We examine the limits of receiver sensitivity at capacity for modulation formats compatible with direct detection receivers, using parameters representative of commercial Avalanche Photodiodes (APDs). Considering sources of noise to be shot noise of the signal and dark current, and thermal noise of post-detection electronics (transimpedance amplifier, or TIA), we determine Shannon capacities for On-Off Keying and M-ary Pulse Position Modulation, assuming silicon APDs for 850 nm and InGaAs APDs for 1550 nm. We also explore the Sb-based APDs presently being investigated in many laboratories. While the low k-factor in silicon produces performance approaching that of preamplified receivers, the higher k-factor in InGaAs produces performance gaps ⪆ 10 dB at 1550 nm compared to other mature detection methods. Although several reported Sb-based APDs have low k-factors, their relatively high dark currents still render performance gaps similar to those of InGaAs.
In order to appropriately budget satellite resources for a new lasercom terminal, system architects must define an accurate size, mass and power (SWaP) estimate in advance. However, SWaP drivers are often tracked individually during initial design phases, when in reality these drivers are intertwined. Consequently, SWaP estimates attempted at the beginning of a build program can differ significantly from the results seen at the completion of the build. A more holistic initial estimate is needed to capture these complex relationships. A data-based model lends empirical insights into drivers for SWaP, providing a baseline reference for future lasercom terminals. Given the significant number of lasercom demonstrations reported over the last several years, it is now possible to explore a baseline model for SWaP founded on empirical data. These lasercom terminals span a wide range of designs with different SWaP to meet link requirements such as communication distance and data-rates. Here, we consider SWaP drivers such as orbit, maximum data rate × range2, and modulation format for 80 unique lasercom terminals. Through iterative analysis of cross-correlation coefficients, p-values, root mean squared errors, and R2 metrics, we establish multivariable parametric regression models as baseline SWaP references for future system design.
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