In this paper, we study the performance of a Radio over Free-Space Optical (RoFSO) system for transmitting Code Division Multiple Access (CDMA) signals using aperture averaging (AA) technique, in terms of Carrier-to-Noise-plus- Interference Ratio (CNIR) and outage probability. We propose a modified analytical model for AA, taking into consideration the intermodulation distortion term due to the laser diode nonlinearity and the multiple interference access. By investigating the impact of AA on our model across weak-to-strong turbulence regimes, we show that there is a design tradeoff between the receiver lens aperture and the number of users to achieve a required CNIR ensuring a substantial scintillation fade reduction.

When we use the free space optical(FSO) communication in the near-ground, it will be great influenced by the atmospheric turbulence. There are many studies on the effects of atmospheric turbulence in FSO. Recently gamma-gamma is a widely accepted model for the optical propagating through the atmosphere in normal and strong turbulence. In order to enhance bit error rate(BER) performance influenced by turbulence-induced fading, we promote a new time-diversity scheme which use optical code division multiple access(OCDMA) as channel division code. As we know, time-diversity is an effective method to enhance the throughput performance of wireless communication system. In order to provide a higher performing and cost-efficient solution OCDMA time-diversity scheme is proposed. In this paper, we analyze the performance of the new scheme with gamma-gamma model. We first present the structure of the OCDMA time-diversity scheme. Then we present the temporal covariance of gamma-gamma model to get the independent time-interval of atmospheric turbulence. We use experiment data to confirm theoretical result. At last we give the theoretical analysis on the BER of new scheme, and use numerical results to prove the theoretical analysis. We find that the new OCDMA time-diversity scheme can enhance the BER for several orders in strong turbulence. Furthermore, the performance of the new scheme in strong turbulence is even better than the traditional scheme in normal turbulence.

Motivated by the requirement of processing large datahigh-resolution videos, a research on peer to peer (P2P) large data parallel computing is made. The proposed P2P system is unstructured, completely self-organized and load balanced, which make it very efficient in computing any kinds of dividable large data tasks. The system models and algorithms are described, and simulation results show that the proposed system has better performance than an existing grid system.

In this paper we present the design concept and experimental evaluation results of a newly developed DWDM Radio on Free Space Optics (RoFSO) system capable of transmitting simultaneously multiple RF service signals. The system performance is evaluated under effects of atmospheric turbulence over 1-km free-space transmission. Effectiveness of a proposed tracking scheme used to mitigate beam angle-of-arrival (AOA) effect and the viability of the communication system using a specially designed optical antenna are illustrated. An initial attempt to estimate an additional link margin to compensate for tracking error loss is also presented. Finally, we evaluate the performance of heterogeneous wireless signals after being transmitted over the system. We verify that the system can provide a stable connection for heterogeneous wireless services especially in the absence of strong atmospheric turbulence.

The proliferation of continuous boundary monitoring in large-scale wireless sensor networks in various applications such as fires and hazardous bio-chemical material diffusion, soil moisture draws tremendous significant attentions. In this paper, we propose an energy-efficient EUCOW algorithm that monitors both interior and exterior boundary of unsmoothed object by selecting only the nodes are within transmission range r distance far from event boundary and a minimum set of representative nodes that actually report to the sink. The simulation results significantly verify that our algorithm can achieve a thinner accurate boundary with less boundary nodes as well as greatly reduce the report messages to save energy, especially when numerous event objects emerge into less number of objects.

We review a novel free space optical (FSO) system that represents a significant breakthrough in the area of FSO communications. The system encompasses a pair of novel terminals: these allow direct and transparent optical connection to common single mode fibers and include a dedicated electronic control unit that effectively tracks the signal beam wandering due to atmospheric turbulence and mechanical vibrations. Further improvement in the signal power stabilization is achieved by means of saturated EDFAs. These solutions allow to realize a new FSO system, which is tested in a double-pass FSO link between two buildings in Pisa, Italy. When the terminals are fed by common WDM signals they allow enough power budget and margins to support a record high capacity transmission (32times40 Gbit/s), with a enormous improvement of stability (six hours with no error burst). During day-long transmission, the system behavior has been deeply characterized to correlate any increase of bit error ratio (BER) to the FSO control parameters.

Mobile learning is related to and embedded in the learnerspsila situational context. Contrasting representational notions of context as established in ubiquitous computing as well as phenomenological notions of context as the generation of subjective meaning, we propose a dialectical and learner-oriented view. Learning is expansion into a context where meaning-making practices and objective opportunities for development relate. Implications of this notion for learner-centered design will be discussed within two application scenarios. Both provide opportunities for learners to expand their abilities for engagement in a given environment, one involving portable devices, and the other relying on embedded systems.

The identification and construction of patterns play a fundamental role in learning, but to date design patterns have been used for communication between professionals, rather than for learning purposes. We adapt the design pattern approach and develop software for mobile and other touch-sensitive devices in order to support design students to learn with patterns. We describe the multi-platform system and its gesture-based interaction for formal and informal environments, and present some application scenarios.

Mass casualty incidents generate a sequence of response events from the emergency services, requiring the allocation and use of resources in a timely fashion. In this paper we describe a pervasive system that helps emergency services optimize their efficiency and coordination. The system emulates a multiple casualty emergency response environment in which contextual information, retrieved from victims' wearable or mobile devices, guides early assessments on the health condition of the affected population. Additionally, we analyze the behavior of our system under different conditions and derive the necessary parameters for achieving accurate estimations. Our main contribution is the enhancement of the existing emergency response process for mass casualty incidents through the use of pervasive computing technology.

We introduce a first ever soft keyboard for stylus-based devices such as Personal Digital Assistant (PDA) for Khmer, official language of Cambodia. The contribution of this study is twofold — a key layout arrangement and a word-based predictive text entry method. First, we design a non-QWERTY key layout in which consonants and vowels are grouped phonetically and orthographically, respectively. As a result, the number of soft keys is much less than that of Khmer character sets. Second, we present a word-based predictive text entry method based on the careful analysis of the structure of Khmer word composition. In spite of the word-based predictive mechanism, this soft keyboard provides as well the ability to input unknown words without swapping to other modes. A prototype has been developed and preliminary experiment shows that the proposed soft keyboard is user-friendly easy to use with little training. In addition to the application to stylus-based devices, it can also be extended to be a soft keyboard for conventional desktop.

In recent years we've seen an increase in number of mobile devices and mobile applications, running over different types of networks (e.g., WLAN, 3G, 4G,, UMTS, WiMAX...) that enable any-where, any-time kind of applications. The user is getting flooded with these applications and the information they provide. Seamless mobility intersystem roaming across heterogeneous wireless access networks will be one of the main features in the management architecture of future generation mobile networks. In this paper we propose an ontology-based context management agent policy to manage access networks and handover fuzzy logic decision algorithm for future heterogeneous wireless networks

Software for interactive whiteboards in the classroom usually combines tools for showing prefabricated presentations with annotation features. Instead of encouraging students to participate by contributing, this design promotes a teacher-centered interaction in the classroom. Through literature review, observation, and interviews with teachers we identified pedagogical and situational limitations of this approach and derived design guidelines. We developed an application with an open space interface for interactive whiteboards. It applies a gesture-based interaction paradigm and allows teachers and students to flexibly create, structure, present and document learning materials. Within collaborative learning activities multiple students may synchronously access the whiteboard through pen-tablets.

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IrSimple is a high-speed Infrared communications protocol to provide simple and instant wireless communications between mobile devices and digital home appliances. This paper provides a mathematical model with which we derive a simple equation for IrSimple throughput efficiency. Based on this model, we compare the performance of IrSimple protocol with the existing IrDA protocol for exchanging digital contents at high data rates. Results are presented which reveal that IrSimple protocol scales well for use with high data rates compared to the existing OBEX protocol. The significance of parameters such as IrSMP block size and link minimum turnaround time on IrSimple performance is also examined. Finally, an enhancement of existing error control scheme to provide robustness for IrSimple protocol at high bit error rates and an improvement in flow control to reduce redundant data retransmissions are presented.

This paper provides a mathematical model with which we derive a simple equation for IrBurst throughput efficiency over IrDA protocol stacks. Based on this model, we compare the performance of IrBurst protocol with the existing OBEX protocol for large data blocks exchange at high data rates considering both error free and erroneous environment in order to investigate the suitability of IrBurst protocol. A study of the importance of parameters such as IrLAP window size and IrPHY minimum turnaround time on IrBurst performance is also presented. Finally, a protocol improvement that employs an effective Automatic Repeat Request error control scheme to provide robustness at high bit error rate is proposed.

The greatest obstacle in developing distance learning system is the lack of real-time interaction. This paper provides a real-time interactive shared system for distance learning that combines the audio, video and seminar. The remote learners can study and exchange opinions with the instructor through this system in real time. After the test between Waseda University and Guilin University, we find that the system can well simulate traditional classroom and improve interaction among participators, which not only saves learners' study time and improves their learning interests and efficiency, but also improves the teaching freedom of instructor for e-whiteboard is introducing

This paper examines the suitability of IrBurst, a higher layer protocol recently proposed by IrDA, for large data block exchange over high-speed IrDA links. A complete analytical model for IrBurst throughput efficiency over the IrDA protocol stacks is carried out. Results are presented which reveal that IrBurst scales well for use with large data blocks and high data rates compared to the existing OBEX protocol. We also examine the effect of lower layer parameters such as IrLAP window size and frame length, and IrPHY minimum turnaround time that significantly impact the IrBurst performance. Consequently, a new automatic repeat request (ARQ) scheme is also proposed at IrLAP layer to maximize the throughput efficiency for IrBurst protocol as well as for next generation high speed IrDA links. Simulation result indicates that employment of the proposed ARQ scheme results in significant improvement of IrBurst throughput efficiency at high BER

Ad hoc network has become the primary target for many communications. Recently it is a big issue how we can select best route maintaining highest Quality of Service(QoS). In this paper we have proposed an agent based routing for ad hoc environment which ensures certain level of QoS compared to the traditional system. The proposed protocol also reduces route discovery latency and the end-to-end delay by providing high connectivity without requiring much of the scarce network capacity.

In this paper, we propose an improved selective-repeat automatic repeat request (ARQ) scheme which operates with a finite receiver buffer. The throughput performance of the proposed ARQ scheme is examined and compared with the throughput of the IrDA adopted go-back-N ARQ scheme over half-duplex infrared links. Simulation results show that it significantly outperforms the existing go-back-N ARQ scheme, particularly for links with high bit error rate. We also explore that without adapting window size at high bit error rate, the proposed scheme provides a significant improvement in the throughput over a range of bit error rates including high bit error rate. The proposed ARQ scheme is a good compromise between the go-back-N ARQ and the ideal selective repeat ARQ in throughput performance and receiver buffer size. Therefore, it would be applied on IrDA links for achieving high throughput at high error rate.

This paper presents a new voice objective measurement method of VoIP (voice over IP). Although the subjective evaluation by human MOS (mean opinion score) is the best evaluation, many testees must participate in the voice experiments and expensive measuring instruments and environments, such as a special acoustic room are needed. In order to measure the voice quality easily, the new objective measurement method is presented and studied using experiments.

Internet has become the primary means for worldwide communications. In terms of recreation, business, and various imaginative reasons for information distribution it is the most used communication method today. In recent times, it is a big issue of how we can make the best use of Internet in an emergency period. The goal of this paper is to ensure Internet's best effort services to help during emergencies without any major changes in existing technology. Here, we present a system architecture that reflects a general overview of how it can work parallel to the authorized Emergency Telecommunications Services (ETS). To detect location information in a loosely coupled network environment is the most challenging aspect using IP's flat address model. Our conceptual view of the system architecture shows how the service can be provided extending DHCP, XML with existing core technology. In succession, a simulation of the system is shown to realize call setup delay and end to end VoIP packet delay over the IP network.

The progress of ICT has brought us numerous benefits, and the concept of ICT has continuously been extended from "network" to "global network," then to "ubiquitous network." The infrastructure of broadband environment such as ADSL or FTTH in Japan has been effectively developed. Likewise, mobile phones have become extremely popular and widely used. Ninety percent of all the mobile phones in Japan are browser phones, and they are contributing to forming a high-mobility society. In this paper, we would like to present possibilities of mobile terminals, especially mobile phones utilizing the RFID (Radio Frequency Identification) technology. The RFID technology has increased the capacities in memory, widened reading ranges, and accelerated processing speeds. Based on the premise of the RFID technology, we would like to discuss the challenges in operating wireless devices from the customers' perspectives.

Accessing the Internet on the move via wireless link requires some provisioning in the network and the terminal part so that we can overcome the difficulties of wireless link, mobility, and device capability limitations. In this paper we propose a mobile agent based system for wireless mobile Internet. We use static agents (terminal and provider) at the two ends of wireless link. We represent the user by a mobile agent on the provider side, mobilize this agent when necessary. We show when, how and what to mobilize. We show that our agent based system has some desirable properties which are effective in compensating the drawbacks of wireless environment, mobile device limitations and TCP, HTTP protocol limitations in wireless environment. We describe the system architecture and operation scenario. Benefits of using agent in this scenario are discussed and we show how different optimization techniques can easily be incorporated in such a system due to its flexibility.

A high-speed wireless network has been constructed that utilizes the newly approved 60 GHz frequency band. In Japan, this newly allocated millimeter wave can be used without a license. The system configuration and the experimental results are shown. The prototype system has been constructed at the Waseda University campus and the operation of this system is confirmed. Then the transmission characteristics in the experiments show very good and this system can provide the remote lecture service and seminar, etc.

The experiment we conducted for integrated digital satellite communications is aimed at realizing integrated services digital networks by satellite communication. The experiment was carried out in 1980 using the Japanese experimental communication satellite "CS." This experiment uses 30/20 GHz small earth stations and demand-assignment time-division multiple-access (TDMA) systems. Communications between customer terminals, which contain video conferencing, high-speed facsimile communication, high-speed computer communication, and packet-switching signal transmission, were carried out through the experimental digital satellite link. This paper describes the configuration of the experimental integrated digital satellite communications system and the experimental results of communications between customer terminals.

This paper outlines a newly developed high-speed facsimile apparatus for satellite communication. An ISO A4 size document can be transmitted in about 3 s at a transmission rate of 1.536 Mbits/s using the apparatus. In the transmitter, a CCD linear image sensor and a fluorescent lamp are used for photoelectric conversion. In the receiver, an electrostatic recording technique using a multistylus electrode is applied. Furthermore, this apparatus applies a new tone-reproduction technique involving electrostatic recording, which makes it possible to reproduce documents, such as photographs, that have gray-level information without reducing the character quality. A facsimile control procedure which takes into consideration satellite communication circuit characteristics is established. The transmitter sends all documents to be sent continuously, receiving the message confirmation response for one document while transmitting the next one. The results of message transmission tests over experimental satellite communication circuits are described.