitter and ISI are deduced. (5) Performance of the light sources of coherent optical communication (external cavity LD and DFB LD) is analyzed. The non flat FM (frequency modulation) response of LD chip is compensated by external circuitry. The DFB LD module with 4.7 GHz FM response is achieved. (6) Compensation of fiber dispersion in optical communication is investigated. The practical fiber dispersion compensators are achieved. (7) The first Gb/s speed coherent optical Dissertation completed Apr. 1992communication system of China is achieved. The system includes: (a) a 1.1 Gb/s ～ 2.2 Gb/s PRBS high speed signal source; (b) DFB LD modules with 4.7 GHz FM response and 1.1 Gb/s FSK optical transmitter; (c) a low noise preamplifier with 4.2 GHz width; (d) CFT AFC circuitry, which system, CFT AFC scheme not only achieves frequency tracking/locking, but also depressed timing jitter efficiently. In fact, the receiver may extract the timing clock efficiently even received signal with infinite continuous “0”; (e) The LD line width is narrowed by electrical negative feedback of CFT AFC. The characteristics of the system include: (a) the DFB LD modules are taken as the light sources; (b) balanced PIN is taken as photoelectron detector of the receiver; (c) CFT AFC scheme is taken as AFC, timing extracting, and LD line width narrowing; (e) the system speed: 1.1 Gb/s, the wavelength of LD: 1.536 4 μm, the transmission distance: 3.87 km, and the receiver sensitivity: 34.2 dBm (BER=10 9 ). Huang Shouhua Born in Hubei province, 1956, graduated from Physics Department of Nanjing University in 1980. He received the ME degree in Wuhan Research Institute of Posts and Telecom (WRIPT), in 1986. He joined WRIPT in 1986. Since 1988, he has been working towards Ph.D. degree at Beijing University of Posts and Telecom. He is the authors of over 30 journal and conference papers.展开更多
This paper deals with noncoherent Maximum-likelihood Block Detection (MLBD) of uncodedCPM signals (full response CPM and parrtal response CPM) over an additive white noise (AWGN)channel. Based on the work of W. Osborn...This paper deals with noncoherent Maximum-likelihood Block Detection (MLBD) of uncodedCPM signals (full response CPM and parrtal response CPM) over an additive white noise (AWGN)channel. Based on the work of W. Osborne and M. Simon ,this paper generalizes Maximum-likelihoodBlork Detection. Then we focus on the error performance of MLBD, which is named one-symbol MLBDand N-symbol MLBD respectively. By computer simulation of CPFSK, 1RC and 2RC , it is found thatMLBD can improve the error performance over traditional noncoherent detection.展开更多
We propose a novel hybrid algorithm of BP neural ytetwork and apply it to blind equalization.The algorithm combines the merits of Rosario algorithm and random optimization method. Its cost function has strict convex c...We propose a novel hybrid algorithm of BP neural ytetwork and apply it to blind equalization.The algorithm combines the merits of Rosario algorithm and random optimization method. Its cost function has strict convex character (after a threshold) and the algorithm converges much faster than the BPmethod[2], as an exalople, we evaluate its performance by using it into blind equalization. With the help ofHigher Order Culnulants (HOC), the blind equalization scheme converges much faster than the CMAalgorithm and superior to the Back-propagation,nethod[2] due to its ability of finding the optimal solutionwith relatively fewer iteration stops.展开更多
A new waveguide to coaxial line transition adopted to microwave band is proposed in this paper.The configuration and design of the transition is studied. It has the merits of simplicity in structure, ease ofconstructi...A new waveguide to coaxial line transition adopted to microwave band is proposed in this paper.The configuration and design of the transition is studied. It has the merits of simplicity in structure, ease ofconstruction and repeatable performance, especially that the coaxial line is in the same direction with thewaveguide. At X band, the pass bandwidth of the transition is about 6%, and the insertion loss less than 1dB.展开更多
This paper presents the real-time implementation of 6.75kb/s speech codec for the GSM half-rate digital cellular system based on CELP[1]. Logarithmic Area Ratio (LAN).[2] quanrizarion for short term Parameters and e...This paper presents the real-time implementation of 6.75kb/s speech codec for the GSM half-rate digital cellular system based on CELP[1]. Logarithmic Area Ratio (LAN).[2] quanrizarion for short term Parameters and eeeicient adaptive codebook search are used. An overlapping center-clipping codebook and the fonnufor for fast searching are proposed. The MOS of the synthesized speech is over 3.5.展开更多
In desktop video conferencing systems, the quality of video as well as the response speed of user′s data is important element of systematic performance. In this paper, four video and data multiplexing strategies in t...In desktop video conferencing systems, the quality of video as well as the response speed of user′s data is important element of systematic performance. In this paper, four video and data multiplexing strategies in terminals: the Alternate Method, the Video Priority Method, the Data Priority Method, and the Dynamic Priority Method, are investigated. Their influences on transmission performances of data and video are discussed.展开更多
文摘Evolutionary computation is a field of simulating evolution on a computer.Both aspects of it ,the problem solving aspect and the aspect of modeling natural evolution,are important.Simulating evolution on a computer results in stochastic optimization techniques that can outperform classical methods of optimization when applied to difficult real-world problems.There are currently four main avenues of research in simulated evolution:genetic algorithms,evolutionary programming,evolution strategies,and genetic programming.This paper presents a brief overview of thd field on evolutionary computation,including some theoretical issues,adaptive mechanisms,improvements,constrained optimizqtion,constrained satisfaction,evolutionary neural networks,evolutionary fuzzy systems,hardware evolution,evolutionary robotics,parallel evolutionary computation,and co-evolutionary models.The applications of evolutionary computation for optimizing system and intelligent information processing in telecommunications are also introduced.
文摘NP hard problems have appeared in many areas. In this article, it is discussed how to solve this kind of problems using artificial neural network— Hopfield/Tank model, especially the Travelling Salesman Problem (TSP). At first, a stability analysis shows the conditions of the model to converge to the vertices of the hypercube and its relation with the parameters. And then, a HT model for solving TSP is formulated. Some theorems are given to analyze the influence of parameter D on the three subspaces of the connection matrix in which D is set to zero. Based on these analyses, a dynamic analysis of the model is given and a set of parameters′ rules are established. It is indicated that, if the parameters are selected according to these rules, the final solutions are optimal or near optimal. However, the initial noise would have some influences on the final solutions. According to these theories, a 'damping' optimal method is proposed which can not only guarantee the final solutions are high quality, but also weaken the influence of the initial noise. On the other hand, many kinds of modified HT models are summarized and a more simple and effective model is given. Compared with some traditional and modern methods for solving TSP, the performance of our method is very good. Linking with the practice, some applications are exploited. Our method has also been used for programming the posts route of some city in China. Finally, a theoretical analysis is given for com munication network routing problem using HT model. Liu Rong Born in October 1966. He received the Engineering Ph.D in Beijing University Posts and Telecommunications in April 1994.
文摘The paper deals with a new VQ+DPCM+DCT algorithm based on Self-Organizing Feature Maps(SOFM) algorithm for image coding. In addition. a Frequency sensitive SOFM (FSOFM) has been also devel-oped. Simulation results show that a very good visual quality of the coded image at 0.252 bits/pixel is obtained.
文摘Because it has the advantages of high sensitivity, and it is easy to demodulate and convenient to select in FDM system, the coherent optical fiber communication system is much suitable to be used in long distance optical communication systems and in optical fiber WANs. There are two major patterns in coherent optical fiber communication: heterodyne and homodyne. Compared with the heterodyne scheme, the homodyne optical fiber communication system has the following advantages: (1) The sensitivity of the homodyne receiver is higher than that of the heterodyne receiver. As we know, the PSK homodyne optical fiber communication system has the highest sensitivity in coherent optical fiber communication systems. So it is much suitable to be used in long distance optical communication systems or in FDM systems. (2) Because the homodyne receiver only uses the baseband to demodulate the transmitted signals, it occupies much narrower frequency domain than the heterodyne receiver does, which makes it more suitable to be used in multichannel systems. (3) The demodulation pattern used in homodyne receiver is much easier than that used in the heterodyne receiver, since it only needs the baseband demodulation. Usually we construct a homodyne receiver with an optical phase locked loop (OPLL). The research of the OPLL began at 1960′s and the study of the homodyne receiver has been made gradually. In 1984, the first homodyne optical fiber communication system was demonstrated in BTRL, in which the signal laser and the local laser were all 1.5 μm He Ne gas lasers, and the OPLL used was a balanced one. In 1989, L.G.Kazovsky demonstrated experimentally a homodyne receiver in Bellcore using two 1.3 μm Nd:YAG lasers as the signal laser and the local laser and also using a balanced OPLL. Because the linewidth of the normal semiconductor laser is too large and its frequency stability is much poorer, it is very difficult to construct a homodyne receiver with the semiconductor lasers. At the end of 1989, the first Dissertation completed Jul. 1992homodyne optical fiber communication system using two 1.5 μm external cavity semiconductor lasers as the signal laser and the local laser, respectively, was finished in AT&T Bell Lab by J. M. Kahn, in which the OPLL was also a balanced one. In China, the research of the homodyne optical fiber communication system was funded by the National Seventh Five Year Program and by the National Natural Science Foundation. The difficulties to construct a homodyne optical fiber communication system are listed as follows: (1) In homodyne communication systems, the signal laser′s frequency should be stable to avoid the penalty of the receiver′s BER and the crosstalk to other channels in a FDM system, and the local laser could be tuned widely and easily to cover all the signal lasers′ frequency domain. Both the signal laser and the local laser should be narrow in linewidth to decrease the influence of the laser′s phase noise on the BER of the receiver. (2) The modulation pattern used should be studied and chosen carefully because the requirements of different kinds of modulation on the laser, the receiver and the channel are different. (3) Since the construction of the linear OPLL (the balanced) and the nonlinear OPLL (the Costas OPLL, or the Decision Driven OPLL) are rather different, their requirements on the linewidths of the lasers are different too, we should study the theory and the construction of the OPLL carefully to select the suitable scheme to realize. (4) In a multichannel system (such as a FDM system), the influence of crosstalk between channels on the homodyne system should be researched carefully. The technology used to stabilize the channel interval should also be studied. In this thesis, the homodyne optical fiber communication system has been theoretically analyzed, the technical difficulties of constructing the system have been studied. Several kinds of external cavity semiconductor laser have been researched experimentally. Compared
文摘The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a few communication laboratories around the world to the field demonstration stage. This is mainly because of the possibility of receiver sensitivity improvement reaching 10～20 dB, that of frequency division multiplexing (FDM) with very fine frequency separation and the possibility of using electronic equalization network to compensate for the effect of optical pulse dispersion in the Single Mode Fiber (SMF). The author of the dissertation has engaged in the study on COFCSs since 1987. Undergoing 3 years of hard work, the finished research work includes two parts: Part I is the study on heterodyne COFCSs and their key components; Part II is the study on two branch phase diversity COFCS and its components. In the first part, using the Lamb′s semi classical theory and the model of vector field, the effects of various kinds of parameters, such as cavity detuning, cavity′s Q factor and the transverse magnetic field strength, on the intramode beat frequency tuning characteristics are analyzed. On the basis of the theoretical analysis, the equipment of 1 523 nm He Ne Stabilized Transverse Zeeman Lasee (STZL) with high frequency stability and certain continuous single frequency tuning range, has been established domestically for the first time. With the development of long waveband semi conductor laser diodes fabricated domestically, the author mainly deals with the long waveband COFCSs using semiconductor laser diodes as transmitter and local oscillator. To counter the poor spectrum characteristics of the conventional double heterojunction semi conductor laser diodes, the characteristics of 1.5 um InGaAsP GRINROD External Cavity Semi conductor Lasers (ECSL) in the case of strong and weak feedback conditions, is experimentally studied. Then the GRINROD Dissertation completed Apr.1991ECSLs with complete closed and compact structure are developed. Using this kind of lasers and other components made domestically, the long waveband large deviation FSK heterodyne single filter/ envelope detection systems and small deviation FSK heterodyne single filter/delay line frequency discriminator detection system are achieved for the first time. In those experiments, the frequency modulation characteristics, line width, single frequency continuous tuning range and frequency stability of the GRINROD ECSL are measured by means of IF spectrum. Meanwhile, the IF receiving circuits are optimized for obtaining stable transmission properties. The main research achievements in part II are the theoretical analysis of the diversity COFCSs. Firstly, the Bit Error Rate (BER) performance of two branch homodyne phase diversity ASK, DPSK and two branch homodyne phase polarization DPSK receivers are analyzed by means of characteristic function model. In the analysis, the effects of pre and post detection filters on the system performance are especially studied. Secondly, the impacts of the phase noise, shot noise, polarization mismatch and imbalance of branch circuits on the two branch homodyne phase diversity ASK receiver, and that of modulation frequency deviation on FSK receiver are analyzed in terms of Gaussian approximation. Lastly, an improved all fiber 90 degree optical hybrid is fabricated. Utilizing the hybrid and 1.5 um InGaAsP GRINROD and grating ECSLs, a low IF, two branch phase diversity FSK coherent optical fiber transmission system is experimented for the first time in China. Guan Kejian Born in Jan. 1963. He received his Ph. D degree in Apr. 1991, in Radio Engineering, Beijing Uni versity of Posts and Telecommunications.
文摘So far, the problem of the harmonic retrieval with quadratic phase coupling in mixed noises has not been resolved well. For this reason, this paper, based on the third , forth order cumulants and Hilbert transform, proposes a new method named HBTFCH SVD TLS.The method can realize harmonic retrieval in mixed noises even when the harmonic signal includes the components of quadratic phase coupling.Simulation results show the effectiveness of the method.
文摘Now, the problem of modeling MPEG 1 video traffic still needs studying further. Based on the analysis of statistical characteristics of this kind of traffic, this paper presents a new traffic model. Simulation results show that the proposed model can reflect the statistical characteristics of the real MPEG 1 video traffic well.
文摘In packet switched communication networks, traffic between any source destination (SD) pair is expected to be transmitted over multiple paths. In this paper, we focus on the problem how to optimally distribute the load on a set of paths so that the overall network performance is maximized. This problem is first formulated as a nonlinear programming problem and then we propose a neural network (NN) to solve it. The NN architecture is discussed in detail. At last, we verify the effectiveness of our approach by applying it to a specific network model. The experimental results demonstrate that our method can yield optimal solutions with good stability.
文摘Performance of high speed coherent optical communication systems has been investigated. A novel frequency tracking/locking automatical fre quency control (clock frequency tracking AFC, CFT AFC) scheme has been presented. The first Gb/s speed coherent optical communication system of China (1.1 Gb/s FSK optical communication system) has been achieved. The achievements of this paper are as follows: (1) Performance of coherent optical communication system has been investigated. A set of expressions are deduced. In the expressions, the effects of the LD line width, waveform of modulation signal, the signal phase jitter, intersymbol interference (ISI) and various kinds of noises are comprehensively included for the first time. (2) The jitter performance of coherent optical communication system is analyzed for the first time. The timing jitter theory of coherent optical communication system is achieved. (3) A novel frequency tracking/locking automatic frequency control (clock frequency tracking AFC, CFT AFC) scheme is presented. The scheme has three advantages compared with other AFC schemes: (a) frequency tracking/locking may be achieved efficiently; (b) timing clock may be extracted efficiently; and (c) the circuitry is simpler and steadier. (4) Performance of phase diversity (PD) optical communication systems is analyzed. The BER expressions of PD systems modulated under various kinds of signal waveforms are presented. The power penalties of PD systems resulted from signal phase jitter and ISI are deduced. (5) Performance of the light sources of coherent optical communication (external cavity LD and DFB LD) is analyzed. The non flat FM (frequency modulation) response of LD chip is compensated by external circuitry. The DFB LD module with 4.7 GHz FM response is achieved. (6) Compensation of fiber dispersion in optical communication is investigated. The practical fiber dispersion compensators are achieved. (7) The first Gb/s speed coherent optical Dissertation completed Apr. 1992communication system of China is achieved. The system includes: (a) a 1.1 Gb/s ～ 2.2 Gb/s PRBS high speed signal source; (b) DFB LD modules with 4.7 GHz FM response and 1.1 Gb/s FSK optical transmitter; (c) a low noise preamplifier with 4.2 GHz width; (d) CFT AFC circuitry, which system, CFT AFC scheme not only achieves frequency tracking/locking, but also depressed timing jitter efficiently. In fact, the receiver may extract the timing clock efficiently even received signal with infinite continuous “0”; (e) The LD line width is narrowed by electrical negative feedback of CFT AFC. The characteristics of the system include: (a) the DFB LD modules are taken as the light sources; (b) balanced PIN is taken as photoelectron detector of the receiver; (c) CFT AFC scheme is taken as AFC, timing extracting, and LD line width narrowing; (e) the system speed: 1.1 Gb/s, the wavelength of LD: 1.536 4 μm, the transmission distance: 3.87 km, and the receiver sensitivity: 34.2 dBm (BER=10 9 ). Huang Shouhua Born in Hubei province, 1956, graduated from Physics Department of Nanjing University in 1980. He received the ME degree in Wuhan Research Institute of Posts and Telecom (WRIPT), in 1986. He joined WRIPT in 1986. Since 1988, he has been working towards Ph.D. degree at Beijing University of Posts and Telecom. He is the authors of over 30 journal and conference papers.
文摘This paper deals with noncoherent Maximum-likelihood Block Detection (MLBD) of uncodedCPM signals (full response CPM and parrtal response CPM) over an additive white noise (AWGN)channel. Based on the work of W. Osborne and M. Simon ,this paper generalizes Maximum-likelihoodBlork Detection. Then we focus on the error performance of MLBD, which is named one-symbol MLBDand N-symbol MLBD respectively. By computer simulation of CPFSK, 1RC and 2RC , it is found thatMLBD can improve the error performance over traditional noncoherent detection.
文摘We propose a novel hybrid algorithm of BP neural ytetwork and apply it to blind equalization.The algorithm combines the merits of Rosario algorithm and random optimization method. Its cost function has strict convex character (after a threshold) and the algorithm converges much faster than the BPmethod[2], as an exalople, we evaluate its performance by using it into blind equalization. With the help ofHigher Order Culnulants (HOC), the blind equalization scheme converges much faster than the CMAalgorithm and superior to the Back-propagation,nethod[2] due to its ability of finding the optimal solutionwith relatively fewer iteration stops.
文摘A new waveguide to coaxial line transition adopted to microwave band is proposed in this paper.The configuration and design of the transition is studied. It has the merits of simplicity in structure, ease ofconstruction and repeatable performance, especially that the coaxial line is in the same direction with thewaveguide. At X band, the pass bandwidth of the transition is about 6%, and the insertion loss less than 1dB.
基金the Ministry of Posts and Telecommunications of China.
文摘This paper presents the real-time implementation of 6.75kb/s speech codec for the GSM half-rate digital cellular system based on CELP[1]. Logarithmic Area Ratio (LAN).[2] quanrizarion for short term Parameters and eeeicient adaptive codebook search are used. An overlapping center-clipping codebook and the fonnufor for fast searching are proposed. The MOS of the synthesized speech is over 3.5.
文摘In desktop video conferencing systems, the quality of video as well as the response speed of user′s data is important element of systematic performance. In this paper, four video and data multiplexing strategies in terminals: the Alternate Method, the Video Priority Method, the Data Priority Method, and the Dynamic Priority Method, are investigated. Their influences on transmission performances of data and video are discussed.
