Method of measuring disturbances at telecommunication ports has been published by IEC/CISPR. A method using both disturbance voltage and current probes is useful because it does not require any impedance stabilization networks (ISNs). In this paper, the values measured using this method are theoretically and experimentally compared with those measured using ISNs. An experiment using a simple circuit model presents that the value obtained by using this method is lower than that by using ISNs in some cases. A theoretical analysis however derives that the estimated value by adding the margin to the measured value is always guaranteed to be large compared with the value measured by ISNs. The analysis also indicates that the margin is dependent on the deviation of phase angle of ISN and can be calculated by a simple equation. The experiment using actual equipment shows that the estimated results including the margin is always larger than those measured by ISNs. The results of the study show that the method using both disturbance voltage and current probes can be used for measuring the disturbances by taking the margin into account, and this margin can be reduced by improving the phase angle characteristics of the common mode impedance of ISNs.

In this paper, we discuss the performance and computational complexity of modulo-type Viterbi decoder (MVD) for high-speed digital transmission applications. It is shown that the MVD, which is a combination of modulo operation and Viterbi decoder at the receiver, has the same performance as a conventional Viterbi decoder (CVD) with extended constellations. We also show by complexity analysis that the MVD in conjunction with the Tomlinson-Harashima (TH) precoder at the transmitter reduces the system complexity significantly as compared to the CVD. The performance of the digital subscriber line (xDSL) system employing the MVD is investigated in the presence of near-end crosstalk (NEXT) and impulsive noise.

This paper proposes three MAC protocols over APON to provide residential and small business customers with multimedia services. The proposed protocols support the frame structure of ITU-T recommendation G.983.1 and also provide diverse ATM service classes such as CBR, rtVBR, nrtVBR, ABR, and UBR traffics. Each service is allocated on the basis of priority. Especially, for allocating CBR and rtVBR services, each protocol uses different cell arrival timing information which is achieved with specific coding and ranging procedure. Focusing the difference of cell arrival timing information, we will investigate the performance of proposed protocols. For the proposed MAC protocols, we present grant field format, minislot format, and bandwidth allocation algorithm. Computer simulation shows the performance of the proposed protocols in terms of CDV and delay, comparing with the normal FIFO protocol.

In this paper we propose a new timing and phase recovery algorithm to mitigate the inter-symbol interference (ISI) effect and to increase the permissible data rate. We use the mean excess delay of the channel as the timing instant for sampling no matter what symbol rates are transmitted and use the phase of the complex baseband impulse response sampled at the corresponding instant as the carrier phase for compensation. The mean excess delay of a channel is independent of the data transmission rates and can be estimated by the conventional timing recovery circuit by transmitting a low rate data sequence with symbol interval longer than the channel delay spread. We have numerically compared the transmission performances without and with applying our proposed algorithm in the timing and phase recovery. We also compare the transmission performance of the decision feedback equalizer (DFE) when the inputs to the DFE are sampled by the conventional method and by our proposed method. We found that the new scheme has a better performance. Compare with the conventional method, the normalized permissible data rate at a BER threshold of 10^-5 and an outage probability of less than 2% can be increased by 5 times. While the new scheme is employed together with DFE, the performance can be further improved. Simulation results for both simulated and physical channels have verified the effectiveness of the new scheme.

To enhance throughput and reuse bandwidth, clustering techniques can effectively manage nodes in multi-hop wireless networks. However, in such networks, hidden terminal interference degrades the system performance and increases the average packet delay time. Therefore, this work presents novel two-level cluster-based code assignment techniques to resolve the hidden terminal problems. At the low level, five basic and an optimized intra-cluster code assignment schemes are developed to calculate the number of codes used in each cluster. At the high level, two inter-cluster code assignment schemes (coarse-grained and fine-grained controls) are proposed to obtain the minimal number of code sets. The merits of our schemes include low execution time, low probability of code re-assignment, and low overhead. Furthermore, the proposed schemes allow us to regionally update orthogonal codes when the topology varies. Experimental results demonstrate that the proposed schemes outperform conventional techniques. Among the five basic intra-cluster code assignment schemes, the ordering criteria of increasing number of one-hop neighbors is the best in terms of the number of orthogonal codes to avoid hidden terminal interference. The optimized intra-cluster code assignment scheme generally obtains fewer orthogonal codes than other schemes. For inter-cluster code assignment schemes, the coarse-grained control has a lower code allocation time. However, the fine-grained control requires fewer orthogonal codes.

A timer-based scheme is proposed to manage information within terminal and service profiles for both incall registration/deregistration of UPT users and incall registration resets of terminal owners. In the timer-based scheme, information related to incall registration for a UPT user in a terminal profile is deleted due to a timer expiration without accessing the terminal profile. The performance of the timer-based scheme is compared with the previously proposed request-based scheme in terms of; 1) total cost and, 2) the number of terminal profile accesses per unit time for a terminal. Even though provision of the timer-based scheme requires the modification of incoming call delivery procedure, the timer-based scheme can reduce both the total cost and the number of terminal profile accesses compared to the previously proposed request-based scheme.

2.4-GHz-band mid-speed (1- to 2-Mbit/sec) wireless LAN systems are being widely used in offices and factories. Electromagnetic interference can occur between these systems because they use the same frequency range. In this paper, we investigate the characteristics of the interference between wireless LAN systems that use direct-sequence (DS) systems and frequency-hopping (FH) systems. The interference characteristics were measured for three DS systems and one FH system that meet the IEEE 802.11 and RCR standards and that use different modulation methods. Our results indicate that throughput depends on the system and the modulation method. We have also developed a model that can be used to calculate the interference characteristics between DS and FH systems by considering the bandwidth of their transmission signals, the dwell time of the FH system, and the time that the DS system needs to transmit a data frame. We used this model to calculate the bit error rate (BER) characteristics of the systems used in our experiment, and the results indicate that BER characteristics depend on the modulation method. The throughput characteristics of the systems used in our experiment were also calculated, and agreed with the experiment results within +/- 5 dB. The throughput characteristics of wireless LAN systems based on IEEE 802.11 were also calculated when the signal level was higher than the receiver noise level. The results show that FH systems require a D/U ratio about 7 or 8 dB higher than the ratio required in DS systems because the parameters in the standard differ between FH and DS systems.

We evaluate the BER performance of the OFDM system with the one-tap equalizer bank under the two-ray multipath channel with the frequency offset by the simple Gaussian analysis method and by a proposed modified Gaussian analysis method. The proposed analysis method considers two adjacent inter-channel interferences, separately, and models the other inter-channel interferences as a Gaussian noise. It is shown that the proposed analysis method affords much closer results to the simulations than those by the simple Gaussian analysis method, when the frequency offset exists.

This paper presents efficient time slot assignment algorithms applicable to the uplink of SDMA system. A frame consists of one control time slot and multiple communication time slots where terminals in different angular positions share the same time slot. In the proposed algorithms, a time slot is assigned to a new terminal considering not only the signal quality of the new terminal but also the signal quality of active terminals. Simple calculation method for estimated signal-to-interference plus noise ratio (SINR) is employed to decrease the computational complexity. The performance of the proposed algorithms is evaluated by computer simulation and compared with sectorized systems to show the validity of the proposed algorithms.

This paper describes the results of a series of laboratory experiments for performance evaluations of our proposed Maximum Likelihood Sequence Estimation (MLSE) based interference canceller, the Interference Canceling Equalizer (ICE), which can cancel both co-channel interference (CCI) and inter-symbol interference (ISI). To verify the feasibility of ICE for the Japanese cellular communications system, a standard of which has been released under the name of Personal Digital Cellular (PDC) system, a prototype system was constructed using 27 TI TMS320C40 Digital Signal Processor (DSP) chips. The ICE prototype works in real-time on the PDC air interface, major specifications of which are π/4 QDPSK 21 k symbols/s 3-channel time-division multiple-access (TDMA). Two-branch diversity reception is used to enhance the signal detection performance of ICE. In the experiments, BER performances were evaluated using the prototype system. Under a single-path Rayleigh fading and a single CCI condition, the ICE receiver attains the BER of less than 310^-2 with the negative values of the average CIR: for f_D = 5 Hz and 40 Hz, the average CIR more than -20 dB and -10 dB, respectively. Under a double-path Rayleigh fading and a single CCI condition, the ICE receiver attains the BER of less than 1.510^-2 with the negative values of the average CIR: for f_D = 5 Hz and 40 Hz, the average CIR more than -20 dB and -10 dB, respectively. The laboratory test results suggest that the ICE receiver has potential for system capacity enhancement.

The reverse-link of the DS-CDMA cellular system requires transmit power control (TPC) and diversity reception. This paper develops the expression of the received signal-to-interference ratio (SIR), and evaluates the outage probability using the Monte Carlo simulation to obtain the link capacity. The link capacities with received signal strength (SS)-based TPC and SIR-based TPC are compared. This paper investigates the required maximum and minimum transmit powers and the capacity gain of the SIR-based TPC over SS-based TPC as well as the effect of the diversity reception on the link capacity and transmit power. The reverse-link capacity is compared with the forward-link capacity to check the balance of capacities between both links.

In this paper, we present an alternative design, RBMoM (Range-Based Mobile Multicast), for efficiently supporting multicast for mobile hosts on the Internet. The current version of Mobile IP proposes two approaches to support mobile multicast, which are remote subscription and bi-directional tunneling. The former provides the shortest routes for delivery of multicast datagrams to mobile hosts; the latter hides host mobility from all other members of the group (therefore, no any overhead in the multicast tree maintenance). RBMoM intends to trade off between the shortest delivery path and the frequency of the multicast tree reconfiguration by controlling the service range of the multicast home agent (MHA). Actually, we will find that remote subscription and bi-directional tunneling are the extremes of RBMoM. From the point of view of the MHA and the service range concepts, RBMoM is a generalization of both approaches and a unifying mobile multicast approach. The simulation results show that RBMoM can adapt to the fluctuation of both host movement and the number of mobile group members, and has much better performance than the current two IP mobile multicast solutions.

The paper proposes a transmitter diversity scheme with a desired signal selection for the mobile communication systems in which the severe cochannel interference (CCI) is assumed to occur at the base station. The feature of the proposed scheme is that the criterion of the downlink branch selection is based on the desired signal power estimated by the correlation between the received signal and the unique word at the matched filter. Moreover, the unique word length control method according to the instantaneous SIR is applied to the proposed scheme, taking account of the uplink transmission efficiency. Computer simulation results show that the proposed scheme provides the better performance than the conventional transmitter diversity in the severe CCI environments, and that the unique word length control method applied to the proposed scheme decreases the unique word length without the degradation of the transmission quality, comparing with the fixed unique word length method.

We consider a dynamically reconfigureable network where dynamically changing traffic is offered. Rearrangement and adjustment of network capacity can be performed to maintain Quality of Service (QoS) requirements for different traffic classes in the dynamic traffic environment. In this work, we consider the case of a single, dynamic traffic class scenario in a loss mode environment. We have developed a numerical, analytical tool which models the dynamically changing network traffic environment using a time-varying, fluid-flow, differential equation; of which we can use to study the impact of adaptive capacity adjustment control schemes. We present several capacity adjustment control schemes including schemes which use blocking and system utilization as means to calculate when and how much adjustment should be made. Through numerical studies, we show that a purely blocking-based capacity adjustment control scheme with a preset adjustment value can be very sensitive to capacity changes and can lead to network instability. We also show that schemes, that uses system utilization as a means to calculate the amount of capacity adjustment needed, is consistently stable for the load scenarios considered. Finally, we introduce a minimum time interval threshold between adjustments, which can avoid network instability, in the cases where the results showed that capacity adjustment had been performed too often.

In order to ease the impact of the packet fragmentation problem and to avoid network congestion in TCP over UBR, packet discard schemes in ATM layer (such as PPD and EPD) have been proposed. These schemes drop packets before they reach their intended destinations if the network is congested and the packets are to be partially discarded. On the other hand, TCP also regulates data flow with its own flow control method. Due to restriction of data flow at the TCP layer, buffer space is not fully used in an ATM switch. In order to make use of more buffer resources, this paper generalizes the PPD and EDP schemes. From this generalization, an optimistic packet discard scheme named the "Probability-Based Delayed Packet Discard" (PDPD) scheme is proposed. Depending on a particular probability, this scheme sets a discard flag to delay actual discard operation. This paper presents the results of several simulated models to find out the potential of improvement of goodput by PDPD. The results of these simulations indicate that PDPD obtains higher goodput than ordinary schemes when the packet size is large and the input load is not light. This author concludes that a PDPD scheme should achieve effective goodput and link utilization while using more buffer resources effectively.

In this paper, we investigate the performance of Fast Reservation Protocols (FRP) for burst-level bandwidth allocation in ATM networks. FRP schemes can be classified into delayed transmission (DT) and immediate transmission (IT) methods according to reservation procedure. Moreover, according to the responsibility for negative acknowledgment (NAK) cell generations when burst blocking occurs, FRP schemes can be further classified into blocking node NAK (BNAK) and destination node NAK (DNAK) schemes. We analize the FRP schemes with different reservation and NAK methods for single node and multihop network models, respectively. We then discuss the dependence of performance for each FRP scheme on propagation delay, peak rate, and the number of hops.

It is always difficult to monitor stringent cell loss ratio (CLR), e.g. 10^-9, in asynchronous transfer mode (ATM) networks, because its measurement period is too long for real-time measurement. In this paper, we propose new performance monitoring mechanisms for stringent CLR. We consider virtual ATM switches whose resources are much smaller than the real system and thus much higher CLRs will be obtained within a relatively short measurement period. By applying some regression methods in the CLRs obtained from the virtual system, we can estimate the actual CLR of the real system quite accurately and our performance monitoring mechanisms will be operated based on the estimation. Through the numerical examples, our mechanisms are not only more accurate than the traditional methods, but also have shorter measurement periods compared with direct measurement.

While spatial reuse in a high-speed ring increases the throughput performance, it leads to a fairness problem in distributing the network bandwidth among distinct nodes. To alleviate this problem, fairness control algorithms based on a packet window have been developed. Under these algorithms, satisfied nodes are forced to pass empty slots to starved downstream nodes until their windows are refilled by a reset signal. This regulation incurs a bandwidth waste corresponding to the travel distance of those empty slots. In this paper, a waste-free fairness control method based on a two-layer window composed of the cycle and packet windows is developed. Using the proposed method, packets allocated to multiple fairness cycles are simultaneously transferred and, in consequence, the otherwise wasted bandwidth can be reused to carry, in advance, packets allocated to future fairness cycles. This method is applied to two typical ring protocols with only the packet window, ATMR and MetaRing, and their performances are investigated. The simulation results show that the cycle window is very effective to improve the performance of the ATMR and MetaRing protocols.

This paper presents an error resilient H.263 video compression scheme over noisy channels. The start codes in the H.263 bit stream syntax, which inherently provide the resynchronization functionality for error handling, may cause significant error damage if they are incorrectly decoded. Therefore, we develop a video segment regulation algorithm at the decoder to efficiently identify and correct erroneous start codes and block addresses. In addition, the precise error tracking technique is used to further reduce the error propagation effects. After performing the video segment regulation, the decoder can report the exact addresses of detected corrupt blocks back to the encoder via a feedback channel. With these negative acknowledgments, the encoder can precisely calculate and trace the propagated errors by examining the backward motion dependency for each pixel in the current encoding frame. With this precise tracking strategy, the error propagation effects can be terminated completely by INTRA refreshing the affected blocks. Simulation results show that the proposed scheme yields significant video quality improvements over the motion compensated concealment by gains of 4.1 to 6.2 dB PSNRs at bit rate around 35 kbps in error-prone DECT environments. In particular, this scheme complies with the H.263 standard and has the advantages of low memory requirement and low computation complexity that are suitable for practical real-time implementation.

In this letter, we introduce new parameters for classifying digitally modulated unknown QAM and PSK signals. Our two parameters for the classification are the variance of magnitude ratios and the mean of mod 2π phase differences. The gain adjustments of amplitudes are not required for the classification. Five different types of QAM constellations and three different types of PSK constellations are tested and the characteristics of our classification parameters are investigated in various SNR environments. Simulation results demonstrate the effectiveness of our proposed technique.

The authors propose and experimentally demonstrate an all-optical exclusive OR (XOR) logic gate based on self-phase modulation (SPM) of a semiconductor optical amplifier (SOA). The scheme is insensitive to the polarization of the input signal and requires no additional synchronized clock. The output of the XOR gate showed the contrast ratio of more than 17 dB for the input signal at 2.5 GHz.

The distribution for the envelope of the received signal over frequency-nonselective slow fading channels with additive white Gaussian noise (AWGN) is derived in this paper. System performances of noncoherent M-ary signals over slow and flat fading channels in the presence of AWGN can be evaluated from the new probability density function (PDF) of the envelope.

In this paper, a new expression is derived for the bit error rate (BER) performance of Gray-encoded MDPSK for M=2 and 4 in orthogonal frequency division multiplexing (OFDM) systems over time-variant and frequency-selective Rayleigh fading channels. We assume that the guard time is sufficiently larger than the delay spread to solve the intersymbol interference (ISI) problem on the demodulated OFDM signal. In this case, the performance depends on the Doppler spread of fading channel. The closed form expression for the bit error probability of MDPSK/OFDM extended from the result in [5] shows that the BER performance of MDPSK is determined by (N + N_G ) f_D T_s where N is the number of subchannels, N_G the length of the guard interval, f_D the maximum Doppler frequency, and T_s the sampling period. The theoretical analysis results are confirmed by computer simulations for DPSK and QDPSK signals.

This paper investigates the asymptotic error rate behaviour for noncoherent OOK signalling scheme in the presence of Nakagami-m fading. A transcendental equation to compute the optimum threshold level is also derived. Comparison on trends in optimum threshold level and its corresponding ratio of the Mark and Space error probabilities between different channels are presented.

The transmission S-parameter, S₂₁, between dipole elements on a rectangular finite ground plane is calculated by the MoM with planar-segments in the horizontally and vertically polarized configurations. Supposed a 1/10 scaling, the frequency range is selected 0.15-0.8 GHz. The size of the finite ground plane is 40 cm 100 cm. The dipole-element length is 18.8 cm (half-wavelength at 0.8 GHz). The distance between dipole elements is 30 cm. The results are compared to the calculated results with the conventional MoM-GTD hybrid method and also the measured results with a TRL-calibrated network analyzer. It makes clear that the MoM-GTD hybrid method is not applicable to a small ground plane in the vertically polarized configuration. The results calculated by the MoM with planar-segments agree well to the measured results both in the horizontal and vertical polarizations. The results show that the size of the finite ground plane for the vertical polarization should be much larger than for the horizontal polarization.

A modified moving DFT algorithm and a new SMTD structure are proposed in this paper. The new SMTD structure adopts both batch-mode signal channel estimating and the modified moving DFT algorithm, which leads to dramatic decline of the computational load.