The market for IP convergence services is expanding rapidly due to the rising number of Internet users. To respond to market trends, service systems must provide services quickly. This paper discusses that application server called the service agent which provides IP convergence services. The service agent meets the requirements for four application servers, centralized intelligence, supporting various interfaces: service creativity and scalability. The architecture is based on that of AIN systems, but whole system is written in Java especially to achieve service creativity and scalability. As a result of trial manufacture, feasibility of the service agent and scalability was achieved. Enough performance was also confirmed to obtain for commercial services.

Recently, broadband access is widely spreading, and many broadband network E-commerce services are planned and developed. This article proposes a broadband online shop where a videoconferencing system is used to enable direct, face-to-face communication. It is important for a broadband online shop to understand what preference their customers want in order to provide them with more appropriate information. By using customer preferences, a salesclerk can have a serviceable conversation with few questions to his online customers. So, we are developing a visual Customer Relationship Management system (v-CRM system) that offers customer preferences to broadband network service such as broadband online shop. In this paper, we classify customer preferences, and describe three visualization methods that enable customer preferences to be intuitively understood quickly. We outline the v-CRM evaluation system and describe an experiment where we evaluated how accurately customer preferences can be recognized using these methods. The results show that v-CRM system is effective for understanding customer preferences.

To address the extreme dynamism and the rapidly changing user's requirements in current information systems, an Autonomous Community Information System (ACIS) has been developed. ACIS is a decentralized architecture that forms a community of individual end-users (community members) having the same interests and demands at specified time and location. It admits them to mutually cooperate and share information without loading up any single node excessively. ACIS does not embrace the advantage of heterogeneity of the community nodes-nodes latencies. In this paper, ACIS-Hierarchy, decentralized hierarchical community architecture is proposed. It considers latency between community nodes as an important criterion that need to be optimized. It takes advantage of heterogeneity of the community nodes-nodes latencies to improve the communication delay among the community. In this paper, an efficient autonomous decentralized community construction technology is proposed to reduce: the communication delays among members taking into consideration the latency among them and the required time to join/leave. This paper illustrates the step-step construction technology and the membership management operations for ACIS-Hierarchy. Experimental results show that ACIS-Hierarchy improves the community communication delay.

Decentralized and unstructured peer-to-peer (P2P) networks such as Gnutella are attractive for large-scale information retrieval and search systems because of their scalability, fault-tolerance, and self-organizing nature. Because of this decentralized architecture, however, traditional P2P keyword search systems are difficult to globally share useful semantic knowledge among nodes. As a result, traditional P2P keyword search systems cannot support semantic search (support only naive text-match search). In this paper, we describe a design of the semantic P2P keyword search system. We exploit the semantics of correlation among keywords rather than synonym. The key mechanism is query expansion, where a received query is expanded based on keyword relationships. Keyword relationships are improved through search and retrieval processes and each relationship is shared among nodes holding similar data items. This semantic P2P search system has two main advantages. First, expanding search results through query expansion increases the possibility of locating desired data items which would not be found by traditional P2P search systems due to the keywords' textual mismatch. Second, keyword relationships originally introduced for query expansion, can be used for result ranking. Our main challenges are 1) managing keyword relationships in a fully decentralized manner and 2) maintaining the quality of search results, while suppressing result implosion. We also describe the prototype implementation and evaluation of the semantic P2P search system.

Recently with the advent of the IT and the wide spread use of the Internet, new user oriented production and logistic systems, such as the Supply Chain Management System, have been required in order to cope with the drastic and continuous changes on the markets and users' preferences. Therefore, heterogeneous database systems need to be integrated in a common environment which can cope with the heterogeneous requirements of each company under an ever-evolving changing environment. That is assurance. Autonomous Decentralized Database System (ADDS) is proposed as a system architecture in order to realize assurance in distributed database systems. In this system architecture, a loosely-consistency management technology is proposed in order to maintain the consistency of the system, each database can update autonomously, and confer the real time property. A background coordination technology, performed by an autonomous mobile agent, is devised to adapt the system to evolving situations. The system can achieve real time by allocating the information in advance among the sites that has different time constraints for updating. Moreover, an assurance information allocation technology is proposed when considering that a failure in the background coordination mechanism may lead to loss of data and unavailability of the system. This mechanism, in which the mobile agent autonomously regulate its own capacity for allocating the information, is proposed based on the real-time property and system's availability considerations. The effectiveness of the proposed architecture and technologies are evaluated by simulation.

In this paper we present a component approach for configurable network processing for active documents. The approach has two key ideas. The first is to enable documents to process themselves on networks. That is, documents can define their own itineraries, like the notion of active packets in active network technology. The second is to enable documents to transmit other documents to their destinations as first-class objects, such as the notion of active nodes in active netwwork technology. The approach also enables buidling and managing active documents as compound documents. The dynamic deployment of network processing for exchanging documents can be defined and achieved by means of GUI-based manipulation of compound documents. Therefore, the approach allows a user to easily and rapidly develop and customize network processing in the same way as if that user had edited the documents. A prototype implementation of the approach and its applications were constructed on a Java-based mobile agent system to evaluate the effectiveness of the approach.

Integration of the MPLS network and the optical mesh network is a promising approach to realize an efficient backbone network. Because large volumes of traffic incur damage from failure, survivability is important in the backbone network. In the MPLS over optical networks, a pair of primary LSP (Label Switched Path) and secondary LSP needs to be established on two optical link-disjoint routes assuming all single optical link failures. However, two link-disjoint routes in the MPLS layer may not correspond to two link-disjoint routes in the optical layer. Thus, a pair of primary and secondary LSPs should be routed considering link-disjointness in the optical layer. In the MPLS over optical networks, secondary LSPs can mutually share lightpath bandwidth if those secondary LSPs correspond to the primary LSPs that never fail simultaneously. Thus, routing of secondary LSPs should promote sharing of the lightpath bandwidth among the secondary LSPs. The primary and secondary LSPs with variable bandwidths should efficiently be packed into fewer lightpaths with a fixed bandwidth. Moreover, if all the LSPs accommodated in a lightpath can be re-routed to other lightpaths, this lightpath can then be released. By re-routing only secondary LSPs, unnecessary lightpaths may be released without disturbance of the conveyed traffic. This paper proposes an efficient routing scheme to establish primary and secondary LSPs with variable bandwidths through the MPLS over optical network. This routing scheme satisfies the above conditions. The bandwidth of each lightpath is efficiently utilized by this routing scheme, and the loss rate of LSP requests can be reduced. This paper also proposes an efficient re-routing scheme to remove secondary LSPs from selected lightpaths through which the efficiency of channel utilization in the optical links is increased, and the loss rate of LSP requests can be reduced as a result. Both the proposed routing and re-routing schemes are quantitatively evaluated and the effectiveness of those schemes is verified by computer simulation.

The cost-effective provision of IP services requires multi-layered traffic engineering to obtain dynamic cooperation between IP and photonic layers. The effective control and management of generalized multi-protocol label-switching (GMPLS) networks is an essential part of this. Huge photonic capacities and the number of IP and photonic networks make it likely that enormous amounts of GMPLS network-related data will have to be managed in the near future. At the same time, routing burdens on individual GMPLS routers are critical because of the strong need for per-path quality of service (QoS). To solve these problems, we propose a hierarchically distributed network-management system (NMS) in which we flexibly allocate a GMPLS subnetwork to each sub-NMS and at the same time conduct QoS routing. The distributed nature of our architecture reduces the burden on the NMS as a whole and also lets us remove the routing-burden from GMPLS routers with minimum effect on management processes.

In policy-based management, in addition to deliver and enforce policies in managed systems, it is inevitable to manage the policy life-cycle. We mean the policy life-cycle as cyclic iteration of processes involving monitoring to see if the enforced policies actually work at operators' will and their adaptation based on monitoring. Enabling such policy life-cycle management by the current centralized management paradigm such as SNMP may, however, result in poor scalability and reliability. This is typically due to much bandwidth consumption for monitoring and communication failure between a management system and a managed system. It may also impose a heavy burden on the operators in analyzing management information for the policy adaptation. For a solution to that, we propose a scalable and reliable policy-based management scheme enabling the policy life-cycle management based on distributed management paradigm. In the scheme, we provide a new management script describing policies and how their life-cycle should be managed, and execute the script on the managed system with enough computation resources. The scheme can make the current policy-based management more scalable by reducing management traffic, more reliable by distributing management tasks to the managed systems, and more promising by relieving of the operators' burden. We implement a prototype system based on the scheme taking Differentiated Services as a policy enforcement mechanism, and evaluate the scheme from the following viewpoints: 1) the reliability, 2) relievability, and 3) scalability. The first two will be shown with a policy adaptation scenario in an operational network. The last one will be investigated in terms of the management traffic reduction by a management script, the management traffic required for the management of a management script, and the load on a managed system to execute management scripts. As deployment consideration of the proposed scheme besides technical aspects, we also discuss how the prototype system could be integrated with managed systems compliant to the standards emerging in the marketplace.

There have been many researches on providing mobility under mobile/wireless environment. However, previous researches had several problems as disruption and unnecessary traffic. Disruption happens when messages are exchanged between nodes as registration is made after handoff, and unnecessary traffic occurs because of the use of Random-walk model, in which the probability for MN to move to the neighboring cells is equal. In order to solve these problems, this study proposes a technique and algorithm for composing Directional Shadow Registration Region (DSRR) that provides seamless mobility. The core of DSRR is to prevent disruption and unnecessary traffic by shadow registration at neighboring cells with a high probability of handoff (AAAF). We are introduced a cell division scheme and decided minimal DSRR. DSRR can sensed the optimal time for handoff through Regional Cell Division and applied Direction Vector (DV) obtained through Directional Cell Sectoring. According to the result of the experiment, the proposed DSRR processes message exchange between nodes within the intra-domain, the frequency of disruptions decreased significantly compared to that in previous researches held in inter-domain environment. In addition, traffic that occurs at every handoff happened twice in DSRR compared to n (the number of neighboring cells) times in previous researches.

Various demands for next generation networks can be condensed into always-best-connected, ubiquitous, mobile, all-IP, application-aware, and converged networks. Vehicles have also come to be ubiquitous computing platforms associated with mobile communication functions. IPv6 has been introduced for all-IP ubiquitous communications. This paper proposes application-aware resource management for in-vehicle IPv6 networks, which are adaptive to different hardware configurations. We focus on power and bandwidth, since their management is critical for mobile communications. To manage these two critical resources, we identify the mobility characteristics and hardware configurations of in-vehicle networks. Based on these characteristics, we propose vehicle-aware power saving schemes. Our main idea for power saving is to dynamically adjust the mobile router (MR) advertisement interval and binding update lifetime. In addition, depending on the hardware configuration of the wireless environment, we propose two adaptive bandwidth management schemes using multihoming, which we refer to as best-connected MR selection based on location and high-data-rate MR selection based on priority. We evaluate the performance of our bandwidth management schemes by performing simulations, and that of our power saving schemes by mathematical analysis. Based on the results, it was found that the performance of each software scheme depends on the hardware configuration, so that an application-aware adaptive scheme is needed to optimize resource consumption.

Mobile agent systems are essential in the next generation of electronic commercial applications. However, existing solutions for mobile agents to sign documents without user intervention are problematic because there is no restriction on who can generate the signatures. In this paper, we present a modified version of undetachable signature scheme with which the power to generate digital signatures can be designated to a neutral party. We also give a transaction model to support the scheme. Discussions regarding the security of the signature scheme as well as some attacks on its application in our model are presented too.

As the Internet has become the infrastructure for the global communication, the quality degradation due to network failures and illegal traffic such as DDoS (Distributed Denial of Service) have become a serious problem. In order to solve the problem, a network monitoring system that monitors the traffic of Internet in real time is strongly desired. Traffic monitors that collect the statistics from captured packets play a key roll in the system; however, they are not flexible enough for being used in the rapidly changing Internet. The traditional approach such that a new traffic monitor is developed for a new requirement results in a long turn around time of the development. Therefore, we have proposed a flexible network monitoring system that consists of programmable traffic monitors. Traffic monitors are made programmable by introducing active network techniques; therefore, we call the network monitoring system as the programmable monitor network. This paper describes the implementation of the programmable monitor network and its application to DDoS (Distributed Denial of Service) attack detection.

Effective counteraction to Distributed Denial-of-Services (DDoS) attacks is a pressing problem over the Internet. For this counteraction, it is considered important to locate the router interfaces closest to the attackers in order to effectively filter a great number of identification jammed packets with spoofed source addresses from widely distributed area. Edge sample (ES) based Probabilistic Packet Marking (PPM) is an encouraging method to cope with source IP spoofing, which usually accompanies DDoS attacks. But its fragmentation of path information leads to inefficiency in terms of necessary number of packets, path calculation time and identification accuracy. We propose Branch Label (BL) based PPM to solve the above inefficiency problem. In BL, a whole single path information is marked in a packet without fragmentation in contrast to ES based PPM. The whole path information in packets by the BL approach is expressed with branch information of each router interfaces. This brings the following three key advantages in the process of detecting the interfaces: quick increase in true-positives detected (efficiency), quick decrease in false-negatives detected (accuracy) and fast convergence (quickness).

This paper proposes an algorithm for detecting 3-way interactions. As far as the authors know, this is the first proposal ever made for a detection algorithm of 3-way interactions. In this paper, by analyzing examples, the mechanism of 3-way interactions is clarified and a detection algorithm of 3-way interactions is proposed. Namely the proposed detection algorithm is heuristic. To evaluate the algorithm, we implemented a detection system based on the proposed algorithm and applied it to 12 services, and 82 3-way interactions were detected. This shows the proposed algorithm is effective.

We describe a next generation service creation environment (SCE), which is designed to support efficient service application development for IP networks. Considering the IP-network environment we extract the features required for the next generation SCE and propose an architecture for the next generation SCE based on design concepts to provide these features. In our approach, we do not create large components, such as service features, or construct chains of them. Instead, we define application-programming interface (API) control flows through which we utilize existing APIs, such as open APIs. Since service providers, such as ASPs and third parties, must have some knowledge of the APIs, this capability will enable the development of services that correspond to various service provisioning patterns as well as to differentiation of services from those offered by other providers, without the addition of service components. The feasibility and productivity of the next generation SCE are evaluated by developing sample services, including a general Voice over IP (VoIP) service using a Parlay API and a presence service using a presence and availability management (PAM) API. Evaluation shows that the environment not only assists in the development of service applications but also raises the productivity of the next generation SCE itself, thus confirming its effectiveness the rapid, economical development of high-quality IP network services.

In ad-hoc on-demand routing algorithm, when a route is broken a relay node must perform error transaction and the source node must do rerouting to discover an alternate route. It is important to construct a stable route when route discovery occurs. In this paper, we use relative speeds among nodes as a measure of node mobility. Our routing algorithm chooses nodes of lower relative speed as relay nodes. As a result of our simulation, when there is one session in the network, our proposing algorithm can reduce the number of route breaks: about 3 times smaller than DSR. And our proposing algorithm can deliver more packets than DSR: 18% higher rate. However, in the congested traffic situation our algorithm should be improved.

The ATM Forum recommends the use of the Generic Cell Rate Algorithm (GCRA) to perform Usage Parameter Control at the User Network Interface of ATM networks. In order to facilitate the Call Admission Control and resource allocation procedure, it is important to investigate the characteristics of the model in which GCRA-enforced sources are merged together by a multiplexer. Such a multiplexer could be the one arranged in front of a switch to concentrate user traffic and reduce the number of required input ports. It may also represent the logical multiplexer at the output port of a switch that collects cells routed from various input ports. Moreover, it may represent the service function of the edge router situated between the integrated-services (IntServ) networks and the backbone networks that provide differentiated-services (DiffServ). In this paper, the environment under discussion is a multiplexer in which every traffic source is enforced by a dual-stage GCRA enforcer before being merged. The worst traffic pattern that maximizes the average waiting time in the multiplexer is found. The maximum average waiting time is deduced and expressed as a function of the GCRA parameters and the number of multiplexed sources. In particular, the analysis considers the speed-up function, which is widely used for ATM multiplexers and switches. The results can also be applied to a GCRA shaper without any modification.

Space-time block coded orthogonal frequency division multiplexing (ST-OFDM) has been proposed as an attractive solution for a high bit rate data transmission in a multipath fading environment. Space-frequency block coded OFDM (SF-OFDM) has been also proposed as another solution. These two systems utilize STBC with a 22 transmission matrix, using two transmit antennas. In ST-OFDM the block codes are formed over the space-time domains. In SF-OFDM the block codes are formed over the space-frequency domains. If we apply STBC with a 44 transmission matrix to OFDM, using four transmit antennas, we can expect the performance improvement. However, when the block codes are formed over space-time (frequency) domains with four transmit antennas, the conditions of the orthogonality become more strict. We can expect that if the block codes are formed over space-time-frequency domains with four transmit antennas, that is, if we implement space-time-frequency block coded OFDM (STF-OFDM), the condition of the orthogonality is more relaxed. In this paper, we apply STBC with a 44 transmission matrix to OFDM and propose STF-OFDM. We evaluate the performance of the three types of systems (ST-OFDM, SF-OFDM, STF-OFDM). We show that the best system with respect to the error rate performance differs in the different channel conditions. When the effect of the Doppler spread is large and the effect of the delay spread is small, SF-OFDM has the best error rate performance, and STF-OFDM and ST-OFDM follow in order. When the effect of the delay spread is large and the effect of the Doppler spread is small, ST-OFDM has the best error rate performance, and STF-OFDM and SF-OFDM follow in order. We also show that STF-OFDM is attractive in wireless communications. STF-OFDM is more tolerant than ST-OFDM with respect to the Doppler spread and SF-OFDM with respect to the delay spread, respectively.

The joint use of frequency-domain equalization and antenna diversity is presented for single-carrier (SC) transmission in a frequency-selective fading channel. Frequency-domain equalization techniques using minimum mean square error (MMSE), orthogonal restoration combining (ORC) and maximum ratio combining (MRC), those used in multi-carrier code division multiple access (MC-CDMA), are considered. As antenna diversity techniques, receive diversity and delay transmit diversity (DTD) are considered. Bit error rate (BER) performance achievable with the joint use of frequency-domain equalization and antenna diversity is evaluated by computer simulation.

Orthogonal multicode direct sequence code division multiple access (DS-CDMA) has the flexibility in offering various data rate services. However, in a frequency-selective fading channel, the bit error rate (BER) performance is severely degraded since the othogonality among spreading codes is partially lost. In this paper, we apply frequency-domain equalization and antenna diversity combining, used in multi-carrier CDMA (MC-CDMA), to orthogonal multicode DS-CDMA in order to restore the code othogonality while achieving frequency and antenna diversity effect. It is found by computer simulations that the joint use of frequency-domain equalization and antenna diversity combining can significantly improve the BER performance of orthogonal multicode DS-CDMA in a frequency-selective fading channel.

Independent shadowing losses are often assumed for computing the frequency reuse distance of cellular mobile communication systems. However, shadowing losses may be partially correlated since the obstacles surrounding a mobile station block similarly the desired signal and interfering signals. We investigate, by computer simulation, how the shadowing correlation impacts the frequency reuse distance of a power controlled cellular system. It is pointed out that the shadowing correlation impacts the frequency reuse distance differently for the uplink and downlink.

An adaptive filtering algorithm based on the sliding window criterion is known to be very attractive for violent changing environments. In this paper, a new sliding window linearly constrained recursive least squares (SW-LC-RLS) algorithm based on the modified minimum mean squared error (MMSE) structure is devised for the RAKE receiver in direct sequence spread spectrum code-division multiple access (DS-SS CDMA) system over multipath fading channels, where the channel estimation scheme is accomplished at the output of adaptive filter. The proposed SW-LC-RLS algorithm has the advantage of having faster convergence property and tracking ability, and can be applied to the environments, where the narrowband interference is joined suddenly to the system, to achieve desired performance. Via computer simulation, we show that the performance, in terms of mean square errors (MSE), signal to interference plus noise ratio (SINR) and bit error rate (BER), is superior to the conventional LC-RLS and orthogonal decomposition-based LMS algorithms based on the MMSE structure.

A large-scale packet-switch architecture for a tera bit/s system--which uses a combined-packet-distribution (CPD) method for a crossbar packet switch--was developed. This method eliminates the restriction on scheduling processing time by extending a switching data unit. The data unit is called a combined packet that consists of plural variable-length packets or their fragments. The combined packets are sequentially distributed among multiple crossbar switch planes and their sequence integrity is preserved. Distributive targets among the switch planes are selectable. As a result, when one or more switch planes are damaged, redundancy of the switch fabric is easily attained in a so-called "graceful degradation" manner. Moreover, this switch uses a novel algorithm called hierarchical priority scheduling. This algorithm enables fairness of scheduling by taking account of queuing state. The repetition required for priority scheduling is reduced by a novel hierarchical approach. The simulated performance of this algorithm shows that it performs better than the simple maximal matching method under both uniform and non-uniform traffic.

Differentiated Services architecture provides a framework that enables relative differentiation of Assured Forwarding (AF) service. The differentiation is quantified by QoS parameters in terms of loss probability and maximum delay. We develop herein an efficient model to compute resource allocation in terms of buffer and service rate that satisfies the QoS differentiation between classes of service. To evaluate the performance of the proposed model, we conducted extensive simulation on both single-node and multi-node cases. The simulation studies show that the model can provide an efficient method to allocate network resources for aggregated traffic.

We propose an adaptive load balancing method for multiple paths that makes it possible to achieve high TCP performance on each path. In conventional load balancing methods, link utilization is the main parameter to be balanced among multiple paths that are established between an ingress and egress node pair. However, when we take into account TCP-level performance, balancing the traffic in terms of only link utilization may not always result in balanced TCP performance on each path. Our method utilizes flow statistics such as the number of active flows in each path, which is easy to measure, and can treat TCP performance. By adaptively equalizing the average bandwidth used per active flow in each path, which is calculated by dividing the input rate to the path by the mean number of active flows, our method achieves fair and high TCP performance on each path. Unlike other methods, intermediate nodes between an ingress-egress pair are not required to perform traffic controls or measurements besides normal packet forwarding. We describe a load balancing method for adaptively equalizing the average bandwidth used per active flow on each path and show its effectiveness under heterogeneous conditions through simulation analysis.

Real-world IP networks are heterogeneous in terms of server and link capacities. A sophisticated and comprehensive load balancing method is essential if we are to avoid congestion in the servers and links of heterogeneous networks. If such a method is not available, network throughput is limited by bottleneck servers or links. This paper proposes an anycast technique that achieves load balancing under heterogeneity. The proposed method well suits implementation on active networks. By taking advantage of the processing ability provided by active nodes, the method can decide packet routes flexibly on the basis of various criteria to realize a variety of load balancing schemes. Some of these schemes can successfully prevent the congestion of heterogeneous networks by tackling bottlenecks in both server and link capacities. The method is also advantageous given its light control load even when using many mirrored servers. Computer simulations confirm the effectiveness of these features.

In this letter, we propose joint frequency offset and SNR estimation technique. The frequency offset may degrade the system performance greatly by deleterious effect. The proposed frequency offset estimation technique estimates frequency offset by employing the interpolation technique in the frequency domain. Also we propose SNR estimation technique using the estimated frequency offset for FFT-based system. The SNR estimated by the receiver can be used to adapt the demodulation algorithm to enhance its performance, as well as to provide the channel quality information. Simulation results show the performance of frequency offset and SNR estimator.

We consider vector channel estimation for differentially modulated systems with transmit diversity. We propose a blind estimation scheme to yield superior performance to that of the pilot-aided estimation. The proposed scheme utilizes the repeated transmission of space-time coded data symbols. We compare the performance of the proposed blind scheme with the pilot-based estimation scheme via computer simulations.

Multiple-input multiple-output (MIMO) systems can improve the spectral efficiency of a wireless link, by transmitting several data streams simultaneously from different transmit antennas. However, at the receiver, multi-stream detection is needed for extracting the transmitted data streams from the received signals. This letter considers ordered successive detection (OSD) for multi-stream detection. OSD consists of several stages, and at each stage only one data stream is chosen to be detected among the remaining streams according to a specified ordering metric. OSD has been formulated using both the zero forcing (ZF) and minimum mean square error (MMSE) criteria. This letter clarifies the reason behind the superiority of OSD using the MMSE criterion to OSD using the ZF criterion through the investigation of the relation between their ordering metrics. For uncorrelated MIMO channels, we show that both ordering metrics yield the same performance for OSD using either ZF or MMSE criterion. Accordingly, the superiority of OSD using the MMSE criterion to OSD using the ZF criterion is clarified to be a direct result of the inherent superiority of MMSE nulling to ZF nulling, and to be independent of the ordering operation. Performance comparisons of OSD and maximum likelihood detection are also given for modulation schemes of different sizes.

A power and spreading gain allocation strategy is considered to effectively provide data services for mobile users with different levels of priorities in a DS-CDMA system. The priority level of a user is specified by a factor that is a weighting on the data throughput of the user. Our strategy implements a relative prioritization that affords a trade-off between spectral efficiency and strict prioritization.

Recently, Space-Time Block Coded OFDM (ST-OFDM) that applies Space-Time Block Code (STBC) to OFDM has been proposed. Space-Frequency Block Coded OFDM (SF-OFDM) has been also proposed where the block codes are formed over the space and frequency domain. ST-OFDM and SF-OFDM are known as the schemes that achieve good performance over the multipath fading environments and the fast fading environments, respectively. For the systems with two transmit antennas, the orthogonal conditions required to separate the received signals are that in ST-OFDM, the frequency responses of the consecutive two OFDM symbols are almost identical and that in SF-OFDM, the frequency responses of the adjacent two subcarriers are almost identical. In practical fading environments, however, these conditions of the orthogonality sometimes cannot be satisfied. In those environments, the received signals cannot be well separated and the performances are degraded. Recently, the diagonalized maximum likelihood decoder (DMLD) of new zero-forcing (ZF) type was proposed for the space-time block coded single carrier QPSK system to maintain the orthogonality of STBC under the fast fading environments and the flat fading environments, where the channel separation in DMLD is performed by the ZF algorithm using two receive signals at time index 2n, 2n+1 (Space Time Code: STC) or two subcarriers (Space Frequency Code: SFC). Note that the matrix generated after the channel separation is not an identity matrix but the matrix proportional to an identity matrix. We show that ST/SF-OFDM with DMLD outperform ST/SF-OFDM in terms of Bit Error Rate (BER).

Reduced-state sequence estimation (RSSE) for trellis-coded modulation (TCM) in cyclic prefixed single carrier (CPSC) with minimum mean-square error-linear equalization (MMSE-LE) on frequency-selective Rayleigh fading channels is proposed. The Viterbi algorithm (VA) is used to search for the best path through the reduced-state trellis combined equalization and TCM decoding. Computer simulations confirm the symbol error probability of the proposed scheme.

A very general form of the probability density distribution of the fading envelope has been presented by M.Nakagami, including the Nakagami-Rice and Nakagami-Hoyt distributions as special cases. This paper gives the series form expanded in positive terms of the m-distribution for it. Previously, the feasibility of such an expansion was predicted, but there has been no explicit description to date. The properties of the well-known m-distribution and the positive sign in each term of this series make it practical for numerical calculation, approximation and analysis.

In this paper, a meander-type microstrip patch antenna for application in 5 GHz-band is designed and fabricated. To obtain enough bandwidth in VSWR<2, the foam is inserted between substrate and ground plane, the coaxial probe source is used. The measured result of fabricated antenna is obtained 1 GHz (17.5%) of bandwidth in VSWR<2, the gain of 7.3-9.5 dBi and unidirectional pattern.

We measured the optical propagation characteristics during rainfall over a 72-m propagation distance at the wavelengths of 0.78, 1.55, and 2.0 µm. In addition to the common attenuations, we observed sudden drops (dips) in the received optical power, which affect communication errors. The temporal interval of most dips is approximately 1 ms.

A flexible and robust rate-distortion optimization algorithm is presented to select macroblock coding mode for H.264/AVC transmission over wireless channels subject to burst errors. A two-state Markov model is used to describe the burst errors on the packet level. With the feedback information from the receiver and the estimation of the channel errors, the algorithm analyzes the distortion of the reconstructed macroblock at the decoder due to the channel errors and spatial and temporal error propagation. The optimal coding mode is chosen for each macroblock in rate-distortion (R-D)-based framework. Experimental results using the H.264/AVC test model show a significant performance of resilience to the burst errors.