Optical EngineeringReceiver architectures for the detection of spatially correlated optical field using avalanche photodiode detector arrays
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Receiver architectures are suggested for the detection of optical field using avalanche photodiode (APD) arrays. It is assumed that optical field is modulated using either binary pulse-position modulated (BPPM) or on-off keying (OOK), and that direct-detection is used to recover the optical signal. It is further assumed that the optical field is exposed to weak atmospheric turbulence. Receivers motivated by the maximum a posteriori (MAP) rule for OOK and BPPM communications are suggested. Due to the complexity of the suggested receivers, suboptimum combining schemes are presented. In one scheme, a simple summation of the output of APDs is utilized to render a decision. In alternate schemes, for BPPM and OOK scenarios, weighting mechanisms that combine the output of detectors in an optimum manner are suggested. For binary PPM signaling, the proposed weighting mechanism maximizes the signal-to-noise ratio (SNR). For OOK signaling, the weighting mechanism is an improvised optimization of the linear summation of the outputs of the APDs. Simulation results are presented to underscore the superiority of the weighted combining methods as compared to the simple summation algorithm.