Showing papers in "IEEE Journal on Selected Areas in Communications in 1993"
TL;DR: A recursive method for evaluating the impulse response of an indoor free-space optical channel with Lambertian reflectors, which enables accurate analysis of the effects of multipath dispersion on high-speed indoor optical communication systems.
Abstract: A recursive method for evaluating the impulse response of an indoor free-space optical channel with Lambertian reflectors is presented. The method, which accounts for multiple reflections of any order, enables accurate analysis of the effects of multipath dispersion on high-speed indoor optical communication systems. A simple algorithm for computer implementation of the technique and computer simulation results for both line-of-sight and diffuse transmitter configurations are also presented. In both cases, it is shown that reflections of multiple order are a significant source of intersymbol interference. Experimental measurements of optical multipath, which help verify the accuracy of the simulations, are discussed. >
867 citations
TL;DR: This work presents an approach to the evaluation of the reverse link capacity of a code-division multiple access (CDMA) cellular voice system which employs power control and a variable rate vocoder based on voice activity.
Abstract: This work presents an approach to the evaluation of the reverse link capacity of a code-division multiple access (CDMA) cellular voice system which employs power control and a variable rate vocoder based on voice activity. It is shown that the Erlang capacity of CDMA is many times that of conventional analog systems and several times that of other digital multiple access systems. >
804 citations
TL;DR: In this paper, the authors present the results of average and impulsive noise measurements inside several office buildings and retail stores at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40-MHz, 3dB RF bandwidth.
Abstract: The authors present the results of average and impulsive noise measurements inside several office buildings and retail stores. The noise measurement system operated at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40-MHz, 3-dB RF bandwidth. Omnidirectional and directional antennas were used to investigate the characteristics and sources of RF noise in indoor channels. Statistical analyses of the measurements are presented in the form of peak amplitude probability distributions, pulse duration distributions, and interarrival time distributions. Simple first-order mathematical models for these statistical characterizations are also presented. These analyses indicate that photocopiers, printers (both line printers and cash register receipt printers), elevators, and microwave ovens are significant sources of impulse noise in office and retail environments. >
496 citations
TL;DR: It is shown that the number of multipath components in each impulse response estimate is a normally-distributed random variable with a mean value that increases with increasing antenna separations, and the RMS delay spread over large areas is normally distributed with mean values that increase with increasing antennas separation.
Abstract: If indoor radio propagation channels are modeled as linear filters, they can be characterized by reporting the parameters of their equivalent impulse response functions. The measurement and modeling of estimates for such functions in two different office buildings are reported. The resulting data base consists of 12000 impulse response estimates of the channel that were obtained by inverse Fourier transforming of the channel's transfer functions. It is shown that the number of multipath components in each impulse response estimate is a normally-distributed random variable with a mean value that increases with increasing antenna separations; a modified Poisson distribution shows a good fit to the arrival time of the multipath components; amplitudes are lognormally distributed over both local and global areas, with a log-mean value that decreases almost linearly with increasing excess delay; for small displacements of the receiving antenna, the amplitude of the multipath components are correlated; the amplitudes of adjacent multipath components of the same impulse response function show negligible correlations; and the RMS delay spread over large areas is normally distributed with mean values that increase with increasing antenna separation. >
460 citations
TL;DR: The basic idea is to ensure that data available to the attacker is sufficiently unpredictable to prevent an offline verification of whether a guess is successful or not and to examine protocols to detect vulnerabilities to such attacks.
Abstract: In a security system that allows people to choose their own passwords, people tend to choose passwords that can be easily guessed. This weakness exists in practically all widely used systems. Instead of forcing users to choose secrets that are likely to be difficult for them to remember, solutions that maintain user convenience and a high level of security at the same time are proposed. The basic idea is to ensure that data available to the attacker is sufficiently unpredictable to prevent an offline verification of whether a guess is successful or not. Common forms of guessing attacks are examined, examples of cryptographic protocols that are immune to such attacks are developed, and a systematic way to examine protocols to detect vulnerabilities to such attacks is suggested. >
425 citations
TL;DR: It is shown how matched multiresolution source and channel coding can provide a stepwise graceful degradation and improve the behavior, in terms of coverage and robustness of the transmission scheme, over systems not specifically designed for broadcast situations.
Abstract: The use of multiresolution (MR) joint source-channel coding in the context of digital terrestrial broadcasting of high-definition television (HDTV) is shown to be an efficient alternative to single-resolution techniques, which suffer from a sharp threshold effect in the fringes of the broadcast area. It is shown how matched multiresolution source and channel coding can provide a stepwise graceful degradation and improve the behavior, in terms of coverage and robustness of the transmission scheme, over systems not specifically designed for broadcast situations. The alternative available for multiresolution transmission through embedded modulation and error correction codes are examined. It is also shown how multiresolution trellis-coded modulation (TCM) can be used to increase coverage range. Coding results and simulations of noisy transmission are presented, and tradeoffs are discussed. >
344 citations
TL;DR: The authors investigate the canceller's bit error rate (BER) performance in both the absence and presence of errors in the amplitude and phase estimates of each user's received signal.
Abstract: The authors propose and analyze a direct-sequence spread-spectrum multiaccess (DS/SSMA) receiver that employs a cascade of cochannel interference (CCl) cancellers for communication over multipath fading channels. The receiver first coherently demodulates and despreads the received signal to produce correlator outputs and initial data estimates. Based on these estimates, the cancellation scheme essentially creates replicas of the contributions of the CCl embedded in the correlator outputs and removes them for a second improved hard data decision. By repeating this operation over and over, a cascade of CCl cancellers is derived. Through theoretical analysis and simulation, the authors investigate the canceller's bit error rate (BER) performance in both the absence and presence of errors in the amplitude and phase estimates of each user's received signal. Numerical results show the considerably large improvement in performance that can be attained by the cancellation scheme, even under partially degraded estimates. >
301 citations
TL;DR: The paper explores the refinement of general high-level policies into a number of more specific policies to form a policy hierarchy in which each policy in the hierarchy represents, to its maker, his plans to meet his objectives and, to the subject, the objectives which he must plan to meet.
Abstract: Distributed system management, involves monitoring the activity of a system, making management decisions and performing control actions to modify the behavior of the system. Most of the research on management has concentrated on management mechanisms related to network management or operating systems. However, in order to automate the management of very large distributed systems, it is necessary to be able to represent and manipulate management policy within the system. These objectives are typically set out in the form of general policies which require detailed interpretation by the system managers. The paper explores the refinement of general high-level policies into a number of more specific policies to form a policy hierarchy in which each policy in the hierarchy represents, to its maker, his plans to meet his objectives and, to its subject, the objectives which he must plan to meet. Management action policies are introduced, and the distinction between imperatival and authority policies is made. The relationship of hierarchies of imperatival policies to responsibility, and to authority policies, is discussed. An outline approach to the provision of automated support for the analysis of policy hierarchies is provided, by means of a more formal definition of policy hierarchy refinement relationships in Prolog. >
286 citations
TL;DR: The authors present a quantitative study of designing a multiuser HDTV server and present efficient techniques for storing multiple HDTV videos on disk and servicing multiple subscriber requests simultaneously, both under the constraint of guaranteeing HDTV playback rates.
Abstract: The authors present a quantitative study of designing a multiuser HDTV server, and they present efficient techniques for storing multiple HDTV videos on disk and servicing multiple subscriber requests simultaneously, both under the constraint of guaranteeing HDTV playback rates. They develop a model that relates disk and device characteristics to the HDTV playback rate and derive a storage pattern for HDTV video streams that guarantees their real-time retrieval. Given multiple HDTV streams, mechanisms for merging their individual storage patterns are developed. Merging algorithms that yield a large improvement in space utilization over storing each of the streams independently are proposed. Policies such as round robin and quality proportional for servicing multiple subscribers simultaneously are studied. These studies provide a quantitative demonstration of the technological feasibility and economic viability of HDTV-on-demand servers on metropolitan area networks (MANs). >
265 citations
TL;DR: The authors describe a VLSI Galois field processor and how it can be applied to the implementation of elliptic curve groups and demonstrate the feasibility of constructing very fast, and very secure, public key systems with a relatively simple device.
Abstract: The authors describe a VLSI Galois field processor and how it can be applied to the implementation of elliptic curve groups. They demonstrate the feasibility of constructing very fast, and very secure, public key systems with a relatively simple device, and the possibility of putting such a system on a smart card. The registers necessary to implement the elliptic curve system will require less than 1 mm/sup 2/ (or less than 4%) of the area available on the card. >
261 citations
TL;DR: Analysis of a wireless network having a two-tier architecture to serve both conventional mobile subscribers and quasi-stationary subscribers shows that the capacity tradeoffs are poor for Systems I and II because of the large amounts of cross-tier interference: and that System IV gives the best capacity tradeoff.
Abstract: Th authors explore the use of a wireless network having a two-tier architecture to serve both conventional mobile subscribers and quasi-stationary (e.g., PCN (personal communications network)) subscribers. The latter are served by microcells which are embedded within macrocells that serve the mobile users. This provides a balance between maximizing the number of users per unit area (which favors small cells) and minimizing the network control associated with handoff (which favors large cells). Four approaches to sharing the spectrum between the two tiers, using per-cell capacity as the measure, are evaluated. The first two feature spread-spectrum sharing, i.e., they use TDMA (time-division multiple access) among microcell users and CDMA (code-division multiple access) among macrocell users (System I), or vice versa (System II). The other two approaches feature orthogonal sharing, i.e., they use TDMA in both tiers, with time slots (System III) or frequency channels (System IV) partitioned so there is no overlap between tiers. Analysis shows that the capacity tradeoffs are poor for Systems I and II because of the large amounts of cross-tier interference: and that System IV gives the best capacity tradeoffs. >
TL;DR: Wave interactions, like diffraction and scattering, over the propagation path are described by the uniform theory of diffraction (UTD) and physical optics (PO) and models for rural and urban areas are presented for 2-D and 3-D ray tracing.
Abstract: Mobile communication links are severely influenced by propagation effects. Wave propagation in the VHF/UHF frequency range over natural and man-made terrain is strongly dependent on topography and morphography. Propagation modeling is based on a ray-optical approach. Wave interactions, like diffraction and scattering, over the propagation path are described by the uniform theory of diffraction (UTD) and physical optics (PO). Propagation models for rural and urban areas are presented for 2-D and 3-D ray tracing. Near-range models apply to the corresponding areas in forest and urban sites. The field-strength delay spectrum describes ray contributions with deterministic amplitudes but statistical phases are used to derive time-and frequency-domain channel characteristics. Comparisons between measured and predicted data are presented. >
TL;DR: Simulation-based network models which have been developed for performance evaluation of these competing access techniques are outlined and comparative system performance measures such as channel utilization, voice blocking probability, and data delay are obtained.
Abstract: A comparative evaluation of dynamic time-division multiple access (TDMA) and spread-spectrum packet code-division multiple access (CDMA) approaches to multiple access in an integrated voice/data personal communications network (PCN) environment are presented. After briefly outlining a cellular packet-switching architecture for voice/data PCN systems, dynamic TDMA and packet CDMA protocols appropriate for such traffic scenarios are described. Simulation-based network models which have been developed for performance evaluation of these competing access techniques are then outlined. These models are exercised with example integrated voice/data traffic models to obtain comparative system performance measures such as channel utilization, voice blocking probability, and data delay. Operating points based on typical performance constraints such as voice blocking probability 0.01 (for TDMA), voice packet loss rate 10/sup -3/ (for CDMA), and data delay 250 ms are obtained, and results are presented. >
TL;DR: Public-key/private-key hybrid key agreements and authentication protocols which maintain privacy of conversation and location information, and deter usage fraud, are presented, and the tradeoffs are discussed.
Abstract: Public-key/private-key hybrid key agreements and authentication protocols which maintain privacy of conversation and location information, and deter usage fraud, are presented. These protocols are optimized for low complexity in the portable unit and network infrastructure. The basic cryptographic techniques are described, and some complexity information obtained from these laboratory experiments and from other sources are presented. The three public-key protocols described have differing levels of security and complexity: and the tradeoffs are discussed. Because of the complexity concerns mentioned above, the public-key protocols are compared to a representative private-key approach in the areas of both security and computational complexity. >
TL;DR: It is shown that in the proposed UPCS system, the maximum database size is 0.51% and the database updating cost is 6.86% of that needed by a central database system under a specified scenario.
Abstract: The universal personal communication system (UPCS) is a system that enables anyone to communicate instantly with anyone else anywhere in the world. One of the crucial problems of such a system is locating hundreds of millions of moving portables in an efficient manner. The location registration strategy described is able to locate active portables automatically in the system with a small overhead in a distributed fashion. The system knows the exact position of an active portable in its service areas. The connection is set up by the system directly to its destination using the direct (shortest) path. The system capacity, efficiency, and inquiry time delay have been improved greatly compared to the leading existing techniques. It is shown that in the proposed system, the maximum database size is 0.51% and the database updating cost is 6.86% of that needed by a central database system under a specified scenario. >
TL;DR: The resulting average uncoded bit error probabilities lead to the conclusion that systems applying the linear unbiased data estimation algorithm are well suited for mobile radio applications.
Abstract: Data estimation in the uplink of a synchronous mobile radio system applying code-division multiple access (CDMA) is considered. In mobile radio systems applying CDMA, multipath propagation leads to intersymbol interference (ISI) and together with time variance, to cross interference between the signals of different users regardless of whether the user codes are chosen orthogonal or not. A linear unbiased data estimation algorithm is presented that eliminates both ISI and cross interference perfectly by jointly detecting the different user signals, leading to unbiased estimates of the transmitted data symbols. By theoretical analysis and simulation, the performance of the linear unbiased data estimation algorithm is examined under the assumption that the radio channel impulse responses are known at the receiver. The price to be paid for the interference elimination are SNR degradations, which are calculated for typical mobile radio situations in urban areas. The resulting average uncoded bit error probabilities lead to the conclusion that systems applying the linear unbiased data estimation algorithm are well suited for mobile radio applications. >
TL;DR: Here, performance issues and algorithms for DCA in a TDMA portable radio system are considered and the DCA efficiency is compared mainly through the signal-to-interference ratio in both the uplink and downlink directions.
Abstract: Using dynamic channel assignment (DCA) algorithms to select communications channels as needed, time-division multiple access (TDMA) or frequency-division multiple access (FDMA) systems can serve dynamic and nonuniform traffic demands without frequency planning as long as quality is sufficient and equipment is available. Here, performance issues and algorithms for DCA in a TDMA portable radio system are considered. A fixed number of traffic servers (time slots) per radio port is assumed: therefore, the system capacity is hard-limited by the equipment availability, and the DCA efficiency is compared mainly through the signal-to-interference ratio in both the uplink and downlink directions. >
TL;DR: Three call handling schemes for a base station which can handle both originating calls and prioritized handoff calls, and which serves these calls under the blocked-call-delayed basis, are presented and compared.
Abstract: Three call handling schemes for a base station which can handle both originating calls (OCs) and prioritized handoff calls (HCs), and which serves these calls under the blocked-call-delayed basis, are presented and compared. Delayed calls are assumed to be stored in a finite storage buffer. One scheme (Scheme I) exclusively allows handoff calls to be stored and to use a fixed number of guard channels. The other two schemes without guard channels (Scheme II-using the last-in/first-out policy for OC's and Scheme III-using the first-in first-out policy for OC's) allow both types of calls to be stored, and allow prioritized handoff calls to pushout originating calls if the buffer is full. For these three schemes, the blocking probabilities and delay distributions of both types of calls are numerically obtained, and a boundary for call handling schemes between with and without guard channels is found. From the numerical results, it is shown that Scheme II can be considered a good candidate for a call handling scheme for microcellular systems. >
TL;DR: The authors have performed data reductions on 900 MHz signal attenuations measured on numerous streets in Manhattan and it is shown that the contours have the shapes of convex diamonds and proposed that squares inscribed within these contours be used as the building blocks of microcellular environments.
Abstract: The authors have performed data reductions on 900 MHz signal attenuations measured on numerous streets in Manhattan. The database consists of both local spatial averages of signal attenuation and the short-term fluctuations about this average. The former, which is termed the local mean attenuation (LMA), is the primary focus. The database is used to obtain contours of constant LMA for two neighborhoods. It is shown that the contours have the shapes of convex diamonds. The authors propose that squares inscribed within these contours be used as the building blocks of microcellular environments. A theory is developed that explains the contours and predicts, with reasonable accuracy, the sizes of the inscribed squares. It is also shown that the prediction method can be applied without the need for measured data. The short-term fluctuation statistics of the signal attenuation are examined. They are shown to be Rayleigh-like in the non-line-of-sight regions of a microcell and Rice-like in the line-of-sight region. Possible extensions to other frequency bands and other urban environments are discussed. >
TL;DR: A methodology for systematically building and testing the security of a family of cryptographic two-way authentication protocols that are as simple as possible yet resistant to a wide class of attacks, efficient, easy to implement and use, and amenable to many different networking environments is described.
Abstract: Most existing designs for two-way cryptographic authentication protocols suffer from one or more limitations. Among other things, they require synchronization of local clocks, they are subject to export restrictions because of the way they use cryptographic functions, and they are not amenable to use in lower layers of network protocols because of the size and complexity of messages they use. Designing suitable cryptographic protocols that cater to large and dynamic network communities but do not suffer from these problems presents substantial problems. It is shown how a few simple protocols, including one proposed by ISO, can easily be broken, and properties that authentication protocols should exhibit are derived. A methodology for systematically building and testing the security of a family of cryptographic two-way authentication protocols that are as simple as possible yet resistant to a wide class of attacks, efficient, easy to implement and use, and amenable to many different networking environments is described. Examples of protocols of that family that presents various advantages in specific distributed system scenarios are discussed. >
TL;DR: A general solution in which the authentication server is replicated so that a minority of malicious and colluding servers cannot compromise security or disrupt service is proposed.
Abstract: Authentication, the process by which one satisfies another about one's claim of identity, is typically provided by an authentication server via an authentication protocol. Compromise of the authentication service can lead to the compromise of the whole system, and the service is a performance bottleneck because many activities cannot proceed unless the identities of concerned parties can be satisfactorily established. Therefore, a desirable authentication service should be both highly secure and highly available. A general solution in which the authentication server is replicated so that a minority of malicious and colluding servers cannot compromise security or disrupt service is proposed. Some unusual features of such a distributed authentication service, including the tradeoff between availability and security, are discussed. Such a distributed service is also useful when clients cannot identify or agree upon trusted servers prior to authentication. For example, in some cooperative or federated systems, clients simply cannot all trust the same set of servers. >
TL;DR: A function-based communication model that allows applications to request individually tailored services from the communication subsystem is presented, and the concept of layering is abandoned for both flexibility and efficiency reasons.
Abstract: A function-based communication model that allows applications to request individually tailored services from the communication subsystem is presented. Based on service requirements and available resources, suitable protocol machines are configured to serve the application. This configuration is done using a proper combination of functional modules. The concept of layering is therefore abandoned for both flexibility and efficiency reasons. >
TL;DR: A successful hardware/software architecture that resolves performance bottlenecks at the workstation- to-network host interface and offers high end-to-end performance is described and carefully splits protocol processing functions into hardware and software implementations.
Abstract: A successful hardware/software architecture that resolves performance bottlenecks at the workstation-to-network host interface and offers high end-to-end performance is described. The solution reported carefully splits protocol processing functions into hardware and software implementations. The interface hardware is highly parallel and performs all per-cell functions with dedicated logic to maximize performance. Software provides support for the transfer of data between the interface and application memory, as well as the state management necessary for virtual circuit setup and maintenance. In addition, all higher-level protocol processing is implemented with host software. The prototype connects a RISC System/6000 to a SONET-based asynchronous transfer model (ATM) network carrying data at the OC-3c rate of 155 Mb/s. An experimental evaluation of the interface hardware and software has been performed. Several conclusions are drawn about this host interface architecture and the workstations to which it is connected. >
TL;DR: Analysis of the design and performance of a workstation's network interface to the 100-Mb/s FDDI token ring reveals that providing a DMA engine for data movement provides significant improvements in throughput.
Abstract: Design issues that affect the performance of network input/output (I/O) are examined by analyzing the design and performance of a workstation's network interface to the 100-Mb/s FDDI token ring. Several design alternatives for partitioning functions between the network interface and the host software are evaluated. A simple model is proposed for looking at the performance of network I/O, and an effective analysis approach for predicting user-perceived throughput is demonstrated. The analysis reveals that, particularly for network interfaces that reside on an I/O bus, providing a DMA engine for data movement provides significant improvements in throughput. However, the designs for the receive and transmit sides are not necessarily symmetrical, and it is shown that host architecture considerations influence the design of each direction differently. The analysis is used to show the potential benefits of having all protocol functions on the network interface and also to point out the potential processing power needed on that network interface. >
TL;DR: Media access control protocols for an optically interconnected star-coupled system with preallocated wavelength-division multiple-access channels are discussed and semi-Markov analytic models are developed to investigate the performance of the two protocols.
Abstract: Media access control protocols for an optically interconnected star-coupled system with preallocated wavelength-division multiple-access channels are discussed. The photonic network is based on a passive star-coupled configuration in which high topological connectivity is achieved with low complexity and excellent fault tolerance. The channels are preallocated to the nodes with the proposed approach, and each node has a home channel it uses either for data packet transmission or data packet reception. The performance of a generalized random access protocol is compared to an approach based on interleaved time multiplexing. Semi-Markov analytic models are developed to investigate the performance of the two protocols. The analytic models are validated through extensive simulation. The performance is evaluated in terms of network throughput and packet delay with variations in the number of nodes, data channels, and packet generation rate. >
TL;DR: It is shown that FEC is not effective for the two homogeneous scenarios, however, FEC reduces the loss rate for the video sources by several orders of magnitude for a heterogeneous scenario consisting of video and burst sources.
Abstract: The loss behavior of a cell multiplexer and the performance of forward error correction (FEC) for two homogeneous and one heterogeneous traffic scenarios are discussed. The loss behavior depends on the statistics of the source and on the traffic scenario. Simulation results indicate that the percentage of cells lost in a block is geometrically distributed. Using these results a mathematical model for the performance of FEC is developed, and the effectiveness of FEC for the three traffic scenarios is computed. It is shown that FEC is not effective for the two homogeneous scenarios. However, FEC reduces the loss rate for the video sources by several orders of magnitude for a heterogeneous scenario consisting of video and burst sources. >
TL;DR: The authors discuss the design of a single-copy network architecture, where data is copied directly between the application buffer and the network interface, and report some early results that demonstrate twice the throughput of a conventional network architecture and significantly lower latency.
Abstract: With current low-cost high-performance workstations, application-to-application throughput is limited more by host memory bandwidth than by the cost of protocol processing. Conventional network architectures are inefficient in their use of this memory bandwidth, because data is copied several times between the application and the network. As network speeds increase further, network architectures must be developed that reduce the demands on host memory bandwidth. The authors discuss the design of a single-copy network architecture, where data is copied directly between the application buffer and the network interface. Protocol processing is performed by the host, and transport layer buffering is provided on the network interface. They describe a prototype implementation for the HP Apollo Series 700 workstation family that consists of an FDDI network interface and a modified 4.3BSD TCP/IP protocol stack, and report some early results that demonstrate twice the throughput of a conventional network architecture and significantly lower latency. >
TL;DR: It is shown that channel segregation can resolve the problem of unaccessible channel with a small modification of its algorithm and its applications to the TDMA/FDMA or multicarrier TDMA system is discussed.
Abstract: Channel segregation was previously proposed as a self-organized dynamic channel assignment. Its performance was examined by applying it to frequency-division multiple access systems. Its applications to the TDMA/FDMA (time-division multiple access/frequency-division multiple access) or multicarrier TDMA system is discussed. The spectrum efficiency of the TDMA/FDMA cellular system deteriorates due to the problem of unaccessible channel: a call can be blocked in a cell even when there are idle channels because of the restriction on simultaneous use of different carrier frequencies in the cell. It is shown that channel segregation can resolve this problem with a small modification of its algorithm. The performance of the TDMA/FDMA system with channel segregation on the call blocking probability versus traffic density is analyzed with computer simulation experiments. The effect of losing the TDMA frame synchronization between cells on the performance is also discussed. >
TL;DR: A multiscale video representation using wavelet decomposition and variable-block-size multiresolution motion estimation (MRME) is presented and appears suitable for the broadcast environment where various standards may coexist simultaneously.
Abstract: A multiscale video representation using wavelet decomposition and variable-block-size multiresolution motion estimation (MRME) is presented. The multiresolution/multifrequency nature of the discrete wavelet transform makes it an ideal tool for representing video sources with different resolutions and scan formats. The proposed variable-block-size MRME scheme utilizes motion correlation among different scaled subbands and adapts to their importance at different layers. The algorithm is well suited for interframe HDTV coding applications and facilitates conversions and interactions between different video coding standards. Four scenarios for the proposed motion-compensated coding schemes are compared. A pel-recursive motion estimation scheme is implemented in a multiresolution form. The proposed approach appears suitable for the broadcast environment where various standards may coexist simultaneously. >
TL;DR: An overview and comparison of various simulation design strategies and some results on the optimization of general mean translation and variance scaling biasing schemes for nonlinear systems are presented.
Abstract: A simulation algorithm design strategy based on the combination of event simulation, conditional importance sampling, and asymptotically optimal biasing of Gaussian noise inputs is discussed. The utility of this approach is illustrated by presenting numerical results for a satellite channel model that includes uplink and downlink noise sources, a travelling-wave tube amplifier (TWTA) nonlinearity, and intersymbol interference (ISI) from both uplink and downlink filtering. An overview and comparison of various simulation design strategies and some results on the optimization of general mean translation and variance scaling biasing schemes for nonlinear systems are presented. >