Showing papers by "Beijing University of Posts and Telecommunications published in 2000"

Theory and experiments of a three-cavity wavelength-selective photodetector

Abstract: We propose a novel wavelength-selective photodetector with three subcavities, i.e., a filtering cavity, a spacer cavity, and an absorption cavity, for obtaining a narrow spectral response linewidth and a high quantum efficiency simultaneously. A theoretical prediction has been made that a less than 1-nm linewidth and a quantum efficiency as high as 90% are possible. We discuss the effects of the key factors on the performance of this type of photodetector that has been designed and fabricated. A spectral response linewidth of approximately 1.4 nm (FWHM) and an external quantum efficiency higher than 50% have been achieved experimentally. Such devices are promising for wavelength-division multiplexing applications.

A QoS routing algorithm based on ant algorithm

Abstract: The requirements of routing due to multimedia applications are 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 search for food. Simulation results show that the proposed approach can realize QoS routing effectively and efficiently.

Analytical study of spatiotemporal chaos control by applying local injections

Abstract: Spatiotemporal chaos control by applying local feedback injections is investigated analytically. The influence of gradient force on the controllability is investigated. It is shown that as the gradient force of the system is larger than a critical value, local control can reach very high efficiency to drive the turbulent system of infinite size to a regular target state by using a single control signal. The complex Ginzburg-Landau equation is used as a model to confirm the above analysis, and a four-wave-mixing mode is revealed to determine the dynamical behavior of the controlled system at the onset of instability.

Multicast routing based on ant algorithm for delay-bounded and load-balancing traffic

Abstract: Multicast routing is to find the paths from a source node to all multicast destinations. In this paper based on the ant algorithm, we propose a distributed multicast routing scheme with delay-bounded and load-balancing traffic in real-time packet switched computer communication networks. We first describe the ant algorithm model and give the ant-network model, then present an approach using the ant algorithm to optimize the multicast routes with delay-bounded and load-balancing traffic. Finally a simulation has been done to show the efficiency of the algorithm in the environment of OPNET simulation software, and the simulation results show that the proposed approach can find the best optimal multicast routes which can satisfy the delay-bounded requirement and avoid to congested nodes.

An effective way to improve TCP performance in wireless/mobile networks

Abstract: TCP congestion control has been developed on the assumption that congestion in the network to be the only cause for packet loss. Thus, it drops its transmit window upon detecting a packet loss. In the presence of high error rates and intermittent connective characteristic of the wireless link, these results in an unnecessary reduction in link bandwidth utilization for packet losses are not mainly due to congestion. This paper provides an effective way to improve TCP performance in wireless and mobile networks. As routers will still have to rely on packet drops as indications of congestion, we propose to add wireless-ECN just upon the first packet loss that occurs. In this way, it strongly achieves separation of the congestion control and loss recovery mechanism by quickly informing the sender that a loss happened because of reasons related to network congestion. The unnecessary window reduction caused by lost packets due to link errors is avoided. Compared to the current ECN proposal used in traditional wired networks with the purpose of avoiding unnecessary packet losses, it is simple to implement for the complexity and inconsistency of buffer management in the networks and more conservative TCP congestion control over a short-scale period which is required in the ECN scheme is avoided. Since packet losses due to buffer overflow are not allowed to invoke congestion control if applied in an ECN wireless environment, when encountering congestion losses in such a case the addition of wireless-ECN can represent these packet losses to initiate window reduction in time and improve the ECN performance across imperfect links.

Multicast routing based on ant-algorithm with delay and delay variation constraints

Abstract: In this paper, based on the ant algorithm, we propose a distributed multicast routing scheme with delay-bounded and delay variation constraints in real-time communications. This paper first describes the ant algorithm model and gives an ant network model, then presents an approach using the ant algorithm to optimize the multicast routes with delay and delay-variation constraints. The great amount of simulation has been done to show efficiency of the algorithm, and the simulation results show that the proposed approached can find the best optimal multicast routes which satisfy the above constraints.

Prototyping SIP-based VoIP services in Java

Abstract: Next to the binary-based H.323 signaling protocol for IP telephony developed by the telecommunication community (ITU-T), a more lightweight text-based protocol was deemed necessary to address the specific needs of the Internet community. The session initiation protocol (SIP) (see Handley, M. et al., IETF-RFC 2543, March 1999) was introduced in the IETF conference control working group and has meanwhile gained maturity and support. This paper presents a Java-based implementation of the SIP protocol stack, based on a layered SW architecture, reusable object oriented software components and application programming interfaces (API). This protocol stack has been used as a basis to realize the main network components necessary for SIP based call setup: user agent, proxy server, redirect server, and registration server. The interaction between these components is illustrated through a number of service scenarios, focusing on PC-to-PC communication within the context of a virtual private network (VPN) service.

A performance analysis of all-optical clock extraction circuit based on stimulated Brillouin scattering

Abstract: In this paper, we develop an analytical method to deal with the timing performance in an optical clock extraction circuit based on stimulated Brillouin scattering (SBS). Three kinds of SBS active filters are considered and their frequency-transfer functions are obtained under the assumption that pump depletion caused by SBS is negligible. When pump depletion is taken into account, an SBS active filter acts as a nonlinear filter. To investigate the timing performance at this situation, we introduce the concept of "dynamic frequency-transfer function" to describe its frequency-response property for a fixed-signal light and pump light. Using the obtained "frequency-transfer function," we give analytical expressions for both root-mean-square (rms) phase jitter and rms amplitude jitter of the extracted optical clock, in which we have taken the impacts of SBS gain, pump light linewidth, optical pulse chirp, and pump detuning into account. Finally, a detailed numerical investigation on the timing performance for the three active filters is presented.

An analysis of the interference in the TDD-CDMA system

Abstract: This paper gives descriptions of the kinds of interference in the TDD-CDMA system. There are some specific interference modes in the TDD mode. Intra-cell, inter-cell, inter-operator and TDD/FDD interference are studied. Some simple simulations are done to study these kinds of interference and some suggestions are proposed for avoiding or reducing interference in the TDD-CDMA system.

The implementation of Viterbi decoder on TMS320C6201 DSP in W-CDMA system

Abstract: This paper describes the design and implementation of a soft-decision Viterbi decoder on TMS320C6201 DSP developed by Texas Instruments (TI) in 1998. With an incomparable operating speed, which is 200 MHz (5 ns cycle time), the TMS320C6201 DSP can achieve the performance of up to 1600 million instructions per second (MIPS) and consequently has gained more and more popularity in many applications. In this paper, a soft-decision Viterbi decoder is implemented on the TMS320C6201 evaluation module (EVM) board with the code rate 1/3 and constraint length 9. Our original aim was to achieve a decoding rate of 32 kbits/s which is requested by the W-CDMA recommendation. To our delight, however, we have finally implemented a Viterbi decoder with the decoding rate of 88 kbits/s, which is quite comparable to what has been developed on FPGAs. We also mention some bottleneck problems of TMS320C6201 DSP and some applications of this kind of Viterbi decoder at the end of this paper.

A new scheme for WDM-based passive optical access network

Abstract: Wavelength division multiplexing (WDM) offers the potential to transport very high bit rates in access systems serving residential and small business customers. In this paper, we present a new scheme that combines the advantages of WDMA and TDMA for a broadband fiber access network, and propose a medium access control (MAC) protocol that can easily realize full service access.

Distributed dynamic routing using ant algorithm for telecommunication networks

Abstract: In telecommunication networks, routing is an important issue. For this reason, we study a distributed dynamic routing (DDR) approach, and propose a novel distributed real-time dynamic routing (DRDR) approach which considers not only the utilization of resources but also the load balance in telecommunication networks. In the approach, according to the concrete problems of dynamic routing, 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 when looking for food, to realize the route optimization. Simulation results show that the proposed approach can realize distributed dynamic routing effectively according to the current traffic states in the networks and the user-specified delay requirements.

An investigation of interference between UTRA-TDD and FDD system

Abstract: Interference between the UTRA-TDD and FDD system is investigated. There are some specific interference modes in the TDD mode because the uplink and the downlink use the same frequency band in the TDD mode. The UTRA-TDD and the UTRA-FDD have severe adjacent channel interference if they use the adjacent carrier. Some simulations are done to study the interference. Impacts of four different interference instances were considered in the simulation. The impact on the UTRA-FDD uplink capacity is evaluated. Some interesting results are given from the simulations. The TDD and FDD base station can not be co-located if they use the adjacent frequency band between which the value of ACIR is below about 70 dB. The TDD and FDD cells can use the same frequency in some scenarios, which will increase the capacity, and utilize the underused UTRA-FDD uplink resources.

A new dynamic distributed routing algorithm on telecommunication networks

Abstract: A new dynamic distributed routing scheme on connection-oriented telecommunication networks, which is called the ant colony routing (ACR) scheme, is proposed. It is inspired by the phenomena that ants are always able to find the shortest path between food source and nest. In the ACR scheme, pheromone tables, which are tables of probabilities, replace traditional routing tables. They are updated according to both the lengths of paths and loads on links. Routes of newly arriving calls are selected in accordance with pheromones and loads on links. Simulation results show that the performance of ACR scheme is satisfactory.

Streaming technique and its application in distance learning system

Abstract: A streaming technique and its application in distance learning system are discussed. By using this new technique, people can distribute continuous media information over the Internet without downloading it first, which means that you can play it while you downloading it. This property is very useful in the Internet environment because the bandwidth is not wide enough and much time are needed to download a multimedia file, such MPEG video/audio files. As we know, a distance learning system is a typical multimedia application system. It involves in many kinds of information media, for example, video, audio, graphic and text. The outstanding property of the distance learning system is that these media information are not independent, they have temporal and spatial relationship to some extent. After transmission through the network, how to keep the synchronization relationship of these media information is the central issue in the distance learning system. In this article, we will also discuss how to keep media synchronization by using streaming technique.

An enhanced TCP mechanism—fast-TCP in IP networks with wireless links

Abstract: This paper presents the results of the first study on performance of Fast‐TCP over wireless links with transmission errors. We have studied a case in which a TCP source is connected with a TCP receiver over two routers. The link between the routers is wireless and has bit errors. We compare the performance of Fast‐TCP with plain TCP in the wireless environment. We evaluate Fast‐TCP using the OPNET Radio ModelerTM discrete event simulation tool. Simulation results show that even without any adaptations of other wireless protocols Fast‐TCP still has more advantages over plain TCP.

Analysis of common structure and software download for software defined radio

Abstract: The mode switching and software downloading is very important to software defined radio (SDR). This paper proposes a new idea for the software reconfiguration with over-the-air download. We present a new method for implementing the function module switching among mobile systems employing the combination of common algorithm structure and appropriate parameters. We describe the parameter expression for several function modules and analyze the real-time issue for software downloading and module switching in software defined radio.

The new mechanism for MPLS supporting IP multicast

Abstract: MPLS which combines the flexibility of Layer3 routing with Layer2 switching is being widely developed. Unfortunately, existing MPLS specifications can only support unicast well, but lack of supporting multicast. The main difficulty in MPLS supporting multicast is how to bind labels to multicast FEC. This paper mainly presents a new mechanism for MPLS supporting IP multicast routing protocol. In the proposed mechanism, label distribution is triggered by traffic not by control messages. This mechanism makes the network's scalability and dynamic property better than the mechanism whose label distribution is triggered by control messages. The simulation of this mechanism is for further study.

Single-term divisible electronic cash based on bit commitment

Abstract: In the literature, several "divisible" untraceable offline electronic cash schemes have been presented. An efficient single-term divisible electronic cash based on bit commitment scheme and one-time knowledge proof is proposed. The complexity of every protocol in our scheme is O(log N), where N is the precision of divisibility, i.e., N=(the total coin value)/(minimum divisible unit value). This scheme overcomes the problems of previous schemes through its greater efficiency and clarified assumptions.

Combination effect of fretting and corrosion on bolt-type power connectors

Abstract: Analysis of failed bolt-type power connectors showed serious contamination and low contact force (Luo et al, 1999). Further studies show that combined fretting and corrosion effects greatly aggravate connection performance. Electrochemical corrosion occurs and white corrosion products are observed between Al connector and steel flat washer. XPS shows that the product is mainly a compound of Al/sub 2/O/sub 3/ and its hydrate. Crevice corrosion between nut, lock washer and flat washer is also found. Corrosion not only decreases mechanical strength, but also reduces the lock washer load-bearing area. Several lock washers and connectors have cracks at their maximum tension stress position, which is evidence of stress corrosion. This corrosion damage may develop soon after a period of latency, quickly causes loss of contact force, and is much more dangerous than other kinds of corrosion. Reduced compressive force allows fretting to take place at contact interfaces. Analysis shows various kinds of micro-motion at contact interfaces, with one-third of samples showing fretting tracks. A tarnish film of oxide debris and dust accumulates on the contact surface. Connection resistance increases, body temperature increases and corrosion is thus accelerated. This cycle may finally cause connector failure. Therefore, appropriate protective measures are needed for harsh environments. Surface analysis devices such as SEM/EDS and XPS are used to observe electric contact interface morphology and analyze corrosion product compound formation. Metallographic examination is also used to analyze corrosion products and metallurgical structure.

Performance analysis of MMSE multiuser detection

Abstract: Performance analysis of minimum mean-squared error (MMSE) multiuser detection over a synchronous multipath channel is considered in this paper. Assuming the channel parameters are known, analysis shows that both the signal-to-noise ratio at the output of the MMSE detector and near-far resistance are related to the cross-correlation matrix of the combined spreading waveforms. Computation results demonstrate that the MMSE detector can achieve good performance under severe conditions, including large number of users and large channel length.

Effective fairness queuing algorithms

Abstract: In this paper we present two effective fair queuing algorithms (EFQs), which achieves fairness properties and delay properties similar to WFQ (which is currently the better scheduling algorithm among others), and uses a system potential function of O(l) complexity. In EFQs, computation of system potential function does not require any division or multiplication operations such as in minimum delay-self clocked fair queuing (MD-SCFQ). Compared to MD-SCFQ, EFQs have lower complexity and can be easily implemented on chips. We verify the effectiveness of the proposed EFQs through theoretical analysis and give some simulation results.

An adaptive array antenna with optimally formed beams for CDMA

Abstract: The adaptive antenna (AA) or smart antenna for mobile telecommunication especially for code division multiple access (CDMA) systems has developed at an extraordinary pace. Most professional people and related papers centered their attention on the so-called "optimum combining (OC)" AA which is represented by algorithms using least mean squares (LMS) and recursive least squares (RLS). These types of AA were able to provide an optimum signal to interference plus noise ratio (SINR), through the use of a desirable antenna radiation pattern whose mainlobe pointed towards the desired signal while the nulls pointed towards the source of interference. For computing these adaptive algorithms, the requirements of the CPU time and the memory usage are proportional to the number of antenna elements, and speed of computations depends on the velocity of the mobiles. Finally, there is a restriction on the number of users. In order to avoid the above shortcomings, this paper proposes a type of AA which is close to the category of "direction finding (DF)" AA, but it is a "beam forming in advance" array antenna with super low sidelobes. This AA possesses similar adaptive functions as found in the OCAA, but without the computation of complex weight vectors. When this AA is operating only a few computational procedures are needed. Another advantage of this AA is that it does not mind whether the number of users M is much larger than the number of antenna elements N or not.

A PHB reservation mechanism in DiffServ network

Abstract: A new DiffServ per-hop behavior (PHB) reservation protocol (DPRP) is proposed to support the end-to-end QoS guarantee in a DiffServ network through several domains. It is a reservation mechanism that inherits the advantages of RSVP but is a lightweight version of RSVP. DPRP transports and negotiates the QoS requirement between sources and destinations as well as reserves PHB for service levels in each DS domain. It negotiates a dynamic service level agreement (SLA) between various domains efficiently and guarantees the end-to-end QoS of the DiffServ network. Essential principles and advantages of DPRP are presented.

Investigation of a combined power control scheme for a time-division duplex CDMA system

Abstract: Time-Division Duplex (TDD)-CDMA technique is now accepted as a candidate of 3/sup rd/ generation mobile communication system (IMT-2000). As for Code Division Multiple Access (CDMA) system, power control is essential to mitigate the "Near-Far" effect and improve the system performance. A TDD system requires a special power control scheme due to its link characteristics. In this paper we present a combined power control in TDD and also investigate its performance by computer simulations. The simulation results show that the proposed power control scheme can overcome the deficiency of open-loop power control and work well in a TDD-CDMA scenario.

The electrical and mechanical performance of corroded products on gold plating after long term indoor air exposure

Abstract: The corroded products formed on gold plating after long term indoor air exposure appear as a set of concentric black rings surrounding a large corroded core on top of a pore. A visible stain is frequently observed between and even beyond the rings. Dust particles also distribute on the exposed coupons. All of these insulated products cause high probability of static contact failure. Concentration of the corroded composition increases and decreases as the morphology is changed from the core to the rings. The contact resistance also goes up and down the same way as the composition alternates, which is high on both the core and the concentric rings, but low on the stained areas among the core and the rings. The contact resistance on the dark stains also fails, which seriously increases the failure probability. It is found that the wearing out of the products which reduces the contact resistance depends on the normal force, geometry of the contact pairs and shearing strength of the corroded products. The effect of pores on contact reliability is much more serious than was predicted previously, especially in low signal applications.

Fingerprint classification based on fractal analysis

Abstract: A new algorithm using the discrete fractal Brownian motion to classify fingerprint images is presented. It computes certain fractal parameters in a sub-fingerprint image and performs a mask-based classification. Experimental results demonstrate that this method provides a classification scheme that performs well and is more noise resistant than the traditional schemes.