Free-space laser communication performance in the atmospheric channel

Wavelength division multiplexing (WDM) has been proposed for fibre, intersatellite, free space and indoor optical communication systems. Digital pulse position modulation (DPPM) is a more power efficient modulation format than on-off keying (OOK) and a strong contender for the modulation of free space systems. While DPPM obtains this advantage in exchange for a bandwidth expansion WDM systems using it are still potentially attractive, particularly for moderate coding levels. However WDM systems are susceptible to interchannel crosstalk and modelling this in a WDM DPPM system is necessary. Models of varying complexity, based on simplifying assumptions, are presented and evaluated for the case of a single crosstalk wavelength. For a single crosstalk, results can be straightforwardly obtained by artificially imposing the computationally convenient constraint that frames (and thus slots also) align (FA). Multiple crosstalk effects are additionally investigated, for the most practically relevant 2 cases of modest coding level, and using both simulation and analytical methods. In general, DPPM maintains its sensitivity advantage over OOK even in the presence of crosstalk while predicting lower power penalty at low coding level in WDM systems.

Section: Single Crosstalk Resultsmentioning

confidence: 99%

Performance evaluation of digital pulse position modulation for wavelength division multiplexing FSO systems impaired by interchannel crosstalk

Mbah

Walker

Phillips

2014

“…The GG distribution model is widely accepted for characterising the weak, moderate and strong turbulence conditions because results achieved match closely with experimental results [1,9,21]. The GG probability density function (pdf) is given as [1,2,6]   a mean value of 1, and in the turbulent free limit, this mean value is attained at all times.…”

Section: Channel Statisticsmentioning

confidence: 62%

Saturation in cascaded optical amplifier free‐space optical communication systems

Bandele

Desai

Woolfson

et al. 2016

The performance of a free-space optical (FSO) communication system in a turbulent atmosphere employing an optical amplifier (OA) cascade to extend reach is investigated. Analysis of both single and cascaded OA FSO communication links is given and the implications of using both adaptive (to channel state) and non-adaptive decision threshold schemes are analysed. The benefits of amplifier saturation, for example in the form of effective scintillation reduction when a non-adaptive decision threshold scheme is utilized at the receiver for different atmospheric turbulence regimes, are presented. Monte Carlo simulation techniques are used to model the probability distributions of the optical signal power, noise and the average bit error rate (BER) due to scintillation for the cascade.The performance of an adaptive decision threshold is superior to a non-adaptive decision threshold for both saturated and fixed gain preamplified receivers and that the ability of a saturated gain OA to suppress scintillation is only meaningful for system performance when a non-adaptive decision threshold is used at the receiver. An OA cascade can be successfully used to extend reach in FSO communication systems and specific system implementations are presented. The optimal cascade scheme with a non-adaptive receiver would use frequent low gain saturated amplification.2

“…The effects of turbulence are characterized using the gamma-gamma (GG) probability density function (pdf), which is given as [10,13,29] Desired ONU Transmitter (Tx,d)…”

Section: Turbulence Channel Modellingmentioning

confidence: 99%

Performance evaluation of turbulence‐accentuated interchannel crosstalk for hybrid fibre and free‐space optical wavelength‐division‐multiplexing systems using digital pulse‐position modulation

Mbah

Walker

Phillips

2016

A hybrid fibre and free space optical (FSO) communication link using digital pulse position modulation (DPPM) in a wavelength division multiplexing (WDM) system is proposed. Such a system, which could provide a power efficient, robust and flexible solution to high speed access networks, is a contender for a passive optical network (PON) solution and could readily be deployed in areas with restrictions in optical fibre installation, or alternatively as a disaster recovery network. However, the effects of interchannel crosstalk, which is common in WDM systems, and atmospheric turbulence-induced scintillation, limit the performance of such system. Both impairments, which could combine in some cases to further degrade the system performance, are investigated here. Specifically, the symbol error probability, the required optical transmission power and power penalties are derived. Furthermore, the required performance of the demultiplexers in terms of adjacent channel rejection is studied with respect to the FSO link length. A simple relationship between the turbulence attenuation and crosstalk 2 is derived to facilitate demultiplexer selection in the design and analysis of practical systems without forward error correction (FEC) coding. Results also show that DPPM systems are more power efficient than OOK systems in the presence of crosstalk accentuated by atmospheric turbulence.