White lighting LEDs offer great potential for high speed communications, especially for indoor applications. However, for their widespread adoption, two important issues need to be addressed: the lack of diversity in ...
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White lighting LEDs offer great potential for high speed communications, especially for indoor applications. However, for their widespread adoption, two important issues need to be addressed: the lack of diversity in multiple-input multiple output (MIMO) systems, and the small field of view of receivers. In this paper, we describe a design using a hemispherical lens in the receiver that solves these problems. By using classical optics, we derive exact expressions for the channel gain and the optical power density of the projected images. Simulation results of a typical indoor scenario show that the new system has a wide field of view, and provides adequate channel gain for angles of incidence as large as 70 degrees. We present the distribution of optical power on the imaging plane for various receiving positions and tilted receivers over a number of representative indoor scenarios. They show that the images of LEDs are clearly distinguishable. The results demonstrate the presence of low channel correlations between individual transmitters and receivers. Consequently, this confirms that the new technique is capable of providing significant diversity order for MIMO optical wireless applications.
We report on a novel optical single sideband-orthogonal frequency division multiplexing system for access and metro networks based on a single, low cost dual electro-absorption modulated laser. The experimental result...
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We report on a novel optical single sideband-orthogonal frequency division multiplexing system for access and metro networks based on a single, low cost dual electro-absorption modulated laser. The experimental results successfully demonstrate transmissions at 11.11 Gb/s over 200 km uncompensated standard single mode fiber through intensity modulation and direct detection.
We propose a modified single-carrier frequency domain equalization (SC-FDE) scheme implemented in directly detected wavelength-division-multiplexed passive optical networks (WDM-PONs). A time-clipping technique is use...
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We propose a modified single-carrier frequency domain equalization (SC-FDE) scheme implemented in directly detected wavelength-division-multiplexed passive optical networks (WDM-PONs). A time-clipping technique is used in FDE to perform noise filtering. In the simulation, where the channel is modeled with chromatic dispersion and directdetection, performance improvement is achieved by exploring the clipping position and retained gradient vector length. In the experiment, we investigate the time-clipping SC-FDE implemented in 10-Gb/s direct-detected WDM-PON using an uncooled free-running 1550-nm vertical cavity surface emitting laser. After 30-km transmission, it is observed that the time-clipping scheme can bring roughly 1-dB power penalty improvement over conventional equalization schemes.
In this paper, N-CSK (N parallel Codes Shift Keying) using modified pseudo orthogonal M-sequence sets (MPOMSs) to realize the parallel combinatory spread spectrum (PC/SS) communication system for the optical communica...
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In this paper, N-CSK (N parallel Codes Shift Keying) using modified pseudo orthogonal M-sequence sets (MPOMSs) to realize the parallel combinatory spread spectrum (PC/SS) communication system for the optical communications is proposed. Moreover, the upper bound of data transmission rate and the bit error rate (BER) performance of this N-CSK system using the chip-level detection are evaluated through theoretical analysis by taking into account the scintillation, background-noise, avalanche photo-diode (APD) noise, thermal noise, and signal dependence noise. It is shown that the upper bound of data transmission rate of the proposed system is better than those of OOK/CDM and SIK/CDM. Moreover, the upper bound of data transmission rate of the proposed system can achieve about 1.5 [bit/chip] when the code length of MPOMS is 64 [chip].
Atmospheric turbulence-induced fading is one of the main impairments affecting free-space optics (FSO) communications. In this paper, we consider FSO systems with intensity modulation and direct detection (IM/DD) and ...
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Atmospheric turbulence-induced fading is one of the main impairments affecting free-space optics (FSO) communications. In this paper, we consider FSO systems with intensity modulation and direct detection (IM/DD) and derive a closed-form expression for the asymptotic pairwise error probability of general FSO space-time codes (STCs) for two lasers and an arbitrary number of photodetectors for channels suffering from Gamma-Gamma fading. Furthermore, we provide a simple design criterion for FSO STCs which is used to establish the quasi-optimality of previously proposed FSO repetition codes. We also show that STCs optimized for RF systems achieve full diversity in FSO systems but are suboptimal as far as the coding gain is concerned. Simulation results confirm the analytical findings of this paper.
In optical communications through the atmosphere, the evaluation of a link feasibility often requires the quantification of the scintillation penalty in terms of power loss. To find how much additional optical power i...
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In optical communications through the atmosphere, the evaluation of a link feasibility often requires the quantification of the scintillation penalty in terms of power loss. To find how much additional optical power is needed to reach the bit-error-rate (BER) requirements, the optical-power fluctuations must be characterized as well as the response of the receiver to those fluctuations. In the present analysis, the direct-detected optical power is assumed to be either lognormal or gamma-gamma distributed. To account for the dynamics of the atmospheric channel, a distinction is made between short-term and long-term BERs. For a simple On-Off Keying (OOK) modulation, expressions of scintillation losses are given for different system requirements. Specifically, an upper bound is set to any of the three following quantities: the long-term BER, the probability of having a too-high short-term BER, or the mean time during which the short-term BER is too high. Results show that, without any fade mitigation, losses under moderate scintillation are considerable. Finally, a simple code-word approach shows how scintillation losses can be reduced by channel coding. (c) 2007 Society of Photo-Optical Instrumentation Engineers.
The performances of optical and radio frequency communication systems are compared for long distance applications, such as deep space communications, where the signal-to-noise ratio (SNR) is crucial. We compare an opt...
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The performances of optical and radio frequency communication systems are compared for long distance applications, such as deep space communications, where the signal-to-noise ratio (SNR) is crucial. We compare an optical communication system operating at 0.8 mu m using intensity modulation and direct detection with an avalanche photodiode, an optical communication system operating at 1.5 mu m using on-off keying and an optical preamplifier, and a radio frequency communication system operating in the X band. Assuming typical system parameters for the link budget analysis, we find that for distances between the transmitting and receiving antennas (R) of 10(7) km, the SNR for the optical systems is proportional to R-4, while for the radio frequency system it is always proportional to R-2. The maximum data rate achievable with the radio frequency system is higher than that with the optical systems for distances beyond 10(8) km. For near-Earth communication links, an optical system with optical preamplification is preferable when the data rate is higher than several gigabits per second. Clearly our results are based on specific system parameters. However, the equations involved and the method of comparison will be applicable for a wide range of system parameters. (c) 2007 Society of Photo-Optical Instrumentation Engineers.
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