Signal estimators for p-i-n and APD-based free-space optical communication systems

2008

Opt. Eng

Receiver architectures are suggested for the detection of optical field using avalanche photodiode ͑APD͒ arrays. It is assumed that optical field is modulated using either binary pulse-position modulated ͑BPPM͒ or on-off keying ͑OOK͒, 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 ͑MAP͒ 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 ͑SNR͒. 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.

Section: Introductionmentioning

confidence: 96%

“…In a recent study, we proposed a signal intensity estimation method. 6 In Ref. 6, a number of architectures were proposed for the estimation of signal intensity in a turbulent medium, governed by log-normal and negative exponential fading.…”

Section: Introductionmentioning

confidence: 99%

Receiver architectures for the detection of spatially correlated optical field using avalanche photodiode detector arrays

Cole

2008

Opt. Eng

“…Array detectors can offer enhanced performance in free-space optical (FSO) channels impaired by pointing inaccuracies and other scenarios, which lead to uncertainty in the direction of arrival of optical beams. Such uncertainties may be due to atmospheric tilt or spacecraft/receiver motion or orientation [1][2][3][4][5][6][7][8][9][10][11] . To elaborate, array detectors enable an FSO receiver to compensate for the misalignment at the receiver and capture optical fields that are extended beyond the diffraction-limited field of view of the receiver.…”

Section: Introductionmentioning

confidence: 99%

A novel detection strategy for optical receivers with focal plane array

International Conference on Space Optics — ICSO 2020

2021

In this paper, the problem of optimizing the performance of a free-space optical system with large field of view (FOV) focal plane array is addressed. A large FVO detector is desired when beam tilt, large pointing inaccuracies, or other impairments leading to uncertainties in the angle of arrival of the beam are present. For such an arrangement, when we consider a large aperture size, which results in a small diffraction-limited FOV, a large number of photo-detectors in the array are exposed to background radiation only. In addition, in adaptive optics system without a wave-front sensor (WFS), one has to contend with the same issue when large FOV system with small diffraction-limited FOV is considered. Hence, detection strategies to deal with the excess background noise in this scenario is of interest in this paper. We assume here that the receiver is utilizing a recently proposed technique to identify the presence and the location of the beam footprint in the focal plane, thereby reducing the "area" of consideration in the focal plane to a subset of the total photodetectors. It is shown here that, when the proposed receiver is utilized, one can expect an improvement in the overall bit error rate of several orders of magnitude as compared with the standard array detector.

“…The use of array of detectors has been subject of a number of studies for deep-space applications [1][2][3][4][5][6][7][8] . Array detection has also been proposed for FSO communications in urban arenas in the presence of turbulence [4][5][6][7]9 . In general, the use of arrays enables one to compensate for the misalignment at the receiver, to capture the received optical beams that are subjected to the atmosphere-induced tilt and wander, and to capture optical fields that have been extended beyond the diffractionlimited field of view of the receiver due to atmospheric effects.…”

Section: Introductionmentioning

confidence: 99%

“…One approach is to estimate the presence of the desired optical field in one or several PDs and only consider the outputs of such detectors 3 . However, such a technique requires that one performs estimation of the signal level 4,5,7 . Such estimation techniques are prohibitively complex and can lead to an unacceptable level of complexity in multi gigabit per second (Gbps) optical communication link when a large number of array elements are brought to bear.…”

Section: Introductionmentioning

confidence: 99%

Nonlinear Array detection strategies for optical beams in long range fee-space optics channels

International Conference on Space Optics — ICSO 2018

2019

In this study, we examine the problem of array detectors for free-space optical (FSO) communication systems when the optical field is detected using an array of detectors in the presence of large background noise and non-negligible pointing error. It is assumed that the spatial pointing errors are due to beam tilt and/or platform vibration. We propose and study a nonlinear detection mechanism for processing the outputs of the photodetectors (PD). The proposed strategy performs photodetector array combining that favors the PDs with non-negligible signal strengths, which are proportional to the spatial characteristics of the beam. Provided that the spatial profiles of the optical beams in single and multiple-spatialmode scenarios are non-uniform, uniform aperture detector arrays will provide only a suboptimal performance. That is, the spatial feature of the detector is assumed to match the spatial feature of the received beam. This principle mirrors the concept of matched filtering in time domain for the detection of signals buried in additive white Gaussian noise. Performance in this paper is established in terms of the overall bit error rate for direct-detection receivers. It is shown that the proposed detection strategy results in a sizeable gain in performance in terms of reducing the bit error rate by an order of magnitude for all conditions, including when the pointing error is substantial.