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Articles 7321 - 7350 of 7445

Full-Text Articles in Physical Sciences and Mathematics

Measurement Of Hadron And Lepton-Pair Production From E+E- Annihilation At Centre-Of-Mass Energies Of 130 And 136 Gev, Buskulic, D.; Et Al., M. Thulasidas Jun 1996

Measurement Of Hadron And Lepton-Pair Production From E+E- Annihilation At Centre-Of-Mass Energies Of 130 And 136 Gev, Buskulic, D.; Et Al., M. Thulasidas

Research Collection School Of Computing and Information Systems

No abstract provided.

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Supporting Search For Reusable Software Objects, T. Isakowitz, Robert J. Kauffman Jun 1996

Supporting Search For Reusable Software Objects, T. Isakowitz, Robert J. Kauffman

Research Collection School Of Computing and Information Systems

Prior research has shown that achieving high levels of software reuse in the presence of repository and object-based computer-aided software engineering (CASE) development methods presents interesting human, managerial and technical challenges. This article presents research that seeks to enhanced software development performance through reuse. We propose automated support for developers who search large repositories for the appropriate reusable software objects. We characterize search for repository objects in terms of a multistage model involving screening, identification, and the subsequent choice between new object construction or reusable object implementation. We propose automated support tools, including ORCA, a software Object Reuse Classification Analyzer, …

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Specifying Object-Oriented Federated Database From Existing Databases, Ee Peng Lim, M. L. Lim, J. Srivastava Jun 1996

Specifying Object-Oriented Federated Database From Existing Databases, Ee Peng Lim, M. L. Lim, J. Srivastava

Research Collection School Of Computing and Information Systems

In this paper, we present a mapping strategy that is based on a proposed set of DB integration operations. We first define an OO federated DB as a virtual view on multiple OO export DBs. Our DB mapping strategy systematically derives each of the class extents, deep class extents and relationships of the federated DB using an operator tree consisting of the integration operations. This mapping approach differs from the other existing approaches in that it is algebraic based, and is therefore very suitable for implementing federated query processing.

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A Precise Measurement Of The Average B Hadron Lifetime, D. Buskulic, M. Thulasidas Feb 1996

A Precise Measurement Of The Average B Hadron Lifetime, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

An improved measurement of the average b hadron lifetime is performed using a sample of 1.5 million hadronic Z decays, collected during the 1991–1993 runs of ALEPH, with the silicon vertex detector fully operational. This uses the three-dimensional impact parameter distribution of lepton tracks coming from semileptonic b decays and yields an average b hadron lifetime of 1.533 ± 0.013 ± 0.022 ps.

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Entity Identification In Database Integration, Ee Peng Lim, Jaideep Srivastava, Satya Prabhakar, James Richardson Feb 1996

Entity Identification In Database Integration, Ee Peng Lim, Jaideep Srivastava, Satya Prabhakar, James Richardson

Research Collection School Of Computing and Information Systems

The objective of entity identification is to determine the correspondence between objective instances from more than one database. This paper examines the problem at the instance level assuming that schema level heterogeneity has been resolved a priori. Soundness and completeness are defined as the desired properties of any entity-identification technique. To achieve soundness, a set of identity and distinctness rules have to be established for the entities in the integrated world. We then propose the use of extended key, which is the union of keys (and possibly other attributes) from the relations to be matched, and its corresponding identity rule …

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Measurement Of The Λb Polarization In Z Decays, Buskulic, D.; Et Al., M. Thulasidas Jan 1996

Measurement Of The Λb Polarization In Z Decays, Buskulic, D.; Et Al., M. Thulasidas

Research Collection School Of Computing and Information Systems

The Λb polarization in hadronic Z decays is measured in semileptonic decays from the average energies of the charged lepton and the neutrino. In a data sample of approximately 3 million hadronic Z decays collected by the ALEPH detector at LEP between 1991 and 1994, 462 ± 31 Λb candidates are selected using (Λπ+)-lepton correlations. From this event sample, the Λb polarization is measured to be PΛb = −0.23−0.20+0.24(stat.)−0.07+0.08(syst.).

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Improved Measurement Of The B0 And B+ Meson Lifetimes, D. Buskulic, M. Thulasidas Jan 1996

Improved Measurement Of The B0 And B+ Meson Lifetimes, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

Updated measurements of the B0 and B+ meson lifetimes are presented. From a data sample of 1.72 million hadronic Z0 decays recorded during the period 1991 to 1993, a sample of approximately 1000 semileptonic B meson decays containing a D0, D+ or D*+ has been isolated. From the distribution of decay times in the different samples the lifetimes of the B0 and B+ mesons are determined to be 1.53±0.12±0.08 ps and 1.52±0.14±0.09 ps, respectively, where the first error is statistical and the second systematic. The ratio of the B+ to B0 lifetimes is measured to be 0.99±0.14+0.05−0.04, confirming expectations that …

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Determination Of Sin2Θw Eff Using Jet Charge Measurements In Hadronic Z Decays, D. Buskulic, M. Thulasidas Jan 1996

Determination Of Sin2Θw Eff Using Jet Charge Measurements In Hadronic Z Decays, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured forbb¯bb¯ andcc¯cc¯ events in subsamples selected by their long lifetimes or using fastD*’s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite …

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Randomized Approximation Of The Constraint Satisfaction Problem, Hoong Chuin Lau, Osamu Watanabe Jan 1996

Randomized Approximation Of The Constraint Satisfaction Problem, Hoong Chuin Lau, Osamu Watanabe

Research Collection School Of Computing and Information Systems

We consider the Weighted Constraint Satisfaction Problem (W-CSP) which is a fundamental problem in Artificial Intelligence and a generalization of important combinatorial problems such as MAX CUT and MAX SAT. In this paper, we prove non-approximability properties of W-CSP and give improved approximations of W-CSP via randomized rounding of linear programming and semidefinite programming relaxations. Our algorithms are simple to implement and experiments show that they are run-time efficient.

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Tau Hadronic Branching Ratios, D. Buskulic, M. Thulasidas Jan 1996

Tau Hadronic Branching Ratios, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

From 64492 selected τ-pair events, produced at the Z0 resonance, the measurement of the tau decays into hadrons from a global analysis using 1991, 1992 and 1993 ALEPH data is presented. Special emphasis is given to the reconstruction of photons and π0s, and the removal of fake photons. A detailed study of the systematics entering the π0 reconstruction is also given. A complete and consistent set of tau hadronic branching ratios is presented for 18 exclusive modes. Most measurements are more precise than the present world average. The new level of precision reached allows a stringent test τ-μ, universality in …

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On The Complexity Of Manpower Shift Scheduling, Hoong Chuin Lau Jan 1996

On The Complexity Of Manpower Shift Scheduling, Hoong Chuin Lau

Research Collection School Of Computing and Information Systems

We consider the shift assignment problem in manpower scheduling, and show that a restricted version of it is NP-hard by a reduction from 3SAT. We then present polynomial algorithms to solve special cases of the problem and show how they can be deployed to solve more complex versions of the shift assignment problem. Our work formally defines the computational intractibility of manpower shift scheduling and thus justifies existing works in developing manpower scheduling systems using combinatorial and heuristic techniques.

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Combinatorial Approaches For Hard Problems In Manpower Scheduling, Hoong Chuin Lau Jan 1996

Combinatorial Approaches For Hard Problems In Manpower Scheduling, Hoong Chuin Lau

Research Collection School Of Computing and Information Systems

Manpower scheduling is concerned with the construction of a workers' schedule which meets demands while satisfying given constraints. We consider a manpower scheduling Problem, called the Change Shift Assignment Problem(CSAP). In previous work, we proved that CSAP is NP-hard and presented greedy methods to solve some restricted versions. In this paper, we present combinatorial algorithms to solve more general and realistic versions of CSAP which are unlikely solvable by greedy methods. First, we model CSAP as a fixed-charge network and show that a feasible schedule can be obtained by finding disjoint paths in the network, which can be derived from …

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Tau Leptonic Branching Ratios, D. Buskulic, M. Thulasidas Jan 1996

Tau Leptonic Branching Ratios, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

A sample of 62249 τ-pair events is selected from data taken with the ALEPH detector in 1991, 1992 and 1993. The measurement of the branching fractions for τ decays into electrons and muons is presented with emphasis on the study of systematic effects from selection, particle identification and decay classification. The results obtained are: B e = 17.79±0.12(stat)±0.06(syst)(%) and Bμ = 17.31±0.11(stat)±0.05(syst)(%). Combined with the most recent ALEPH determination of the τ lifetime, these results provide a relative measurement of the leptonic couplings in the weak charged current for transverse W bosons: ${cal G}_{ώ}/{cal G}_{e}=1.0002pm 0.0051$ and ${cal G}_{∢u}/{cal G}_{u}=0.9943pm …

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Measurement Of The Bs0 Lifetime And Production Rate With Ds- ℓ+ Combinations In Z Decays, D. Buskulic, M. Thulasidas Nov 1995

Measurement Of The Bs0 Lifetime And Production Rate With Ds- ℓ+ Combinations In Z Decays, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

A precise determination of the effective Bs0→K+K− lifetime can be used to constrain contributions from physics beyond the Standard Model in the Bs0 meson system. Conventional approaches select B meson decay products that are significantly displaced from the B meson production vertex. As a consequence, B mesons with low decay times are suppressed, introducing a bias to the decay time spectrum which must be corrected. This analysis uses a technique that explicitly avoids a lifetime bias by using a neural network based trigger and event selection. Using 1.0fb−1 of data recorded by the LHCb experiment, the effective Bs0→K+K− lifetime is …

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Measurement Of Αs From Scaling Violations In Fragmentation Functions In E+E- Annihilation, D. Buskulic, Manoj Thulasidas Sep 1995

Measurement Of Αs From Scaling Violations In Fragmentation Functions In E+E- Annihilation, D. Buskulic, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

A study of scaling violations in fragmentation functions performed by the ALEPH collaboration at LEP is presented.

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Measurements Of The B Baryon Lifetime, D. Buskulic, Manoj Thulasidas Sep 1995

Measurements Of The B Baryon Lifetime, D. Buskulic, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

The average lifetime of b-flavoured baryons measured with the OPAL detector is updated to include data collected between 1990 and 1994 at LEP. Bottom-flavoured baryons that decay semileptonically and produce aΛ baryon are identified through the correlation of the baryon number of theΛ and the electric charge of the lepton. To measure the lifetime, the decay point of the b baryon is estimated by theΛ-lepton vertex, and the observed distribution of decay lengths is fitted simultaneously in 874 right-sign and 384 wrong-sign combinations. In a separate method, the impact parameter distribution of the leptons is fitted in a subset of …

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Measurement Of The Effective B Quark Fragmentation Function At The Z Resonance, Buskulic, D.; Et Al., M. Thulasidas Sep 1995

Measurement Of The Effective B Quark Fragmentation Function At The Z Resonance, Buskulic, D.; Et Al., M. Thulasidas

Research Collection School Of Computing and Information Systems

Using a sample of about 1.46 million hadronic Z decays collected between 1991 and 1993 with the ALEPH detector at LEP, the energy distribution of the B0 and B± mesons produced at the Z resonance is measured by reconstructing semileptonic decays B → ℓνℓD(X) or B→ ℓνℓD∗+(X). The charmed mesons are reconstructed through the decay modes D0 → K−π+, D0 → K−π+π−π+, D+ → K−π+π+ and D∗+→ D0π+. The neutrino energy is estimated from the missing energy in the lepton hemisphere. Accounting for B∗ and B∗∗ production, the shape of the scaled energy distribution xE(b) for mesons containing a b …

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Measurement Of The D*± Cross Section In Two Photon Collisions At Lep, D. Buskulic, M. Thulasidas Aug 1995

Measurement Of The D*± Cross Section In Two Photon Collisions At Lep, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

The inclusive production of D∗± mesons in photon-photon collisions has been measured by the Aleph experiment at LEP with a beam energy of 45 GeV. The D∗+ are detected in their decay to D0π+ with the D0 observed in three separate decay modes: (1) K−π+, (2) K−π+π0 and (3) K−π+π−π+, and analagously for the D∗− modes. A total of 33 events was observed from an integrated luminosity of 73 pb−1 which corresponds to a cross section for Σ(e+e−→ e+e−D∗±X) of 155 ± 33 ± 21 pb. This result is compatible with both the direct production γγ → cc in the …

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Limit On B0s Oscillation Using A Jet Charge Method, D. Buskulic, M. Thulasidas Aug 1995

Limit On B0s Oscillation Using A Jet Charge Method, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

A lower limit is set on the Bs0 meson oscillation parameter Δms using data collected from 1991 to 1994 by the ALEPH detector. Events with a high transverse momentum lepton and a reconstructed secondary vertex are used. The high transverse momentum leptons are produced mainly by b hadron decays, and the sign of the lepton indicates the particle/antiparticle final state in decays of neutral B mesons. The initial state is determined by a jet charge technique using both sides of the event. A maximum likelihood method is used to set a lower limit of Δms. The 95% confidence level lower …

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Multiclass Query Scheduling In Real-Time Database Systems, Hwee Hwa Pang, Michael J. Carey, Miron Livny Aug 1995

Multiclass Query Scheduling In Real-Time Database Systems, Hwee Hwa Pang, Michael J. Carey, Miron Livny

Research Collection School Of Computing and Information Systems

In recent years, a demand for real-time systems that can manipulate large amounts of shared data has led to the emergence of real-time database systems (RTDBS) as a research area. This paper focuses on the problem of scheduling queries in RTDBSs. We introduce and evaluate a new algorithm called Priority Adaptation Query Resource Scheduling (PAQRS) for handling both single class and multiclass query workloads. The performance objective of the algorithm is to minimize the number of missed deadlines, while at the same time ensuring that any deadline misses are scattered across the different classes according to an administratively-defined miss distribution. …

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Test Of The Flavour Independence Of Αs, D. Buskulic, Manoj Thulasidas Jul 1995

Test Of The Flavour Independence Of Αs, D. Buskulic, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

Using about 950 000 hadronic events collected during 1991 and 1992 with the ALEPH detector, the ratios r b = bs=udsc s and r uds = uds s =cbs have been measured in order to test the avour independence of the strong coupling constant s . The analysis is based on event{shape variables using the full hadronic sample, two b-quark samples enriched by lepton tagging and lifetime tagging, and a light-quark sample enriched by lifetime antitagging. The combined results are r b = 1:002 0:023 and r uds = 0:971 0:023.

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The Forward-Backward Asymmetry For Charm Quarks At The Z Pole, D. Buskulic, Manoj Thulasidas Jun 1995

The Forward-Backward Asymmetry For Charm Quarks At The Z Pole, D. Buskulic, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

From 1.4 million hadronic Z decays collected by the ALEPH detector at LEP, an enriched sample of Z → cc̄ events is extracted by requiring the presence of a high momentum D∗±. The charm quark forward-backward charge asymmetry at the Z pole is measured to be AFB0.c = (8.0 ± 2.4) % corresponding to an effective electroweak mixing angle of sin2θWeff = 0.2302 ± 0.0054.

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Myriad: Design And Implementation Of A Federated Database Prototype, Ee Peng Lim, San-Yih Hwang, Jaideep Srivastava, Dave Clements, M. Ganesh May 1995

Myriad: Design And Implementation Of A Federated Database Prototype, Ee Peng Lim, San-Yih Hwang, Jaideep Srivastava, Dave Clements, M. Ganesh

Research Collection School Of Computing and Information Systems

A key problem in providing enterprise-wide information is the integration of databases that have been independently developed. An important requirement is to accommodate heterogeneity and maintain the autonomy of component databases. Myriad is a federated database prototype developed at the University of Minnesota, to provide a testbed for investigating alternatives in architecture and algorithms for database integration, query processing and optimization, and concurrency control and recovery. The system incorporates our group's research results in these areas. This paper describes our experiences in the design and implementation of Myriad, and in the project management. Special emphasis is given to discussing design …

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Search For Supersymmetric Particles With R-Parity Violation In Z Decays, D. Buskulic, Manoj Thulasidas Apr 1995

Search For Supersymmetric Particles With R-Parity Violation In Z Decays, D. Buskulic, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

Searches for supersymmetric particles produced in e+e− interactions at the Z peak have been performed under the assumptions that R-parity is not conserved, that the dominant R-parity violating coupling involves only leptonic fields, and that the lifetime of the lightest supersymmetric particle can be neglected. In a data sample collected by the ALEPH detector at LEP up to 1993, and corresponding to almost two million hadronic Z decays, no signal was observed. As a result, supersymmetric particle masses and couplings are at least as well constrained as under the usual assumption of R-parity conservation.

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An Upper Limit For The Τ Neutrino Mass From Τ → 5Π(Π0)Ντ Decays, D. Buskulic, M. Thulasidas Apr 1995

An Upper Limit For The Τ Neutrino Mass From Τ → 5Π(Π0)Ντ Decays, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

From a sample of 152,000 τ decays collected by the ALEPH detector at LEP an upper limit of 24 MeV at 95% CL on the τ neutrino mass has been determined. The limit is obtained using a two dimensional likelihood fit of the visible energy and the invariant mass distribution of 25 τ → 5π(π0)ντ events.

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Exceptions And Exception Handling In Computerized Information Processes, Diane M. Strong, Steven M. Miller Apr 1995

Exceptions And Exception Handling In Computerized Information Processes, Diane M. Strong, Steven M. Miller

Research Collection School Of Computing and Information Systems

Exceptions, situations that cannot be correctly processed by computer systems, occur frequently in computer-based information processes. Five perspectives on exceptions provide insights into why exceptions occur and how they might be eliminated or more efficiently handled. We investigate these perspectives using an in-depth study of an operating information process that has frequent exceptions. Our results support the use of a total quality management (TQM) approach of eliminating exceptions for some exceptions, in particular, those caused by computer systems that are poor matches to organizational processes. However, some exceptions are explained better by a political system perspective of conflicting goals between …

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Study Of The Subjet Structure Of Quark And Gluon Jets, D. Buskulic, D., M. Thulasidas Mar 1995

Study Of The Subjet Structure Of Quark And Gluon Jets, D. Buskulic, D., M. Thulasidas

Research Collection School Of Computing and Information Systems

Measurements of the subjet structure of quark and gluon jets in hadronic Z decays are presented. The analysis is based on one million hadronic events recorded by the Aleph detector. Roughly symmetric three-jet events are selected with a coarse jet-resolution cut-off, y1. Gluon jets are identified with a purity of 94.6% in those events where evidence of long-lived heavy-flavour hadrons in the other two jets is found. The jets are then analyzed using a smaller cut-off y0 (< y1) so that subjets are resolved. The properties of the jets (subjet multiplicities (Nq), (Ng) and rates Rng(q) for n = 1, 2, 3, 4) are determined and are found to be in good agreement with the expectations of perturbative QCD as long as the subjet resolution parameter y0 is sufficiently large to keep non-perturbative effects small. In particular, the ratio , which to leading order in QCD is given by the ratio of colour factors , is measured to be 1.96 ± 0.15 for y0 = 2 · 10−3, but falls to 1.29 ± 0.03 for y0 = 1.6 · 10−5.

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Michel Parameters And Τ Neutrino Helicity From Decay Correlations In Z → Τ+Τ-, D. Buskulic, Manoj Thulasidas Mar 1995

Michel Parameters And Τ Neutrino Helicity From Decay Correlations In Z → Τ+Τ-, D. Buskulic, Manoj Thulasidas

Research Collection School Of Computing and Information Systems

No abstract provided.

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A Study Of D*+ Π- Production In Semileptonic B Decay, D. Buskulic, M. Thulasidas Feb 1995

A Study Of D*+ Π- Production In Semileptonic B Decay, D. Buskulic, M. Thulasidas

Research Collection School Of Computing and Information Systems

In a sample of 1.5 million hadronic decays of the Z collected by the ALEPH detector, a search is carried out for the decays B→ D10(2420)l−νX and B→ D2∗0(2460)l−νX. The product branching ratio for D10 production is measured to be Br(b →B) × Br(B→ D10l−νX) × Br(D10→ D∗+π−) = (2.04 ± 0.58stat± 0.34syst) × 10−3, and a 95% confidence level limit of Br(b →B) × Br(B→ D2∗0l−νX) × Br(D2∗0→ D∗+π−) ≤ 0.81 × 10−3 is obtained for D2∗0 production.A topological search sensitive to the processes above, but also to wide resonances that decay to D∗+π− and to non-resonant D∗+π− production …

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A Type I Hybrid Arq System With Adaptive Code Rates, Robert H. Deng, Michael L. Lin Feb 1995

A Type I Hybrid Arq System With Adaptive Code Rates, Robert H. Deng, Michael L. Lin

Research Collection School Of Computing and Information Systems

Type I hybrid ARQ systems use an error-control code of fixed rate for error-correction in each transmitted packet. In such systems, the code rate must be carefully chosen to match the channel bit error rate (BER) in order to maximize system throughput. Whenever there is a mismatch between code rate and channel BER, the throughput suffers. In this paper, we proposed a type I hybrid ARQ system which automatically adjusts its code rates to match channel BERs. The proposed system is very simple to implement and yet performs significantly better than type I hybrid ARQ systems of fixed code rate

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