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Channel Conditions (channel + condition)

Distribution by Scientific Domains

Engineering	85%

Selected Abstracts

Error-aware and energy-efficient routing approach in MANETs

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 1 2009
Liansheng Tan
Abstract The lifetime of a network is the key design factor of mobile ad hoc networks (MANETs). To prolong the lifetime of MANETs, one is forced to attain a tradeoff of minimizing the energy consumption and load balancing. In MANETs, energy waste resulting from retransmission due to high bit error rate (BER) and high frame error rate (FER) of wireless channel is significant. In this paper, we propose two novel protocols termed multi-threshold routing protocol (MTRP) and enhanced multi-threshold routing protocol (EMTRP). MTRP divides the total energy of a wireless node into multiple ranges. The lower bound of each range corresponds to a threshold. The protocol iterates from the highest threshold to the lowest one and chooses those routes with bottleneck energy being larger than the current threshold during each iteration. This approach thus avoids overusing certain routes and achieves load balancing. If multiple routes satisfy the threshold constraint, MTRP selects a route with the smallest hop count to further attain energy efficiency. Based on MTRP, EMTRP further takes channel condition into consideration and selects routes with better channel condition and consequently reduces the number of retransmissions and saves energy. We analyze the average loss probability (ALP) of the uniform error model and Gilbert error model and give a distributed algorithm to obtain the maximal ALP along a route. Descriptions of MTRP and EMTRP are given in pseudocode form. Simulation results demonstrate that our proposed EMTRP outperforms the representative protocol CMMBCR in terms of total energy consumption and load balancing. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Empirical evaluation of receiver-based TCP delay control in CDMA2000 networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2007
Oh-keun Kwon
Abstract Wide-area broadband wireless technologies such as CDMA2000 often suffer from variable transfer rate and long latency. In particular, TCP window-based rate control causes excessive buffering at the base station because of the lower transfer rate of the wireless link than that of the wired backhaul link. This performance characteristic of TCP further increases the end-to-end delay, and additional resources are required at the base station. This paper presents a practical mechanism to control the end-to-end TCP delay for CDMA2000 networks (or other similar wireless technologies). The key idea is to reduce and stabilize RTT (round-trip time) by dynamically controlling the TCP advertised window size, based on a runtime measurement of the wireless channel condition at the mobile station. The proposed system has been implemented by modifying the Linux protocol stack. The experiment results, conducted on a commercial CDMA2000 1x network, show that the proposed scheme greatly reduces the TCP delay in non-congested networks, while not sacrificing the TCP throughput in congested networks. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Ka-band link optimization with rate adaptation for Mars and lunar communications

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2007
Jun Sun
Abstract On-going development of Ka-band capability for the Deep Space Networks (DSN) will radically increase the bandwidth available to support advanced mission concepts envisioned for future robotic as well as human exploration of Mars and beyond. While Ka-band links can operate at much higher data rate than X-band, they are much more susceptible to fluctuating weather conditions and manifest a significant trade-off between throughput and availability. If the operating point is fixed, the maximum average throughput for deep space Ka-band link is achieved at about 80% availability, i.e. weather-related outages will occur about 20% of the time. Low availability increases the complexity of space mission operation, while higher availability would require additional link margins that lowers the overall throughput. To improve this fundamental throughput-availability trade-off, data rate adaptation based on real-time observation of the channel condition is necessary. In this paper, we model the Ka-band channel using a Markov process to capture the impact of the temporal correlation in weather conditions. We then develop a rate adaptation algorithm to optimize the data rate based on real time feedback on the measured channel conditions. Our algorithm achieves both higher throughput and link availability as compared to the constant rate scheme presently in use. Copyright © 2007 John Wiley & Sons, Ltd. [source]

The soft-output principle,reminiscences and new developments,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 8 2007
Peter A. Hoeher
A major breakthrough in digital communications was the provisioning of ,soft' outputs at each processing stage, with appropriate capabilities to use this as soft inputs in the next processing stage. This allowed for much more performant receivers especially in difficult mobile radio channel conditions, and set the stage for iterative processing. This article will outline the development of soft output algorithms over the last two decades along with associated state-of-the-art applications and conclude with an outlook towards novel applications of the soft principle. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Broadband wireless access based on VSF-OFCDM and VSCRF-CDMA and its experiments

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2004
Hiroyuki Atarashi
This paper presents broadband packet wireless access schemes based on variable spreading factor (VSF)-orthogonal frequency and code division multiplexing (OFCDM) in the downlink and variable spreading and chip repetition factors (VSCRF)-CDMA in the uplink for the systems beyond IMT-2000. In our design concept for wireless access in both links, radio parameters such as the spreading factor (SF) are optimally controlled so that the system capacity is maximized according to the cell configuration, channel load and radio channel conditions, based on the tradeoff between efficient suppression of other-cell interference and the capacity increase in the target cell by exploiting orthogonality in the time and frequency domains. We demonstrate that the peak throughput of greater than 100,Mbps and 20,Mbps is achieved by the implemented base station and mobile station transceivers using the 100-MHz and 40-MHz bandwidths in the downlink and uplink respectively. Moreover, the simulation results show the possibility of the peak throughput of approximately 1,Gbps for short-range area applications using the 100-MHz bandwidth OFCDM downlink by applying four-branch multiple input multiple output (MIMO) multiplexing with 16,QAM data modulation and punctured turbo coding. Copyright © 2004 AEI [source]

Prioritisation of data partitioned MPEG,4 video over mobile networks,

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2001
Stewart T. Worrall
Despite much research in the field of mobile multimedia, delivery of real,time,interactive video over noisy wireless channels remains a challenging problem. Two of the major issues in providing true end,to,end mobile multimedia capability are interoperability between platforms and networks and the poor performance of video compression algorithms in error,prone environments. This paper presents a method for prioritising data partitioned MPEG,4 video in a way suitable for transmission over a mobile network. The effectiveness of the technique is demonstrated by examining the performance when transmitted using the Real,Time Transport protocol over GPRS (General Packet Radio Service) data channels under varying channel conditions. [source]

Comparison of coded orthogonal frequency division multiplexing and multicarrier code division multiple access systems for power line communications

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2004
P. L. Katsis
Abstract Orthogonal frequency division multiplexing (OFDM) and multicarrier code division multiple access (MC-CDMA) systems are comparatively evaluated for power line communications (PLC) in a frequency-selective fading environment with additive coloured Gaussian noise which is used to model the actual in-home power line channel. OFDM serves as a benchmark in order to measure the performance of various MC-CDMA systems, since multicarrier modulation systems are considered the best candidate for this kind of channel. Both single-user and multi-user cases are taken into account, making use of the appropriate combiner schemes to take full advantage of each case. System efficiency is enhanced by the application of different coding techniques, a fact which shows that powerful coding can make the difference under such a hostile medium. The impact of block interleaving is investigated, while the simulation examines how different modulation schemes fair under the imposed channel conditions as well. The performance of the system is assessed by the commonly used bit error rate vs signal-to-noise ratio diagrams and there is also a comparison regarding throughput efficiency among all the tested systems. As stated in Section 4, a promising PLC application is attained. Copyright © 2004 John Wiley & Sons, Ltd. [source]

A multi-user CDMA receiver utilizing decorrelating detector with additional dummy pilot response

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2003
Mitsuhiro Tomita
Abstract A pilot assisted CDMA system which uses extended spreading sequences with guard sequences under a quasi-synchronous condition is capable of separating the interference components included in the input of a de-correlating receiver by solving a system of linear equations. The performance of such a system, however, depends on the property of the de-correlating matrix consisting of the received pilots, which correspond to the respective user spreading sequences and the multi-path channel conditions. That is, the regularity of the matrix often tends to degrade, and the rank reduces occasionally primarily due to the multi-paths, resulting in solutions that are vulnerable to AWGN. The present paper proposes an effective technique to solve this problem by introducing a virtual user into a group of real users that are to be served. The simulation results indicate a remarkable improvement in the bit-error-rate (BER) performance. In addition, based on the BER performance, the system has a RAKE-like function that has power-sum characteristics. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Adaptive coding and modulation for satellite broadband networks: From theory to practice

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2010
Hermann Bischl
Abstract This paper presents the detailed design and the key system performance results of a comprehensive laboratory demonstrator for a broadband Ka-band multi-beam satellite system exploiting the new DVB-S2 standard with adaptive coding and modulation (ACM). This complete demonstrator allows in-depth verification and optimization of the ACM techniques applied to large satellite broadband networks, as well as complementing and confirming the more theoretical or simulation-based findings published so far. It is demonstrated that few ACM configurations (in terms of modulation and coding) are able to efficiently cope with a typical Ka-band multi-beam satellite system with negligible capacity loss. It is also demonstrated that the exploitation of ACM thresholds with hysteresis represents the most reliable way to adapt the physical layer configuration to the spatial and time variability of the channel conditions while avoiding too many physical layer configuration changes. Simple ACM adaptation techniques, readily implementable over large-scale networks, are shown to perform very well, fulfilling the target packet-error rate requirements even in the presence of deep fading conditions. The impact of carrier phase noise and satellite nonlinearity has also been measured. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A feedback suppression algorithm for reliable satellite multicast based on spatial,temporal prediction of the satellite channel

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2009
Markos P. Anastasopoulos
Abstract The major problem limiting the scalability of large-scale multicast satellite networks is feedback implosion that arises whenever a large number of users simultaneously transmit feedback messages (FBMs) through the network, thus occupying a significant portion of satellite system resources. In satellite networks operating above 10,GHz, attenuation due to rain constitutes the dominant fading mechanism deteriorating the quality of service. In this paper, a novel scheme for providing large-scale reliable multicast services through a star-based geostationary satellite topology is presented incorporating accurate channel modeling of the propagation phenomena. The new protocol is based on the selection of an area representative that provides quick FBMs aiming at suppressing FBMs originating from the rest of the network users. The scheme provides a timely reaction to changes of either the channel conditions or the network topology by properly updating the selection of representatives. Through appropriate simulations, comparisons and examples it is demonstrated that the new approach suppresses FBMs very effectively. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Ka-band link optimization with rate adaptation for Mars and lunar communications

Layered coding for satellite-plus-terrestrial multipath correlated fading channels

INTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 5 2004
A. Levissianos
Abstract This paper introduces two alternative layered-coding (LC) structures suitable for a combination of a geostationary (GEO) satellite and a terrestrial system providing multicasting multimedia services. Both schemes include a RAKE receiver and their performance results are presented under realistic satellite and terrestrial channel conditions. The structures are based on mapping the coded bits either onto 8-PSK symbols or onto QPSK symbols. The LC parameters (such as the interleaver design and the convolutional encoder structures) are analysed and their effect on performance is quantified, especially in cases of highly correlated channels (low vehicular speeds). The various impairments that are associated to the transmission through both terrestrial and satellite correlated fading channels will be taken into account and link level performance results as well as a complexity discussion will be presented. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Evaluating the effects of riparian restoration on a temperate river-system using standardized habitat survey

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2010
E. Clews
Abstract 1.The restoration of degraded riparian zones to improve a range of functions is attracting increasing interest, but there are still questions about (i) how effectively restoration changes riparian or channel conditions; (ii) whether riparian management offsets the effects of wider catchment pressures; and (iii) whether these effects can be detected quantitatively. 2.A catchment-scale experiment was used to assess the effects of riparian restoration on riparian and channel conditions in the Welsh River Wye. In a hierarchically designed survey, variations in river habitat character were assessed among tributaries where riparian zones were recently managed for restoration (n=9 streams), unmanaged controls (n=12), intensively grazed pastures (n=3) and coniferous plantation (n=3). Management between 1997 and 2003, largely involving coppicing, was designed to exclude grazing through fencing in order to enable vegetation development while creating salmonid refuges. River habitat character was assessed using the UK ,River Habitat Survey' (RHS) method, with habitat variation quantified using Principal Components Analysis. 3.Stream habitats varied significantly among treatment categories. Streams draining plantation conifer had ,harder' channel features, while those draining intensively grazed pasture were characterized by finer substrata and more active channels than elsewhere. Riparian management reduced livestock trampling (= poaching) and increased algal cover relative to controls. Coppicing and riparian fencing successfully excluded grazing on banks while increasing in-stream vegetation cover, but did not affect substrata, flow-types and channel features. 4.These data show that RHS can detect habitat variation among streams in contrasting riparian land-use, revealing some apparently significant effects of recent restoration. We advocate longer-term investigations at reach to catchment scales to assess longer-term effects on channel and flow character, and to appraise fully the extent to which local riparian management can offset impairments at a catchment or larger scale, such as altered run-off regimes, sediment delivery and climate change. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Evolution of the reverse link of CDMA-based systems to support high-speed data

BELL LABS TECHNICAL JOURNAL, Issue 3 2002
Nandu Gopalakrishnan
Development of an upcoming release of the CDMA2000* family of standards is expected to focus on enhancing the reverse link (RL) operation to support high-speed packet data applications. The challenge is to design a system that yields substantial throughput gain while causing only minimal perturbations to the existing standard. We are proposing a system that evolves features already present in the CDMA2000 Release B and IS-856 (1xEV-DO) standards and reuses concepts and capabilities that have been introduced for high-speed packet data support on the forward link (FL) in Release C of the CDMA2000 standard. The RL of Release C of the CDMA2000 standard supports a relatively slow scheduled operation of this link using signaling messages. Scheduling with shorter latencies can be achieved by moving this functionality to the physical layer. Concurrently, both the FL and RL channel conditions may be tracked, and users may be scheduled based on this knowledge. To further manage the power and bandwidth cost on the FL, that is, of scheduling users' transmissions on the RL, the mobile station (MS) is permitted to operate in either a scheduled mode or an autonomous mode. A capability is provided for the MS station to switch the mode of operation. Performance impact of, and gain from, some of the system features is characterized through simulation results. © 2003 Lucent Technologies Inc. [source]