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Channel Capacity (channel + capacity)

Distribution by Scientific Domains

Engineering	87%

Selected Abstracts

ADJUSTMENT OF STREAM CHANNEL CAPACITY FOLLOWING DAM CLOSURE, YEGUA CREEK, TEXAS,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 6 2002
Anne Chin
ABSTRACT: In Yegua Creek, a principal tributary of the Brazos River in Texas, surveys of a 19 km channel reach downstream of Somerville Dam show that channel capacity decreased by an average of 65 percent in a 34 year period following dam closure. The decrease corresponds with an approximately 85 percent reduction in annual flood peaks. Channel depth has changed the most, decreasing by an average of 61 percent. Channel width remained stable with an average decrease of only 9 percent, reflecting cohesive bank materials along with the growth of riparian vegetation resulting from increased low flows during dry summer months. Although large changes in stream channel geometry are not uncommon downstream of dams, such pronounced reductions in channel capacity could have long-term implications for sediment delivery through the system. [source]

Flooding and geomorphic impacts in a mountain torrent: Raise Beck, central Lake District, England

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2002
R. M. Johnson
Abstract Raise Beck is a mountain torrent located in the central Lake District fells, northern England (drainage area of 1·27 km2). The torrent shows evidence of several major flood events, the most recent of which was in January 1995. This event caused a major channel avulsion at the fan apex diverting the main flood flow to the south, blocking the A591 trunk road and causing local flooding. The meteorological conditions associated with this event are described using local rainfall records and climatic data. Records show 164 mm of rainfall in the 24 hours preceding the flood. The peak flood discharge is reconstructed using palaeohydrological and rainfall,runoff methods, which provide discharge values of 27,74 m3 s,1, and 4,6 m3 s,1, respectively. The flood transported boulders with b-axes up to 1400 mm. These results raise some important general questions about flood estimation in steep mountain catchments. The geomorphological impact of the event is evaluated by comparing aerial photographs from before and after the flood, along with direct field observations. Over the historical timescale the impact and occurrence of flooding is investigated using lichenometry, long-term rainfall data, and documentary records. Two major historical floods events are identified in the middle of the nineteenth century. The deposits of the recent and historical flood events dominate the sedimentological evidence of flooding at Raise Beck, therefore the catchment is sensitive to high magnitude, low frequency events. Following the 1995 flood much of the lower catchment was channelized using rip-rap bank protection, re-establishing flow north towards Thirlmere. The likely success of this management strategy in containing future floods is considered, based on an analysis of channel capacities. It is concluded that the channelization scheme is only a short-term solution, which would fail to contain the discharge of an event equivalent to the January 1995 flood. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Wideband MIMO measurements of outdoor NLOS channels

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2006
Yaoqing Yang
Abstract The measurement results of the wideband wireless multiple-input multiple-output (MIMO) channels in outdoor environments are presented. Our wideband wireless MIMO channel sounder consists of four transmitters and eight receivers, and operates at a carrier frequency of 1.8 GHz with a bandwidth of 2.5 MHz. After obtaining the multipath delay profiles from the data collected in non-line-of-sight (NLOS) environments, realistic wideband MIMO channel capacities are computed and compared with the ideal channel simulation. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 216,218, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21309 [source]

Stream geomorphology in a mountain lake district: hydraulic geometry, sediment sources and sinks, and downstream lake effects

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2007
C. D. Arp
Abstract Lakes are common in glaciated mountain regions and geomorphic principles suggest that lake modifications to water and sediment fluxes should affect downstream channels. Lakes in the Sawtooth Mountains, Idaho, USA, were created during glaciation and we sought to understand how and to what extent glacial morphology and lake disruption of fluxes control stream physical form and functions. First, we described downstream patterns in channel form including analyses of sediment entrainment and hydraulic geometry in one catchment with a lake. To expand on these observations and understand the role of glacial legacy, we collected data from 33 stream reaches throughout the region to compare channel form and functions among catchments with lakes, meadows (filled lakes), and no past or present lakes. Downstream hydraulic geometry relationships were weak for both the single catchment and regionally. Our data show that downstream patterns in sediment size, channel shape, sediment entrainment and channel hydraulic adjustment are explained by locations of sediment sources (hillslopes and tributaries) and sediment sinks (lakes). Stream reaches throughout the region are best differentiated by landscape position relative to lakes and meadows according to channel shape and sediment size, where outlets are wide and shallow with coarse sediment, and inlets are narrow and deep with finer sediment. Meadow outlets and lake outlets show similarities in the coarse-sediment fraction and channel capacity, but meadow outlets have a smaller fine-sediment fraction and nearly mobile sediment. Estimates of downstream recovery from lake effects on streams suggest 50 per cent recovery within 2,4 km downstream, but full recovery may not be reached within 20 km downstream. These results suggest that sediment sinks, such as lakes, in addition to sources, such as tributaries, are important local controls on mountain drainage networks. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Fuzzy-based multiuser detector for impulsive CDMA channel

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 7 2007
Adel M. Hmidat
A new fuzzy multiuser detector for non-Gaussian synchronous direct sequence code division multiple access (DS-CDMA) is proposed for jointly mitigating the effects of impulsive noise and multiple access interference (MAI). The proposed scheme combines a linear decorrelator and antenna array with a nonlinear preprocessor based on fuzzy logic and rank ordering. The fuzzy rule is incorporated to combat impulsive noise by eliminating outliers from the received signal. The performance of the proposed scheme is assessed by Monte Carlo simulations and the obtained results demonstrate that the proposed fuzzy detector outperforms other reported schemes in terms of bit error rate (BER) and channel capacity. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Choosing the parameters of multiple-repetition strategies,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2007
Thijs Veugen
The class of multiple-repetition strategies is known to achieve capacity for specific discrete memoryless channels with noiseless feedback. We show, given an arbitrary discrete memoryless channel with noiseless feedback, that the repetition parameters should be chosen close to the self information of a transmission error to maximise the transmission rate. Furthermore, it is indicated how close the channel capacity can be approached in the general case. Finally, we compare some results on a related problem: the capacity of a discrete noiseless channel with constraints on the input symbols. Copyright © 2006 AEIT [source]

On extrinsic information of good binary codes operating over Gaussian channels

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 2 2007
M. Peleg
We show that the extrinsic information about the coded bits of any good (capacity achieving) binary code operating over a Gaussian channel is zero when the channel capacity is lower than the code rate and unity when capacity exceeds the code rate, that is, the extrinsic information transfer (EXIT) chart is a step function of the signal to noise ratio and independent of the code. It follows that, for a common class of iterative receivers where the error correcting decoder must operate at first iteration at rate above capacity (such as in turbo equalization, iterative channel estimation, parallel and serial concatenated coding and the like), classical good codes which achieve capacity over the Additive White Gaussian Noise Channel are not effective and should be replaced by different new ones. Copyright © 2006 AEIT. [source]

The performance evaluation of spatial,temporal algorithms in W-CDMA systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2005
Shiann-Shiun Jeng
Abstract Differing from FDMA, TDMA, and CDMA, space division multiple access (SDMA) uses space resources to improve communication system performance. Utilizing the smart antenna system is an approach to realize the SDMA technique. Smart antenna systems using the beamforming technique can reduce the co-channel interference and multipath fading to increase the channel capacity and communication quality. In this study the smart antenna system and rake receiver are integrated. The performance of spatial,temporal structure applied to the W-CDMA system is evaluated. From the cumulative distribution function simulation results, W-CDMA system with spatial,temporal algorithm can exactly provide SINR gain to improve the system performance and capacity. Copyright © 2005 John Wiley & Sons, Ltd. [source]

On the design of bandwidth efficient signalling for indoor wireless optical channels

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2005
Steve HranilovicArticle first published online: 15 MAR 200
Abstract It is well known that indoor wireless optical channels are limited not only in transmitted optical power, but also in signalling bandwidth. This bandwidth constraint arises due to multipath dispersion in indoor settings as well as due to response time limitations of optoelectronic components. This paper presents an overview of theoretical and practical issues in the design of signalling for bandwidth constrained intensity modulated, direct detection wireless optical channels. A brief overview of the salient qualities of the wireless optical channel are presented to highlight the amplitude constraints which arise. A survey of modulation design is then presented which includes the review of a general technique to represent optical intensity modulation in a signal space and to construct optical intensity lattice codes. Results on the channel capacity of indoor wireless optical channels are surveyed and particular emphasis is placed on recently derived asymptotically exact bounds. The use of multiple emitters and receivers in wireless optical channels is also presented and particular emphasis is placed on techniques which exploit spatial dimensions to improve spectral performance. The paper concludes with some remarks regarding the status of the research area and suggestions for future work. Copyright © 2005 John Wiley & Sons, Ltd. [source]

On the performance of recursive space,frequency codes and iterative decoding in wideband OFDM-MIMO systems: simulated and measured results

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2004
Paul N. Fletcher
Abstract In this paper, we study the performance of a bandwidth efficient space,frequency turbo encoding scheme over wideband channels. Results are presented for simulated wideband MIMO channels consisting of two transmit antennas and up to two receive antennas. In addition, wideband channel measurements undertaken with practical multi-element antenna structures at both the access point (AP) and mobile terminal (MT) are presented. Analysis is in terms of channel capacity, 10% channel outage capacity and space,frequency iterative decoding for an lEEE802.11a physical layer complaint modem. It is shown when operating with a spectral efficiency of 1.2 bits/s/Hz, the iterative decoded space,time codes comes within approximately 4.7 dB of 10% outage capacity over Rayleigh fading wideband channels with two transmit and two receive antennas. Over measured channels the iterative decoding scheme performs within 7.7 dB 10% of outage capacity. Losses due to channel state information estimation are also investigated. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Experimental studies of direction of arrivals using a smart antenna testbed in wireless communication systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2003
Shiann-Shiun Jeng
Abstract This paper presents some preliminary results from experimental studies on space-division-multiple-access (SDMA) for wireless communications. A smart antenna system utilizing direction-of-arrival (DOA)-based beamforming techniques can enhance signal quality by reducing co-channel interference from mobiles located at angles spatially distinct from the base station. Adopting both smart uplink and downlink beamforming, a communication system with an antenna array can increase the cell coverage of a base station and significantly boost capacity compared with conventional antenna systems. However, successful implementation of DOA-based beamforming techniques depends on the DOA characteristics. This paper presented the feasibility of direction finding and DOA variation with respect to frequency. Furthermore, the angle spread was studied for selected environments. The results demonstrate the feasibility of applying proposed smart antenna system utilizing DOA-based beamforming algorithm for increasing channel capacity and improving system performance in frequency-division-duplex (FDD) wireless communication systems. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Robust and efficient quantization and coding for control of multidimensional linear systems under data rate constraints

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 10-11 2007
K. Li
Abstract Recently, we reported results on coding strategies for scalar feedback systems with data-rate-limited feedback channels in which the data-rate constraints are time varying. Such rate-varying channels are typically encountered in communication networks in which links between nodes are subject to noise, congestion, and intermittent disruption. The present paper describes results of extending this research into the multidimensional domain. An important consideration is that for systems of dimension greater than one, many classical feedback designs cannot be realized for operation near the theoretical minimum possible data rate. A novel control coding scheme will be presented, and in terms of this, it will be shown that the advantages of coarse signal quantization that had been reported earlier for scalar systems remain in the multidimensional case. The key is to allocate the communication bandwidth efficiently among faster and slower modes. We discuss various strategies that allocate bandwidth by scheduling the time slots assigned to each mode. In particular, we propose a ,robust attention varying' technique, whose merit will be discussed in terms of its robustness with respect to time-varying communication channel capacity and also in terms of how well it operates when the feedback channel capacity is near the theoretical minimum data rate. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Novel down link rain fade mitigation technique for Ka-band multibeam systems

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 1 2007
Parimal Majithiya
Abstract Rain fades at Ka-Band degrades the link quality and performance significantly. Several rain fade mitigation techniques for Ka-band satellite systems are being investigated to improve the channel capacity. Methods such as power control and adaptive waveform techniques have been proposed for use in the uplink as they are capable of straightforward implementation. A novel down link power control technique for multi-beam Ka-band system has been proposed in this paper. It is based on the use of multi-port amplifier, which is commonly used for dynamic power sharing of the beams depending upon the traffic. Payload architecture for multi-beam coverage using multi-port amplifiers has been designed for the proposed technique. The simulation results to compensate for the rain fade attenuation of one beam by sharing the unused power from other beams have been presented Copyright © 2006 John Wiley & Sons, Ltd. [source]

ADJUSTMENT OF STREAM CHANNEL CAPACITY FOLLOWING DAM CLOSURE, YEGUA CREEK, TEXAS,

Experimental evaluation of indoor MIMO channel capacity for compact arrays of planar inverted-F antennas

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 7 2007
Héctor Carrasco
Abstract Empirical results on indoor multiple input multiple output (MIMO) channel capacity obtained through the use of planar inverted-F antennas (PIFA) are presented. An extensive statistical study done at 2.45 GHz reveals how antenna proximity and array configuration affects MIMO capacity. It is concluded that certain linear or square PIFA based arrays allow very compact multi-antenna arrangements without significant capacity loss. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1754,1756, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22526 [source]