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Start Over Author "Uysal, Murat" Journal ieee transactions on communications
20 results on '"Uysal, Murat"'

6. An efficient implementation of a maximum-likelihood detector for space-time block coded systems

Author

Uysal, Murat and Georghiades, Costas N.

Subjects
Communications technology, Telecommunication -- Research
Abstract

We investigate maximum-likelihood (ML) sequence estimation for space-time block coded systems without assuming channel knowledge. The quadratic form of the ML receiver in this case does not readily lend itself to efficient implementation. However, under quasi-static channel conditions, the likelihood function reduces to a simple form similar to the classical correlation receiver in matrix notation. It also allows the development of a recursive expression that can be easily implemented by a Viterbi-type algorithm with a reasonable complexity. Although the receiver is suboptimum for the nonstatic case, its performance is close to the optimum for a range of signal-to-noise ratios. Index Terms--Fading channels, maximum-likelihood (ML) sequence estimation, space-time block coding (STBC).

Published
2003

19. Performance Analysis of Parallel Relaying in Free-Space Optical Systems

Author

Murat Uysal, Sahar Molla Aghajanzadeh, Özyeğin University, and Uysal, Murat

Subjects
Computer science, ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS, Data_CODINGANDINFORMATIONTHEORY, Diversity gain, Multiplexing, Coding gain, law.invention, Relay, law, Diversity-multiplexing tradeoff, Computer Science::Networking and Internet Architecture, Electronic engineering, Fading, Parallel relaying, Electrical and Electronic Engineering, Free-space optical communications, Computer Science::Information Theory, Communication channel, Diversity scheme
Abstract

Due to copyright restrictions, the access to the full text of this article is only available via subscription. In this paper, we investigate the information theoretic performance of parallel relaying in free-space optical (FSO) communications over Gamma-Gamma fading channels. We consider an intensity modulation/direct-detection (IM/DD) FSO system with a single relay and a line-of-sight link between the source and the destination. Considering both amplify-and-forward and decode-and-forward relaying, we develop performance characterizations of each relaying mode in terms of outage probability, diversity gain, coding gain, and diversity-multiplexing tradeoff (DMT). Our results demonstrate that parallel relaying improves the performance of FSO systems by bringing diversity advantages. In addition, both relaying modes achieve the same DMT and diversity gain while their coding gains can be different depending on underlying channels' characteristics. Qatar Foundation

Published
2015

20. Multi-Hop Coherent Free-Space Optical Communications over Atmospheric Turbulence Channels

Author

Sahar Molla Aghajanzadeh, Murat Uysal, Özyeğin University, and Uysal, Murat

Subjects
Computer science, ComputerSystemsOrganization_COMPUTER-COMMUNICATIONNETWORKS, Optical communication, Free-space optical systems, 020206 networking & telecommunications, Data_CODINGANDINFORMATIONTHEORY, 02 engineering and technology, Finite-SNR diversity-multiplexing tradeoff, Multiplexing, law.invention, Multi-hop transmission, 020210 optoelectronics & photonics, Relay, law, Diversity gain, Computer Science::Networking and Internet Architecture, 0202 electrical engineering, electronic engineering, information engineering, Electronic engineering, Atmospheric turbulence-induced fading, Fading, Heterodyne detection, Electrical and Electronic Engineering, Computer Science::Information Theory, Communication channel
Abstract

Due to copyright restrictions, the access to the full text of this article is only available via subscription. In this paper, we investigate multi-hop relaying as an efficient fading mitigation tool for coherent free-space optical (FSO) systems over atmospheric turbulence channels. We consider an FSO relaying system with decode-and-forward relay nodes and multiple heterodyne receivers with modal compensation. Based on a recently introduced statistical characterization for the combined effects of log-normal turbulence fading and modal compensation, we derive the outage probability and quantify the potential performance improvements through the derivation of diversity multiplexing tradeoff (DMT) and diversity gain. Our outage analysis yields impressive power savings for multi-hop relaying even with a single-relay. In addition, the DMT analysis in practical signal-to-noise ratio (SNR) ranges demonstrates that multi-hop transmission scheme improves finite-SNR diversity gain throughout the range of the multiplexing gain. European Commission

Published
2011

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