In provisioning packet data service on wireless cellular networks, a scheme of altering connection status between mobile and base stations appeared intending to efficiently utilize resource during idle periods. In such a scheme, connection components are sequentially released as an idle period persists, while the transmitting station converts to an transmission activity mode as the station is loaded with packets. However, actual resume of transmission activity is postponed by connection retrieval time to restore lost connection components. In general, an idle period affects the following connection retrieval time, which in turn produces an impact on the forthcoming idle period. Such chain reaction also makes a significant influence on overall packet delay performance. In this paper, as a way of improving packet delay performance, we propose two schemes identified as conservative extension and load threshold schemes. In the conservative extension scheme, we intentionally extend connection retrieval times so that each connection retrieval time is guaranteed not to be lower than a certain value. On the other hand, according to the load threshold scheme, a retrieval of lost connection components is postponed until packets are accumulated at the transmitting station up to a prescribed threshold. An increase in the value and threshold incurs an additional stand-by before resuming transmission activity in both proposed schemes. In turn, such intentional stand-by may contribute to regulating the length of idle period and connection retrieval time, and subsequently improving packet delay performance. To inspect the impact of conservative extension and load threshold schemes on packet delay performance, we first investigate the properties of idle periods. Secondly, for Poisson packet arrivals, we present an analytical method to exactly calculate the moments of packet delay time (at steady state) in each scheme. From numerical examples, we confirm the existence of non-trivial optimal value and threshold minimizing average packet delay or packet delay variation and conclude that conservative extension and load threshold schemes are able to enhance packet delay performance in various environments.

In this letter, we investigate the path length priority effect of existing just-enough-time (JET) scheme for optical burst switching (OBS) in the multiple hop network environments. And, we propose a novel hop-by-hop priority increasing (HPI) scheme using the input fiber delay lines (FDLs) at each node. Simulation results showed that the proposed FDL/delayed reservation (DR) with HPI scheme can avoid the path length priority effect and enhance the end-to-end throughput in multiple hop network environments.

This paper considers the problem of providing relative service differentiation in IEEE 802.11 Wireless LAN by using different Medium Access Control (MAC) parameters for different service classes. We present an analytical model which predicts the saturation throughput of IEEE 802.11 Distributed Coordination Function with multiple classes of service. This model allows us to show that relative service differentiation can be achieved by varying the initial contention window alone. In this case, the saturation throughput of a station can be shown to be approximately inversely proportional to the initial contention window size being used by that station. The simulation results validate our analytical model.

In this article we analyze the performance of a space division output buffered multichannel switch operating in an ATM multimedia environment as follows. Fixed size packets belonging to two classes arrive onto the switch inputs in each time slot. Class-1 packets, representing real time traffic such as live audio and live video communications, are sensitive to delay but insensitive to loss and have their own service time needs. Class-2 packets, representing nonreal time communications such as file transfers, are insensitive to delay but sensitive to loss and have their different service time needs. To respond to the class-1 delay sensitivity, the switch gives class-1 packets higher service priority over class-2. And to respond to the difference in service time needs, the switch operates at two service rates, one for each class. This latter assumption is the major feature of the article, as previous studies have usually assumed that the two classes have the same service needs and thus the same service rate. For the purpose of the analysis, the switch is modelled as a priority, discrete time, batch arrival, multiserver queueing system, with infinite buffer and two geometric service times with two parameters. Performance measures analyzed are system occupancy and packet waiting time.

Quality of Service (QoS) provisioning is a new but challenging research area in the field of Mobile Ad hoc Network (MANET) to support multimedia data communication. However, the existing QoS routing protocols in ad hoc network did not consider a major aspect of wireless environment, i.e., mutual interference. Interference between nodes belonging to two or more routes within the proximity of one another causes Route Coupling. This can be avoided by using zone-disjoint routes. Two routes are said to be zone disjoint if data communication over one path does not interfere with the data communication along the other path. In this paper, we have proposed a scheme for supporting priority-based QoS in MANET by classifying the traffic flows in the network into different priority classes and giving different treatment to the flows belonging to different classes during routing so that the high priority flows will achieve best possible throughput. Our objective is to reduce the effect of coupling between routes used by high and low priority traffic by reserving zone of communication. The part of the network, used for high priority data communication, i.e, high priority zone, will be avoided by low priority data through the selection of a different route that is maximally zone-disjoint with respect to high priority zones and which consequently allows contention-free transmission of high priority traffic. The suggested protocol in our paper selects shortest path for high priority traffic and diverse routes for low priority traffic that will minimally interfere with high priority flows, thus reducing the effect of coupling between high and low priority routes. This adaptive, priority-based routing protocol is implemented on Qualnet Simulator using directional antenna to prove the effectiveness of our proposal. The use of directional antenna in our protocol largely reduces the probability of radio interference between communicating hosts compared to omni-directional antenna and improves the overall utilization of the wireless medium in the context of ad hoc wireless network through Space Division Multiple Access (SDMA).

We study the user reneging behavior in a hybrid Multimedia-on-Demand (MoD) system, which provides both interactive and batch services. Reneging happens when users become reluctant to wait for a batch service and quit the service. They will either join the interactive service or quit the system. In this letter, the analytical model for the MoD system with user reneging behavior is provided. Numerical results show that the reneging behavior has a significant impact on system performance. Therefore, careful consideration on reneging behavior should be made for designing a MoD system.

In mobile multimedia environment, it is very important to minimize handoff latency due to mobility. In terms of reducing handoff latency, Hierarchical Mobile IPv6 (HMIPv6) can be an efficient approach, which uses a mobility agent called Mobility Anchor Point (MAP) in order to localize registration process. However, MAP can be a single point of failure or performance bottleneck. In order to provide mobile users with satisfactory quality of service and fault-tolerant service, it is required to cope with the failure of mobility agents. In, we proposed Robust Hierarchical Mobile IPv6 (RH-MIPv6), which is an enhanced HMIPv6 for fault-tolerant mobile services. In RH-MIPv6, an MN configures two regional CoA and registers them to two MAPs during binding update procedures. When a MAP fails, MNs serviced by the faulty MAP (i.e., primary MAP) can be served by a failure-free MAP (i.e., secondary MAP) by failure detection/recovery schemes in the case of the RH-MIPv6. In this paper, we investigate the comparative study of RH-MIPv6 and HMIPv6 under several performance factors such as MAP unavailability, MAP reliability, packet loss rate, and MAP blocking probability. To do this, we utilize a semi-Markov chain and a M/G/C/C queuing model. Numerical results indicate that RH-MIPv6 outperforms HMIPv6 for all performance factors, especially when failure rate is high.

We present a new space-time successive interference cancellation (ST-SIC) scheme with multiple transceiver antennas for direct-sequence code division multiple access (DS-CDMA) systems. The proposed scheme is computationally very efficient, while maintains the performance close to the previous space-time multiuser detection (ST-MUD) scheme. The bit error rate (BER) performance of the ST-SIC scheme for coherent phase shift keying (PSK) modulation is analytically examined in Rayleigh fading channels, and its validity and usefulness are demonstrated by computer simulations.

We propose a burst optical packet generator based on a novel photonic parallel-to-serial conversion scheme, and demonstrate 40-Gbit/s 16-bit optical packet generation from 16-ch parallel low-voltage TTL data streams. It consists of electrical 4:1 parallel-to-serial converters that employ InP metal-semiconductor-metal photodetectors, and an optical time-domain multiplexer with electroabsorption modulators. The proposed optical packet generator is suitable for burst optical packet generation and overcomes the electronic bandwidth limitation, which is prerequisite for achieving high-speed photonic packet switched networks. In addition, it can be driven by simple low-cost low-power CMOS logic circuits, and is compact and extensible in terms of the number of input channels due to the effective combination of electrical and optical multiplexing.

This paper presents recursive algorithms for the least mean-squared error linear filtering and fixed-interval smoothing estimators, from uncertain observations for the case of white and white plus coloured observation noises. The estimators are obtained by an innovation approach and do not use the state-space model, but only covariance information about the signal and the observation noises, as well as the probability that the signal exists in the observed values. Therefore the algorithms are applicable not only to signal processes that can be estimated by the conventional formulation using the state-space model but also to those for which a realization of the state-space model is not available. It is assumed that both the signal and the coloured noise autocovariance functions are expressed in a semi-degenerate kernel form. Since the semi-degenerate kernel is suitable for expressing autocovariance functions of non-stationary or stationary signal processes, the proposed estimators provide estimates of general signal processes.

Future mobile communication systems 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 requirements on the mobile wireless networks. In order to provide mobile hosts with high quality of service in the next generation mobile multimedia wireless networks, efficient and better bandwidth reservation schemes must be developed. A novel traffic-based bandwidth reservation scheme is proposed in this paper as a solution to support quality of service guarantees in the mobile multimedia wireless networks. Based on the existing network conditions, the proposed scheme makes an adaptive decision for bandwidth reservation and call admission by employing fuzzy inference mechanism, timing based reservation strategy, and round-borrowing strategy in each base station. The amount of reserved bandwidth for each base station is dynamically adjusted, according to the on-line traffic information of each base station. We use the dynamically adaptive approach to reduce the connection-blocking probability and connection-dropping probability, while increasing the bandwidth utilization for quality of service sensitive mobile multimedia wireless networks. Simulation results show that our traffic-based bandwidth reservation scheme outperforms the previously known schemes in terms of connection-blocking probability, connection-dropping probability, and bandwidth utilization.

Future IP networks will provide multi-class-services that have multiple levels of Quality of Services (QoS) at different prices. One of the issues for the network service provider (NSP) will be how to profit by providing them. This paper proposes a scheme that maximizes the profit of the NSP by controlling the service-list under the constraint of the available network resources. We introduce a model in which the users' selection from among the multiple classes is influenced not just by the price and QoS of one class, but the prices and QoS levels of all classes. In short, the user's selection involves a balance between the price and QoS levels of all classes. To model the users' class choice, we adopt discrete choice analysis; it can estimate the model parameters such that the model fits actual choice data. This paper proposes a functional framework that consists of User Choice Model Function, Original Demand Forecast Function, and Service-list Determination Function. The proposed model has the advantage of following actual changes adaptively. Effectiveness of the proposed scheme is evaluated by computer simulation for a multiple class service; even if the real parameters are changed, the proposal can follow the change and provide the optimal service-list that maximizes profit adaptively.

Multiuser diversity, identified by recent information theoretic results, is a form of diversity inherent in a wireless network. The diversity gain is obtained from independent time-varying fading channels across different users. The main practical issue in multiuser diversity is lack of Quality of Service (QoS) guarantees. This study proposes a wireless scheduling algorithm named MUDSEQ for downlink channels exploiting multiuser diversity under explicit QoS constraints. The numerical results demonstrate that the novel algorithm can yield non-negligible diversity gain even under tight QoS constraints and little scattering or slow fading environments. Additionally, a system framework for dynamic resource allocation based on the proposed algorithm is developed.

A simple method has been proposed for the measurement of the output power and phase characteristics of the 3rd-order inter-modulation distortion (IM3) components appearing in multistage power amplifiers. By adopting a unique definition of the phase for the IM3 components that is independent of the delay time caused by transmission lines and other instrument devices, it is possible to measure the phase, merely by using a vector signal analyzer. It is demonstrated that an accurate estimation of the IM3 characteristics of two-stage cascaded power amplifiers for cellular radio handheld terminals can be made by using the IM3 characteristics of the 1st and 2nd-stage amplifiers as measured by the proposed method. The results indicate that it is possible to reduce the dissipation power by 18% at 28 dBm RF output power with respect to conventional measurement methods. Further studies show that the error in the resultant vector of the estimated IM3 is less than 1 dB, when the asymmetry characteristics of the IM3 sidebands in the 2nd-stage amplifier are less than 7.3%.

This paper considers the least-squares linear estimation problem of signals from randomly delayed observations when the additive white noise is correlated with the signal. The delay values are treated as unknown variables, modelled by a binary white noise with values zero or one; these values indicate that the measurements arrive in time or they are delayed by one sampling time. A recursive one-stage prediction and filtering algorithm is obtained by an innovation approach and do not use the state-space model of the signal. It is assumed that both, the autocovariance functions of the signal and the crosscovariance function between the signal and the observation noise are expressed in a semi-degenerate kernel form; using this information and the delay probabilities, the estimators are recursively obtained.

This paper presents ACIS, an Autonomous Community Information System. ACIS is a proposition made to meet the rapidly changing users' requirements and cope with the extreme dynamism in current information services. ACIS is a decentralized bilateral-hierarchy architecture formed by a community of individual end-users (community members) having the same interests and demands at specified time and location. It allows those members to mutually cooperate and share information without loading up any single node excessively. In this paper, autonomous decentralized community construction and communication technologies are proposed to assure a productive cooperation, a flexible and timely communication among large number of community members. The main ideas behind the proposed communication technology are: content-code communication (service-based) for flexibility and multilateral benefits communication for timely and productive cooperation among members. All members communicate productively for the satisfaction of all the community members. The scalability of the system's response time regardless of the number of the community members has been shown by simulation. Thus, the autonomous decentralized community communication technology reveals interesting results when the total number of members in the community increases dramatically.

A new power-down circuit scheme using data-preserving complementary pass transistor flip-flop circuit for low-power, high-performance Multi-Threshold voltage CMOS (MTCMOS) LSI is presented. The proposed circuit can preserve a stored data during power-down period while maintaining low leakage current without any extra circuit and complex timing design. The flip-flop provides 24% improved delay and 30% less silicon area compared to conventional MTCMOS flip-flop circuit. A 16-bits DSP processor core using the proposed circuit and 0.18 µ m CMOS technology was designed. The DSP chip was successfully operated at 120 MHz, 1.65 V and its total leakage current in power-down mode was four orders smaller than conventional DSP chip.

We describe a framework for deriving specifications of wizard-like tools by detecting coherent patterns of behaviour among user actions observed in a portal environment. Implementation in the portal of tools compliant with these specifications can then provide useful support for the kind of work patterns observed. The derivation process employs a customizable knowledge base which defines coherent patterns and seeks concrete instances of them among series of actions that occur with sufficient frequency among those observed.

In this letter, we propose a groupwise successive interference cancellation (GSIC) receiver with gradient descent search for multi-rate DS-CDMA system. Proposed receiver incorporates iterative gradient descent search algorithm into conventional GSIC receiver for multi-rate DS-CDMA system. It is shown that the receiver achieves significant performance improvement over the matched filter (MF) receiver, GSIC receiver, multi-stage parallel interference cacnellation (PIC) receiver, multi-stage partial PIC receiver, and GSIC receiver with PIC in a Rayleigh fading channel.

Flexible Resource Allocation (FRA) strategies selectively control the transmission rates of users allowing them to specify maximum and minimum bandwidth requirements for the service type requested ensuring a minimum quality of service (QoS) is met. Complete, Partial, and Non Resource Sharing are the three types of resource sharing policies that can be used in systems with integrated services (voice, video and data) with different QoS and elasticities requirements. In this paper, an FRA strategy with Partial Resource Sharing, called Primary Unavailable Secondary Minimum (PUSMin), is presented. An analytical method is developed to assess its performance in an environment where several service types (with different bandwidth and elasticities requirements) exist. Results show that PUSMin decreases the resource reassignment rate as the offered traffic increases. This decreases the signalling overhead and computational complexity in the Base Station Controller (BSC) or Base Transceiver Station (BTS).