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Showing papers by "Beijing University of Posts and Telecommunications published in 1995"


Journal ArticleDOI
TL;DR: In this article, the structure and magnetic properties of RFe12−xMox series and their nitrides with R=Y,Gd,Nd and x=0.8, 1.0,1.5, 2.5 have been studied by x-ray-diffraction and magnetic measurements.
Abstract: The structure and magnetic properties of RFe12−xMox series and their nitrides with R=Y,Gd,Nd and x=0.8,1.0,1.5,2.0,2.5 have been studied by x‐ray‐diffraction and magnetic measurements. It is found that with the increment of Mo content x, the lattice parameters increase, whereas the saturation magnetization, Curie temperature, and anisotropy field decreases in the RFe12−xMox series. Upon nitrogenation lattice parameters, saturation magnetization, and Curie temperature increase. Correspondingly, the easy c‐axis magnetocrystalline anisotropy of the Fe sublattice decreases in YFe12−xMoxNy and GdFe12−xMoxNy but increases in NdFe12−xMoxNy although its variation with the Mo content is the same as in their original counterparts. NdFe12−xMoxNy compound in the low Mo content shows great potential for permanent magnet applications.

19 citations


Journal ArticleDOI
TL;DR: An efficient full-duplex fast training algorithm is proposed which can simultaneously estimate the impulse responses of echo paths and channels at both ends and can reduce the tap-setting time to half of that required by the traditional half-duple fast training schemes.
Abstract: To reduce the system initialization time in high-speed full-duplex data transmission over two-wire lines, we propose an efficient full-duplex fast training algorithm which can simultaneously estimate the impulse responses of echo paths and channels at both ends. Two mutually orthogonal periodic sequences are designed and used to co-estimate the near echo, the far echo with bulk delay, and the channel response. The new algorithm can reduce the tap-setting time to half of that required by the traditional half-duplex fast training schemes. The effects of channel noise and symbol rate offset between two ends are examined in terms of both mean-square error (MSE) and signal-to-noise ratio (SNR). Both the theoretical analysis and computer simulation show that there are three degrading factors due to symbol rate offset. The SNR is inversely proportional to the sum of the estimated coefficients, the half period of the training sequences, and the square of symbol rate offset. If the far-signal-to-channel-noise ratio is 30 dB, then the degradation is significant when the symbol rate offset is more than 10/sup -4/. If it is 40 dB, then the degradation is significant when the symbol rate offset is above 3/spl times/10/sup -5/. >

11 citations


Journal ArticleDOI
TL;DR: In this article, a nonuniform conducting cylindrical cavity with a slot in a uniform electric field was analyzed in bipolar coordinates, and the electric field penetration through the slot and perturbation of an incomplete conducting cylinder were investigated.
Abstract: In bipolar coordinates, a nonuniform conducting cylindrical cavity with a slot in a uniform electric field E/sub 0/ is analyzed. The authors investigate the electric field penetration of a slotted cylindrical cavity through the slot and the electric field perturbation of an incomplete conducting cylinder. A family of objects are included by changing the structural parameters of the nonuniform cylindrical cavity with a slot. Both analytical expressions and numerical results of some special structures are given. >

7 citations


Journal ArticleDOI
TL;DR: The authors present a method for improving the Gaussian approximation accuracy and use a number of moments of multiple-access interference (MAI) to make the approximation more accurate.
Abstract: Many papers have described the calculation of error probabilities for a direct-sequence/spread-spectrum multiple-access system. The exact calculation is computationally difficult, so emphasis has been placed on the approximation and the bounds. A simple and attractive approximation is the Gaussian approximation in which the signal/noise ratio is used. Unfortunately, this approximation is not accurate enough in some cases. The authors present a method for improving the Gaussian approximation accuracy. The authors use a number of moments of multiple-access interference (MAI) to make the approximation more accurate.

6 citations


Proceedings ArticleDOI
27 Nov 1995
TL;DR: The results indicate that significantly better performance is available by using new spreading codes than using conventional pseudonoise codes.
Abstract: In this paper the BER performance of a generalized quasi-synchronous code division multiple access (QS-CDMA) system over a multipath fading channel is evaluated. The maximal ratio combining (MRC) and the selection diversity reception are used in the system. The results indicate that significantly better performance is available by using new spreading codes than using conventional pseudonoise codes.

4 citations


Journal ArticleDOI
TL;DR: Data traffic from a wireline network to its mobile data terminal, such as access to large commercial databases or data transmission from a main computer to its remote mobile terminal, is studied.
Abstract: Buffers are used to overcome the data losses due to the interruption of data transmission when a mobile station is handed over in a cellular network. Data traffic from a wireline network to its mobile data terminal, such as access to large commercial databases or data transmission from a main computer to its remote mobile terminal, is studied. Compound Poisson (CP) is used to approximate the arrival process of the data traffic, and a modulated D (MD) distribution is used to approximate the service and handover process. The performance of the queueing model CP/MD/1/N is analyzed. Probability generating functions and characteristic functions are used to evaluate the mean queue length and the mean burst delay for an infinite buffer system and the overflow probabilities versus the buffer size for a finite buffer system. A method is presented to find the probability transition matrix entries by recursively taking derivatives of the probability generating function of the number of the characters arriving during the service-time. The queue length distributions for a finite buffer, both at departure instants and at arbitrary time instants are derived. Comparison with simulation indicates that the model is accurate. The numerical results of the model confirm the effectiveness of the scheme. >

4 citations


Proceedings ArticleDOI
27 Nov 1995
TL;DR: A new reinforcement learning structure which is adaptive to DEDS supervision is developed, the close relationship between reinforcement learning and the neural network is presented, and a foundation for the further development of reinforcement learning based on neural network theory is built.
Abstract: In this paper, based on a new way of specifying the system close-loop behavior, we propose a reinforcement learning method for discrete event dynamic system (DEDS) supervision. By means of the concept of subconnection neural networks we develop a new reinforcement learning structure which is adaptive to DEDS supervision, present the close relationship between reinforcement learning and the neural network, and build a foundation for the further development of our reinforcement learning based on neural network theory. Using two examples about the optimization and control of telecommunication networks, we have illustrated the application prospect of our method. Computer simulations have confirmed its effectiveness.

1 citations


Journal ArticleDOI
TL;DR: Based on the built-in self-test for logic circuit, a new approach is proposed to reduce pseudorandom test length by using the relation between input probability and test length to shorten the test sequence length.
Abstract: Based on the built-in self-test for logic circuit, a new approach is proposed to reduce pseudorandom test length. After finding worst faults in the circuit and creating their circuit models the output signals of these models will be compressed by linear feedback shift register. The test length for the worst faults can be obtained by analyzing compressed signature. Finally, using the relation between input probability and test length, we propose a new algorithm to shorten the test sequence length. So the optimum input probability and the shortest test length can be received.

1 citations


Proceedings ArticleDOI
23 Oct 1995
TL;DR: A genetic back-propagation algorithm is used to solve the optimal design problem of multistage weighted order statistic filter under the mean absolute error criterion and it is shown experimentally that this algorithm can find the optimal WOS filter in image restoration application.
Abstract: A genetic back-propagation (BP) algorithm is used to solve the optimal design problem of multistage weighted order statistic filter under the mean absolute error criterion. It is shown experimentally that this algorithm can find the optimal WOS filter in image restoration application.

1 citations


Proceedings ArticleDOI
07 Aug 1995
TL;DR: In this paper, based on bidirectional optical amplifiers and n couplers, a biddirectional transparent (BTL) network configuration is proposed that can save much optical fiber and optical filters.
Abstract: In this paper, based on bidirectional optical amplifiers and n couplers, we propose a bidirectional transparent (BTL) network configuration Compared to the MPL and SLB schemes, the BTL structure can save much optical fiber and optical filters

Proceedings ArticleDOI
18 Sep 1995
TL;DR: In this article, a set of new low power radio propagation models in the picocell environments suitable to some urban and rural conditions in China were given. But the authors only used two antenna height of 32 m to 75 m at frequency 900 MHZ.
Abstract: The paper gives a set of new low power radio propagation models in the picocell environments suitable to some urban and rural conditions in China A number of propagation measurements was taken by the authors using two antenna height of 32 m to 75 m at frequency 900 MHZ Test settings were chosen in rural open areas, suburban streets, and urban streets, crossroads and overbridges in order to study propagation in variety of environments Based on the obtained data in different environments, this paper takes the further steps to discuss the variations of signal strength with distance that have distinct near and far regions separated by a breakpoint and the effect of antenna height and type by analyzing the two ray model, and then gives a new propagation model, which was proved well-fitted to the measured results in some places Moreover, this model was applied to make the radio propagation prediction for CT2 Campus Network, which is now running well This also shows the practicality and reliability of the model in Chinese environments Up to present, the measurement database has been established and a CAD software package which can predict the radio coverage area for rural and urban in China is going to be finished

Proceedings ArticleDOI
30 Oct 1995
TL;DR: In this article, the influence of SRS and four wave mixing (FWM) on the WDM soliton communication system with lumped amplifiers is studied, and the degradation characteristics of signal-to-noise ratio and bit-error rate are given.
Abstract: The influence of SRS and four wave mixing (FWM) effects on the WDM soliton communication system with lumped amplifiers are studied, and the degradation characteristics of signal-to-noise ratio and bit-error rate are given. The numerical results show that the influence of SRS and FWM on the system depends very strongly on the soliton pulse width. The larger the pulse width is, the weaker the influence becomes. In order to reduce the influence of SRS and increase the capacity of the system a shorter channel spacing and relatively large pulse width is preferred.

Proceedings ArticleDOI
14 Aug 1995
TL;DR: The closed form theoretical formulae for the screening effects of the buried shield wires are given and the theory of earth conduction effects in a transmission system to analyze this problem.
Abstract: When lightning strikes the ground near an optical fiber cable, there may be a discharge between the stroke point and the cable or it may induce currents and voltages on the metal structures of the optical cable. The buried shield wires laid close by the cable can reduce the harmful effects of the lightning. This paper uses the theory of earth conduction effects in a transmission system to analyze this problem. The closed form theoretical formulae for the screening effects of the buried shield wires are given.

Proceedings ArticleDOI
28 Aug 1995
TL;DR: The logic function of the memory unit (MEU) board is described, a type of dynamic random access memory unit which includes a refresh circuit for data retention, and a fault detection and location algorithm based on the fault models are presented.
Abstract: In this paper, we describe the logic function of the memory unit (MEU) board, a type of dynamic random access memory unit which includes a refresh circuit for data retention, and present a fault detection and location algorithm based on the fault models we describe. This method has been used to diagnose the MEU board of AXE-10 SPC digital telephone system.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Proceedings ArticleDOI
27 Nov 1995
TL;DR: In this paper, a method is presented to simulate the time and frequency-selective behavior of urban microcell mobile radio channels, which is based on a physical model for the GMSK signal radio wave propagation in these environments.
Abstract: To simulate the time- and frequency-selective behavior of urban microcell mobile radio channels, a method is presented, which is based on a physical model for the GMSK signal radio wave propagation in these environments. The approach enables generation of complex impulse responses as given by the statistics of the underlying channel behavior. Delay profiles and fading characteristics of the multipath structures can be efficiently simulated by reproducing the physical wave interference process, thereby incorporating the different channel characteristics that are observed in different urban environments. Based on previous analyses, we discuss the propagation characteristics of the GMSK signal with the help of the geometry of fractal sets.

Proceedings ArticleDOI
27 Nov 1995
TL;DR: A three-hierarchical structure of neural networks is proposed and applied to the speaker-independent speech recognition for Chinese digits 0-9 and shows good performance on persons under test from different provinces speaking the same Chinese words in a normal environment.
Abstract: A three-hierarchical structure of neural networks is proposed in this paper. The structure is applied to the speaker-independent speech recognition for Chinese digits 0-9. The experimental result shows that the system gave good performance on persons under test from different provinces speaking the same Chinese words in a normal environment.

Proceedings ArticleDOI
27 Nov 1995
TL;DR: A quick repeated learning rule, which is based on the Hebb rule and the Hamming distance distribution of the pattern set to be learned, is studied and not only can the learned patterns be addressable, but an attraction basin with a predetermined radius is established for each attractor.
Abstract: In this paper, a quick repeated learning rule, which is based on the Hebb rule and the Hamming distance distribution of the pattern set to be learned, is studied. With the help of the proposed learning rule, not only can the learned patterns be addressable, but an attraction basin with a predetermined radius is established for each attractor.