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This paper presents an analysis framework for estimating spatio-temporal distortion associated with data-gathering algorithms in sensor networks. We assume that the underlying data field being sensed is spatially and temporally correlated and that the sink node performs real-time reconstruction of the field. Unlike existing work, the proposed analysis framework assumes realistic transmission schemes and network/routing parameters, such as congestion and limited transmission range. Our simulations show that, even for a simple collision-free transmission scheme and regular deployment patterns, the distortion analyses yield starkly different results, compared with the analyses performed in the absence of these assumptions. The analytical method presented in this paper could easily be extended to consider the real-time data-reconstruction problem under different transmission schemes, node distributions, and reconstruction methods. [ABSTRACT FROM AUTHOR]

Checkpointing, the process of saving program/application state, usually to a stable storage, has been the most common fault-tolerance methodology for high-performance applications. The rate of checkpointing (how often) is primarily driven by the failure rate of the system. If the checkpointing rate is low, fewer resources are consumed but the chance of high computational loss is increased and vice versa if the checkpointing rate is high. It is important to strike a balance, and an optimum rate of checkpointing is required. In this paper, we analytically model the process of checkpointing in terms of mean-time-between-failure of the system, amount of memory being checkpointed, sustainable I/O bandwidth to the stable storage, and frequency of checkpointing. We identify the optimum frequency of checkpointing to be used on systems with given specifications thereby making way for efficient use of available resources and maximum performance of the system without compromising on the fault-tolerance aspects. Further, we develop discrete-event models simulating the checkpointing process to verify the analytical model for optimum checkpointing. Using the analytical model, we also investigate the optimum rate of checkpointing for systems of varying resource levels ranging from small embedded cluster systems to large supercomputers. [ABSTRACT FROM AUTHOR]

This paper presents a novel generalized transceiver architecture, i.e., Multicarrier Interleave-Division-Multiplexing-aided Interleave Division Multiple Access (MC-LDM-IDMA). A parallel interference cancellation (PIC)-aided iterative multi- user detection (MUD) algorithm is introduced, and the convergence behavior of the system is evaluated with the aid of EXtrinsic Information Transfer (EXIT) charts under the assumption of an equal-power multiuser scenario. Three interesting design tradeoffs of the MC-IDM-IDMA system are analyzed: 1) the multiplexing versus diversity tradeoffs; 2) the coding versus spreading tradeoffs, where the achievable bandwidth efficiency of both MC-IDM and MC-IDMA are characterized, and a general design rule is provided for low-rate codes; and 3) the complexity versus performance tradeoffs and the EXIT characteristics of two different MUD algorithms are investigated, leading to a reduced- complexity hybrid MUD. [ABSTRACT FROM AUTHOR]

This paper addresses when and how to adjust bandwidth allocation on uplink and downlink in a multiservice mobile wireless network under dynamic traffic load conditions. Our design objective is to improve system bandwidth utilization while satisfying call level QoS requirements of various call classes. We develop a new threshold-based multiservice admission control scheme (DMS-AC) as a study base for bandwidth reallocation. When the traffic load brought by some specific classes under dynamic traffic conditions in a system exceeds the control range of DMS-AC, the QoS of some call classes may not be guaranteed. In such a situation, bandwidth reallocation process is activated and the admission control scheme will try to meet the QoS requirements under the adjusted bandwidth allocation. We explore the relationship between admission thresholds and bandwidth allocation by identifying certain constraints for verifying the feasibility of the adjusted bandwidth allocation. We conduct extensive simulation experiments to validate the effectiveness of the proposed bandwidth reallocation scheme. Numerical results show that when traffic pattern with certain bandwidth asymmetry between uplink and downlink changes, the system can reallocate the bandwidth on uplink and downlink adaptively. With the designed bandwidth reallocation scheme in conjunction with the distributed admission control scheme, the QoS requirements of various call classes can be guaranteed under dynamic traffic conditions, and in the meantime, the system bandwidth utilization is improved significantly. [ABSTRACT FROM AUTHOR]

Fast sampling is desirable to describe signal transmission through wide-bandwidth systems. The delta-operator provides an ideal discrete-time modeling description for such fast-sampled systems. However, the estimation of delta-domain model parameters is usually biased by directly applying the delta-transformations to a sampled signal corrupted by additive measurement noise. This problem is solved here by expectation-maximization, where the delta-transformations of the true signal are estimated and then used to obtain the model parameters. The method is demonstrated on a numerical example to improve on the accuracy of using a shift operator approach when the sample rate is fast. [ABSTRACT FROM AUTHOR]

We develop a new wideband digital feedback predistortion (WDFBPD) technique for modulated signals with wide bandwidths by combining digital feedback predistortion (DFBPD) linearization and memory-effect compensation techniques. For the experiments, a class-AB amplifier using an LDMOSFET with 90-W peak envelope power is employed. The proposed technique is compared with existing DFBPD and memory polynomial (MP) techniques for a 2.14-GHz forward-link WCDMA 2FA signal with 10-MHz carrier spacing. The experimental results show that the new WDFBPD technique has better linearization performance than conventional DFBPD and lower computational complexity than the MP technique. [ABSTRACT FROM AUTHOR]

We introduce a single-loop PLL that operates in a narrower-bandwidth, integer-N mode during phase lock and in a wider-bandwidth, fractional-N mode during transient. This hybrid PLL, as a generalization of the conventional variable-band-width PLL that shifts only its bandwidth, simultaneously achieves the fast-locking advantage of the fractional-N PLL and design simplicity of the integer-N PLL, and as such, brings benefits in certain important PLL applications. In addition, the frequency division mode switching, unique in the hybrid PLL, enables a new, more digital protocol to execute bandwidth switching. A CMOS IC prototype attests to the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper we address the emerging application of mobility to DVB-S2/DVB-RCS systems, sometimes also referred to as Satellite-On-The Move (SOTM) communications. Satellite communications have great commercial success in digital audio and video broadcasting as they exploit the inherent wide area coverage for distribution content. It was a natural consequence to extend its use to multimedia applications; DVB-S2/DVB-RCS standards offer a commercially proven solution for fixed terminals in that sense. In addition, communication on the move is becoming a key market sector. Therefore broadband mobile communications represent an additional market for the satellite, addressing primarily transport operators (planes, ships, trains) but also end-users in cars. To ensure economies of scale and fast development and deployment of equipments, the adaptation of current satellite broadcast and interactive broadband standards is foreseen. This paper presents possible techniques applicable to different market segments for both the forward and the return links of the system, with associated performance and impact on the standards. [ABSTRACT FROM AUTHOR]

In this paper, the MoBISAT (Mobile Broadband Interactive Satellite Access Technology) system, the BcSAT (Broadband adaptive satellite communicationS and broadcAsting convergence Technology) system and the STC (Satellite and Terrestrial Convergence) system for interactive service on high speed train environment mainly deal with the information identified as system introduction, detail design description and implementation issues, respectively. First, MoBISAT system which represents a mobile broadband satellite access technology, provides satellite TV broadcasting service in Ku-band and high speed Internet service in Ka band based on DVB-S/DVB-RCS standard to the passengers and crews for land mobile, maritime and aeronautical environments (ETSI EN 301 790). BcSAT system aims at realizing the next generation satellite broadcasting service in Ka-band through DVB-S2 standard (ETSI EN 302 307). It can be implemented through high bandwidth-efficient and flexible transmission mode with provision of high order modulation scheme and robust channel coding technique. Furthermore, we're pursuing the development of prospective convergence system composed with satellite and terrestrial networks for realization of ubiquitous service, briefly. In a result, information of this paper will be useful to figure out the main design features and realistic consideration (IEEE Wireless Commun. 12(5) (2005), 91–97). [ABSTRACT FROM AUTHOR]

The use of Wireless in Local Loop (WILL) has generated considerable interest due to the advantages it offers such as ease and low cost of deployment and maintenance. With an increase in the number of subscribers in the network, it becomes expedient to employ spectrum reusability techniques such as the use of multihop relaying in order to improve the capacity of the wireless systems. Throughput enhanced Wireless in Local Loop (TWILL) is one such architecture that employs multihop relaying and shortcut relaying to reuse bandwidth in WiLL Systems. Compared to other multihop wireless network architectures, TWILL architecture assumes significance due to its potential use in fixed wireless broadband services such as LMDS (Local Multipoint Distribution Service) and MMDS (Multichannel Multipoint Distribution System). Analysis of the Call Acceptance Ratio (CAR) in multihop wireless architectures including TWILL is nontrivial as the Erlang B formula no longer holds. In this paper, we build multidimensional Markov Chains to analyze the performance of multihop wireless systems such as TWILL that has multiple types of channels. We also compare the results of our analysis with results from simulations. We observe that multihop relaying and shortcut relaying lead to a significant increase in the CAR of WiLL systems. Also, the free space propagation model that is normally used to model the radio channel is a very unrealistic model and does not consider reflection, diffraction, scattering, and multipath propagation that hinder transmissions in WiLL systems. In this paper, we studied the effect of several realistic radio channel propagation models on the performance of the TWILL system through analysis and simulations. [ABSTRACT FROM AUTHOR]

We propose a service architecture for the next-generation wireless networks. In the interest of creating a ‘Ubiquitous’ Service Platform (USP) for heterogeneous networking environments, we address important issues related to ‘service convergence’ and ‘service mobility.’ The objectives of our work are threefold: firstly, making services available across different administrative and technology domains; secondly, facilitating dynamic provision of services that can be discovered and used without preconfigured subscription; and lastly, making services movable in geographical and topological locations. We build our USP architecture over the IP Multimedia Subsystem (IMS) infrastructure, making extensions where the current IMS falls short as a generalized service platform while exploiting its strengths, such as support for user roaming and session mobility. We define generic USP functional elements and their operations and interfaces, and then map them onto IMS elements and SIP messages. [ABSTRACT FROM AUTHOR]

In multi-service wireless networks, asymmetric bandwidth allocation has been proposed to satisfy the requirements of asymmetric traffic load introduced by some data applications. However, it is difficult to promptly adjust bandwidth allocation on uplink and downlink according to the dynamics of traffic load. Inappropriate call admission control (CAC) policies in this environment may admit superfluous real-time (RT) calls or non real-time (NRT) calls and thus lead to low bandwidth utilization. In this paper, we propose and evaluate two new CAC schemes to address the problems caused by the mismatch of bandwidth allocation and traffic changing in multi-service wireless networks with bandwidth asymmetry between uplink and downlink. By determining the admissible regions for the RT calls and the NRT calls, the proposed schemes prevent the calls of a specific class from overusing the bandwidth resources. Mathematical analysis and simulation experiments are employed to study and compare the performance of the proposed schemes and the existing schemes. The numerical results show that the proposed schemes can achieve better performances in terms of call blocking probability and bandwidth utilization compared to some existing schemes, even those performing well in bandwidth asymmetry wireless networks. [ABSTRACT FROM AUTHOR]

The growing demand of high speed multi-class data transmissions poses new challenges on wireless networks. The major objectives of the next generation wireless networks include: (1) achieving high data throughput in the fast varying wireless channel; (2) transmitting multi-class data by service multiplexing; and (3) controlling the delay for delay sensitive service. To achieve these goals, in the context of wideband code division multiple access (WCDMA) system, we propose a cost-function based rate adaptation mechanism by taking account of both physical layer channel impacts and higher layer performance parameters, such as buffer occupancy and service priority. We implement this cross-layer rate mechanism by exploiting the transport format (TF) selection procedure in the medium access control (MAC) layer of the WCDMA system. Through the proposed cross-layer cost function, the TF selection procedure can dynamically adapt suitable spreading factors every transmission time interval (TTI), usually 10–80 ms. Through simulations in a flat Rayleigh fading channel, we show that the proposed cross-layer cost-function based rate adaptation mechanism can effectively improve throughput and reduce the buffer occupancy for multi-class services for the WCDMA system at the cost of slightly higher power efficiency. Copyright © 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, a new architecture for baseband digital predistortion dedicated to wide-hand transmissions is presented. The proposed predistorter consists of a cascade of a static lookup table-based predistorter and a subband filtering block. The subband filtering technique is used to improve the correction bandwidth limitation of conventional architectures. The cases of four- and eight-subband decomposition were considered and compared to the case where the fullband signal is processed. This revealed that the subband processing results in a better sensitivity and an independent tuning ability of the predistorter at each subband. In addition, it was shown that, in the proposed predistorter, the computational complexity and the required processing speed are reduced proportionally to the number of subbands. Moreover, in an adaptive digital predistortion context, a quicker convergence can be achieved. Experimental validation of the subband-based predistortion concept was successfully carried on a 100-W peak envelop power lateral double diffused metal-oxide semiconductor power amplifier. [ABSTRACT FROM AUTHOR]

The design and analysis is presented of a low profile and dual-frequency inverted L-F antenna for WLAN and short range wireless communications, providing a compromise between size reduction and attainable bandwidth. The optimum (minimized) volume of 30 × 30 × 8 mm of the proposed antenna gives 8% bandwidth at lower resonant mode of 2400 MHz, while at the higher resonant mode of 5500 MHz a bandwidth of 12.2% is obtained. Both the simulated and measured characteristics of the proposed antenna are shown. [ABSTRACT FROM AUTHOR]