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Free space optical communication method and system based on LDPC code
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An LDPC code and free space technology, applied in the field of optical communication, can solve problems such as low bit error rate and failure to meet system communication performance requirements
Active Publication Date: 2017-05-17
武汉全信通通信工程有限公司
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Today's LDPC coding technology is mainly concentrated on Gaussian channels and Rayleigh channels, which have lower bit error rates; but AWGN channels and Rayleigh channels belong to small-scale fading effects, which cannot meet the requirements of strong turbulence effects. system communication performance requirements
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Embodiment 1
[0064] Embodiment 1: In the case of weak turbulence, set the turbulence coefficient to 0.2 and 0.4 respectively, construct QC-LDPC codes with code rates of 0.5, 0.67 and 0.75, and then perform LLR-BP decoding; the specific method is as follows:
[0065] (1) Establish the data model of the received signal, and propose a channel model for different atmospheric turbulence intensities:
[0066] (1-1) Establish the data model r(t) of the received signal,
[0067] r(t)=y(t)·n 1 (t)+n 0 (t)
[0068] where t is the time, y(t) is the transmitted signal, n 1 (t) is the multiplicative noise caused by atmospheric turbulence, n 0 (t) is additive Gaussiannoise including thermal noise and amplified noise, n 0 (t) mean is 0, variance is σ 2 ;
[0069] (1-2) Construct a channel model for weak turbulence intensity, and use lognormal distribution for model simulation. The probability density of light intensity V under weak turbulence conditions is Among them, σ x 2 is the logarithmic...
Embodiment 2
[0101] Example 2: Under the strong turbulence effect, when the k distribution order α is set to 1 and 4, the corresponding turbulence coefficient σ is 3 and 1.5, respectively constructing QC-LDPC codes with a code rate of 0.5 and 0.75, and then performing LLR -BP decoding; the specific method is as follows:
[0102] (1) Establish the data model of the received signal, and propose a channel model for different atmospheric turbulence intensities:
[0103] (1-1) Establish the data model r(t) of the received signal,
[0104] r(t)=y(t)·n 1 (t)+n 0 (t)
[0105] where t is the time, y(t) is the transmitted signal, n 1 (t) is the multiplicative noise caused by atmospheric turbulence, n 0 (t) is additive Gaussian noise including thermal noise and amplified noise, n 0 (t) mean is 0, variance is σ 2 ;
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Abstract
The invention provides a free spaceoptical communication method and system based on an LDPC code. The method and system aim at a problem that the error rate, communication distance and communication bandwidth of a system are affected by the flicker and light beam drift and extension caused by atmosphere turbulence and the reduction of signal to noise ratio of a receiving end in laser communication. The method comprises the steps: firstly proposing a logarithmic normal distribution channel model under weak turbulence and a K-distribution channel model under strong turbulence according to the characteristics of atmosphere turbulence channels; secondly constructing an irregular QC-LDPC code on the basis of the proposed channel models; finally deducing an LLR probability density function, and carrying out the decoding through an LLR-BP algorithm. A confidence decoding BP result indicates the error rate of the system remarkably decreases along with the increase of signal to noise ratio. An experiment indicates that the method and system can effectively reduce the performance of an FSO system.
Description
technical field [0001] The invention relates to a free spaceoptical communication method and a communication system, belonging to the technical field of optical communication. Background technique [0002] Free-Space-Optical communication (FSO for short), also known as Wireless-Optical-communication (WOC for short), uses laser as the carrier of information transmission and the atmosphere as the transmission medium to transmit data, images, A communication technology for two-way transmission of voice and other information. On the one hand, the FSO system adopts the characteristics of high transmission rate of light in the process of optical fiber communication and photoelectric conversion technology, which has the characteristics of high bandwidth, high modulation rate and less spectrum resource occupation; on the other hand, the FSO system combines radio wave communication The advantages of technology greatly reduce the cost of communication, the construction period of the...
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