On the communication over strong atmospheric turbulence channels by adaptive modulation and coding

Department of Electrical and Computer Engineering, University of Arizona, Tucson, AZ 85721, USA.
Optics Express (Impact Factor: 3.53). 09/2009; 17(20):18250-62. DOI: 10.1364/OE.17.018250
Source: PubMed

ABSTRACT The free-space optical (FSO) communications can provide any connectivity need at high-speed. However, an optical wave propagating through the atmosphere experiences the variation in amplitude and phase due to scintillation. To enable high-speed communication over strong atmospheric turbulence channels, we propose to transmit the encoded sequence over both FSO and wireless channels, feedback channel state information of both channels by RF-feedback, and adapt powers and rates so that total channel capacity is maximized. The optimum power adaptation policy maximizing total channel capacity is derived. We show significant spectral efficiency performance improvement by employing this approach. We further show that deep fades in the order 35 dB and above can be tolerated by proposed hybrid communication scheme.


Available from: Goran Djordjevic, May 30, 2015
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    ABSTRACT: The impact of relay placement on diversity order in adaptive selective decode-and-forward (DF) cooperative strategies is here investigated in the context of free-space optical (FSO) communications over atmospheric turbulence channels with pointing errors when line of sight is available. The irradiance of the transmitted optical beam here considered is susceptible to moderate-to-strong turbulence conditions, following a gamma-gamma (GG) distribution together with a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Novel closed-form approximate bit error-rate (BER) expressions are obtained for a cooperative FSO communication setup with N relays, assuming that these relays are located in an area similar to an annulus around source or destination node. An analytical expression is here found that determines the best selection criterion based on the knowledge of the channel state information (CSI) of source-relay or relay-destination links in order to significantly increase the diversity order corresponding to the cooperative strategy under study. It is concluded that the highest diversity order is achieved when the relation βSRmin > βSD + βRminD is satisfied, wherein βSRmin, βRminD and βSD are parameters corresponding to the atmospheric turbulence conditions of source-relay and relay-destination link with the greatest scintillation index, and source-destination link, respectively.
    Optics Express 02/2015; 23:2600-2617. DOI:10.1364/OE.23.002600 · 3.53 Impact Factor
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    Optical Communication, Edited by Dr. Narottam Das, 01/2012: chapter Rate-Adaptive Free-Space Optical Links Over Atmospheric Turbulence and Misalignment Fading Channels: pages 321-340; InTech., ISBN: 978-953-51-0784-2
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    IEEE Communications Surveys &amp Tutorials 11/2014; 16(8):2231-2258. DOI:10.1109/COMST.2014.2329501 · 6.49 Impact Factor