Showing papers by "Beijing University of Posts and Telecommunications published in 2001"
TL;DR: A squaring method is presented to simplify the decoding of orthogonal space-time block codes in a wireless communication system with an arbitrary number of transmit and receive antennas and gives the same decoding performance as the maximum-likelihood ratio decoding while it shows much lower complexity.
Abstract: We present a squaring method to simplify the decoding of orthogonal space-time block codes in a wireless communication system with an arbitrary number of transmit and receive antennas. Using this squaring method, a closed-form expression of signal-to-noise ratio after space-time decoding is also derived. It gives the same decoding performance as the maximum-likelihood ratio decoding while it shows much lower complexity.
163 citations
11 Jun 2001
TL;DR: A globally optimizing ant algorithm is constructed, which is based on the ability of ants to find the shortest path between their nest and the food source during their looking for food, which can realize QoS routing effectively and efficiently.
Abstract: In this paper, the requirements of routing due to multimedia applications are briefly discussed. In order to solve the QoS constrained routing effectively and efficiently, we construct a globally optimizing ant algorithm, which is based on the ability of ants to find the shortest path between their nest and the food source during their looking for food. Simulation results show that the proposed approach can realize QoS routing effectively and efficiently.
49 citations
TL;DR: In this paper, a performance analysis of an optical clock extraction circuit based on a Fabry-Perot filter (FPF) is presented, in which two analytical methods, time-domain and frequency-domain analysis, are developed.
Abstract: A performance analysis of an optical clock extraction circuit based on a Fabry-Perot filter (FPF) is presented. Two analytical methods, time-domain and frequency-domain analysis, are developed in this paper. Time-domain analysis shows that there is no phase jitter in the extracted optical clock if the free spectral range (FSR) of the FPF is exactly equal to the signal clock frequency. Based on this, we obtain an analytical expression for root mean square (rms) amplitude jitter of the extracted optical clock in time domain, in which we have taken the impacts of carrier frequency drift and carrier phase noise into account. When the FSR of the FPF deviates from the signal clock frequency, both phase jitter and amplitude jitter will occur in the extracted optical clock. In this situation, a more general frequency-domain method is developed to deal with the timing performance under the assumption that carrier phase noise is negligible. This method allows us to calculate both rms phase jitter and rms amplitude jitter of the extracted optical clock. Using the developed two methods, we present a detailed numerical investigation on the impacts of finesse of the FPF, carrier frequency drift, resonator detuning, carrier phase noise, and optical pulse chirp on the timing performance. Finally, the application of this circuit in multiwavelength clock recovery is discussed.
44 citations
29 Oct 2001
TL;DR: This paper proposes an analytical model to compute the saturated throughput of 802.11 DCF, that is, both the basic access mechanism and the optional RTS/CTS mechanism, and is shown to be able to follow the behavior of802.11 more accurately, which is verified by elaborate simulations.
Abstract: In IEEE project 802, the 802.11 medium access control (MAC) is used to support asynchronous and time bounded delivery of radio data packets. A distributed coordination function (DCF), which is a carrier sense multiple access with collision avoidance (CSMA/CA) with exponential backoff, is the basis of the IEEE 802.11 WLAN MAC protocols. This paper proposes an analytical model to compute the saturated throughput of 802.11 DCF, that is, both the basic access mechanism and the optional RTS/CTS mechanism. Compared with other models, this model is shown to be able to follow the behavior of 802.11 more accurately, which is verified by elaborate simulations.
38 citations
35 citations
29 May 2001
TL;DR: Although the proposed three load balancing algorithms are only suitable for non-priority unicast traffic, they can be easily extended for priority traffic conditions.
Abstract: This paper present three load-balancing algorithms for multiprotocol label switching (MPLS) traffic engineering: topology-based static load-balancing algorithm (TSLB), resource-based static load-balancing algorithm (RSLB) and dynamic load-balancing algorithm (DLB). We also evaluate the performance of these algorithms using NS-2 simulator. The simulation results show that the performance of our algorithms is better than the traditional shortest path algorithm. Moreover, the performance of RSLB and DLB is much better than the performance of TSLB. Although the proposed three load balancing algorithms are only suitable for non-priority unicast traffic, they can be easily extended for priority traffic conditions. The load balancing algorithms under multicast priority conditions are the subject for further study.
32 citations
TL;DR: In this article, the authors developed a systematic method that employs transfer function considering encoder, fiber channel, and decoder to analyze the frequency-hopping (FH) optical code-division multiple access (OCDMA) system.
Abstract: In this paper, we develop a systematic method that employs transfer function considering encoder, fiber channel, and decoder to analyze the frequency-hopping (FH) optical code-division multiple-access (OCDMA) system. We analyze the FH-OCDMA system when both single-mode fiber and dispersion-shifted fiber are employed as the transmission medium. The difference of group velocities affects system performance more seriously than dispersion effect does. The results show that single-mode fiber is not proper for a FH-OCDMA system, even if the transmission length is no more than 1 km. The dispersion-shifted fiber is suitable for a FH-OCDMA system, especially in an access network. We also propose an optical device to compensate the group velocities.
24 citations
TL;DR: An IP with multiprotocol label switching (MPLS) over wavelength division multiplexing (WDM)-based broad-band IP network architecture and protocol is proposed and analyzed in this paper, which supports variable-length IP-like optical packet label switching and optical virtual path routing.
Abstract: This paper presents a new technology for constructing IP over photonic systems. An IP with multiprotocol label switching (MPLS) over wavelength division multiplexing (WDM)-based broad-band IP network architecture and protocol is proposed and analyzed in this paper, which supports variable-length IP-like optical packet label switching and optical virtual path routing. This system tries to merge into one layer the functionalities of the wavelength switching, SONET mux/demux, and IP routing, and is sometimes known as the concept of optical MPLS. The label banding, forwarding/switching process, and node architecture of the proposed network are discussed and studied. A unique as well as important function of a lambda/label edge router (LER) is a flow assembly device that can encompass MPLS' forward equivalence classes, label stacking, and label switching path aggregation function. At the same time, a particular function of the core label switching router is wavelength merging. A fiber delay line is used to delay the data stream in order to process the label information and resolve contention. Transmission bit error rate measurements of the baseband data stream and back-to-back is also demonstrated to show its feasibility.
24 citations
29 Oct 2001
TL;DR: A novel random access method is proposed in this paper to repair the corrupted stream structure of MPEG-1 and it consists of two main steps: first, it should extract necessary information from the multicast stream, and then a system header would be constructed using the information.
Abstract: MPEG-1 is a successful international standard for video and audio coding, and has been widely used in many fields, such as entertainment, education, digital library, video on demand etc. As the MPEG-1 stream has its own semantic structure, the multicast application may destroy its syntax which results in decoding failure. To deal with this problem, a novel random access method is proposed in this paper to repair the corrupted stream structure. This solution consists of two main steps: first, it should extract necessary information from the multicast stream, and then a system header would be constructed using the information, whereafter this header would be inserted to the beginning of the decoder buffer. By this way, the decoder can play the received multicast stream without any problem.
21 citations
TL;DR: A new model is proposed based on the China Mobile Intelligent Network version 02 (CMIN02) system from Beijing University of Posts and Telecommunications (BUPT), which adds modifications and refinements to the former two reference models.
17 citations
01 Oct 2001
TL;DR: In this paper, a closed-loop space-time block code (STBC) was proposed for the 3GPP FDD specifications and an optimized power allocation scheme based on closed loop STBC was proposed.
Abstract: In 3GPP FDD specifications, space time transmit diversity (STTD) employs space-time block code (STBC) to maintain orthogonality between the two antennas in order to avoid self-interference in fading channels. However, the STTD technique is just open loop transmit diversity, and we investigate whether we can obtain further gain if closed loop STBC is used. A novel scheme based on closed loop STBC is proposed first. And then an optimized allocation scheme of a fixed transmitter power budget between two transmit antennas is presented. Finally, COSSAP simulation results show a significant performance improvement between closed loop STBC and traditional STBC. Moreover, these simulation results also show a good agreement with our theoretical analyses.
07 Oct 2001
TL;DR: Simulation results are presented to verify the BER performance of the new scheme based on parallel symbol cancellation, which has a lower time delay than the traditional detection algorithm of V-BLAST space-time code.
Abstract: Space-time code techniques have been widely studied in wireless communications, for they provide better signal qualities in fading channel environments and increase the system capacity. As an important space-time code, Bell Lab Layered Space-Time (BLAST) code has been paid more attention. However, the traditional detection algorithm of V-BLAST space-time code needs much time to perform linear combination nulling and successive symbol cancellation. The greater the number of transmit antennas, the greater the time delay. To overcome this disadvantage, a new scheme based on linear combination nulling and parallel symbol cancellation is proposed. The new scheme has a lower time delay. The simulation results of this new scheme are obtained by COSSAP simulation in flat Rayleigh channels. These simulation results are presented to verify the BER performance of the new scheme based on parallel symbol cancellation.
29 Oct 2001
TL;DR: A combination of end-to-end mechanisms and hop-by-hop mechanisms is the future of TCP-friendly congestion control as well as a combination of the additive-increase multiplicative-decrease (AIMD)-based scheme and the model-based scheme.
Abstract: This paper investigates several TCP-friendly congestion control mechanisms and sorts them according to their implementation methods. The advantages and disadvantages of every kind of these TCP-friendly schemes are listed after their principles are outlined. This paper also suggests that a combination of end-to-end mechanisms and hop-by-hop mechanisms is the future of TCP-friendly congestion control as well as a combination of the additive-increase multiplicative-decrease (AIMD)-based scheme and the model-based scheme.
29 Oct 2001
TL;DR: This work focuses on the simulation analysis of the TCP performance over the DCF access mode of IEEE 802.11 WLAN, which provides users with high-speed wireless data access to the network and voice capabilities for telephone conversations.
Abstract: The TCP protocol is the most frequently used transport layer protocol in the Internet, and it is originally designed, improved and tuned to work efficiently on wired network where the packet loss is very small. When packet loss is detected, TCP will trigger the congestion recovery algorithms. While in the wireless environment, the bit error rate of a wireless link is much higher and a wireless connection might be temporally broken not only for the reason of congestion but also due to temporal link impairment such as shadowing effect or buffer overflow. So, it is valuable to research the current versions of the TCP performance over a wireless environment. Wireless local area networks (WLAN) provide users with high-speed wireless data access to the network and voice capabilities for telephone conversations. We focus on the simulation analysis of the TCP performance over the DCF access mode of IEEE 802.11 WLAN.
TL;DR: In this paper, double orthogonal pump in a semiconductor fiber ring laser was used to improve the conversion efficiency and to deduce the noise figure of wavelength converters based on four-wave mixing.
Abstract: A new scheme is presented in this letter that, by using double orthogonal pump in a semiconductor fiber ring laser, gives a better solution to improve the conversion efficiency and to deduce noise figure of wavelength converters based on four-wave mixing. The noise figure in this scheme is smaller than normal broad-band orthogonal-pump scheme. Experimental results show nearly flat conversion efficiency and signal-to-noise ratio in a wavelength-shift range of more than 40 nm.
06 May 2001
TL;DR: An algorithm in neural network weights training for ATM Call Admission Control (CAC) and Usage Parameter Control (UPC) is used and the simulation results show that this approach is efficient and feasible.
Abstract: To maintain the QoS using the traditional mathematical approaches to build an efficient network traffic controller in ATM traffic control is a difficult task. The advantage of using NNs is that the QoS can be accurately estimated without detailed user action models or knowledge about the switching system architecture. The disadvantage is that it will take longer time to train with ATM network changes. In this paper, we use an algorithm in neural network weights training for ATM Call Admission Control (CAC) and Usage Parameter Control (UPC). The simulation results show that this approach is efficient and feasible.
29 Oct 2001
TL;DR: A transform-domain processing method of channel estimation is proposed in this paper, which is equivalent to interpolation in the frequency domain, and a simple time-domain noise-suppression method is utilized to improve the accuracy of the channel estimation.
Abstract: For the sake of bandwidth efficiency, one preamble pilot OFDM symbol is preferable for channel estimation of an OFDM system with two transmit antennas; a transform-domain processing method of channel estimation is proposed in this paper, which is equivalent to interpolation in the frequency domain. And a simple time-domain noise-suppression method is utilized to improve the accuracy of the channel estimation. Theoretic analysis and simulation results validate the accuracy of the channel estimation method proposed in this paper.
07 Oct 2001
TL;DR: Three new CMAs, recursive variable step size CMA, normalized constrained CMA and recursiveVariable step size constrained C MA, are obtained under a uniform framework and can be expressed in a general form.
Abstract: Conventional constant modulus algorithms (CMAs) suffer shortcomings of slow convergence rate and possibility of improper convergence, which obstruct their application in real-time multiuser detection for CDMA cellular system. This paper focuses on developing new algorithms to alleviate these problems. Three new CMAs, recursive variable step size CMA, normalized constrained CMA and recursive variable step size constrained CMA, are obtained under a uniform framework. Interestingly they can be expressed in a general form. Since they automatically and adaptively choose the optimal variable step size there is no need to worry about whether the step size works and they converge much faster. To solve the modulus parameter sensitivity problem of constrained CMA, modulus parameter correction is integrated into RVSS-CCMA. Various simulations validate the efficiency and robustness of our new algorithms, especially the RVSS-CCMA with modulus parameter correction.
11 Jun 2001
TL;DR: In this paper, an effective scheduling algorithm based on the RPS model, called simple weighted fair queueing (SWFQ), is presented, which has lower complexity and can be easily implemented in chips.
Abstract: In this paper, we present an effective scheduling algorithm based on the RPS model, called simple weighted fair queueing (SWFQ). In SWFQ, computation of the system potential function does not require such division or multiplication operations as in MD-SCFQ. Compared with MD-SCFQ, SWFQ has lower complexity and can be easily implemented in chips. We verify the effectivity of proposed SWFQ through strict theoretical analysis.
24 Oct 2001
TL;DR: This paper proposes a new scheme, called the Best-Effort Patching (BEP), that offers a TVoD service in terms of both request admission and VCR interaction for multicast VoD system, and shows that BEP outperforms the conventional multicastTVoD interaction protocols.
Abstract: Multicast Video-on-Demand (VoD) has excellent performance, but it is very difficult to equip such a system with full support for interactive VCR functions. In this paper, we propose a new scheme, called the Best-Effort Patching (BEP), that offers a TVoD service in terms of both request admission and VCR interaction for multicast VoD system. Moreover, by using a novel dynamic merging algorithm, BEP significantly improves the efficiency of TVoD interactivity, especially for popular videos. Our extensive simulation results show that BEP outperforms the conventional multicast TVoD interaction protocols.
TL;DR: The size of these families equals their period, and it is shown that in the binary case, the linear complexities of these sequences are much larger than those of cascaded geometric sequences, although in these cases the maximum correlations are larger.
Abstract: In this correspondence, we study families of generalized geometric sequences formed bp applying a feedforward function to certain sums of decimated m-sequences with elements in a finite field. We compute their correlation functions, which for certain families turn out to be close to the square root of the period. The size of these families equals their period. We also show that in the binary case, the linear complexities of these sequences are much larger than those of cascaded geometric sequences, although in these cases the maximum correlations are larger.
16 Oct 2001
TL;DR: It is shown that the OADM realized by the authors is advanced, practical, reliable, and applied in China Advanced Info-Optical Network (CAINONet).
Abstract: Optical Add/Drop Multiplexer (OADM) is an important network element. In the ring architecture, OADM can be introduced to make efficient use of network capacity, network protection, wavelength routing and many more good features. In this paper, an OADM with high performance realized by us is demonstrated. The key technical problem , solving method and design rule for the OADM are given. The experiment results of long distance transmission by use of the OADM are illuminated by some figure . It shows that the OADM realized by us is advanced, practical, reliable, and applied in China Advanced Info-Optical Network (CAINONet).
TL;DR: In this article, a new scheme was presented which, by using a dispersion-imbalanced fiber loop mirror, gave a better solution to improve the extinction ratio degradation of wavelength converter based on cross-gain modulation.
29 Oct 2001
TL;DR: The comparison with traditional TCP shows that MPLS ATCC can find and control the congestion in time, reduce the round-trip delay, and edit the ingress traffic, and achieves the objective of improving the total throughput and the utility of the buffer.
Abstract: The paper proposes an active traffic and congestion control mechanism in MPLS (MPLS ATCC) and its model, which integrate the characters of the multiprotocol label switch (MPLS) and an active network. MPLS ATCC moves the endpoint congestion control algorithms into the network. The comparison with traditional TCP shows that MPLS ATCC can find and control the congestion in time, reduce the round-trip delay, edit the ingress traffic. MPLS ATCC therefore achieves the objective of improving the total throughput and the utility of the buffer.
10 Sep 2001
TL;DR: In this paper, the effects of contact failure on the digital signal transmission in unmatched circuits were investigated theoretically and experimentally, and it was shown that multi-reflection of the signals may occur in the circuit and the probability of occurrence of error codes can be increased significantly.
Abstract: It is found that one of the most important reasons for high error code rates in optical communication systems is the contact failure of the coaxial electrical connectors installed in the systems. The influences of the contact failure on the digital signal transmission in ideal circuits have already been studied theoretically and experimentally. Based on those results, this paper further studies theoretically the effects of contact failure on the digital signal transmission in unmatched circuits, which can happen widely in practical applications. Derivation shows that the effects of contact failure in unmatched circuits on the signal transmission are very complex. Multi-reflection of the signals may occur in the circuit, and the probability of occurrence of error codes can be increased significantly.
29 Oct 2001
TL;DR: An overview of the human immune system is presented and its salient features that can contribute to the design of competent network-based IDS are analyzed.
Abstract: Network intrusion detection is one of the most popular research topics. Existing network-based intrusion detection systems have drawbacks in many aspects, among of which the two outstanding problems are the high ratio of false alarms and the lack of self-adaptation. An overview of the human immune system is presented and its salient features that can contribute to the design of competent network-based IDS are analyzed. Then a network-based intrusion detection model is described, which is inspired by the human immune system, and its characteristics are analyzed in full.
29 Oct 2001
TL;DR: In this paper, the characters of the optimum TPC command sequence under some typical radio channel are investigated by computer simulation and it is found that the 0 and 1 alternative sequence is an optimum T PC command sequence.
Abstract: In a WCDMA system, the single-bit adaptive step-size closed-loop power control scheme is popularly investigated. But the only information which the transmitter can apply to adjust the transmit power is the received TPC command sequence. On the other hand, we need a reference TPC command sequence (we call it the optimum TPC command sequence), if the transmitter receives such a TPC command, the SIR at the receiver meets the quality of service demand. To compare the optimum TPC command sequence with the transmitter received TPC command sequence, we can choose the step-size according to the amount of the difference between them. In this paper, we investigate the characters of the optimum TPC command sequence under some typical radio channel by computer simulation; it is found that the 0 and 1 alternative sequence is an optimum TPC command sequence.
29 Oct 2001
TL;DR: A variable additive increase adaptive algorithm, which utilizes RTP/RTCP as the protocol to collect QoS information is presented, which shows that the flow enhanced by the variable increase algorithm is more stable.
Abstract: We present a variable additive increase adaptive algorithm, which utilizes RTP/RTCP as the protocol to collect QoS information. Compared with the constant additive algorithm, the flow enhanced by the variable increase algorithm is more stable. We also simulate the algorithm and analyze the results.
07 Oct 2001
TL;DR: A new dynamic channel allocation (DCA) model based on Markov decision programming (MDP) has been established to dynamically adapt the switching point in the TDD radio frame according to the states of the system.
Abstract: In the 3G mobile communication systems, the services consist of symmetric services such as voice service and asymmetric services such as WWW browsing. The TDD mode CDMA systems can adapt itself well to time varying asymmetric traffic. In this paper, a new dynamic channel allocation (DCA) model based on Markov decision programming (MDP) has been established to dynamically adapt the switching point in the TDD radio frame according to the states of the system. Simulation results have shown that it will decrease the system blocking rate and increase the resource usage compared with the fixed channel allocation (FCA) scheme.
01 Jan 2001
TL;DR: The results of simulation prove that the network-assisted congestion control (NACC) algorithm could fulfil the max-min fairness and TCP-friendliness.
Abstract: The research on end-to-end congestion control scheme has been developed widely. But the end-to-end adaptation scheme naturally has some limitations, such as the probing problem and fairness problem. In order to solve these problems, the assistance of network is necessary. Therefore, a network-assisted congestion control (NACC) algorithm is presented. The network-assisted congestion control algorithm is quite simple, but very efficient. Additionally, the NACC algorithm could provide a TCP-friendliness. Finally, the results of simulation prove that the NACC algorithm could fulfil the max-min fairness and TCP-friendliness.