Discrete-time queueing models have been studied for many years because of their direct applicability in the performance evaluation of digital communication system and networks, where buffers are used to temporarily store information packets which cannot be transmitted instantaneously. In this paper, we investigate the behavior of a discrete-time multiserver buffer system with infinite buffer size. Packets arrive in the system according to a two-state correlated arrival process. The service times of the packets are assumed to be independent and identically distributed according to a geometric distribution. We present an analytical technique, based on the use of generating functions, for the analysis of the system. Explicit expressions are obtained for the mean values, the variances and the tail distributions of the system contents and the packet delay. The influence of the various model parameters on the behavior of the system is shown by means of some numerical examples.

In this paper we present a new type of CMOS Time-of-Flight (TOF) range image sensor based on CMOS Active Pixel Sensor (APS) techniques. The TOF sensor features high-speed and efficient photo-charge transfer that is essential in range imaging. The rapid and efficient charge transfer is made possible by the use of a high-gain inverting amplifier and capacitors connected alternatively to the feedback path. This leads to the cost-effective implementation of the system. The analysis of simulation results suggests that the proposed technique can achieve a sufficient range resolution of millimeters to centimeters depending on the maximum measured range, if the noise is dominated by photon shot noise.

We have developed a two-dimensional flat-panel imager (FPI) utilizing conventional amorphous silicon (a-Si) thin film transistor (TFT) technology for AM-LCDs, and we have made a prototype. We can experimentally manufacture the FPI basically by utilizing conventional production lines of AM-LCDs, because the imager is based on the TFT array for AM-LCDs. The TFT performs both switching and photo-detecting functions itself. Using the FPI, we can capture monochrome images in real time, and can also achieve full-color images by introducing time-sequential driving based on a color backlight system with RGB-LEDs. The reliability of the TFT under bias and irradiation stress caused by capturing images is maintained by introducing an original driving method and processing the captured image. By making use of advantages the FPI has over conventional imaging systems, we hope that the FPI will be a useful compact imaging device for documents, pictures, fingerprints, and the like.

Next generation wireless networks are expected to support multimedia applications (audio phone, video on demand, video conference, file transfer, etc.). Multimedia applications make a great demand for bandwidth and impose stringent quality of service (QoS) requirements on the wireless networks. In order to provide mobile hosts with high QoS, efficient and better bandwidth reservation is necessary in multimedia wireless networks. This paper presents a novel hybrid dynamic-grouping bandwidth reservation scheme to support QoS guarantees in the next generation wireless networks. The proposed scheme is based on probabilistic resource estimation to provide QoS guarantees for multimedia traffic in cellular networks. We establish several reservation time-sections, called groups, according to the mobility information of mobile hosts (MHs) of each base station (BS). The amount of reserved bandwidth for each BS is dynamically adjusted for each reservation group. We use the hybrid dynamic-grouping bandwidth reservation scheme to decrease the connection-dropping probability (CDP) and connection-blocking probability (CBP), while increasing the bandwidth utilization. The simulation results show that the hybrid dynamic-grouping bandwidth reservation scheme provides less CDP and less CBP, and achieves high bandwidth utilization.

This letter presents a novel video and audio PTSs self-adaptive interlace strategy in MPEG-2 transport stream. By adaptive regulating the relative position of audio and video access units in bit-stream according to their PTSs, the proposed strategy provides reliable video and audio synchronization.

This paper investigates a random-interleaver-based approach to space-time coding. The basic principle is to employ a good forward error correction (FEC) code and transmit randomly interleaved codewords over an antenna array. A low-cost estimation technique is considered. The complexity involved grows only linearly with the number of transmit antennas. Near-capacity performance can be achieved with moderate complexity.

This letter presents a new probability expression for a multi-carrier (MC) DS/CDMA acquisition system with a reference matched filter (RMF). To evaluate the mean acquisition time (MAT) as a measure of the system performance, the probabilities of detection, miss, and false alarm are derived. From the results, it is shown that the MAT of the MC-CDMA hybrid system with RMF is comparable to the optimum mean acquisition time of the conventional MC-CDMA hybrid system, maintaining approximately the same degree of structuring complexity.

In this paper, we evaluate the performance of single- and multi-antenna multi-carrier code division multiple access (MC-CDMA) downlink (base station to mobile terminal) systems in single- and multi-cell environments. We first propose a minimum mean square error (MMSE) filter with a Gaussian approximation for a single input single output (SISO) MC-CDMA downlink system. Then, we apply it to a SIMO (single input multiple output) system with a conventional turbo coding. Furthermore, we compare the performance of SISO (11) and SIMO (12) MC-CDMA systems with that of a multiple input multiple output (MIMO) (22) system employing space-time turbo coded modulation (STTuCM) in a multi-cell environment with 7 cells by computer simulation. Based on the computer simulation results, it is found that the considered MIMO system can achieve twofold capacity with the same transmission power in the multi-cell environment.

Unitary space-time modulation (USTM) is well-tailored for flat fading channels where neither the transmitter nor the receiver knows the fading coefficients. A systematic approach to designing USTM is proposed by Hochwald et al., which is not guaranteed full diversity and difficult to put into practice due to the large number of signal points in the two-dimensional constellation. Consequently, we modify the systematic method to search new unitary space-time coded 8PSK with full diversity. Simulation results indicate that the error performances of the searched codes are better than or at least the same as those of the USTM in [2].

All-optical switching is of considerable interest, since it enables the construction of large-capacity networks with protocol- and bit-rate-independent transmission. In this paper, we determine the most desirable of three all-optical architectures for a backbone network, by comparing the following architectures: the wavelength-routed network, the slotted wavelength-routed network, and the optical burst switching network. After proposing an optical path accommodation algorithm that minimizes the total fiber length, we evaluate the total network cost in order to compare the availability of the first two architectures. We then compare the architectures in terms of the burst blocking probability in order to clarify the effectiveness of the third architecture.

We design a DAB system using space-time coding for reliable transmission in the multipath fading channel. This letter assess the performance evaluation of space-time coded DAB system. For channel estimation in the space-time coded DAB system, we introduce two training sequences and derive the mean square error of each training sequence. We then represent the average symbol error rate of the space-time coded DAB system for the specific cases of two, three, four transmit antennas.

In this paper, Pre-Rake scheme for pulse based Ultra Wideband impulse radio (UWB-IR) communications system is proposed considering a standardized UWB channel model from IEEE 802.15 SG3a, which is based on an extensive set of short-range indoor channel measurements. Two kinds of pulse waveforms are taken in account here, namely, Gaussian mono-pulse and newly designed Prolate Spheroidal Wave Functions (PSWF) pulses corresponding to FCC Spectrum Mask. The Pre-Rake scheme is shown to contribute to the low-power, cost-efficient UWB system designing as well as Rake combining gain. Instead of building a Rake receiver at the receiving side (e.g. portable unit), the transmitter (e.g. access point) can pre-combine the UWB signal before transmission in the forward link by estimating the channel impulse response from the reverse link. While the Pre-Raked signal is convolved with the estimated channel impulse response, the function of Rake combination at the receiver is automatically performed. Meanwhile, in order to defeat inter-pulse-interferences (IPI) caused by severe multipath fading conditions, adaptive guard-time scheme for consecutive pulses is proposed as well. Monte-Carlo simulations are carried out to compare the Pre-Rake with Rake results and show that Pre-Rake scheme is as good as Rake combining for both types of pulse waveforms. Then the mobile or portable unit with a conventional receiver can still achieve the diversity gain of Rake combination. Moreover, the effects of placing guard-time between pulses are also verified.

In this paper we consider an approximation method of a formal linearization which transform time-varying nonlinear systems into time-varying linear ones and its applications. This linearization is a kind of a coordinate transformation by introducing a linearizing function which consists of the Chebyshev polynomials. The nonlinear time-varying systems are approximately transformed into linear time-varying systems with respect to this linearizing functions using Chebyshev expansion to the state variable and Laguerre expansion to the time variable. As applications, nonlinear observer and filter are synthesized for time-varying nonlinear systems. Numerical experiments are included to demonstrate the validity of the linearization. The results show that the accuracy of the approximation by the linearization improves as the order of the Chebyshev and Laguerre polynomials increases.

In this paper, we propose a set of broadcast streaming protocols designed for unidirectional radio channels. Considering the limited size and implementation overhead on a mobile terminal, the proposed protocol set is almost compliant with the current mobile streaming protocols, i.e. 3GPP PSS (Packet-switched Streaming Service), except for that the proposed protocols are designed to work on a unidirectional downlink channel. This protocol set enables flexible layout rendering by SMIL (Synchronized Multimedia Integration Language) in combination with SDP (Session Description Protocol), and reliable and synchronized static media (including still image and text) delivery by RTP (Real-time Transport Protocol) carousel. We present the prototype of this protocol set and measure its performance of video quality and waiting time for video presentation through a W-CDMA radio channel emulator and header compression nodes. From the experimental results, we show 1) trade-off between video quality and waiting time, 2) advantage and disadvantage of header compression, 3) effectiveness of synchronized transmission of SDP, SMIL, and I-frames of video objects, and 4) reliability of RTP-carousel. This protocol set is applicable to 3G MBMS (Multimedia Broadcast/Multicast Service) streaming service.

The hardware implementation of a neural network model using stochastic logic has been able to integrate numerous neuron units on a chip. However, the limitation of applications occurred since the stochastic neurosystem could execute only discrete-time dynamics. We have contrived a neuron model with continuous-time dynamics by using stochastic calculations. In this paper, we propose the circuit design of a new neuron circuit, and show the fabricated neurochip comprising 64 neurons with experimental results. Furthermore, a new asynchronous updating method and a new activation function circuit are proposed. These improvements enhance the performance of the neurochip greatly.

This paper proposes the joint beamforming space-time block coding (JBSTBC) scheme for multi-input multi-output (MIMO) communication systems. To enhance the order of spatial diversity in presence of deteriorate fading correlations as well as inter-substream interferences, the proposed JBSTBC method employs joint eigen-beamforming technique together with the block-ordered layered detector (BOLD) for MIMO-STBC. In order to confirm the superiority of the proposed JBSTBC method, computer simulations are conducted in highly correlated fading situations while providing detailed mathematical derivations for clarifying functionality of the proposed scheme.

In this paper, we propose the Synchronized Mobile Multicast (SMM) scheme for the real-time multimedia service to achieve three most important characteristics that the traditional Home Subscription (HS) and Remote Subscription (RS) mobile schemes cannot support. First, the SMM scheme supports the scalable one-to-many and many-to-many synchronized multimedia multicast on mobile IP networks to achieves seamless playback of continuous media streams even when both the mobile sender and receivers handoff simultaneously. Second, it analyzes the minimal buffer requirements of the mobile sender, the core router, the foreign agents and the mobile receivers in the multicast tree and formulates the initial playback delay within a handoff Guarantee Region (GR). Further, combined with the fine granularity scalability (FGS) encoding approach in the MPEG-4 standard, the SMM scheme achieves superior multimedia QoS guarantees and unlimited numbers of handoffs of the mobile sender and receivers only at the cost of degraded video quality for a short period after handoff with minimal extra bandwidth.

This paper describes a real-time blind source separation (BSS) method for moving speech signals in a room. Our method employs frequency domain independent component analysis (ICA) using a blockwise batch algorithm in the first stage, and the separated signals are refined by postprocessing using crosstalk component estimation and non-stationary spectral subtraction in the second stage. The blockwise batch algorithm achieves better performance than an online algorithm when sources are fixed, and the postprocessing compensates for performance degradation caused by source movement. Experimental results using speech signals recorded in a real room show that the proposed method realizes robust real-time separation for moving sources. Our method is implemented on a standard PC and works in realtime.

The issue of guaranteeing Quality of Services (QoS) in a network has emerged in recent years. The Proportional Delay Differentiated Model has been presented to provide the predictable and controllable queueing delay differentiation for different classes of connections. However, most related works have focused on providing this model for a wired network. This study proposes a novel scheduler to provide proportional delay differentiation in a wireless network that includes a multi-state link. This scheduler, Look-ahead Waiting-Time Priority (LWTP), offers proportional delay differentiation and a low queueing delay, by adapting to the location-dependent capacity of the wireless link and solving the head-of-line (HOL) blocking problem. The simulation results demonstrate that the LWTP scheduler actually achieves delay ratios much closer to the target delay proportion between classes and yields smaller queueing delays than past schedulers.

The advanced satellite broadcasting system in the 21 GHz band or higher frequency bands is expected to be suitable for use in high quality multimedia services in the future. To establish this system, rain attenuation mitigation is very important and the time diversity system has been proposed as an appropriate technology for this purpose. This paper shows principle of time diversity as an attenuation mitigation technology and also shows the effect of time diversity. We also propose a method for predicting time diversity gain as a function of the rain attenuation, cumulative time percentage, and time delay of two data contents or broadcasts.