Shannon capacities and error-correction codes for optical atmospheric turbulent channels

Abstract

The propagation of an ON-OFF keying modulated optical signal through an optical atmospheric turbulent channel is considered. The intensity fluctuations of the signal observed at the receiver are modeled using a gamma-gamma distribution. The capacity of this channel is determined for a wide range of turbulence conditions. For a zero inner scale, the capacity decreases monotonically as the turbulence strengthens. For non-zero inner scale, the capacity is not monotonic with turbulence strength. Two error-correction schemes, based on low-density parity-check (LDPC) codes, are investigated as a means to improve the bit-error rate (BER) performance of the system. Very large coding gains-ranging from 5.5 to 14 dB, depending on the turbulence conditions-are obtained by these LDPC codes compared with Reed-Solomon error-correction codes of similar rates and lengths.

Outage Capacity Optimization for Free-Space Optical Links With Pointing Errors

“…The ergodic [11] and outage capacities [12] for a Poisson noise model and a Gaussian noise model [13] have been derived in the absence of misalignment errors. The performance of detection techniques [14], bounds on the pairwise error probability for a variety of coding schemes [15], [16], and low-complexity codes [11] have been considered for FSO channels. However, code rate design and joint optimization with the beam width for a finite detector aperture and pointing jitter has not been considered.…”

Integrated receiver architectures for board-to-board free-space optical interconnects

“…Esener et al [9] have reported extensive studies using hybrid onedimensional arrays of devices to demonstrate free-space optical interconnect on printed circuit boards for computer interconnects [9][10][11]. Previous efforts have mainly focused on understanding the core issues of atmospheric turbulence, beam misalignment, and error corrections [8,12,13], while very minimal work was done on developing the low-cost advanced detector arrays for high-speed FOS links.…”

Multilevel coding in free-space optical MIMO transmission with Q-ary PPM over the atmospheric turbulence channel

“…Coding gains of RS and convolutional codes are sufficient under the regime of weak turbulence and in the absence of fog. However, in the presence of strong turbulence or deep fog, coding gains of RS or convolutional codes are insufficient, as shown in [10], and more advanced FEC schemes, such as turbo [8] or low-density parity-check (LDPC) codes [10], are needed.…”

“…In this letter, we propose a power efficient coded-modulation scheme based on multilevel coding (MLC) [9] with LDPC codes [10] as component codes, suitable for the use in repetition MIMO FSO systems with -ary PPM. The proposed coded modulation scheme allows aggregation of RF/microwave signals and a conversion to the optical domain in a very natural way and may be a good candidate for hybrid RF/microwave-FSO systems.…”

“…The influence of the atmospheric turbulence channel is described by the Gamma-Gamma probability density function (PDF) [4] (6) where is the signal intensity, is the gamma function, and is the modified Bessel function of the second kind and order . The PDF parameters and , defined in [10], represent the effective number of large-scale and small-scale cells for zero-inner scale, respectively [4], and are defined as a function of Rytov variance , given by (7) is the optical wave number, is propagation distance, and is the refractive index structure parameter, which we assume to be constant for horizontal paths.…”