![]() ![]() ![]() The result is a single numerical metric that quantifies how close a transmitter's signal waveform is to the ideal, based on its BER performance with a perfect software-defined matched-filter receiver demodulator. There are two basic parts to this approach: (1) use of a coherent optical receiver to perform frequency down-conversion of a transmitter's optical signal waveform to the electrical domain, preserving both optical field amplitude and phase information, and (2): software-based analysis of the digitized electrical waveform. ![]() This paper describes a new rigorous and computationally based method that isolates which portion of the penalty can be assessed against the transmitter. It is desirable, but usually difficult, to determine the division of this penalty between the transmitter and receiver. A total system penalty is typically assessed in terms of how far the end-to-end bit-error rate (BER) is from these limits. Experimental results demonstrate lossless coherent combining of four lasercom signals, at power levels below 0.1 photons/bit/aperture.ĭigital coherent receiver based transmitter penalty characterization.įor optical communications links where receivers are signal-power-starved, such as through free-space, it is important to design transmitters and receivers that can operate as close as practically possible to theoretical limits. The digitized signals are then combined in a digital signal processing chain. This is accomplished via coherent detection behind each aperture followed by digitization. In contrast, we present a ground terminal receiver architecture in which many small less-expensive apertures are efficiently combined to create a large effective aperture while maintaining excellent receiver sensitivity. One way of reducing the required power-aperture product on a space platform is to implement effective, but costly, single-aperture ground terminals with large collection areas. Space-to-ground optical communication systems can benefit from reducing the size, weight, and power profiles of space terminals. Geisler, David J Yarnall, Timothy M Stevens, Mark L Schieler, Curt M Robinson, Bryan S Hamilton, Scott A ![]() Multi-aperture digital coherent combining for free-space optical communication receivers. We found in our analysis that, instead of field conjugation arrays, digital equalization of time-delay multi-aperture receivers is a simpler and more versatile approach to accomplish reduction of atmospheric fading. Here, we show that multiple apertures, coupled with optical delay lines, combine retarded versions of a signal at a single coherent receiver, which uses digital equalization to obtain diversity gain against atmospheric fading. However, this motivates the use of complex receivers as optical signals collected by different apertures need to be adaptively processed, co-phased, and scaled before they are combined. Digital equalization of time-delay array receivers on coherent laser communications.įield conjugation arrays use adaptive combining techniques on multi-aperture receivers to improve the performance of coherent laser communication links by mitigating the consequences of atmospheric turbulence on the down-converted coherent power. ![]()
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