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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]

Abstract: TCP over bandwidth asymmetric networks such as Cable TV and Asymmetric Digital Subscriber Loop (ADSL) exhibits different characteristics from TCP on symmetric links. A number of techniques have been proposed to address this problem. However, previous research has been largely focused on bulk transfers. This paper investigates the effects of bandwidth asymmetry on Web-like short-lived transfers. Two prediction models, one given in a closed form and the other in a recursive form, are presented for TCP transfers without and with ACK Filtering (AF), a representative optimizing technique for TCP transfers over bandwidth asymmetric links. Ns-2 based experiments show that these models can predict TCP transfer latency with a high degree of accuracy. [Copyright &y& Elsevier]

A rapid control method is proposed to improve the transmission properties of a synchronized QoS ad hoc network (synchronized QoS network). The synchronized QoS network has already been proposed to assure transmission bandwidth in ad hoc networks. However, the VC (virtual circuit) establish time and the VC breakage interval both expand in this network. Furthermore, the rate of successful communication deteriorates in relation to network topology changes. These problems become serious when a synchronized QoS network is applied to the multirobot rescue systems operating in urban disaster areas. The rapid control method modifies the frame structure of the conventional synchronized QoS network. This method accelerates control packet transmission and therefore improves the VC establish time, VC breakage interval, and the rate of successful communications. These improvements are confirmed by computer simulations in which a reconnaissance into distant space by a multirobot rescue system is simulated. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 89(9): 51–59, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20278 [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]

This paper describes a technique for reconstructing one-dimensional stratified permittivity profiles. The proposed technique is based on the inversion of the measured frequency-domain reflection coefficient of the profile into a virtual time domain. The inversion of the reflection coefficient is based on the super-resolution technique root multiple-signal classification. The advantage of using this technique is its ability to remove the sidelobe effect caused by the limited measurement bandwidth. Measurements using different materials have been carried out to validate the quality of the proposed technique. [ABSTRACT FROM AUTHOR]

Carrier frequency offset (CFO) estimation for orthogonal frequency-division multiplexing (OFDM) has caught attention as OFDM systems have become widely adopted in recent years. In this paper, we design a novel double-differential (DD) codec with low computational complexity. Our design bypasses CFO and channel estimation, and is easy to implement at both transmitter and receiver. It also guarantees full multipath diversity, and reduces the peak-to-average power ratio from the number of subcarriers to the channel order. In addition, it is robust to CFO drifting. The closed form of the performance for our design is derived for OFDM transmissions over frequency-selective channels with CFO. Thorough simulation results corroborate our claims. [ABSTRACT FROM AUTHOR]

A microstrip line on very thin membrane substrate (0.05 mm) is slot-coupled through a thick air substrate (12.7 mm) to excite an L-band radiating patch element. A breadboard unit achieved a relatively wide bandwidth of 100 MHz (8%). Very narrow coupling slot is used with aspect ratio of 160 (conventional slot aspect ratio is between 10 to 30). This new feed design makes the thin-membrane or inflatable array antenna technology more practical. It reduces the number of thin-membrane layers required for a dual-pol wide-band inflatable array from three layers in a previous design to two layers. In addition, this technology allows the thin-membrane array antenna elements to be readily integrated with thin-membrane-mounted transmit/receive (T/R) modules. Calculation shows that, without the patch, the micros trip line and slot combination can also radiate as a paper-thin (0.05 mm) radiator at the L-band frequencies. [ABSTRACT FROM AUTHOR]

The trend of increasing areal density, i.e., the number of bits recorded in unit area of the media, continues in the hard disk drive (HDD) industry. This growth is sustained by increasing both the track density and bit density. The track density that can be achieved in a drive depends on many factors such as the dimensions of read/write head and the performance of the head positioning servomechanism. The higher the servo bandwidth, the better the precision achieved in controlling the position of the head. Most of the drives use an embedded servo scheme, which puts a physical constraint on the frequency at which the position error is sampled, and hence, on the achievable bandwidth. The need for a better position error sensing (PES) scheme is the motivation behind exploring alternative methods of servo encoding. This paper addresses different aspects of decoding position error from the dual-frequency servo bursts. It is shown, using both simulation and experimental results, that the proposed scheme offers a feasible solution for generating the PES signal in high-performance HDD. [ABSTRACT FROM AUTHOR]

Bank conflicts can severely reduce the bandwidth of an interleaved multibank memory and conflict misses increase the miss rate of a cache or a predictor. Both occurrences are manifestations of the same problem: Objects which should be mapped to different indices are accidentally mapped to the same index. Suitable chosen hash functions can avoid conflicts in each of these situations by mapping the most frequently occurring patterns conflict-free. A particularly interesting class of hash functions are the XOR-based hash functions, which compute each set index bit as the exclusive-or of a subset of the address bits. When implementing an XOR-based hash function, it is extremely important to understand what patterns are mapped conflict-free and how a hash function can be constructed to map the most frequently occurring patterns without conflicts. Hereto, this paper presents two ways to reason about hash functions: by their null space and by their column space. The null space helps to quickly determine whether a pattern is mapped conflict-free. The column space is more useful for other purposes, e.g., to reduce the fan-in of the XOR-gates without introducing conflicts or to evaluate interbank dispersion in skewed-associative caches. Examples illustrate how these ideas can be applied to construct conflict-free hash functions. [ABSTRACT FROM AUTHOR]

Increasing the bandwidth or bit rate in real-time video applications to improve the quality of images is typically impossible or too expensive. Postprocessing appears to be the most feasible solution because it does not require any existing standards to be changed. Markedly reducing blocking effects can increase compression ratios for a particular image quality or improve the quality with respect to the specific bit rate of compression. This paper proposes a novel deblocking algorithm based on three filtering modes in terms of the activity across block boundaries. By properly considering the masking effect of the human visual system, an adaptive filtering decision is integrated into the deblocking process. According to three different deblocking modes appropriate for local regions with different characteristics, the perceptual and objective quality are improved without over smoothing the image details or insufficient reducing the strong blocking effect on the flat region. According to the simulation results, the proposed method outperforms methods of deblocking MPEG-4 with respect to peak signal-to-noise ratios and computational complexity. [ABSTRACT FROM AUTHOR]

A multi-layered algorithm is proposed that provides a scalable and adaptive method for handling data on a wireless sensor network. Statistical tests, local feedback, and global genetic style material exchange ensure limited resources such as battery and bandwidth which are used efficiently by manipulating data at the source and important features in the time series are not lost when compression needs to be made. The approach leads to a more ‘hands off’ implementation which is demonstrated by a real world oceanographic deployment of the system. [ABSTRACT FROM AUTHOR]

A novel type of distributed superconducting mixer with very low output capacitance has been designed for a 330-420 GHz waveguide mixer. In this design, a pair of lumped element Superconductor-Insulator-Superconductor junctions is connected in series to form the unit cell of a composite transmission line. The mixer utilizes two cascaded cells. Using an intermediate frequency (IF) of 5 GHz, we have measured Double-side-band (DSB) receiver noise temperatures of 90-120 K between 360 and 410 6Hz. This mixer design offers very wide instantaneous bandwidth. The measured IF bandwidth is in excess of 18 6Hz. At a Local Oscillator frequency of 384 6Hz, the Y-factor measured at an IF frequency of 18GHz is 2.1, compared to a Y-factor of 2.2 measured at an IF of 5 6Hz. The mixer also has a high dynamic range. The 1-dB input compression point is only reached with an input black body load of 30,000 K. [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 cellular networks, it is vital to allocate communication channels efficiently because the bandwidth allocated for cellular communication is limited. If channels are statically allocated, as is the case in current cellular networks, a cell may run out of channels when a large number of mobile hosts move to the cell. To overcome this problem, dynamic channel allocation approaches have been proposed. Under dynamic channel allocation, channels are allocated to cells on demand, thus increasing channel utilization. Such channel allocation approaches fall under two categories, namely, centralized and distributed. Centralized approaches are neither scalable nor reliable, while distributed approaches have the potential to be both reliable and scalable. In the distributed approaches, a mobile service station is responsible for allocating channels to mobile hosts in the same cell. In cellular networks, mobile service stations may fail. In addition, the network may encounter intermittent network congestion and/or link failures. It is desirable for a channel allocation algorithm to work well, even in the presence of network congestion, link failures, and/or mobile service station failures. In this paper, we present a distributed dynamic channel allocation scheme for cellular networks that is fault-tolerant. Our approach can tolerate the failure of mobile service stations, link failure, and network congestion, and make efficient reuse of channels. We also provide results of the performance evaluation of our algorithm. [ABSTRACT FROM AUTHOR]

A novel partly shielded-finite ground coplanar waveguide (PS-FGCPW) low pass filter has been designed. The device consists of a PS-FGCPW loaded with metal stubs at periodic positions of the signal line. The width of the metal stubs has a sinusoidal variation as the function of the position along the signal line. By properly choosing the position and dimension of the loaded stubs, a wide stop band, more than four times the pass bandwidth, is obtained through the suppression of spurious frequencies inherent to the distributed structures. The prototype also exhibits very sharp cutoff, very low insertion loss in the passband, slow-wave effect and high isolation performance. [ABSTRACT FROM AUTHOR]

Measurements are presented for microstrip filters on layered media containing magnetized ferrites. The measurements show that the filters can be tuned by adjusting the magnitude of the magnetic-bias field. The measured results are compared with full-wave numerical results obtained by the authors via the method of moments in the spectral domain. The agreement between experimental and numerical results is reasonably good. The results show that the bandwidth of the filters appreciably decreases as the tuning frequency increases for frequencies located above the magnetostatic waves range (MWR). However, tuning is achieved without substantial bandwidth reduction for frequencies located below the MWR. [ABSTRACT FROM AUTHOR]

We report a novel technique for radiometric detection of radiation in the millimeter-wave regime based on optical modulation. Millimeter-wave energy modulated onto an optical carrier is detected using a low-bandwidth photodetector with optical filtering to suppress the carrier. Using this technique, we have achieved noise-equivalent powers as low as 20 pW√Hz for a 44-GHz narrow-band signal using chopping techniques. Such detection was implemented using commercially available components and without RF or optical amplification. Further improvements in sensitivity are expected as the setup is optimized for operation in the frequency band of interest. [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]

We present a new low-frequency noise model of a GaInP-GaAs HBT and the associated extraction process from measurements. Specific measurements enable us to locate the two dominant low-frequency noise sources. Their spectral densities extraction as a function of the emitter bias current is then performed and a normalized scalable model is deduced. The cyclostationarity of the low-frequency noise sources is justified. The whole noise model including the shot noise source is implemented in the nonlinear IJIBT model used in the United Monolithic Semi-conductors foundry. In order to verify the validity of the scalable noise model, several voltage-controlled oscillators with different center frequencies and tuning bandwidth have been designed and processed. Comparisons between the predicted performances and experimental results show an excellent agreement and validate the proposed low-frequency noise modeling of multifinger HBTs. [ABSTRACT FROM AUTHOR]

In this paper, we propose a demodulation method using maximum likelihood sequence estimation (MLSE) after coherent detection for partial response signaling single sideband (SSB) signals and present the bit error rate performance achieved by this configuration. Coherent detection is implemented by a pilot carrier method. The power of the pilot carrier inserted in the SSB modulated wave and the noise bandwidth of the phase locked loop (PLL) that extracts the base carrier cause the degradation in the power efficiency of the SSB signal. We then evaluate the equivalent carrier-to-noise power ratio (CNR) degradation of the pilot carrier method. The partial response demodulated signal can be MLSE decoded since the signal is time correlated. From the characteristics of an SSB demodulated signal, first-order MLSE decoding using only the in-phase channel generally results. Here, we also study a complex MLSE decoding method that considers the quadrature channel. Based on this configuration, we show that the SSB signal power efficiency was improved by about 5 dB compared to the conventional coherent detection and instantaneous identification and demodulation method. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(4): 44–53, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20167 [ABSTRACT FROM AUTHOR]

Video multicast is a challenging problem due to heterogeneous and best-effort nature of the Internet. In this paper, we present a novel video multicast framework that exploits the potential of object scalability offered by MPEG-4. Specifically, we introduce the concept of object transmission proxy (OTP), which filters incoming streams using object-based bandwidth adaptation to meet dynamic network conditions. Multiple OPTs can form an overlay network that interconnects diverse multicast islands with semi uniform demands within each single island. We concur with the wisdom that an application best knows the utility of its data. Hence, the bandwidth adaptation algorithm for the OTPs adaptively allocates bandwidth among video objects according to their respective utilities and then performs application-level filtering based on an effective stream classification and packetization scheme. Extensive simulation results demonstrate that our framework has substantial performance improvement over conventional bandwidth adaptation schemes. It is particularly suitable for object-based video multicasting where the objects are of different importance. [ABSTRACT FROM AUTHOR]

We design novel space-time multipath (STM) coded multi-antenna transmissions over frequency-selective Rayleigh fading channels. We develop STM coded systems that guarantee the maximum possible space-multipath diversity, along with large coding gains, and high bandwidth efficiency for any number of transmit-receive antennas. By incorporating subchannel grouping, we also enable desirable tradeoffs between performance and complexity. Our designs rely on digital phase sweeping or block circular delay operations and apply to both single- and multi-carrier systems. Their merits are confirmed by corroborating simulations and comparisons with existing approaches. [ABSTRACT FROM AUTHOR]

A broadband multiple-input multiple-output (MIMO) OFDM system has been designed and evaluated for a fixed wireless link between tall buildings in an urban area. Channel measurements for a typical installation location are analysed to determine the relevant spatial, temporal and frequency characteristics. The small number of multipath components leads to a high spatial correlation and limited potential for spatial diversity to provide spectral efficiency gains. However, the slowly-varying characteristics support the use of a closed-loop diversity scheme, such as spatial multiplexing along the eigenmodes of the channel matrix, to maximise the achievable throughput. This scheme is evaluated using the measured channel data, and it is shown that the self-interference caused by channel estimation errors is the limiting factor on the system performance. Taking into account the estimation errors and feedback delay, it is demonstrated that a three-fold increase in spectral efficiency relative to a single-element antenna system is achievable using eight-element antennas, even in this highly correlated environment. [ABSTRACT FROM AUTHOR]

Current admission controls that seek to optimise network utilisation create a bias against large-bandwidth calls. A buffer without preemption model is proposed that holds a call in a buffer rather than directly rejecting it when the residual bandwidth is insufficient. No other call can be admitted until this queued call is served. Such a mechanism increases the throughput since the buffer can temporarily hold a call. It also reduces the bias for large-bandwidth calls since all calls are rejected when the buffer is not empty, even when the residual bandwidth is sufficient for small- bandwidth calls. The proposed approach is compared with two alternative models, namely no buffer and buffer with preemption models and the performance of the models is analysed by solving a multi-dimensional Markov chain. Analytical and numerical results indicate that the proposed model achieves perfect fairness. A modified model, in which a waiting threshold is added to prevent an overlong wait for the queued call is also presented. Also, different thresholds for various bandwidth calls are set to maintain the optimal fairness. Analytical and numerical results demonstrate that this latter model actually achieves optimal fairness, even when perfect fairness cannot be achieved. [ABSTRACT FROM AUTHOR]

Planar periodic metallic arrays behave as artificial magnetic conductor (AMC) surfaces when placed on a grounded dielectric substrate and they introduce a zero degrees reflection phase shift to incident waves. In this paper the AMC operation of single-layer arrays without vias is studied using a resonant cavity model and a new application to high-gain printed antennas is presented. A ray analysis is employed in order to give physical insight into the performance of AMCs and derive design guidelines. The bandwidth and center frequency of AMC surfaces are investigated using full-wave analysis and the qualitative predictions of the ray model are validated. Planar AMC surfaces are used for the first time as the ground plane in a high-gain microstrip patch antenna with a partially reflective surface as superstrate. A significant reduction of the antenna profile is achieved. A ray theory approach is employed in order to describe the functioning of the antenna and to predict the existence of quarter wavelength resonant cavities. [ABSTRACT FROM AUTHOR]

A miniaturized dual-mode ring bandpass filter at 1.45 GHz with a bandwidth of 6% is demonstrated. The perturbation of the dual modes is realized by a pair of local ground defects. The miniaturization is achieved by loading the peripheral of the ring with the butterfly radial stub structure. A 41% loading factor has been achieved using this method. The simulated and measured results are in good agreement. [ABSTRACT FROM AUTHOR]

Abstract We describe a novel method of designing a tuning circuit with two half-wave distributed junctions separated by a half-wavelength microstripline, which analytically determines the circuit parameters such as the minimum current density of the junctions and the characteristic impedances of the distributed junctions and the microstripline. The tuning circuit was approximated by simple transmission theory and then simplified with ideal circuit components for analysis. We applied Chebyshevs band-pass filter theory, in part, to optimize the circuit design. The analytical results revealed that a high characteristic-impedance ratio between the distributed junctions and the microstripline is necessary to obtain broadband matching using low-current-density junctions. The experimental results for all-NbN SIS mixers we designed with this method demonstrated double-sideband (DSB) receiver-noise temperatures of 610 quanta from 710 to 810 GHz for a mixer with a current density of only 4 kA/cm2 (estimated ?CJRN product of 37 at 750 GHz). The RF bandwidth was broader than that of a conventional full-wave distributed SIS mixer with the same current density. [ABSTRACT FROM AUTHOR]

This paper presents an efficient method based on inter-field information for video de-interlacing. The basic idea is to classify the field dynamically to background or foreground area. The proposed method interpolates missing pixels using temporal information in the background area, and then interpolates remaining pixels using spatial and temporal information in the foreground area. Extensive simulations conducted for video sequences show that the performance of the proposed method is superior to the previous methods based on the ELA and the line averaging method in terms of the objective and subjective image qualities. Moreover, our proposed algorithm requires lower computational complexity and provides high-quality video sequences on the progressive devices. [ABSTRACT FROM AUTHOR]

The paper presents a new low complexity design of Psycho-A coustic Model (PAM), which is the key technology for MPEG-2/4 Advanced Audio Coding (AAC) encoding. The real-time constraint of MPEG AA C leads to a heavy computational bottleneck on today's portable devices. To overcome this problem, design analysis and optimization of PAM are addressed at the algorithmic level. First, the dominant calculation of spreading function is replaced with small look-up tables. Second, Modified-Discrete-Cosine-Transform-based (MDCT-based) PAM with block type decision in frequency domain is proposed to reduce the overall AAC encoder complexity and maintain the quality. This technique is different from the traditional methods. The computational complexity of PAM is reduced by 82% in total. The proposed design could be implemented in a real-time MPEG-2/4 AA C stereo encoder at Low Complexity profile and bitrate 128 kb/s with computational complexity of less than 20 MOPS while maintaining CD quality. [ABSTRACT FROM AUTHOR]

The problem of call admission control (CAC) is considered for leaky bucket constrained sessions with deterministic service guarantees (zero loss and finite delay bound) served by a generalized processor sharing scheduler at a single node in the presence of best effort traffic. Based on an optimization process, a CAC algorithm capable of determining the (unique) optimal solution is derived. The derived algorithm is also applicable, under a slight modification, in a system when the best effort traffic is absent and is capable of guaranteeing that if it does not find a solution to the CAC problem, then a solution does not exist. The numerical results indicate that the CAC algorithm can achieve a significant improvement on bandwidth utifization as compared to a (deterministic) effective bandwidth-based CAC scheme. [ABSTRACT FROM AUTHOR]

This paper addresses the implementation architecture and protocol procedure of the dedicated broadband access network TV transmission system. According to application-oriented quality of service (QoS), two alternative rate control schemes for multiple DTV programs transmission are proposed collaborating with MPEG-2 system strategy and IP-base network multiplexing mechanism. As to the network bandwidth utilization, a flexible RTP-based synchronization resilience scheme for VBR transport stream (TS) transmission is realized to ensure the performance requirement for MPEG-2 standard As to the MPEG-2 system strategy, moreover, a parallel VBR transcoding/encoding rate control algorithm for CBR TS transmission could achieve a consistent picture quality for multiple DTV programs under a constrained fixed-rate network bandwidth. For adapting the variable access network bandwidth, the system main control module can flexibly schedule the available rate control scheme for multiple slave service multiplexers. Experimental results demonstrate that the proposed schemes not only improve the traditional TV broadcast adaptation to Internet, but also achieve a more ideal program picture quality constrained by multi-program parallel multiplexing. [ABSTRACT FROM AUTHOR]

A modification to the Costas signal is suggested. It involves an increase of the frequency separation δf beyond the inverse of the subpulse duration tb, combined with adding linear FM (LEM) with bandwidth B, in each subpulse. Specific relationships between δf and B will prevent autocorrelation grating lobes, that would normally appear when tbδf > 1. [ABSTRACT FROM AUTHOR]

In bespoke data broadcasting scheme a considerable amount of buffer storage is saved at the cost of comparatively much less latency time. In this paper a modified form of the bespoke scheme has been proposed. In the modified bespoke scheme the buffer requirement is on average less than that in the bespoke scheme. Further the modified bespoke scheme has better performance in regard to user latency as well as disk transfer rate over the bespoke scheme for all values of bandwidth. [ABSTRACT FROM AUTHOR]

The eXtreme Processing Platform (XPPTM) is a new runtime-reconfigurable data processing architecture. It is based on a hierarchical array of coarsegrain, adaptive computing elements, and a packet-oriented communication network. The strength of the XPPTM technology originates from the combination of array processing with unique, powerful run-time reconfiguration mechanisms. Parts of the array can be configured rapidly in parallel while neighboring computing elements are processing data. Reconfiguration is triggered externally or even by special event signals originating within the array, enabling self-reconfiguring designs. The XPPTM architecture is designed to support different types of parallelism: pipelining, instruction level, data flow, and task level parallelism. Therefore this technology is well suited for applications in multimedia, telecommunications, simulation, signal processing (DSP), graphics, and similar stream-based application domains. The anticipated peak performance of the first commercial device running at 150 MHz is estimated to be 57.6 GigaOps/sec, with a peak I/O bandwidth of several GByte/sec. Simulated applications achieve up to 43.5 GigaOps/sec (32-bit fixed point). [ABSTRACT FROM AUTHOR]

While computer processing power, storage capacity, and bandwidth are continuing to experience exponential growth, individual human processing capabilities are not increasing significantly. Pervasive computing offers an opportunity for applications to interact with the physical environment and to provide a task-centric and mobile infrastructure for the user. However, this rich environment can also be distracting, in part because of a lack of convergence between the physical infrastructure observed by users and the information space seen by applications. In this paper we introduce AIPIS, an architecture that bridges the physical and informational realms of the human and the computer, respectively. The purpose of AIPIS is two-fold: (1) provide users with a hands-free computing environment that automates much of the drudgery associated with the use of computers; and (2) require human attention for only critical aspects of task execution that require their input. We also describe the Aura desktop, a first prototype of the AIPIS architecture. [ABSTRACT FROM AUTHOR]

In order to realize beam forming with an identical radiation characteristic over a wide bandwidth, this paper describes a method of design for two-dimensional FIR fan filters with wedge-shaped transition regions. In order to provide excellent amplitude approximations in a wide range from low to high frequencies with different transition range widths, a method based on the two-dimensional Fourier series approximation is used. The approximate amplitude characteristic of the target fan filter for which the widths of the passband and the transition band are specified in proportion to the frequency from the origin is greatly degraded at low frequencies near the origin. To reduce this degradation, the target amplitude characteristic at low frequencies of the fan filter is replaced with a rectangular cross-sectional shape. The width of the rectangular amplitude characteristic is set such that the amplitude of the designed result takes the specified value on the center line. Design examples are given for an axially symmetric fan filter and a diagonally symmetric fan filter. Further, the characteristics of the beam formers using these filters are derived and the effectiveness of the method is demonstrated. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 85(7): 38–49, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.1106 [ABSTRACT FROM AUTHOR]

This study addresses three key issues related to media differences among computer-mediated groups meeting face-to-face, synchronously, and asynchronously: First, do groups using different media perceive characteristics of these media differently? Second, do media-related perceptions remain static or change as they are used over time? And finally, do media differences result in performance differences, i.e., do richer media result in better performance for equivocal tasks as predicted by bandwidth theories? Some results of this study tend to support media-characteristics theories while others offer limited support for more evolutionary perspectives. For instance, initially, face-to-face groups found their medium to be warmer, have a better interface, and be more effective compared to their distributed counterparts. While many of these initial perceptions lingered over time, there was one notable exception. At the start of the study, face-to-face groups rated their medium as being more effective than synchronous groups; however, by the end of the study, no significant differences were apparent. Moreover, despite the persistently lower social presence of leaner media, distributed-synchronous groups performed better than their face-to-face counterparts. Finally, the two types of distributed groups--synchronous and asynchronous--did not differ significantly in their perceptions or performance. This study improves our understanding of distributed interaction while simultaneously highlighting the need to further investigate the relationships among tasks, technologies and teams over time. [ABSTRACT FROM AUTHOR]

In data transmission on a broadband network, such as an ATM network, rate-based congestion control is considered effective in preventing data loss caused by buffer overflow at a relay node and in achieving high throughput. Under this control, the sender node dynamically changes the transmission rate according to the network condition. However as the network grows, the delay for inquiry to the network condition increases so that it becomes hard to control congestion adequately. One of the solutions to that problem is to divide the network into several logical blocks and then to install virtual end systems at the block boundaries. When congestion control is carried out at each block, the delay for inquiry is decreased and the queue length of each node is kept low. As a result, cell discard caused by buffer overflow is reduced. In this paper, we build a queuing network model and then analyze it approximately to evaluate the effect of the virtual end systems. We investigate the influence of delay between the two ends and the locations of the virtual end systems in the network and then find some situations in which the virtual end systems do not work efficiently. The result shows that it is not sufficient simply to increase the number of virtual end systems and/or to consider their locations. The virtual end system should report its rate reduction to the sender node and should reduce its rate reduction ratio to serve more cells in its buffer. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(6): 8–17, 1999 [ABSTRACT FROM AUTHOR]

We describe our experience of designing, implementing, and evaluating two generations of high performance communication libraries, Fast Messages (FM) for Myrinet. In FM 1, we designed a simple interface and provided guarantees of reliable and in-order delivery, and flow control. While this was a significant improvement over previous systems, it was not enough. Layering MPI atop FM 1 showed that only about 35% of the FM 1 bandwidth could be delivered to higher level communication APIs. Our second generation communication layer, FM 2, addresses the identified problems, providing gather-scatter, interlayer scheduling, receiver flow control, as well as some convenient API features which simplify programming. FM 2 can deliver 55–95% to higher level APIs such as MPI. This is especially impressive as the absolute bandwidths delivered have increased over fourfold to 90 MB/s. We describe general issues encountered in matching two communication layers, and our solutions as embodied in FM 2. [ABSTRACT FROM AUTHOR]

Video traffic is expected to become increasingly important with the large scale deployment of broadband ISDN. In the literature, it is suggested that smoothing variable bit rate (VBR) video traffic before transmitting it onto the network would help reduce the probability of cell loss. In this paper we show why deterministic smoothing at the source approximates the minimum achievable loss over the network end-to-end of all possible smoothing schemes. Furthermore, we develop a powerful yet simple analytical technique that can efficiently calculate the loss probability at any point in a network carrying video traffic. We validate our analytical results using traces of actual video segments. The results can be used for admission control and traffic management. We find that in the case of highly correlated traffic such as motion JPEG video, the way to control loss is to ensure that the fraction of time the arrival process exceeds the service process is small. We also find that for such sources increasing the buffer size only marginally decreases the loss. [ABSTRACT FROM AUTHOR]

A V dipole antenna with multiple stub loading is proposed as a traveling wave antenna with a wide bandwidth in both the gain and input impedance. It is considered that the present antenna is essentially a tapered transmission line loaded with open stubs. Then the operating principle is studied by reducing the structure to an equivalent nonuniform transmission line. It is found from the relationship between the equivalent distributed parameters and the stub that the dipole-type stub array with its stub length reduced gradually from a hail wavelength to a quartet wavelength is a basic structure for the broadband nature by the decaying traveling wave. Based on this concept, an actual stub-loaded V dipole antenna was characterized numerically. It is demonstrated that uniform characteristics of an input admittance of 5 mS, a gain of 8 dB and a front-to-back ratio of 10 dB are obtained over ±30 percent around the center frequency in the case of a V dipole with an included angle of 30°. This antenna was fabricated and the validity of the present theory was confirmed because the theoretical and experimental results agreed well. [ABSTRACT FROM AUTHOR]

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This paper describes a new method for evaluating the queue length distribution in an ATM multiplexer assuming the cell arrival process can be assimilated to a variable rate fluid input. The method is based on a result due initially to Beneš allowing the analysis of queues with general input. Its extension to fluid input systems is considered here in the case of a superposition of on/off sources. We derive an upper bound on the complementary queue length distribution. The method is most easily applied in the case of Poisson burst arrivals (infinite sources model). In this case, we derive analytic expressions for the tail of the queue length distribution. A corrective factor is deduced to convert the upper bounds to good approximations. Numerical results justify the accuracy of the method and demonstrate the impact of certain traffic characteristics on queue performance. [ABSTRACT FROM AUTHOR]