Showing papers on "Communication channel published in 2000"

Ultra-wide bandwidth time-hopping spread-spectrum impulse radio for wireless multiple-access communications

Abstract: Attractive features of time-hopping spread-spectrum multiple-access systems employing impulse signal technology are outlined, and emerging design issues are described. Performance of such communications systems in terms of achievable transmission rate and multiple-access capability are estimated for both analog and digital data modulation formats under ideal multiple-access channel conditions.

Digital Communication over Fading Channels: A Unified Approach to Performance Analysis

Abstract: FUNDAMENTALS. Fading Channel Characterization and Modeling. Types of Communication. MATHEMATICAL TOOLS. Alternative Representations of Classical Functions. Useful Expressions for Evaluating Average Error Probability Performance. New Representations of Some PDF's and CDF's for Correlative Fading Applications. OPTIMUM RECEPTION AND PERFORMANCE EVALUATION. Optimum Receivers for Fading Channels. Performance of Single Channel Receivers. Performance of Multichannel Receivers. APPLICATION IN PRACTICAL COMMUNICATION SYSTEMS. Optimum Combining: A Diversity Technique for Communication Over Fading Channels in the Presence of Interference. Direct--Sequence Code--Division Multiple Access. FURTHER EXTENSIONS. Coded Communication Over Fading Channels. INDEX.

The effect upon channel capacity in wireless communications of perfect and imperfect knowledge of the channel

Abstract: We present a model for time-varying communication single-access and multiple-access channels without feedback. We consider the difference between mutual information when the receiver knows the channel perfectly and mutual information when the receiver only has an estimate of the channel. We relate the variance of the channel measurement error at the receiver to upper and lower bounds for this difference in mutual information. We illustrate the use of our bounds on a channel modeled by a Gauss-Markov process, measured by a pilot tone. We relate the rate of time variation of the channel to the loss in mutual information due to imperfect knowledge of the measured channel.

The state of the art in underwater acoustic telemetry

Abstract: Progress in underwater acoustic telemetry since 1982 is reviewed within a framework of six current research areas: (1) underwater channel physics, channel simulations, and measurements; (2) receiver structures; (3) diversity exploitation; (4) error control coding; (5) networked systems; and (6) alternative modulation strategies. Advances in each of these areas as well as perspectives on the future challenges facing them are presented. A primary thesis of this paper is that increased integration of high-fidelity channel models into ongoing underwater telemetry research is needed if the performance envelope (defined in terms of range, rate, and channel complexity) of underwater modems is to expand.

Differential space-time modulation

Abstract: Space-time coding and modulation exploit the presence of multiple transmit antennas to improve the performance on multipath radio channels Thus far, most work on space-time coding has assumed that perfect channel estimates are available at the receiver In certain situations, however, it may be difficult or costly to estimate the channel accurately, in which case it is natural to consider the design of modulation techniques that do not require channel estimates at the transmitter or receiver We propose a general approach to differential modulation for multiple transmit antennas based on group codes This approach ran be applied to any number of transmit and receive antennas, and any signal constellation We also derive low-complexity differential receivers, error bounds, and modulator design criteria, which we use to construct optimal differential modulation schemes for two transmit antennas These schemes can be demodulated with or without channel estimates This permits the receiver to exploit channel estimates when they are available The performance degrades by approximately 3 dB when estimates are not available

A differential detection scheme for transmit diversity

Abstract: We present a transmission scheme for exploiting diversity given by two transmit antennas when neither the transmitter nor the receiver has access to channel state information. The new detection scheme can use equal energy constellations and encoding is simple. At the receiver, decoding is achieved with low decoding complexity. The transmission provides full spatial diversity and requires no channel state side information at the receiver. The scheme can be considered as the extension of differential detection schemes to two transmit antennas.

Analysis of video transmission over lossy channels

Abstract: A theoretical analysis of the overall mean squared error (MSE) in hybrid video coding is presented for the case of error prone transmission. Our model covers the complete transmission system including the rate-distortion performance of the video encoder, forward error correction, interleaving, and the effect of error concealment and interframe error propagation at the video decoder. The channel model used is a 2-state Markov model describing burst errors on the symbol level. Reed-Solomon codes are used for forward error correction. Extensive simulation results using an H.263 video codec are provided for verification. Using the model, the optimal tradeoff between INTRA and INTER coding as well as the optimal channel code rate can be determined for given channel parameters by minimizing the expected MSE at the decoder. The main focus of this paper is to show the accuracy of the derived analytical model and its applicability to the analysis and optimization of an entire video transmission system.

A new multi-channel MAC protocol with on-demand channel assignment for multi-hop mobile ad hoc networks

Abstract: The wireless mobile ad hoc network (MANET) architecture has received a lot of attention recently. This paper considers the access of multiple channels in a MANET with multi-hop communication behavior. We point out several interesting issues when using multiple channels. We then propose a new multi-channel MAC protocol, which is characterized by the following features: (i) it follows an "on-demand" style to assign channels to mobile hosts, (ii) the number of channels required is independent of the network topology and degree, (iii) it flexibly adapts to host mobility and only exchanges few control messages to achieve channel assignment and medium access, and (iv) no clock synchronization is required. Compared to existing protocols, some assign channels to hosts statically (thus a host will occupy a channel even when it has no intention to transmit) some require a number of channels which is a function of the maximum connectivity, and some necessitate a clock synchronization among all hosts in the MANET. Extensive simulations are conducted to evaluate the proposed protocol.

Adaptive Modulation over Nakagami Fading Channels

Abstract: We first study the capacity of Nakagami multipath fading (NMF) channels with an average power constraint for three power and rate adaptation policies. We obtain closed-form solutions for NMF channel capacity for each power and rate adaptation strategy. Results show that rate adaptation is the key to increasing link spectral efficiency. We then analyze the performance of practical constant-power variable-rate M-QAM schemes over NMF channels. We obtain closed-form expressions for the outage probability, spectral efficiency and average bit-error-rate (BER) assuming perfect channel estimation and negligible time delay between channel estimation and signal set adaptation. We also analyze the impact of time delay on the BER of adaptive M-QAM.

Channel assignment schemes for cellular mobile telecommunication systems: A comprehensive survey

Abstract: This article provides a detailed discussion of wireless resource and channel allocation schemes. The authors provide a survey of a large number of published papers in the area of fixed, dynamic, and hybrid allocation schemes and compare their trade-offs in terms of complexity and performance. We also investigate these channel allocation schemes based on other factors such as distributed⁄centralized control and adaptability to traffic conditions. Moreover, we provide a detailed discussion on reuse partitioning schemes, the effect of handoffs, and prioritization schemes. Finally, we discuss other important issues in resource allocation such as overlay cells, frequency planning, and power control.

Modeling the statistical time and angle of arrival characteristics of an indoor multipath channel

Abstract: Most previously proposed statistical models for the indoor multipath channel include only time of arrival characteristics. However, in order to use statistical models in simulating or analyzing the performance of systems employing spatial diversity combining, information about angle of arrival statistics is also required. Ideally, it would be desirable to characterize the full spare-time nature of the channel. In this paper, a system is described that was used to collect simultaneous time and angle of arrival data at 7 GHz. Data processing methods are outlined, and results obtained from data taken in two different buildings are presented. Based on the results, a model is proposed that employs the clustered "double Poisson" time-of-arrival model proposed by Saleh and Valenzuela (1987). The observed angular distribution is also clustered with uniformly distributed clusters and arrivals within clusters that have a Laplacian distribution.

Point-to-point connectivity between neuromorphic chips using address events

Abstract: This paper discusses connectivity between neuromorphic chips, which use the timing of fixed-height fixed-width pulses to encode information. Address-events (log/sub 2/(N)-bit packets that uniquely identify one of N neurons) are used to transmit these pulses in real time on a random-access time-multiplexed communication channel. Activity is assumed to consist of neuronal ensembles-spikes clustered in space and in time. This paper quantifies tradeoffs faced in allocating bandwidth, granting access, and queuing, as well as throughput requirements, and concludes that an arbitered channel design is the best choice. The arbitered channel is implemented with a formal design methodology for asynchronous digital VLSI CMOS systems, after introducing the reader to this top-down synthesis technique. Following the evolution of three generations of designs, it is shown how the overhead of arbitrating, and encoding and decoding, can be reduced in area (from N to /spl radic/N) by organizing neurons into rows and columns, and reduced in time (from log/sub 2/(N) to 2) by exploiting locality in the arbiter tree and in the row-column architecture, and clustered activity. Throughput is boosted by pipelining and by reading spikes in parallel. Simple techniques that reduce crosstalk in these mixed analog-digital systems are described.

An improved error model for noisy channel spelling correction

Abstract: The noisy channel model has been applied to a wide range of problems, including spelling correction. These models consist of two components: a source model and a channel model. Very little research has gone into improving the channel model for spelling correction. This paper describes a new channel model for spelling correction, based on generic string to string edits. Using this model gives significant performance improvements compared to previously proposed models.

Long-range prediction of fading signals

Abstract: It was previously proposed to adapt several transmission methods, including modulation, power control, channel coding, and antenna diversity to rapidly time variant fading channel conditions. Prediction of the channel coefficients several tens-to-hundreds of symbols ahead is essential to realize these methods in practice. We describe a novel adaptive long-range fading channel prediction algorithm (LRP) and its utilization with adaptive transmission methods. The LRP is validated for standard stationary fading models and tested with measured data and with data produced by our novel realistic physical channel model. Both numerical and simulation results show that long-range prediction makes adaptive transmission techniques feasible for mobile radio channels.

Interpreting the Dimensions of Ancient Fluvial Channel Bars, Channels, and Channel Belts from Wireline-Logs and Cores

Abstract: A primary objective in exploration for and development of fluvial reservoirs is determining the thickness and width of sandstone-conglomerate bodies (mainly channel-belt deposits). Most of the existing techniques for estimating the dimensions of fluvial reservoirs have major drawbacks. A fresh approach to the problem is made using recent theoretical, experimental, and field studies. This new approach involves (1) new models for the lateral and vertical variation of lithofacies and petrophysical-log response of river-channel deposits with explicit recognition of the different superimposed scales of strata, (2) distinction among single and superimposed channel bars, channels, and channel belts, (3) interpretation of maximum paleochannel depth from the thickness of channel bars and the thickness of sets of cross-strata formed by dunes, and (4) evaluation of various methods for estimation of widths of sandstone-conglomerate bodies that represent either single or connected channel belts (outcrop analogs; correlation of sandstone-conglomerate bodies between wells; use of empirical equations relating channel depth, channel width, and channel-belt width; theoretical models; and three-dimensional seismic data).

Large system performance of linear multiuser receivers in multipath fading channels

Abstract: A linear multiuser receiver for a particular user in a code-division multiple-access (CDMA) network gains potential benefits from knowledge of the channels of all users in the system. In fast multipath fading environments we cannot assume that the channel estimates are perfect and the inevitable channel estimation errors will limit this potential gain. We study the impact of channel estimation errors on the performance of linear multiuser receivers, as well as the channel estimation problem itself. Of particular interest are the scalability properties of the channel and data estimation algorithms: what happens to the performance as the system bandwidth and the number of users (and hence channels to estimate) grows? Our main results involve asymptotic expressions for the signal-to-interference ratio of linear multiuser receivers in the limit of large processing gain, with the number of users divided by the processing gain held constant. We employ a random model for the spreading sequences and the limiting signal-to-interference ratio expressions are independent of the actual signature sequences, depending only on the system loading and the channel statistics: background noise power, energy profile of resolvable multipaths, and channel coherence time. The effect of channel uncertainty on the performance of multiuser receivers is succinctly captured by the notion of effective interference.

An efficient multiuser loading algorithm for OFDM-based broadband wireless systems

Abstract: In this paper we present a novel loading algorithm for OFDM-based multiuser communication system to maximize the total system throughput while satisfying the total power and users' rate constraints. The new scheme determines the subcarrier, bit, and power allocation by decoupling an NP-hard combinatorial problem into two steps: (1) resource allocation (how much power and how many subcarriers for each user) based on users' average channel gains and their rate requirements; and (2) subcarrier assignment and bit loading based on users' channel profiles across all subcarriers. Compared to existing iterative methods, the two-step approach offers comparable capacity gain with much lower complexity.

A generalized RAKE receiver for interference suppression

Abstract: Currently, a global third-generation cellular system based on code-division multiple-access (CDMA) is being developed with a wider bandwidth than existing second-generation systems. The wider bandwidth provides increased multipath resolution in a time-dispersive channel, leading to higher frequency-selectivity. A generalized RAKE receiver for interference suppression and multipath mitigation is proposed. The receiver exploits the fact that time dispersion significantly distorts the interference spectrum from each base station in the downlink of a wideband CDMA system. Compared to the conventional RAKE receiver, this generalized RAKE receiver may have more fingers and different combining weights. The weights are derived from a maximum likelihood formulation, modeling the intracell interference as colored Gaussian noise. This low-complexity detector is especially useful for systems with orthogonal downlink spreading codes, as orthogonality between own cell signals cannot be maintained in a frequency-selective channel. The performance of the proposed receiver is quantified via analysis and simulation for different dispersive channels, including Rayleigh fading channels. Gains on the order of 1-3.5 dB are achieved, depending on the dispersiveness of the channel, with only a modest increase in the number of fingers. For a wideband CDMA (WCDMA) system and a realistic mobile radio channel, this translates to capacity gains of the order of 100%.

Method and wireless systems using multiple antennas and adaptive control for maximizing a communication parameter

Abstract: A method of maximizing a communication parameter, such as data capacity, signal quality or throughput of a channel between a transmit unit (12) with M transmit antennas (18A...18M) and a receive unit (14) with N receive antennas (34A...34N) and a communication system employing the method. The data is first processed to produce parallel spatial-multiplexed streams SMi, where i=1...k, which are converted or mapped to transmit signals TSp, where p=1...M, assigned for transmission from the M transmit antennas (18A...18M). Corresponding receive signals RSj, where j=1...N, are received by the N receive antennas (34A...34N) of the receiver and used to assess a quality parameter, such as a statistical signal parameter or a parameter of the data. The quality parameter is used to adaptively adjust k as well as other parameters to transmit antennas such that the communication parameter of the channel is maximized.

Remotely configurable multimedia entertainment and information system with location based advertising

Abstract: An Internet (280) radio for portable applications and uses such as in an automobile (184). The Internet (280) radio allows access to a host of audio, visual and other information. Normal radio function is provided along with programmable content and channel selection (162), as well as automatic content and channel updating by location and style. Internet access is also provided. Direct or targeted advertising, as well as electronic commerce is supported. Connection to the Internet (280) is through wireless communications (210). Programmability is achieved off-line via a web page and remote computer (206). Customized information is also communicated to the radio such as stock quotes, travel information, advertising, and e-mail. Onboard global positioning (110) allows for channel (162) updating by location, traffic information, geographic advertising and available similar content.

Channel Processes, Classification, and Response

Abstract: l This chapter discusses physical processes, classification, a n d r e s p o n s e p o t e n t i a l o f channels in mountain drainage basins of the Pacific coastal ecoregion. l A relatively simple set of physical processes leads to a wide variety of natural stream channels, the classification of which can guide recognition of functionally similar zones in mountain drainage basins. Different portions of mountain channel networks are dominated by different geomorphic processes and relationships between transport capacity (a function of discharge and boundary shear stress) and sediment supply (size and amount of material available for transport). l Channel classifications use similarities of form and function to impose order on a continuum of natural stream types or morphologies. No single classification can satisfy all possible purposes or is likely to encompass all possible channel types. l This chapter reviews geomorphological channel classifications and their use for systematizing channel morphology and physical processes for the purpose of assessing physical channel condition and response potential. Early classification systems tend to neglect the influence of woody debris or emphasize single scales of influences on channel morphology and processes. In contrast, a hierarchical approach to channel classification addresses different factors influencing channel properties over a range of spatial and temporal scales and is well suited for assessment of channel conditions and response potential in mountain drainage basins. l The spatial distribution of reach types within a drainage basin influences the distribution of potential impacts and responses to disturbance. Alluvial channels with high transport capacities relative to sediment supply generally maintain their morphology while transmitting increased sediment loads; channels with lower ratios of transport capacity to sediment supply tend to exhibit greater morphologic response to increased sediment loads. Steep channels thereby act as sediment delivery conduits connecting zones of sediment production on hillslopes to more responsive lower-gradient channels. l Consideration of channel bed morphology, confinement (the ratio of the width of the valley floor to the width of the bankfull channel), position in the channel network, and external influences (such as riparian vegetation and in-channel woody debris) can guide evaluation of channel condition and response potential in forested mountain drainage basins.

Manufacturer-Retailer Channel Interactions and Implications for Channel Power: An Empirical Investigation of Pricing in a Local Market

Abstract: The issue of "power" in the marketing channels for consumer products has received considerable attention in both academic and practitioner journals as well as in the popular press. Our objective in this paper is to provide an empirical method to measure the power of channel members and to understand the reasons demand factors, cost factors, nature of channel interactions for this power. We confine our analysis to pricing power in channels. We use methods from the game-theory literature in marketing on channel interactions to obtain the theoretical framework for our empirical model. This literature provides us a definition of power-one that is based on the proportion or percentage of channel profits that accrue to each of the channel members. There can be a variety of possible channel interactions between manufacturers and retailers in channels. The theoretical literature has examined some of these games. For example, Choi 1991 examines how channel profits for manufacturers and retailer vary if channel interactions are either vertical Nash, or if they are Stackelberg leaderfollower with either the manufacturer or the retailer being the price leader. Each of these three channel interaction games has different implications for profits made by manufacturers and retailers, and consequently for the relative power of the channel members. In contrast to the previous literature that has focused largely on the above three channel interaction games, our model extends the game-theoretic literature by allowing for a continuum of possible channel interactions between manufacturers and a retailer. Furthermore, for a given product market, we empirically estimate from the data where the channel interactions lie in this continuum. More critically, we obtain measures of how channel profits are divided between manufacturers and the retailer in the product market, where a higher share of channel profit is associated with higher channel power. We then examine how channel power is related to demand conditions facing various brands and cost parameters of various manufacturers. In going from game-theory-based theoretical models of channel interactions to empirical estimation, we use the "new empirical industrial organization" framework Bresnahan 1988. As part of this structural modeling framework, we build retail-level demand functions for the various brands manufacturer and private label in a given product category. Given these demand functions, we obtain optimal pricing rules for manufacturers and the retailer. In determining their optimal prices, manufacturers and the retailer account for how all the players in the channel choose their optimal prices. That is, we account for dependencies in decision making across channel members. These dependencies are characterized by a set of "conduct parameters," which are estimated from market data. The conduct parameters enable us to identify the nature of channel interactions between manufacturers and the retailer along the continuum mentioned previously. In addition to the demand and conduct parameters, manufacturers' marginal costs are also estimated in the model. These marginal cost estimates, along with the manufacturer prices and retail prices available in our dataset, enable us to compute the division of channel profits among the channel members. Hence, we are able to obtain insights into who has pricing power in the channel. In the empirical application of the model, we analyze a local market for two product categories: refrigerated juice and tuna. In both categories, there are three major brands. The difference between them is that the private label has an insignificant market share in the tuna category. Our main empirical results show that the usual games examined in the marketing literature do not hold for the given data. We also.nd that the retailer's market power is very significant in both these product categories, and that the estimated demand and cost parameters are consistent with the estimated pattern of conduct between the manufacturers and the retailer. Given the evidence from the trade press of intense manufacturer competition in these categories, as well as the "commodity" nature of these products, the result of retailer power appears intuitive.

Intelligent medium access for mobile ad hoc networks with busy tones and power control

Abstract: In 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/CTS-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 cochannel interference, does show a promising direction to enhance the performance of MANETs.

A stochastic multiple-input-multiple-output radio channel model for evaluation of space-time coding algorithms

Abstract: A simple framework for Monte Carlo simulations of a multiple-input-multiple-output radio channel is proposed. The derived model includes the partial correlation between the paths in the channel, as well as fast fading and time dispersion. The only input parameters required for the model are the shape of the power delay spectrum and the spatial correlation functions at the transmit and receive end. Thus, the required parameters are available in the open literature for a large variety of environments. It is furthermore demonstrated that the Shannon capacity of the channel is highly dependent on the considered environment.

Selecting an optimal set of transmit antennas for a low rank matrix channel

Abstract: Previous work has shown that the use of multiple antennas in a fading environment results in a linear increase in capacity. This paper examines the capacity of a multiple antenna element array (MEA) in a quasi-static flat fading environment with a rank deficient channel. We assume that the channel is known at the receiver and the existence of a feedback path to the transmitter. For a particular channel realization, we show that the judicious use of fewer transmit antennas when the channel matrix is ill-conditioned can increase system capacity. We develop a criterion for selecting an optimum set of transmit antennas. This selection is optimal in the sense that the capacity of the resulting MEA system is greater than that for any other configuration with the same number of transmit antennas chosen from the original set. The resulting channel is full rank.

System and method for transporting a compressed video and data bit stream over a communication channel

Abstract: Digitally compressed video/audio bit streams, when transmitted over digital communication channels such as digital subscriber loop (DSL) access networks, ATM networks, satellite, or wireless digital transmission facilities, can be corrupted due to lack of sufficient channel bandwidth. This invention describes schemes to ensure lossless transmission of bit streams containing pre-compressed video signals within the communication channels. The schemes herein comprises a rate conversion system that converts the bit rate of a pre-compressed video bit stream from one bit rate to another, and that is integrated with a digital communication channel, and a means to convey the maximum channel transmission rate to the rate conversion system to allow satisfactory transmission of the bit stream from the input of the rate converter through the transmission facility.

Optimal mode selection and synchronization for robust video communications over error-prone networks

Abstract: We describe an effective method for increasing error resilience of video transmission over bit error prone networks. Rate-distortion optimized mode selection and synchronization marker insertion algorithms are introduced. The resulting video communication system takes into account the channel condition and the error concealment method used by the decoder, to optimize video coding mode selection and placement of synchronization markers in the compressed bit stream. The effects of mismatch between the parameters used by the encoder and the parameters associated with the actual channel condition and the decoder error concealment method are evaluated. Results for the binary symmetric channel and wideband code division multiple access mobile network models are presented in order to illustrate the advantages of the proposed method.

Progressive transmission of images over memoryless noisy channels

Abstract: An embedded source code allows the decoder to reconstruct the source progressively from the prefixes of a single bit stream. It is desirable to design joint source-channel coding schemes which retain the capability of progressive reconstruction in the presence of channel noise or packet loss. Here, we address the problem of joint source-channel coding of images for progressive transmission over memoryless bit error or packet erasure channels. We develop a framework for encoding based on embedded source codes and embedded error correcting and error detecting channel codes. For a target transmission rate, we provide solutions and an algorithm for the design of optimal unequal error/erasure protection. Three performance measures are considered: the average distortion, the average peak signal-to-noise ratio, and the average useful source coding rate. Under the assumption of rate compatibility of the underlying channel codes, we provide necessary conditions for progressive transmission of joint source-channel codes. We also show that the unequal error/erasure protection policies that maximize the average useful source coding rate allow progressive transmission with optimal unequal protection at a number of intermediate rates.

Multichannel CSMA with signal power-based channel selection for multihop wireless networks

Abstract: We describe a new carrier-sense multiple access (CSMA) protocol for multihop wireless networks, using multiple channels and a distributed channel selection scheme. The proposed protocol divides the available bandwidth into N channels where the transmitting station selects an appropriate channel for packet transmission. The selection criterion is based on the interference power measurements on the channels. 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.