In this paper, we propose a comparative performance study to characterize the transmission of multiple subcarrier modulation signals with different M-ary phase shift keying (M-ary PSK) schemes over a radio-on-free-space optical system using the aperture averaging (AA) technique. First, we derive modified expressions for carrier-to-noise and distortion ratio (CNDR), outage probability, and bit-error rate (BER) based on the AA technique and take into consideration the laser diode nonlinearity effect. We also show that there is a design trade-off between the receiver lens aperture and the required average CNDR to achieve a given average BER, ensuring substantial scintillation fade reduction. Further, we perform a comparison between different M-ary PSK modulation schemes, i.e., BPSK, QPSK, and 16-PSK, to characterize the achieved performance improvement by using the AA technique. We found out that when higher order PSK modulation techniques are used such as 16-PSK, the fading reduction is far less impressive than that for schemes employing smaller constellation sizes such as BPSK and QPSK. We thus conclude that for more complex modulation techniques no matter how large the receiver aperture size, the accepted BER level cannot be attained only with the use of the AA technique.
Since a deep and long-term fading in optical intensity results in considerable burst errors in the data, a terrestrial free-space optical (FSO) system has to be designed with consideration of a frequency characteristic of optical scintillation to achieve high quality wireless services over the link. In designing a terrestrial FSO link, we had better design the system considering variations caused by some slow time-varying parameters. This paper proposes a Butterworth-type spectral model of optical scintillation to design a terrestrial FSO link, which enables us to estimate the power spectral density of optical scintillation in a current optical wireless channel when time zone and weather parameters, such as temperature and rainfall intensity, are given. The spectral parameters of optical scintillation, cut-off frequency, and spectral slope are estimated from the data obtained in the experiment, and then their dependencies on time zone, temperature, and rainfall intensity are examined.
KEYWORDS: Free space optics, Modulation, Phase shift keying, Receivers, Turbulence, Picosecond phenomena, Free space optical communications, Current controlled current source, Systems modeling, Intermodulation
In this paper, we propose a Free-Space Optical (FSO) system model based on multiple subcarrier modulation
(MSM) using M-ary Phase Shift Keying (M-ary PSK) scheme over Intensity Modulation Direct Detection optical
link. We investigate the impact of aperture averaging on our model across weak-to-strong turbulence regimes
taking into consideration the intermodulation distortion term due to the laser diode non-linearity. By using
a modified model for aperture averaging technique, we also show that there is a design tradeo¤ between the
receiver lens aperture and the required average Carrier-to-Noise and Distortion Ratio to achieve a given average
bit error rate, ensuring substantial scintillation fade reduction.
KEYWORDS: Scintillation, Free space optics, Channel projecting optics, Statistical analysis, Atmospheric optics, Free space, Data modeling, Signal attenuation, Radio over Fiber, Atmospheric propagation
This paper presents empirical probability density functions (p.d.fs) of variance and fluctuation speed of scintillation,
through analyzing a number of experimental data measured in Japan by a statistical model. The model enables us to treat
scintillation speed by one parameter of cut-off frequency in the power spectral density (PDS). By using the model and
based on the two p.d.fs, we also present simulation results on the level crossing rate (LCR) and average fade duration
(AFD). Combined the two results, an outage probabilities corresponding to a threshold optical intensity can be derived.
KEYWORDS: Free space optics, Antennas, Dense wavelength division multiplexing, Radio over Fiber, Modulation, Atmospheric optics, Radio optics, Televisions, Optical amplifiers, Single mode fibers
In this paper we present the design concept plus experimental results and evaluation of a newly developed
advanced DWDM Radio-on-Free-Space Optical (RoFSO) communication system capable of simultaneous transmission
of multiple RF signals. The RoFSO system is evaluated based on the performance metric parameters
defined for the various RF signals comprising of different wireless services including terrestrial digital broadcasting
signals, cellular 3GPP W-CDMA signals, IEEE 802.11 WLAN based signals etc being transmitted over the
RoFSO link. The performance metric parameters being considered include standard optical received power, CNR
and BER characteristics, W-CDMA signal transmission metric parameters like Adjacent Channel Leakage Ratio
(ACLR) and Error Vector Magnitude (EVM), modulation error ratio (MER) for digital terrestrial television
broadcasting signals as well as spectrum mask and EVM for IEEE 802.11 Wireless LAN signal transmission.
Achieving an all-optical connection between any wireless communication systems with optical fiber network is one of
the ultimate goals of communication network design. An all-optical system providing seamless connection between freespace
and optical fiber links by using free-space optical (FSO) communication technology suitable for next generation
network has been developed. In order to realize this next-generation FSO communication system in which the
transmitted light signal does not undergo any conversion thus achieving all-optical connection, it is necessary to develop
a technology for tracking and focusing the free-space optical signal to a single mode fiber (SMF). The developed FSO
system incorporates a fine pointing mirror (FPM) for high speed beam control and steering. This novel tracking method
can suppress the beam intensity variations as a result of angle-of-arrival fluctuation (AOA) caused by atmospheric
turbulence.
This paper presents experimental results of a next-generation FSO system providing stable and reliable single channel
transmission at 10 Gbps data rates as well as multiple channels using dense wavelength division multiplexing (DWDM).
This kind of data rate is not possible to achieve using conventional FSO systems. The developed system can provide
transmission capacity equivalent to optical fiber and from its design concept and configuration it is bit-rate and protocol
transparent.
Furthermore, we present research on Radio-on-FSO (RoFSO) system which is a combination of the developed nextgeneration
FSO system and Radio over Fiber (RoF) technology. We demonstrate the possibility of utilizing this system
for optical and radio frequency signals transmission. RoFSO technology is independent of the difference in the
underlying physical layers for radio system or fiber system, but realizing fusion at the service level. The RoFSO
technology is available to realize a universal platform for transparent forwarding various wireless services in a
ubiquitous network environment.
This paper firstly derives a new model of RoFSO (Radio on Free Space Optics) channel considering fluctuation speed of
the scintillation and the probability density function (p.d.f) of the random and time-correlated optical intensity disturbed
by scintillation. The relationships among frequency characteristic of RoFSO channel, variance of received optical
intensity and atmospheric conditions (temperature and insolation) are statistically analyzed by the proposed model. By
using the proposed model and the relationships, the throughput performance of WLAN (802.11a) over RoFSO link is
evaluated with computer simulations. For two cases of without-shadowing and with-shadowing in the radio propagation
channel, evaluations of degradation due to scintillation are conducted. As a result, it is found that the degradation due to
scintillation is much smaller than that due to shadowing in the throughput performance for WLAN.
We present initial results on research and development of an optical antenna module suitable for Radio-on Free-Space
Optics (RoFSO) links. This new optical communication system is envisaged to be an effective means of realizing a
ubiquitous society and therefore eliminating the digital divide. The RoFSO system is a trial system applying Radio on
Fiber (RoF) technology for transmission through free space. Based on the results of research of next generation high-speed
free-space optical communication system conducted in the past two years at Waseda University, we have
developed an optical antenna module with efficient laser receiving characteristics as well as simple adjustment. The
tracking system adopts two phases including rough tracking by the beacon light at 0.85 μm wavelength and fine tracking
using communication light at 1.55 μm wavelength to improve compensation precision for the atmospheric turbulence at
the time of beam propagation. We present results on the evaluation of performance characteristics (static characteristics)
of the separate functions for RoFSO antenna module we have developed and confirmed the coupling efficiency and fine
tracking characteristics which were set as goals at the beginning.
Radio on Free-Space Optics (RoFSO) communication systems have attracted a considerable attention for a variety of
applications where optical fibers are not feasible, especially in rural areas, to provide ubiquitous wireless services
quickly and more effectively. RoFSO links can be used to transmit signals like cellular W-CDMA, terrestrial digital TV
or WLAN signals. In spite of its potential, such links are highly dependent on the deployment environment
characteristics in particular the weather conditions. Severity and duration of the atmospheric effects have direct impact
on the availability of the links as well as on the quality of RF signal transmitted over it. Thus, the necessity of
investigating the effects of various weather conditions on RF signal transmission using FSO links.
In collaboration with several institutions, we are currently developing an advanced Dense Wavelength Division
Multiplexing (DWDM) RoFSO antenna capable of transporting multiple RF signals. As preliminary work, we are
conducting experiments on a 1 km link using an off-the-shelf Radio Frequency - FSO (RF-FSO) antenna, with the
objective of obtaining and characterizing performance related parameters of RF-FSO transmission in operational
environment. As an example, we examine the influence of atmospheric turbulence on the transmission quality of W-CDMA
signal. Among the performance metric of interest is the Adjacent Channel Leakage Power Ratio (ACLR) which
will be measured, analyzed and correlated with the weather conditions. An atmospheric fluctuation model for estimating
the communication quality of RF signal transmission on FSO links is being developed. Also the obtained results will be
used for the deployment environment characterization as well as baseline for the design and performance evaluation of
new advanced DWDM RoFSO communication systems we are currently developing.
KEYWORDS: Radio over Fiber, Free space optics, Free space, Dense wavelength division multiplexing, Radio optics, Single mode fibers, Scintillation, Optical amplifiers, Optical tracking, Signal attenuation
Radio on Fiber (RoF) technologies are available to realize a universal platform for transparent forwarding various types
of wireless services under multi air interferences coexistence in a ubiquitous network environment. By applying free
space optical techniques for RoF, its concept can be extended to free space channels. This paper describes a development
project of DWDM Radio on Free Space Optics (RoFSO) system, which can realize a universal platform to quickly and
effectively provide ubiquitous wireless services for rural areas. Radio on Free Space networks using RoF, RoFSO, and
Radio on Radio (RoR) realize software definable radio networks, which is configured with the combination of Virtual
Radio Free Space Network using radio on free space networks, software definable radio gateway, wireless service over
IP, and radio agents. This paper also describes the availability of software definable radio networks for ubiquitous wireless.
Free-space optical communication has emerged as a competitive and viable technology for offering high data
rates, improved capacity, cost-effective and an easy to deploy solution for providing connectivity between two
points which are up to a few kilometers apart. In this paper we present experimental work which demonstrates
the practicality of next generation free-space optical (FSO) communication systems suitable for short-haul,
high-speed and robust data links. This experimental system is placed between two buildings in the Waseda
University campus area for a communication link spanning a distance of 1 km.
We outline the design of the optical antenna which uses 1550 nm wavelength and directly coupling a freespace
optical beam to a single-mode fiber without the need for OE/EO conversion, to offer a communication
link with data rates from 2.5 Gbps to 10 Gbps. The antenna is capable of overcoming most common limitations
inherent in FSO communication systems, such as atmospheric induced beam wander and scintillation effects. A
high-speed tracking mechanism which utilizes a fine positioning mirror (FPM) capable of tracking and controlling
the received beam and focusing/steering most of beam power into the fiber is presented. This FPM is capable
of suppressing the frequent power fluctuations caused by beam angle-of-arrival (AOA) variations.
This paper presents experimental results of the FSO communication system capable offering stable performance
in terms of measured bit-error-rate (BER). Performance results showing increasing the systems data rate
from 2.5 Gbps to 10 Gpbs are also presented.
When a free-space optical beam propagates through the atmosphere it experiences deterioration and deformation of its wave-front caused from small scale, randomly localized changes in the atmospheric index of refraction. This results in beam wander and scintillation effects which can reduce the link availability and may introduce burst errors. This paper outlines experimental work on a free-space optical (FSO) communication system which connects an optical beam directly to a single-mode fiber (SMF) without any optical-to-electrical (O-E) conversion. In order to effectively couple the 1550 nm transmitted optical beam to a SMF it is necessary to be able to track and control the beam angle-of-arrival (AOA) changes. To achieve this, we have developed an optical antenna which uses a fine positioning mirror (FPM) capable of performing high-speed beam tracking and steering thus reducing to a great extent the optical power fluctuations of the received beam coupled to the SMF. This optical power fluctuation is partly a result of beam angle-of-arrival fluctuations caused by atmospheric turbulence. In our experiments we have tried to measure and quantify the magnitude of atmospheric turbulence experienced by an optical beam propagating through the atmosphere. First we demonstrate the relation between the AOA fluctuations and the frequency characteristics of the scintillation effects for a free-space optical beam propagating through a turbulent atmosphere. We use this information to determine the optimum antenna FPM tracking speed for improved performance and error free transmission. The results in the improved fiber received power as well as continuous error free transmission are presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.