Title: Free Space Optical MIMO System Using an Optical Pre-Amplifier.
Abstract: Multiple transmitter and receivers can be used to combat link outage due to the atmosphere turbulence and scattering in an urban 'last-mile' free space optical communi- cation system. We investigate the use of an optical preamplifier in the resulting multiple-input-multiple-output (MIMO) system for atmospheric line-of-sight optical communication, with signal repetition across the laser array. The optically preamplified system has better performance than previous MIMO system relying on electronic amplification. Our focus is on determining symbol error probability for uncoded transmission. I. INTRODUCTION Free space optics (FSO) has been proposed as a communi- cations medium for urban high speed 'last-mile' connections. The advantages of FSO include ease in implementation, un- licensed spectrum, and very broad bandwidths. One of the primary impairments to FSO systems is clear-air scintillation, caused by atmospheric turbulence. Several multiple-input- multiple-output (MIMO) techniques have been proposed to combat the fading due to scintillation (1), (2), (3), (4), (5). In these systems multiple lasers and photodetectors comprise the MIMO system. These techniques rely on electronic ampli- fication, used after either a PIN photodetector or an avalanche photodiode (APD). In this paper we propose the use of an optical amplifier placed before photodetection. An optical amplifier can be used by focussing the received signal onto a fiber, which then guides it through the fiber amplifier. This approach promises better performance than the usual electronic amplification because the received signal can be made much stronger than the thermal noise floor that usually limits performance. Optically amplified systems are more difficult to analyze due to the presence of signal dependent noise. The interesting aspect of studying optically amplified faded signals is that this signal dependence then translates into a fading-dependent noise. The paper begins with a system description given in Sec- tion II. The maximum likelihood (ML) detection rule and an equal gain combining (EGC) rule are given in Section III. Section IV summarizes results on system performance based on both analysis and simulation. Conclusions are then drawn in Section V.
Publication Year: 2006
Publication Date: 2006-01-01
Language: en
Type: article
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Cited By Count: 11
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