Browsing by Author "Karagiannidis, G. K."

Now showing 1 - 4 of 4

Metadata only
Generalized maximum-likelihood sequence detection for photon-counting free space optical systems
(IEEE, 2010-12) Chatzidiamantis, N. D.; Karagiannidis, G. K.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
We investigate detection methods for on-off keying (OOK) photon-counting Free Space Optical (FSO) systems in the presence of turbulence-induced fading, assuming no channel state information at the receiver. To recover the performance loss which is associated with symbol-by-symbol detection in such a scenario, we consider sequence detection techniques, exploiting the temporal correlation of the FSO channel. Due to its high complexity in the calculation of its metric, optimal maximum likelihood sequence detection (MLSD) is infeasible for most practical purposes. Hence, we propose a suboptimal low-complexity detection rule, which is based on the generalized maximum-likelihood sequence estimation. The proposed scheme allows the detection of sequence lengths that are prohibitive for conventional MLSD, without using any kind of channel knowledge. Monte Carlo simulation results show its performance to be very close to the optimum for large sequence lengths and various fading models.
Metadata only
Iterative near maximum-likelihood sequence detection for MIMO optical wireless systems
(IEEE, 2010-04) Chatzidiamantis, N. D.; Uysal, Murat; Tsiftsis, T. A.; Karagiannidis, G. K.; Electrical & Electronics Engineering; UYSAL, Murat
A major performance-limiting factor in terrestrial optical wireless (OW) systems is turbulence-induced fading. Exploiting the additional degrees of freedom in the spatial dimension, multiple laser transmitters combined with multiple receive apertures provide an effective solution for fading mitigation. Although multiple-input multiple-output (MIMO) OWsystems have been extensively studied in recent years, most of these works are mainly limited to symbol-by-symbol decoding. MLSD exploits the temporal correlation of turbulence-induced fading and promises further performance gains. In this paper, we investigate MLSD for intensity-modulation/direct-detection MIMO OW systems over log-normal atmospheric turbulence channels. Even with a low-order modulation scheme such as OOK, which is typically used inOWsystems, the complexity ofMLSD might be prohibitive. We therefore present an iterative sequence detector based on the expectation–maximization (EM) algorithm. The complexity of the proposed algorithm is considerably less than a direct evaluation of the log-likelihood function, and it is independent of the channel’s fading statistics. The Monte Carlo simulation results demonstrate that the EM-based algorithm outperforms the symbol-by-symbol decoder and achieves a performance, which lies within 0.3 dB of that of the optimal MLSD.
Metadata only
Simultaneous lightwave information and power transfer in underwater visible light communications
(IEEE, 2019) Ghasvarianjahromi, Sara; Karbalayghareh, Mehdi; Diamantoulakis, P. D.; Karagiannidis, G. K.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat; Ghasvarianjahromi, Sara; Karbalayghareh, Mehdi
Visible light communication (VLC) has emerged as a high-capacity connectivity solution for underwater sensor networks. Since water is relatively transparent to blue or green light, visible light lasers or LEDs can be used as transmitters for underwater wireless connectivity with data rates up to hundreds of Mbps. In underwater networks, a critical system design issue is the network lifetime which highly depends on the battery capacity. Since recharging in underwater scenarios is typically very costly and impractical, energy harvesting can be considered as a promising alternative. In this paper, we explore simultaneous lightwave information and power transfer (SLIPT) for VLC-based USNs. We adopt time splitting method where the receiver switches in time between the modes of energy harvesting (EH) and information decoding (ID). We derive a closed-form expression for the average harvested energy over log-normal model underwater turbulence channel. Using this expression, we determine the splitting factor between EH and ID operation modes to maximize the harvested energy while satisfying a given bit error rate value.
Metadata only
SLIPT for underwater visible light communications: Performance analysis and optimization
(IEEE, 2021-10) Uysal, Murat; Ghasvarianjahromi, Sara; Karbalayghareh, M.; Diamantoulakis, P. D.; Karagiannidis, G. K.; Sait, S. M.; Electrical & Electronics Engineering; UYSAL, Murat; Ghasvarianjahromi, Sara
In this paper, we investigate simultaneous lightwave information and power transfer (SLIPT) for underwater visible light communication systems. We consider three SLIPT methods namely time switching (TS), power splitting (PS) and time switching-power splitting (TS-PS) where the splitting/switching factors are defined as optimization parameters. For each of these methods, we derive closed-form expressions for the average harvested energy, bit error rate and spectral efficiency in the presence of underwater turbulence modeled by lognormal statistics. Using these expressions, we determine the optimal splitting factors to maximize the harvested energy while satisfying a given bit error rate value and a given threshold spectral efficiency value. Our results reveal that, if not optimized, SLIPT methods under consideration are outperformed by the simple AC-DC separation (ADS) method which provides the largest harvested energy versus spectral efficiency (HE-SE) region. Optimization of splitting/switching factors extends the HE-SE regions; hence, optimized versions of TS, PS and TS-PS methods are able to significantly outperform ADS for most cases. We further investigate the effect of various channel and system parameters such as water type, turbulence level, beam divergence, receiver aperture size on the harvested energy and quantify the improvements in battery lifetime through the use of SLIPT methods.