An improved movement-based registration scheme reduces location update cost on conventional movement-based location update scheme but increases uncertainty of the position of a mobile terminal (MT). The effect of this uncertainty of the MT position on the paging cost of the improved movement-based registration scheme is analyzed. We show that the paging cost of the improved movement-based registration scheme in [2] is underestimated, especially for large values of movement threshold. The result shows that the underestimation cannot be ignored.

In this paper, a new narrowband beamformer with derivative constraint is developed for wideband and coherent jammers suppression. The so-called IQML algorithm with linear constraint, which is used to estimate the unknown directions of the jammers in signal-free environment, is shown to be an inappropriate constraint estimator. In this paper, a new IQML algorithm with a norm constraint is considered, which is a consistent estimator and can be used to achieve desired performance. It can be also employed in the CDMA system for MAI suppression. We show that it outperforms the approach with the linear constraint used in the narrowband beamformer, in terms of directional pattern, output SINR and nulling capability for wideband and coherent jammers suppression.

This paper describes an analytical method to estimate the amount of interference in multibeam non-geostationary satellite systems. The performance of CDMA is compared with that of FDMA (or TDMA) by employing the maximum acceptable number of users per cell in uplink as a measure. Numerical examples shows that the maximum acceptable number of users in FDMA (or TDMA) systems varies according to the altitude of the satellites, while the performance is insensitive to the altitude in CDMA systems. Then, it is found that the superior multiple access scheme depends on the altitude of the satellite.

In DS-CDMA mobile radio communications systems, transmit power control (TPC) is indispensable to regulate the variations in the received signal power produced by multipath fading. However, a practical TPC raises and lowers the mobile transmit power only at discrete time instants (the TPC rate is on the order of 1-2 kHz) and by a finite step size of the order of 1 dB. Therefore, TPC cannot completely compensate the received signal power variations and hence, the transmission performance degrades in a fast fading channel. The objective of this paper is to understand how TPC acts in a fast fading channel with antenna diversity reception and, based on this understanding, to model the TPC operation.

The potential role of a network in improving end-to-end TCP control is considered. Communications in the high-speed network age are revealing the limitations of end-to-end TCP control. Especially, fairness among TCP connections is one such example. Solving these problems requires not only end-to-end control but also active network control. A brief overview of related work is given, followed by the proposal of a method for adjusting the Ack interval based on network information. The principle of our algorithm is based on the relationship between TCP transmission rate at TCP sources and Ack packets intervals from the bottleneck router. Our algorithm implicitly controls transmission rate of TCP sources. Special focus is given to a scenario in which a networks has a bottleneck at a router. Simulation based on the proposed interworking algorithm, called AckAdjust, showed a good end-to-end TCP performance as to fairness between multiple TCP connections in various cases.

In the Internet, flow analysis and network monitoring have been studied by various methods. Some methods try to make TCP (Transport Control Protocol) traces more readable by showing them graphically. Others such as MRTG, NetScope, and NetFlow read the traffic counters of the routers and record the data for traffic engineering. Even if all of the above methods are useful, they are made only to perform a single task. This paper describes an improved TCP Protocol Machine, a multipurpose tool that can be used for flow analysis, intrusion detection and link congestion monitoring. It is developed based on a finite state machine (automaton). The machine separates the flows into two main groups. If a flow can be mapped to a set of input symbols of the automaton, it is valid, otherwise it is invalid. It can be observed that intruders' attacks are easily detected by the use of the protocol machine. Also link congestion can be monitored, by measuring the percentage of valid flows to the total number of flows. We demonstrate the capability of this tool through measurement and working examples.

Although TCP is widely used in the Internet, new specifications are still proposed and implemented. In the circumstance above, it is highly possible that some errors are detected on the communication between new and old implementations. Several test tools were developed so far. However, they do not have enough functions to allow test operators to modify test sequences suitable for their test purposes. We have developed a TCP tester which generates test sequence using test scenario. The tester performs exceptional TCP protocol behavior only when the condition specified in the test scenario is satisfied. Otherwise, it performs normal TCP behavior. The tester is implemented by modifying TCP module of NetBSD with SACK code developed by Pittsburgh Supercomputing Center. We have also evaluated implementations of congestion control and SACK algorithms using the tester.

In recent years, requests for new advanced features, decentralization, and improvements in the forwarding speed, have been made for IX. A new IX architecture using MPLS (Multiple Label Switching) technology (MPLS-IX) is proposed to solve these requirements and rectify the problems. In this paper, a comparison between current IX and MPLS-IX based on router's packet forwarding performance is examined, and the feasibility of MPLS-IX is discussed. Moreover, the QoS requirements to provide IX service are discussed.

This paper describes two digital correction algorithms for ADC nonlinearity, targeted for mixed-signal LSI tester applications: an interpolation algorithm and a stochastic algorithm. Numerical simulations show that our algorithms compensate for ADC nonlinearity as well as missing codes and nonmonotonicity characteristics, and improve ADC SNDR and SFDR.

In this paper, we propose an adaptive algorithm for an IIR adaptive line enhancer (ALE) based on constrained FIR ADF. The two constraints that are considered are the unit norm constraint and zeros constraint. By incorporating these two constraints, we show that the effect of a white disturbance signal on the convergence of the ALE is eliminated in the mean sense. The mathematical analysis for exact modeling also indicates that there exists a solution, which gives perfect estimation of the frequencies of the sinusoidal signals. Furthermore, by using a sufficiently small step size and introducing a control mechanism, the convergence of a second order ALE is guaranteed even if there is a sudden change in the frequency of the input sinusoidal signal. Simulation results that are presented, verify these properties.

Based on a modified step-by-step decoding procedure, a high-speed pipelined Reed-Solomon decoder is presented. The decoder requires only the delay time of three 2-input XOR gates for decoding each coded symbol. The decoder can be operated in a bit rate of Gbits/sec order and thus suitable for the very high speed data transmission systems.

This paper presents a hardware-efficient architecture of tree-depth scan (TDS) and multiple quantization (MQ) scheme for zerotree coding in MPEG-4 still texture coder. The proposed TDS architecture can achieve its maximal throughput to area ratio and minimize the external memory access with only one wavelet-tree size on-chip buffer. The MQ scheme adopts the power-of-two (POT) quantization to realize a cost-effective hardware implementation. The prototyping chip has been implemented in TSMC 0.35 µm CMOS 1P4M technology. This architecture can handle 30 4-CIF (704576) frames per second with five spatial scalability and five SNR scalability layers at 100 MHz working frequency.

In 1999, Araki et al. proposed a convertible limited verifier signature scheme. In this letter, we propose a universal forgery attack on their scheme. We show that any one can forge a valid signature of a user UA on an arbitrary message.

This paper presents a framework for modeling and mixed-mode simulation of circuits/interconnects and electromagnetic (EM-) radiations. The proposed framework investigates the signal integrity in VLSI chips, packages and wiring boards at the GHz-band level, and verifies the electromagnetic interference (EMI) and the electromagnetic compatibility (EMC) of high-speed systems. In our framework, the frequency characteristics of interconnects and EM-radiations are extracted by the full-wave FDTD simulation. The macromodels of interconnects are synthesized as SPICE subcircuits, and the impulse responses of EM-radiations are stored in the database. Once the macromodels are synthesized, the circuit simulation with the consideration of EM-effects can be performed by using SPICE. The EM-field distributions can be also easily calculated by taking convolutions of pre-simulated EM impulse responses and the SPICE results.

This paper presents a miniaturized reverse-phase hybrid ring by the use of shunt capacitors, and successfully designs a very miniature hybrid ring of a 0.28-wavelength circumference with a wide bandwidth comparable to the regular reverse-phase hybrid ring based on the equivalent admittance approach. Moreover, a method of broadening the bandwidth with adding a matching network consisting of a very short transmission line and two shunt capacitors at each port is also described. The validity of the proposed design is demonstrated by electromagnetic simulator (Sonnet em) for a uniplanar hybrid ring.

Ray tracing is an efficient method for analyzing transmission characteristic of indoor wireless systems. However for simulating the transmission characteristic, using a path profile obtained by ray tracing, calculation times become enormous and there is no good theoretical model which can link a path analysis result with digital transmission characteristics evaluation. To overcome such problems, in this paper, a simple calculation method on spatial distribution of error occurrence due to intersymbol interference (ISI) based on "the equivalent transmission-path (ETP) model" is proposed. The ETP model is a technique that can simply estimate statistics of errors due to ISI that arise in Rayleigh and Nakagami-Rice fading environments. If a simple calculation method proposed in this paper is used, calculation time of digital transmission characteristics evaluation become tremendously shorter and results of this method agree with those of exact simulations with sufficient accuracy.

As multimedia and high-speed traffic become more popular on the Internet, the various traffic requiring different qualities of service (QoS) must co-exist. In addition, classified services based on Diff-Serv (Differentiated Service), MPLS (Multi-Protocol Label Switching), etc., have come into wide use. Today's Internet environment requires routers to perform control mechanisms in order to guarantee various QoSs. In this paper, we propose a smart buffer management scheme for the Internet router that uses hierarchical priority control with port class and flow level. Furthermore, since the proposed scheme must operate at very high speed, we first propose several design policy for high speed operation and the hardware implementation is performed in VHDL code. Implementation results show that the proposed scheme can scale with high-speed link, achieving the maximum rate of 4.0 Gbps by using the 3.5 µm CMOS technology.

This study investigates the anisotropy substrate and dielectric cover effects of the rectangular microstrip patch antenna on anisotropy substrates with air gap, based on rigorous full-wave analysis and Galerkin's moment method. Results show that the resonant frequencies in the variation of air gap, patch length, and permittivity of superstrate can be determined and analyzed with varying dielectric cover thickness.

A scalable MOSFET parasitic model has been studied using 0.13 µm standard CMOS process. The model consisted of a core BSIM3v3 transistor model and parasitic resistor, capacitor, inductor, and diode. All parasitic components' values were automatically calculated by transistor geometrical parameters, only gate length (Lg), gate width (Wg), and gate multiple numbers (Mg), and some fixed process parameters such as sheet resistance of each part of diffusion layer. This model was confirmed for 0.25 µm to 0.5 µm gate length, 10 to 40 gate multiples with 5 µm gate finger width (Wf), 0.8 V to 1.5 V gate-source voltage (|Vgs|) with 0.6 V threshold voltage (|Vth|), and 1.0 V to 2.5 V drain-source voltage (|Vds|) from the viewpoint of small signal. The measured s-parameter and simulated one are in fairly good agreement in 200 MHz to 20 GHz frequencies range. This model is very simple, scalable, and convenient for RF circuit designers without difficult parameter setting.

TCP congestion control is receiving increased attention in recent years due to their usefulness for network stability, robustness use of network buffer and bandwidth resources on an end-to-end per-connection basis. The RED scheme was designed for a network where a single dropped packet is sufficient to signal the presence of congestion to the TCP protocol. This paper applies matrix-analytic approach to analyze both the long-term and the short-term drop behaviors of a queue with RED scheme and uses this model to quantify the benefits brought about by RED. The result shows that the drop probability between RED and Drop-Tail is very close under heavy load conditions. This indicates that RED not only can resolve the synchronization problem but also has the same loss performance with Drop-Tail scheme under the heavy load circumstances. Our findings also show that the rate oscillation behavior of RED is better than Drop-Tail when TCP applies the additive-increase and multiplication-decrease mechanism. As a consequence, it can help reduce the required buffer capacity in the RED router.