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Showing papers on "Communication channel published in 1999"


Book
15 Sep 1999
TL;DR: This title introduces the basic concepts and specific applications of antennas and propagation to wireless systems, covering terrestrial and satellite radio systems in both mobile and fixed contexts.
Abstract: From the Publisher: This title introduces the basic concepts and specific applications of antennas and propagation to wireless systems, covering terrestrial and satellite radio systems in both mobile and fixed contexts. Includes: Illustrations of the significance and effect of the wireless propagation channelOverview of the fundamental electromagnetic principles underlying propagation and antennasBasic concepts of antennas and their application to specific wireless systemsPropagation measurement, modeling, and predication for fixed links for macrocells, microcells, picocells, and megacellsNarrowband and wideband channel modeling and the effect of the channel on communication system performanceMehtods that overcome and transform channel impairments to enhance performance using diversity, adaptive antennas, and equalizersExamples of real-world practical system problems of communications design and operationExtensive worked examplesEnd-chapter questionsTopical and relevant information for and about the wireless communications industry.

1,367 citations


Journal ArticleDOI
TL;DR: The investigations demonstrate that the SAGE algorithm is a powerful high-resolution tool that can be successfully applied for parameter extraction from extensive channel measurement data, especially for the purpose of channel modeling.
Abstract: This study investigates the application potential of the SAGE (space-alternating generalized expectation-maximization) algorithm to jointly estimate the relative delay, incidence azimuth, Doppler frequency, and complex amplitude of impinging waves in mobile radio environments The performance, ie, high-resolution ability, accuracy, and convergence rate of the scheme, is assessed in synthetic and real macro- and pico-cellular channels The results indicate that the scheme overcomes the resolution limitation inherent to classical techniques like the Fourier or beam-forming methods In particular, it is shown that waves which exhibit an arbitrarily small difference in azimuth can be easily separated as long as their delays or Doppler frequencies differ by a fraction of the intrinsic resolution of the measurement equipment Two waves are claimed to be separated when the mean-squared estimation errors (MSEEs) of the estimates of their parameters are close to the corresponding Cramer-Rao lower bounds (CRLBs) derived in a scenario where only a single wave is impinging The adverb easily means that the MSEEs rapidly approach the CLRBs, ie, within less than 20 iteration cycles Convergence of the log-likelihood sequence is achieved after approximately ten iteration cycles when the scheme is applied in real channels In this use, the estimated dominant waves can be related to a scatterer/reflector in the propagation environment The investigations demonstrate that the SAGE algorithm is a powerful high-resolution tool that can be successfully applied for parameter extraction from extensive channel measurement data, especially for the purpose of channel modeling

1,043 citations


Journal ArticleDOI
TL;DR: With the proposed channel estimator, combining OPDM with transmitter diversity using space-time coding is a promising technique for highly efficient data transmission over mobile wireless channels.
Abstract: Transmitter diversity is an effective technique to improve wireless communication performance. In this paper, we investigate transmitter diversity using space-time coding for orthogonal frequency division multiplexing (OFDM) systems in high-speed wireless data applications. We develop channel parameter estimation approaches, which are crucial for the decoding of the space-time codes, and we derive the MSE bounds of the estimators. The overall receiver performance using such a transmitter diversity scheme is demonstrated by extensive computer simulations. For an OFDM system with two transmitter antennas and two receiver antennas with transmission efficiency as high as 1.475 bits/s/Hz, the required signal-to-noise ratio is only about 7 dB for a 1% bit error rate and 9 dB for a 10% word error rate assuming channels with two-ray, typical urban, and hilly terrain delay profiles, and a 40-Hz Doppler frequency. In summary, with the proposed channel estimator, combining OPDM with transmitter diversity using space-time coding is a promising technique for highly efficient data transmission over mobile wireless channels.

894 citations


Journal ArticleDOI
TL;DR: From the single-user point of view considered in this paper, there exists an optimal repetition diversity order (or spreading factor) that minimizes the information outage probability for given rate, power, and fading statistics.
Abstract: We study optimal constant-rate coding schemes for a block-fading channel with strict transmission delay constraint, under the assumption that both the transmitter and the receiver have perfect channel-state information. We show that the information outage probability is minimized by concatenating a standard "Gaussian" code with an optimal power controller, which allocates the transmitted power dynamically to the transmitted symbols. We solve the minimum outage probability problem under different constraints on the transmitted power and we derive the corresponding power-allocation strategies. In addition, we propose an algorithm that approaches the optimal power allocation when the fading statistics are not known. Numerical examples for different fading channels are provided, and some applications discussed. In particular, we show that minimum outage probability and delay-limited capacity are closely related quantities, and we find a closed-form expression for the delay-limited capacity of the Rayleigh block-fading channel with transmission over two independent blocks. We also discuss repetition diversity and its relation with direct-sequence or multicarrier spread-spectrum transmission. The optimal power-allocation strategy in this case corresponds to selection diversity at the transmitter. From the single-user point of view considered in this paper, there exists an optimal repetition diversity order (or spreading factor) that minimizes the information outage probability for given rate, power, and fading statistics.

822 citations


Journal ArticleDOI
TL;DR: An ideal wireless fair-scheduling algorithm which provides a packetized implementation of the fluid mode, while assuming full knowledge of the current channel conditions is described, and the worst-case throughput and delay bounds are derived.
Abstract: Fair scheduling of delay and rate-sensitive packet flows over a wireless channel is not addressed effectively by most contemporary wireline fair-scheduling algorithms because of two unique characteristics of wireless media: (1) bursty channel errors and (2) location-dependent channel capacity and errors. Besides, in packet cellular networks, the base station typically performs the task of packet scheduling for both downlink and uplink flows in a cell; however, a base station has only a limited knowledge of the arrival processes of uplink flows. We propose a new model for wireless fair-scheduling based on an adaptation of fluid fair queueing (FFQ) to handle location-dependent error bursts. We describe an ideal wireless fair-scheduling algorithm which provides a packetized implementation of the fluid mode, while assuming full knowledge of the current channel conditions. For this algorithm, we derive the worst-case throughput and delay bounds. Finally, we describe a practical wireless scheduling algorithm which approximates the ideal algorithm. Through simulations, we show that the algorithm achieves the desirable properties identified in the wireless FFQ model.

796 citations


Journal ArticleDOI
TL;DR: It is proved that in the absence of ideal channel state information the design criteria for space- time codes is still valid and the diversity order promised by space-time coding is achieved under a variety of mobility conditions and environmental effects.
Abstract: Space-time coding is a bandwidth and power efficient method of communication over fading channels that realizes the benefits of multiple transmit antennas. Specific codes have been constructed using design criteria derived for quasi-static flat Rayleigh or Rician fading, where channel state information is available at the receiver. It is evident that the practicality of space-time codes will be greatly enhanced if the derived design criteria remain valid in the absence of perfect channel state information. It is even more desirable that the design criteria not be unduly sensitive to frequency selectivity and to the Doppler spread. This paper presents a theoretical study of these issues beginning with the effect of channel estimation error. Here it is assumed that a channel estimator extracts fade coefficients at the receiver and for constellations with constant energy, it is proved that in the absence of ideal channel state information the design criteria for space-time codes is still valid. The analysis also demonstrates that standard channel estimation techniques can be used in conjunction with space-time codes provided that the number of transmit antennas is small. We also derive the maximum-likelihood detection metric in the presence of channel estimation errors. Next, the effect of multiple paths on the performance of space-time codes is studied for a slowly changing Rayleigh channel. It is proved that the presence of multiple paths does not decrease the diversity order guaranteed by the design criteria used to construct the space-time codes. Similar results hold for rapid fading channels with or without multiple paths. The conclusion is that the diversity order promised by space-time coding is achieved under a variety of mobility conditions and environmental effects.

619 citations


Proceedings ArticleDOI
21 Sep 1999
TL;DR: It is shown via simulations that this new carrier-sense multiple access (CSMA) protocol provides a higher throughput compared to its single channel counterpart by reducing the packet loss due to collisions and the use of channel reservation provides better performance than multichannel CSMA with purely random idle channel selection.
Abstract: We describe a new carrier-sense multiple access (CSMA) protocol for multihop wireless networks, sometimes also called ad hoc networks. The CSMA protocol divides the available bandwidth into several channels and selects an idle channel randomly for packet transmission. It also employs a notion of "soft" channel reservation as it gives preference to the channel that was used for the last successful transmission. We show via simulations that this multichannel CSMA protocol provides a higher throughput compared to its single channel counterpart by reducing the packet loss due to collisions. We also show that the use of channel reservation provides better performance than multichannel CSMA with purely random idle channel selection.

402 citations


01 Jan 1999
TL;DR: The results have an interesting implication for BLAST, either in a mobile environment, or for TDMA, where both training and data transmission have to occur within a xed interval: if one wishes to maximize the overall transmission rate, then the number of transmit antennas should be chosen such that half of the interval is used for training, and half ofThe interval for data transmission.
Abstract: BLAST (Bell Labs Layered Space-Time) is a multiple-antenna communication scheme whose outage capacity in a Rayleigh at fading environment grows linearly with the minimum of the number of transmit and receive antennas, with no increase in bandwidth or transmitted power. Based on its knowledge of the matrix of propagation coeecients, the receiver performs two critical operations: nulling and cancellation, that in eeect create independent virtual subchannels. Assume that the receiver estimates the propagation matrix from a known set of transmitted training signals, and then uses the estimate as though it were correct for nulling and cancellation. How much training is needed for satisfactory operation? The optimal training signals are orthogonal with respect to time among the transmit antennas, and each transmit antenna is fed equal energy. Errors in estimating the propagation matrix manifest themselves as crosstalk among the virtual subchannels. If its magnitude is too large, the crosstalk constitutes an outage event that is independent of the primary outage event (e.g., that the value of the propagation matrix cannot support the transmission rate). We show that the training interval required to control the probability of the estimation-error induced outage is approximately proportional to the number of transmit antennas, and is independent of the number of receive antennas. Contrary to what is implied by their names, the operations of nulling and cancellation are, in fact, robust with respect to estimation errors. Our results have an interesting implication for BLAST, either in a mobile environment , or for TDMA, where both training and data transmission have to occur within a xed interval: if one wishes to maximize the overall transmission rate, then the number of transmit antennas should be chosen such that half of the interval is used for training, and half of the interval for data transmission.

385 citations


Journal ArticleDOI
TL;DR: By characterizing the effects of fading channel variation on the adaptive signaling paradigm, adaptive trellis-coded modulation schemes are designed that can provide a significant increase in bandwidth efficiency over their nonadaptive counterparts on time-varying channels.
Abstract: The idea of using knowledge of the current channel fading values to optimize the transmitted signal in wireless communication systems has attracted substantial research attention. However, the practicality of this adaptive signaling has been questioned due to the variation of the wireless channel over time, which results in a different channel at the time of data transmission than at the time of channel estimation. By characterizing the effects of fading channel variation on the adaptive signaling paradigm, it is demonstrated here that these misgivings are well founded, as the channel variation greatly alters the nature of the problem. The main goal of this paper is to employ this characterization of the effects of the channel variation to design adaptive signaling schemes that are effective for the time-varying channel. The design of uncoded adaptive quadrature amplitude modulation (QAM) systems is considered first, and it demonstrates the need to consider the channel variation in system design. This is followed by the main contribution of this paper; using only a single outdated fading estimate when neither the Doppler frequency nor the exact shape of the autocorrelation function of the channel fading process is known, adaptive trellis-coded modulation schemes are designed that can provide a significant increase in bandwidth efficiency over their nonadaptive counterparts on time-varying channels.

359 citations


Proceedings ArticleDOI
24 Oct 1999
TL;DR: An efficient multiple description (MD) source coding scheme to achieve robust communication over unreliable channels by proposing channel coding principles to correlate the descriptions, and then using this correlation for combating channel impairments.
Abstract: We present an efficient multiple description (MD) source coding scheme to achieve robust communication over unreliable channels. In contrast to the popular signal processing based methods, we propose channel coding principles to correlate the descriptions, and then use this correlation for combating channel impairments. We propose a fast, nearly optimal algorithm that aims to maximize the expected quality at the receiver given the channel state and the side channel rates. Our scheme can be used in conjunction with any source coder that is scalable, and is most easily matched to coders outputting a progressive bitstream. It has applications to the transmission of audio, images, as well as delay-constrained video signals, and can also be used to achieve reliable multicast transmission over the existing Internet with the use of simple protocols. Comparisons of our scheme on standard test images to some of the existing state-of-the-art signal processing based MD methods suggest that our simple scheme outperforms them by significant margins.

325 citations


Patent
06 Aug 1999
TL;DR: In this paper, the authors present a video data recordable system with integrated channel guides allowing a user to control recording and storage of television signals into personal channels for later playback and viewing.
Abstract: A video data recordable (106) having integrated channel guides allowing a user to control recording and storage of television signals into personal channels (105) for later playback and viewing. In the described embodiment, the user may specify criteria (104) for recording of shows from an input source such as a broadcast signal and shows are then selected based on the user specified criteria (104) and recorded for later playback. Storage of the shows may be organized into personal channels (105) in order to facilitate later playback, e.g., the user may specify a channel of action movies, a channel of nature programming, a channel for sports, etc (103). The shows to be recorded may also have a predefined format which may be used to ease playback of recorded programming by allowing the user to easily locate and playback sections of programming of interest.

Patent
Peter F. King1
21 Sep 1999
TL;DR: In this paper, improved techniques for facilitating secure data transfer over one-way data channels or narrowband channels are disclosed Often, these channels are wireless channels provided by wireless data networks.
Abstract: Improved techniques for facilitating secure data transfer over one-way data channels or narrowband channels are disclosed Often, these channels are wireless channels provided by wireless data networks The techniques enable cryptographic handshake operations for a one-way data channel to be performed over a companion two-way data channel so that the one-way data channel is able to effectively satisfy security protocols that require two-way communications for the cryptographic handshake operations Once the cryptographic handshake operations are complete, data can be transmitted over the one-way data channel in a secure manner Additionally, the techniques also enable the cryptographic handshake operations to be performed more rapidly because the two-way channel is typically a wideband channel In which case, the use of a wideband channel instead of a narrowband channel for the cryptographic handshake operations results in latency reductions, regardless of whether the narrowband channel is a one-way channel or a two-way channel

Journal ArticleDOI
TL;DR: This paper proposes a new mobility model, called the hyper-Erlang distribution model, which is consistent with the requirements of field data processing in PCS network design and performance evaluation and derives analytical results for the channel holding time distribution, which are readily applicable to theHyper Erlang distribution models.
Abstract: Channel holding time is of primary importance in teletraffic analysis of PCS networks. This quantity depends on user's mobility which can be characterized by the cell residence time. We show that when the cell residence time is not exponentially distributed, the channel holding time is not exponentially distributed either, a fact also confirmed by available field data. In order to capture the essence of PCS network behaviour, including the characterization of channel holding time, a correct mobility model is therefore necessary. The new model must be good enough to fit field data, while at the same time resulting in a tractable queueing system. We propose a new mobility model, called the hyper-Erlang distribution model, which is consistent with these requirements. Under the new realistic operational assumption of this model, in which the cell residence time is generally distributed, we derive analytical results for the channel holding time distribution, which are readily applicable to the hyper-Erlang distribution models. Using the derived analytical results we demonstrate how the distribution of the cell residence time affects the channel holding time distribution. The results presented in this paper can provide guidelines for field data processing in PCS network design and performance evaluation.

Journal ArticleDOI
Gerhard Kramer1
TL;DR: Several techniques for improving the bounds are developed: (1) causally conditioned entropy and directed information simplify the inner bounds, (2) code trellises serve as simple code trees, (3) superposition coding and binning with code trees improves rates.
Abstract: A discrete memoryless network (DMN) is a memoryless multiterminal channel with discrete inputs and outputs. A sequence of inner bounds to the DMN capacity region is derived by using code trees. Capacity expressions are given for three classes of DMNs: (1) a single-letter expression for a class with a common output, (2) a two-letter expression for a binary-symmetric broadcast channel (BC) with partial feedback, and (3) a finite-letter expression for push-to-talk DMNs. The first result is a consequence of a new capacity outer bound for common output DMNs. The third result demonstrates that the common practice of using a time-sharing random variable does not include all time-sharing possibilities, namely, time sharing of channels. Several techniques for improving the bounds are developed: (1) causally conditioned entropy and directed information simplify the inner bounds, (2) code trellises serve as simple code trees, (3) superposition coding and binning with code trees improves rates. Numerical computations show that the last technique enlarges the best known rate regions for a multiple-access channel (MAC) and a BC, both with feedback. In addition to the rate bounds, a sequence of inner bounds to the DMN reliability function is derived. A numerical example for a two-way channel illustrates the behavior of the error exponents.

Journal ArticleDOI
TL;DR: A technique to measure channel quality in terms of signal-to-interference plus noise ratio (SINR) for the transmission of signals over fading channels and proposes a set of coded modulation schemes which utilize the SINR estimate to adapt between modulations, thus improving the data throughput.
Abstract: We propose a technique to measure channel quality in terms of signal-to-interference plus noise ratio (SINR) for the transmission of signals over fading channels The Euclidean distance (ED) metric, associated with the decoded information sequence or a suitable modification thereof, is used as a channel quality measure Simulations show that the filtered or averaged metric is a reliable channel quality measure which remains consistent across different coded modulation schemes and at different mobile speeds The average scaled ED metric can be mapped to the SINR per symbol We propose the use of this SINR estimate for data rate adaptation, in addition to mobile assisted handoff (MAHO) and power control We particularly focus on data rate adaptation and propose a set of coded modulation schemes which utilize the SINR estimate to adapt between modulations, thus improving the data throughput Simulation results show that the proposed metric works well across the entire range of Dopplers to provide near-optimal rate adaptation to average SINR This method of adaptation averages out short-term variations due to Rayleigh fading and adapts to the long-term effects such as shadowing At low Dopplers, the metric can track Rayleigh fading and match the rate to a short-term average of the SINR, thus further increasing throughput

Journal ArticleDOI
TL;DR: Simulation results demonstrate that both the video distortion at the decoder and packet loss rate can be significantly reduced when incorporating the channel information provided by the feedback channel and the a priori model into the rate control algorithm.
Abstract: We study the problem of rate control for transmission of video over burst-error wireless channels, i.e., channels such that errors tend to occur in clusters during fading periods. In particular we consider a scenario consisting of packet based transmission with automatic repeat request (ARQ) error control and a back channel. We start by showing how the delay constraints in real time video transmission can be translated into rate constraints at the encoder, where the applicable rate constraints at a given time depend on future channel rates. With the acknowledgments received through the back channel we have an estimate of the current channel state. This information, combined with an a priori model of the channel, allows us to statistically model the future channel rates. Thus the rate constraints at the encoder can be expressed in terms of the expected channel behavior. We can then formalize a rate distortion optimization problem, namely, that of assigning quantizers to each of the video blocks stored in the encoder buffer such that the quality of the received video is maximized. This requires that the rate constraints be included in the optimization, since violating a rate constraint is equivalent to violating a delay constraint and thus results in losing a video block. We formalize two possible approaches. The first one seeks to minimize the distortion for the expected rate constraints given the channel model and current observation. The second approach seeks to allocate bits so as to minimize the expected distortion for the given model. We use both dynamic programming and Lagrangian optimization approaches to solve these problems. Our simulation results demonstrate that both the video distortion at the decoder and packet loss rate can be significantly reduced when incorporating the channel information provided by the feedback channel and the a priori model into the rate control algorithm.

Proceedings ArticleDOI
19 Sep 1999
TL;DR: To deal with the frequently changing channel characteristic of a fast time-varying multipath fading channel, a heuristic algorithm based on constructive assignment and iterative improvement is proposed which can give out a valid solution in real time.
Abstract: In this paper, we propose sub-carrier allocation algorithms for a multiple access scheme in downlink OFDM transmission. Knowing the channel characteristics of all the users at the base station, the sub-carrier allocation algorithm assigns sub-carriers to the users in a way that the total transmit power is minimized. An optimal algorithm is presented to provide the best sub-carrier assignment. The complexity of the optimal solution renders it impractical for real-time application. To deal with the frequently changing channel characteristic of a fast time-varying multipath fading channel, a heuristic algorithm based on constructive assignment and iterative improvement is proposed which can give out a valid solution in real time. Experimental results show that the performance of this real-time algorithm is close to that of the optimal allocation.

Proceedings ArticleDOI
06 Jun 1999
TL;DR: The capacity of multiple input, multiple output wireless channels is computed for Ricean channels using a geometrical interpretation of the MIMO channel capacity formula to find array geometries which greatly enhance channel capacity compared to SISO systems.
Abstract: The capacity of multiple input, multiple output wireless channels is computed for Ricean channels The novelty is a geometrical (ray-tracing) interpretation of the MIMO channel capacity formula to find array geometries which greatly enhance channel capacity compared to SISO systems

Journal ArticleDOI
TL;DR: In this paper, an a posteriori probability (APP) DPSK demodulator is proposed to improve the performance of coherent detection of MPSK without differential encoding and perfect channel estimation for fading cases.
Abstract: Multiple symbol differential detection is known to fill the gap between conventional differential detection of MPSK (M-DPSK) and coherent detection of M-PSK with differential encoding (M-DEPSK). Emphasis has been so far on soft-input/hard-output detectors applied in uncoded systems. In this paper, we investigate a receiver structure suitable for coded DPSK signals on static and time-varying channels. The kernel is an a posteriori probability (APP) DPSK demodulator. This demodulator accepts a priori information and produces reliability outputs. Due to the availability of reliability outputs, an outer soft-decision channel decoder can be applied. Due to the acceptance of a priori information, if the outer channel decoder also outputs reliability information, iterative ("turbo") processing can be done. The proposed "APP DPSK demodulator" uses linear prediction and per-survivor processing to estimate the channel response. The overall transmission scheme represents a type of serial "turbo code," with a differential encoder concatenated with a convolutional code, separated by interleaving. The investigated system has the potential to improve the performance of coherent PSK without differential encoding and perfect channel estimation for fading cases! Only a small number of iterations are required. The receiver under investigation can be applied to several existing standards without changing the transmission format. Results are presented for uncoded and convolutionally coded 4-DPSK modulation transmitted over the Gaussian channel and the Rayleigh flat-fading channel, respectively.

Proceedings ArticleDOI
01 Jan 1999
TL;DR: The possibility of combining the concept of power control with the RTS/CTS-based and busy-tone-based protocols to further increase channel utilization and shows a promising direction to enhance the performance of MANETs.
Abstract: In a mobile ad-hoc networks (MANETs), one essential issue is how to increase channel utilization while avoiding the hidden-terminal and the exposed-terminal problems. Several MAC protocols, such as RTS (request to send)/CTS (clear to send) based and busy tone-based schemes, have been proposed to alleviate these problems. In this paper, we explore the possibility of combining the concept of power control with the RTS/CTS-based and busy tone-based protocols to further increase channel utilization. A sender will use an appropriate power level to transmit its packets so as to increase the possibility of channel reuse. The possibility of using discrete, instead of continuous, power levels is also discussed. Through analyses and simulations, we demonstrate the advantage of our new MAC protocol. This, together with the extra benefits such as saving battery energy and reducing co-channel interference, does show a promising direction to enhance the performance of MANETs.

Patent
Masahiro Kuroda1
13 Dec 1999
TL;DR: A video recorder for recording content signals including audio and video signals, including a module for receiving program information, is described in this article. But it does not specify a program identifier, starting and ending time of a program.
Abstract: A video recorder for recording content signals including audio and video signals, comprises a module for receiving program information signals designating a program identifier, starting and ending time of a program, a first storage device (103), a first recording module for continuously recording the content signals at least one channel in the first storage device, and a module for deleting the content signals of the oldest program recorded in the first storage device in reference with the program information signals.

Book
12 May 1999
TL;DR: Fundamentals of Inductive Magnetic Head and Medium and Fundamental Limitations of Magnetic Recording are explained.
Abstract: Preface. Introduction. Fundamentals of Inductive Magnetic Head and Medium. Read Process in Magnetic Recording. Write Process in Magnetic Recording. Inductive Magnetic Process. Magnetoresistive Heads. Magnetic Recording Media. Channel Coding and Error Correction. Noises. Nonlinear Distortions. Peak Detection Channel. PRML Channel. Decision Feedback Channel. Off-Track Performance. Head-Disk Assembly Servo. Fundamental Limitations of Magnetic Recording. Alternative Information Storage Technologies.

Journal ArticleDOI
TL;DR: An algorithm that allows an ARQ protocol to dynamically optimize the packet size based on estimates of the channel bit‐error‐rate is developed, and it is shown that the algorithm can achieve close to optimal performance using a history of just 10,000 bits.
Abstract: We develop an algorithm that allows an ARQ protocol to dynamically optimize the packet size based on estimates of the channel bit-error-rate. Our algorithm is particularly useful for wireless and satellite channels where the bit-error-rates tend to be relatively high and time variable. Our algorithm uses the acknowledgment history to make estimates of the channel bit-error-rate, based on which the optimal packet size can be chosen. We develop a Markov chain model for the analysis of the system, under static channel conditions, and show that the algorithm can achieve close to optimal performance using a history of just 10,000 bits. We also use the Gilbert–Elliott two-state Markov channel to model dynamic channel conditions. We show, through simulation, that the algorithm performs well even under rapidly changing channel conditions. Finally, we discuss a maximum likelihood approach for choosing the packet size, which performs almost optimally but is much easier to implement.

Patent
03 Dec 1999
TL;DR: In this paper, an interactive system is provided in which information is displayed in response to the entry of the digits of a channel number, such as program listings information such as the channel designator or the program currently airing on the channel.
Abstract: An interactive system is provided in which information is displayed in response to the entry of the digits of a channel number. The interactive system may be implemented on a television, a computer, or a radio system. The displayed information may be program listings information such as the channel designator or the program currently airing on the channel. The displayed information may also be a list of channels. The list of channels may be associated with the entered digits, may be component channels, or channels of the same type and may be sorted by various techniques such as numerically, by favorite channels, by type, etc. The interactive system may allow a user to specify a source identifier to channels from different sources and display the channels with the source identifier when they are entered.

01 Jan 1999
TL;DR: The objective of this paper is to describe the large potential, the flexibility and adaptivity of the OFDM transmission technique in frequency-selective and time variant radio channels.
Abstract: Future multimedia services will require the transmission of very high data rates over broad-band radio channels. In order to provide these services to mobile users, an appropriate transmission technique has to cope with frequency-selective and time-variant radio channels. The computation complexity for an equalizer increases in a frequency-selective radio channel for high data-rate applications. Furthermore, the overhead for channel estimation procedures increases in time-variant channels. To overcome these drawbacks orthogonal frequency division multiplexing (OFDM) has been considered for broad-band applications in many publications. The objective of this paper is to describe the large potential, the flexibility and adaptivity of the OFDM transmission technique in frequency-selective and time-variant radio channels. In this paper several technical aspects of OFDM transmission systems are discussed, especially the topics of differential modulation for which we compare different demodulation methods and channel coding with soft decision decoding. For higher level differential modulation, multilevel coding is taken into consideration.

Patent
07 Dec 1999
TL;DR: In this paper, a statistical multiplexing apparatus and method for generating and combining a plurality of encoded video bit streams is presented, where a storage device contains pre-stored a priori statistics indicative of the encoding complexity of the video signals from which the encoded video bits streams will be generated.
Abstract: A statistical multiplexing apparatus and method for generating and combining a plurality of encoded video bit streams. A storage device contains pre-stored a priori statistics indicative of the encoding complexity of the video signals from which the encoded video bit streams will be generated. The pre-stored a priori statistics may include inter-pixel differences in the same picture or between multiple pictures or pre-encoding a priori statistics generated during a preliminary encoding of the video signals. Examples of pre-encoding a priori statistics include the number of bits per picture at a given quantization level, an average quantization level, picture types, scene change locations and repeat field for one or more of the video bit streams. The video signals are applied to encoders which compress the signals in accordance with bit allocation decisions generated by a statistics computer. The statistics computer uses only pre-encoding a priori statistics from the storage device to generate bit allocation decisions. Alternatively, the statistics computer may use any type of a priori statistics in conjunction with a posteriori statistics received from the encoders in allocating bits. The resulting compressed video bit streams are applied to a multiplexer and combined into a single multiplexed bit stream for transmission on a single channel. The statistics computer thus has access to additional information regarding the encoding complexity of the video bit streams to be encoded and combined, and can therefore generate more accurate bit allocations and better maintain consistent video quality across multiple encoded bit streams.

Journal ArticleDOI
TL;DR: This paper proposes an alternative approach to solving the dynamic channel assignment (DCA) problem through a form of real-time reinforcement learning known as Q learning, which is able to perform better than the FCA in various situations and is capable of achieving a similar performance to that achieved by MAXAVAIL, but with a significantly reduced computational complexity.
Abstract: This paper deals with the problem of channel assignment in mobile communication systems. In particular, we propose an alternative approach to solving the dynamic channel assignment (DCA) problem through a form of real-time reinforcement learning known as Q learning. Instead of relying on a known teacher, the system is designed to learn an optimal assignment policy by directly interacting with the mobile communication environment. The performance of the Q-learning-based DCA was examined by extensive simulation studies on a 49-cell mobile communication system under various conditions including homogeneous and inhomogeneous traffic distributions, time-varying traffic patterns, and channel failures. Comparative studies with the fixed channel assignment (FCA) scheme and one of the best dynamic channel assignment strategies (MAXAVAIL) have revealed that the proposed approach is able to perform better than the FCA in various situations and is capable of achieving a similar performance to that achieved by MAXAVAIL, but with a significantly reduced computational complexity.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a method of automatic extraction of the tidal channel network from topographic data of marsh and tidal flat lands that uses a combination of a threshold elevation and threshold curvature.
Abstract: We propose a method of automatic extraction of the tidal channel network from topographic data of marsh and tidal flat lands that uses a combination of a threshold elevation and threshold curvature. Not only the location but also the area of the channel bed is identified. This method differs substantially from that used to identify terrestrial channel networks, and it successfully predicts all of the main channels and nearly all of the smaller tributaries of the channel networks derived from SPOT imagery of the northern Venice Lagoon. Channel network maps of Venice and other sites (Petaluma Marsh in the San Francisco Bay and Barnstable Marsh in Massachusetts) were examined for scaling properties. Because of the large width of the channels relative to a characteristic length of their drainage area, we had to develop procedures for automatically delineating channel width and then for identifying the skeleton of the channel network (the pattern connecting the loci of the channel centerlines) for box-counting analysis. Box-counting dimensions of the network skeleton proved site-dependent and showed finite-size effects. Because of the large widths we also performed a scaling analysis based on the proportions of the total channel bed area occupied by the tidal networks (i.e., a 'fat' fractal analysis). This analysis showed a strong break in scaling between large and small channels. These analyses suggest that tidal channels differ significantly in their scaling relationships from terrestrial systems. In subsequent papers [Rinaldo et al., this issue (a), (b)] we pursue this point much further.

Journal ArticleDOI
01 Oct 1999
TL;DR: In this paper, the authors describe the large potential, the flexibility and adaptivity of the orthogonal frequency division multiplexing (OFDM) transmission technique in frequency-selective and time-variant radio channels.
Abstract: Future multimedia services will require the transmission of very high data rates over broad-band radio channels. In order to provide these services to mobile users, an appropriate transmission technique has to cope with frequency-selective and time-variant radio channels. The computation complexity for an equalizer increases in a frequency-selective radio channel for high data rate applications. Furthermore, the overhead for channel estimation procedures increases in time-variant channels. To overcome these drawbacks orthogonal frequency division multiplexing (OFDM) has been considered for broadband applications in many publications. The objective of this paper is to describe the large potential, the flexibility and adaptivity of the OFDM transmission technique in frequency-selective and time variant radio channels. Several technical aspects of OFDM transmission systems are discussed, especially the topics of differential modulation for which we compare different demodulation methods and channel coding with soft decision decoding. For higher level differential modulation, multilevel coding is taken into consideration.

Patent
03 Mar 1999
TL;DR: In this paper, the authors proposed a method for computing a channel transfer function (800, 900, 1000, 1100) between the transmitting user device at each of the plurality of receiving antennas by computing a simulated received pilot signal for each receiving antenna.
Abstract: A method and device in a communication system (100) including a receiver (201) having a plurality of receiving antenna (101) for receiving a plurality of information burst (400) transmitted by at least one transmitting user device where the information bursts contain a number of data symbols (430) and a pilot symbol sequence (420) of content known at both the transmitting user device and the receiver. The method provides for computing a channel transfer function (800, 900, 1000, 1100) between the transmitting user device at each of the plurality of receiving antennas (101), by computing a simulated received pilot signal for each receiving antenna, computing an error signal between the simulated received pilot signal and the received pilot symbol sequence, computing a channel modeling sequence, wherein the power of the error signal is minimized, and computing the channel transfer function by weighting predetermined basis functions by the channel modeling sequence.