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Updated: Oct 16, 2025

Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping
Published on: March 20, 2017
Asymmetric constellation transmission for a coherent free-space optical system with spatial diversity
Abstract:
Spatial diversity is widely recognized as an effective technique for free-space optical (FSO) communication to combat channel fading. Most existing works on spatial diversity in FSO systems focus on intensity modulation and direct detection, while fewer mention coherent optical detection, which excels in optical receiver responsivity. Spatial diversity enables the FSO coherent system to demodulate the signal components of in-phase (I) and quadrature (Q) separately and thus simplify the coherent detector. More importantly, due to the differential channel conditions between I and Q components, we are offered a chance to realize an asymmetric quadrature amplitude modulation (QAM) constellation that can utilize the channel capacity of both I and Q components more sufficiently. Performance results demonstrate that the simplified structure and improved spectrum efficiency can be realized in the asymmetric QAM transmission system with an acceptable bit-error-rate loss.
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