KEYWORDS: Free space optics, Telecommunications, Free space optical communications, Atmospheric optics, Atmospheric turbulence, Mathematics, Antennas, Signal processing, Systems modeling, Receivers
Free Space Optical (FSO) communication is a communication pattern in which laser is used as the information carrier in
atmosphere environment. FSO system has been widely applied in the fields of satellite communication and ground sight
distance communication, with a promising application prospect and tremendous market potential.
And space-time processing (using multiple antennas) is now recognized as a key to achieving reliable high data rate
wireless communications and is being incorporated into the physical layer of many wireless standards. In this letter, error
rate performance for space-time block coding (STBC) in FSO communication systems with direct detection operating
over strong atmospheric turbulence channels is analyzed.
The purpose of the paper is: (i) to determine the channel capacity of FSO system in the presence of atmospheric
turbulence, (ii) to see how much this limit can be approached using the best known STBC techniques.
In this paper, we use mathematics tool to establish the channel model of FSO system, and then apply the STBC to the
FSO system, research the decoding method and simulate the performance using MATLAB tools. The mathematics
analysis and simulation results show the great application expectation of STBC in the OOK channel of the FSO system.
Recently, free space optical communication has attracted a considerable amount of interest as an alternative medium to
radio for wireless transmission. It has many advantages such as a huge unregulated bandwidth, high data rates, and
resistance to multi-path fading relative security against eavesdropping. The work presented in this thesis focuses on
modulation schemes. Concerns of eye safety and power consumption limit the average transmitter power, which suggests
that modulation techniques possessing a high peak-to-mean power ratio are favorable. This is generally achieved by
trading off power efficiency against bandwidth efficiency. A novel dual-header pulse interval modulation (DH-PIM) for
optical wireless communications is proposed in this paper. The symbol structure, the spectral properties, and the
expression for bandwidth requirement and optical power requirement of DH-PIM in the absence of and in the presence
of multi-path dispersion is presented in this paper.
In the decade of information, with the increment of the data rate and capacity in communication, free space optical
communication (FSO) has been paid much attention by many countries since it integrates the advantages of fiber
communication and other traditional wireless communication technologies, such as large capacity, low cost, convenient
deployment and flexibility. This paper concerns with the research on the signal tracking technology of FSO. Considering
that suppressing vibration is a difficulty of FSO, so suppressing methods are discussed in the paper. As a base, the ATP
(Acquisition, Tracking, Pointing) technology of FSO communication system is analyzed in this paper. And a new signal
tracking system for FSO communication is described. The main structure, integral parts and detailed work process of this
signal tracking system are introduced in detail.
The 3G network security was a problem in the practice. The particularity of the 3G core network determined that the new firewall technology must be adopt in order to protect the core network. The development of the network processor (NP) technology offered a high-performance realization platform for core network firewall. On the basis analyzing the shelter method of the attack to each interface in the 3G core network, a scheme of 3G core network firewall design was put forward. It was on the network processor hardware platform. How to use IPSEC protocol to protect the GPRS tunnel protocol (GTP) and implement on the NP was discussed in detail. The aggregated bit vector algorithm was applied on NP for packet classification. In the end result table of firewall performance test with SMART BIT instrument was provided.
KEYWORDS: Telecommunications, Free space optical communications, Monte Carlo methods, Systems modeling, Atmospheric turbulence, Mathematical modeling, Turbulence, Receivers, Transmitters, Error analysis
Free space optical communication systems represent one of the most promising approaches for addressing the emerging broadband access market, it can provide high bandwidth with no physical contact, but are hampered by signal fading effects due to particulate scattering caused by atmospheric turbulence. In this paper, we propose a new channel model of MIMO free space optical communication system. The physics meaning of this model is very clear, and its format is very simple. Mathematic results show that MIMO is a very effective way for intensity fluctuation reduction induced by turbulence, thus reduce the bit-error-rate of the system.
The exponential growth in optical link speed has stressed the performance of routers and firewall. Consequently, a new breed of microprocessors, called Network Processors (NP), are designed and fabricated specifically to effectively process packets on firewalls and routers. Packet classification is a major function in network processors to fit requirements of next-generation Internet. The paper presents a hardware-based packet classification algorithm for NP. The innovative aspect of the proposed algorithm is to use the NP's parallel character well enough. The algorithm use hash algorithm to make six-dimension classification be three-dimension classification. Compressing the size of classification fields are used for hash input while TCAM performs the lookup of the hash value and source IP. The memory of the algorithm is the total amount of memory needed to store the rules. The search speed of our algorithm is neither sensitive to the size of the rule table. It is only relate to the collision of the hash function. The performance of the proposed algorithm test result demonstrates that the proposed scheme is a sound approach that can be implemented on NP efficiently.
KEYWORDS: Free space optics, Global Positioning System, Receivers, Telecommunications, Transmitters, Signal processing, Automatic alignment, Free space optical communications, Laser systems engineering, Satellites
Normally free-space laser communication system uses the narrow transmission laser beam. It is important to align the laser beams between two laser communication terminals. We developed the automatic alignment system used in the free-space laser communication system. The alignment system adopts GPS (Global Positioning System), the GPS makes the alignment automatic for initial alignment, to use the signal power received or the signal of CCD camera achieves the fine alignment. The principles and configuration frame of the automatic alignment system are discussed in detail.
The uncooled IRFPA thermal imaging systems, which are designed to operate at room temperature, will make the sensors less expensive, lighter, and more reliable. The sensor of this infrared FPA imaging system is the 320x240 LW IRCOMS uncooled integrated microbolometer detector. The time sequence required by the detector is described. The timing control circuit of the camera is designed using Altera EPLD.
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