CN108093263B - Video transmission method based on minimum distortion optimization in free space optical communication - Google Patents
Video transmission method based on minimum distortion optimization in free space optical communication Download PDFInfo
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- CN108093263B CN108093263B CN201711310564.5A CN201711310564A CN108093263B CN 108093263 B CN108093263 B CN 108093263B CN 201711310564 A CN201711310564 A CN 201711310564A CN 108093263 B CN108093263 B CN 108093263B
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- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/177—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a group of pictures [GOP]
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- H—ELECTRICITY
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- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
- H04N19/146—Data rate or code amount at the encoder output
- H04N19/147—Data rate or code amount at the encoder output according to rate distortion criteria
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- H—ELECTRICITY
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- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/30—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using hierarchical techniques, e.g. scalability
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- H—ELECTRICITY
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- H04N7/00—Television systems
- H04N7/22—Adaptations for optical transmission
Abstract
The invention discloses a video transmission method based on minimum distortion optimization in free space optical communication, which designs a forward error correction code (FEC) redundancy degree distribution strategy of expandable video coding based on unequal protection thought, aims to optimize transmission distortion caused by source distortion and network packet loss caused by video coding in an FSO system, and obtains a redundant data packet adding scheme for different expandable layers (SVC) by solving a distortion model combined with a channel state, thereby overcoming adverse effects caused by high error rate of the FSO system and improving the reconstructed video quality of a receiving end. The invention ensures the real-time requirement of video transmission by fast solving algorithm, and provides an effective way for transmitting reliable and efficient video stream in free space optical communication.
Description
Technical Field
The invention relates to the technical field of video transmission in FSO (free space optical) and particularly relates to a video transmission method based on minimum distortion optimization in free space optical communication.
Background
The free space optical communication technology, also called a wireless optical network, is an information transmission technology that uses laser as a carrier and realizes point-to-point or point-to-multipoint in an air space. The technology has the advantages of high bandwidth, large communication capacity, good anti-electromagnetic interference performance, good confidentiality and the like, so that the technology becomes a new research hotspot. The biggest disadvantage of FSO communication is that the signal is particularly susceptible to the atmospheric environment during transmission, causing problems of power attenuation, beam drift, beam spreading, phase fluctuation, light intensity flicker, and the like of the communication light beam.
In order to achieve reliable transmission, there are many techniques at the physical layer to reduce the effect of the atmospheric turbulence on the optical communication, and in recent years, researchers have shifted to the upper layers including the link layer and the network layer to find a method for improving the system performance of the optical network. The main methods adopted at present can be divided into two strategies before transmission (such as a preceding error correction code and the like) and after transmission (such as a retransmission protocol and the like). The application of forward error correction codes (FEC) in conventional wireless networks has become very popular, and the adaptive mechanism based on unequal protection (UEP) has also led to the research of many researchers.
On the other hand, according to the report of cisco, the wireless video service accounts for the total telecommunication service from 2014 to 2019, and the wireless video service accounts for 55% to 72%, and meanwhile, the FSO technology has very high optical bandwidth availability and just can meet the requirement of large wireless video data volume. However, because the FSO network has a high packet loss rate, a large transmission delay, and an extremely unstable link, it causes many challenges to transmit efficient and reliable video streams over the wireless optical network. Therefore, a reasonable FEC redundancy distribution strategy is designed according to the state of the channel and the importance degree of the video quality layer, the reconstructed video quality can be effectively improved, and the channel bandwidth resource is utilized to the maximum extent.
Disclosure of Invention
The invention provides an efficient and feasible self-adaptive transmission method of an FSO video, aiming at the problem that the efficient and reliable video stream is difficult to transmit due to atmospheric turbulence in a free space optical communication system. By designing reasonable FEC redundancy allocation strategies for different video quality layers, the aim of minimizing end-to-end video distortion in the FSO system is fulfilled, so that the adverse effect caused by high error rate of the FSO system is overcome, and the reconstructed video quality of a receiving end is improved.
In order to achieve the purpose, the invention adopts the following technical scheme.
A video transmission method based on minimum distortion optimization in free space optical communication comprises the following steps:
the first step is as follows: and according to the channel characteristics of the FSO, an FSO channel model is built by using a Monte Carlo method, and the signal-to-noise ratio s and the bandwidth of the channel are fed back to the self-adaptive coding module of the transmitting end.
Secondly, the self-adaptive coding module of the sending end establishes a lookup table L UT in advance through channel state parameters to reflect the mapping relation between the decoding failure probability p and the system signal-to-noise ratio s and FEC redundancy r;
and thirdly, encoding the original video into a plurality of quality layers by using an SVC encoder, wherein the quality layers comprise a base layer (B L) and a plurality of enhancement layers (E L), and dividing the encoded video stream into NA L units.
And fourthly, packing the encoded NA L units by taking the GOP as a unit and taking N as a length, and recording the byte length L i of each SVC layer.
The fifth step: and the self-adaptive coding module of the sending end optimizes and solves the optimal FEC redundancy allocation schemes of different SVC layers according to the established overall video distortion model and the look-up table established in advance, and constructs a coding packet and a redundancy packet.
The video quality distortion model comprehensively considers two aspects of source distortion and transmission distortion caused by an encoder, and the constraint condition is the total FEC redundancy, which is shown as the following formula:
the optimization goal is to arrange the FEC redundancy allocation of different SVC quality layers reasonably, and minimize the distortion of video quality under the limitation of channel bandwidth resources, as shown in the following formula:
s.t.
rl≤1 (4)
wherein the content of the first and second substances,
E[d(Li)]is the total distortion of the video transmission;
l is the number of SVC quality layers;
dlthe source distortion of the l SVC extended layer is mainly related to the coding rate and the quantization parameter QP, and can reflect the importance degree of different extended layers for decoding;
r is a vector L× 1, each element r of whichlRepresenting FEC redundancy distributed for the lth extensible layer, and aiming at optimizing to determine an optimal r so as to minimize the total video distortion;
Pl(s, r) is the probability of decoding failure of the l SVC extension layer, s is the system signal-to-noise ratio (SNR);
|Lll represents the total packet length of the l-th SVC extension layer;
r is the FEC redundancy of the maximum total system;
and a sixth step: and transmitting the coded data to an analog FSO network through BPSK modulation.
The seventh step: and the receiving end receives the data packet from the FSO network, firstly carries out CRC check, if the check is passed, the coding frame is reserved, and if not, the coding frame is discarded.
Eighth step: and carrying out FEC decoding on the coded packet to obtain a video compressed data packet, and recovering the data packet according to the maximum error correction capability of the FEC code.
The ninth step: and further decoding by using an H.264decoder to obtain a video sequence, and simultaneously processing the video frames which cannot be successfully decoded by adopting a frame-copy error concealment technology.
The tenth step: and calculating a peak signal-to-noise ratio (PSNR) value of the reconstructed video quality by comparing the video sequence with the original video sequence, and performing objective video quality evaluation.
The FSO channel model based on the Monte Carlo method comprises the following steps:
1) calculating a probability density function of light intensity distribution according to a Gamma-Gamma channel model;
2) under BPSK modulation, parameters such as average bit error rate, channel capacity, interruption probability and the like are deduced;
3) and performing random simulation and statistical sampling on the model in the matlab by using a Monte Carlo method to obtain a relation curve of packet loss rate (PER) and signal-to-noise ratio (SNR).
The FEC decoding operation performed by the receiving end mainly includes the following steps:
1) firstly, the receiving end carries out the processes of packet recombination, serialization and the like, and extracts a coding block matrix and a coding vector matrix for coding packets in the same group;
2) when the matrix formed by the coding vectors is full-rank, solving a corresponding inverse matrix by using a Gauss-Jordan elimination method;
3) and multiplying the received coding block matrix by the inverse matrix, and circularly finishing the decoding of the data packet according to the quality layer ID.
The invention has the beneficial effects that:
the optimal self-adaptive FSO video transmission system model with the minimum distortion is realized, and an effective way is provided for transmitting reliable and efficient video streams in free space optical communication.
The method is suitable for the free space optical communication environment with high transmission rate, severe channel environment, data loss and high error rate. By reasonably and dynamically distributing FEC redundancy, channel resources can be fully utilized, and the quality of the reconstructed video at the receiving end is maximized.
By establishing an L UT lookup table obtained by channel parameter estimation, FEC redundancy allocation vectors of different video quality layers can be rapidly calculated, and the real-time requirement of video transmission is met.
The invention can be used for expanding the backbone network, solves the problem of the last kilometer, and is an FSO (free space resource) which is a good choice for quickly expanding and extending the existing backbone network outwards.
The flexibility of the FSO makes it applicable to many enterprises and schools, such as the connection of enterprises L AN to L AN and the connection of campus networks.
Drawings
FIG. 1 is a block diagram of an embodiment of the present invention;
fig. 2 is a flow chart of a method in accordance with the practice of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention designs a reasonable FEC redundancy degree distribution strategy according to the state of the FSO channel and the importance degree of the video extensible layer, can effectively improve the reconstructed video quality and furthest utilizes the channel bandwidth resources. The structure of the FSO video self-adaptive transmission system is shown in FIG. 1, and the method specifically refers to the following steps:
the first step is as follows: and according to the channel characteristics of the FSO, an FSO channel model is built by using a Monte Carlo method, and the signal-to-noise ratio s and the bandwidth of the channel are fed back to the self-adaptive coding module of the transmitting end.
Secondly, the self-adaptive coding module of the sending end establishes a lookup table L UT in advance through channel state parameters to reflect the mapping relation between the decoding failure probability p and the system signal-to-noise ratio s and FEC redundancy r;
and thirdly, encoding the original video into a plurality of quality layers by using an SVC encoder, wherein the quality layers comprise a base layer (B L) and a plurality of enhancement layers (E L), and dividing the encoded video stream into NA L units.
And fourthly, packing the encoded NA L units by taking the GOP as a unit and taking N as a length, and recording the byte length L i of each SVC layer.
The fifth step: the adaptive coding module at the transmitting end optimizes and solves the optimal FEC redundancy allocation schemes of different SVC layers according to the established overall video distortion model and the look-up table established in advance, and the specific algorithm flow is shown in FIG. 2, and a coding packet and a redundancy packet are constructed.
The video quality distortion model comprehensively considers two aspects of source distortion and transmission distortion caused by an encoder, and the constraint condition is the total FEC redundancy, which is shown as the following formula:
the optimization goal is to arrange the FEC redundancy allocation of different SVC quality layers reasonably, and minimize the distortion of video quality under the limitation of channel bandwidth resources, as shown in the following formula:
s.t.
rl≤1 (4)
wherein the content of the first and second substances,
E[d(Li)]is the total distortion of the video transmission;
l is the number of SVC scalable quality layers;
dlthe source distortion of the l SVC extended layer is mainly related to the coding rate and the quantization parameter QP, and can reflect the importance degree of different extended layers for decoding;
r is a vector L× 1, each element r of whichlRepresenting FEC redundancy distributed for the lth extensible layer, and aiming at optimizing to determine an optimal r so as to minimize the total video distortion;
Pl(s, r) is the probability of decoding failure of the l SVC extension layer, s is the system signal-to-noise ratio (SNR);
|Lll represents the total packet length of the l-th SVC extension layer;
r is the FEC redundancy of the maximum total system;
and a sixth step: and transmitting the coded data to an analog FSO network through BPSK modulation.
The seventh step: and the receiving end receives the data packet from the FSO network, firstly carries out CRC check, if the check is passed, the coding frame is reserved, and if not, the coding frame is discarded.
Eighth step: and carrying out FEC decoding on the coded packet to obtain a video compressed data packet, and recovering the data packet according to the maximum error correction capability of the FEC code.
The ninth step: the video sequence is obtained by further decoding with an H264decoder, and video frames which cannot be successfully decoded are processed by adopting a frame-copy error concealment technology.
The tenth step: and calculating the PSNR value of the reconstructed video quality by comparing the video sequence with the original video sequence, and evaluating the video quality.
The invention designs a space optical communication (FSO) video self-adaptive transmission technology, and designs a reasonable FEC redundancy allocation strategy for different video extensible layers to minimize the total distortion of end-to-end videos in an FSO system, thereby overcoming the adverse effect caused by high error rate of the FSO system, fully utilizing bandwidth resources and improving the quality of reconstructed videos at a receiving end.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (3)
1. A video transmission method based on minimum distortion optimization in free space optical communication is characterized in that: the method for dynamically distributing the FEC redundancy by the sending end according to the channel parameters and the video parameters comprises the following steps:
the first step is as follows: according to the channel characteristics of the FSO, an FSO channel model is built by a Monte Carlo method, and the signal-to-noise ratio s and the bandwidth of the channel are fed back to a self-adaptive coding module of a sending end;
secondly, the self-adaptive coding module of the sending end establishes a lookup table L UT in advance through channel state parameters to reflect the mapping relation between the decoding failure probability p and the system signal-to-noise ratio s and FEC redundancy r;
thirdly, encoding the original video into a plurality of quality layers by using an SVC encoder, wherein the quality layers comprise a base layer (B L) and a plurality of enhancement layers (E L), and dividing the encoded video stream into NA L units;
packing the encoded NA L unit by taking N as the length and recording the byte length L i of each SVC layer by taking GOP as a unit;
the fifth step: an adaptive coding module at a sending end optimizes and solves the optimal FEC redundancy allocation schemes of different SVC layers according to the established overall video distortion model and a look-up table established in advance, and constructs a coding packet and a redundancy packet;
the video transmission total distortion model comprehensively considers two aspects of source distortion and transmission distortion caused by an encoder, and the constraint condition is the total FEC redundancy, which is shown as the following formula:
the optimization goal is to reasonably arrange FEC redundancy allocation of different SVC quality layers, and minimize the total video transmission distortion under the limitation of channel bandwidth resources, as shown in the following formula:
rl≤1 (4)
wherein the content of the first and second substances,
E[d(Li)]is the total distortion of the video transmission;
l is the number of SVC quality layers;
dlthe source distortion of the l-th svc extension layer is mainly related to the coding rate and the quantization parameter QP, and can reflect the importance degree of different extension layers for decoding;
r is a vector L× 1, each element r of whichlExpressed as FEC redundancy allocated to the lth scalable layer, the optimization is to determine an optimal r so that the video is always lostTrue minimum;
Pl(s, r) is the probability of decoding failure of the l SVC extension layer, s is the system signal-to-noise ratio (SNR);
|Lll represents the total packet length of the l-th SVC extension layer;
r is the FEC redundancy of the maximum total system;
and a sixth step: transmitting the coded data to an analog FSO network through BPSK modulation;
the seventh step: the receiving end receives the data packet from the FSO network, firstly, CRC is carried out, if the CRC passes, the coding frame is reserved, otherwise, the coding frame is discarded;
eighth step: carrying out FEC decoding on the coded packet to obtain a video compressed data packet, and recovering the data packet according to the maximum error correction capability of the FEC code;
the ninth step: further decoding by using an H264decoder to obtain a video sequence, and processing video frames which cannot be successfully decoded by adopting a frame-copy error concealment technology;
the tenth step: and calculating the PSNR value of the reconstructed video quality by comparing the video sequence with the original video sequence, and evaluating the video quality.
2. The video transmission method based on minimum distortion optimization in free space optical communication according to claim 1, wherein: the FSO channel model based on the Monte Carlo method comprises the following steps:
1) calculating a probability density function of light intensity distribution according to a Gamma-Gamma channel model;
2) under BPSK modulation, parameters such as average bit error rate, channel capacity, interruption probability and the like are deduced;
3) and performing random simulation and statistical sampling on the model in the matlab by using a Monte Carlo method to obtain a relation curve of packet loss rate (PER) and signal-to-noise ratio (SNR).
3. The video transmission method based on minimum distortion optimization in free space optical communication according to claim 1, characterized in that: the FEC decoding operation performed by the receiving end mainly includes the following steps:
1) firstly, the receiving end carries out the processes of packet recombination, serialization and the like, and extracts a coding block matrix and a coding vector matrix for coding packets in the same group;
2) when the matrix formed by the coding vectors is full-rank, solving a corresponding inverse matrix by using a Gauss-Jordan elimination method;
3) and multiplying the received coding block matrix by the inverse matrix, and circularly finishing the decoding of the data packet according to the quality layer ID.
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| Dynamic FEC-Distortion Optimization for H.264 Scalable Video Streaming;Wei-Chung Wen等;《IEEE 9th Workshop on Multimedia Signal Processing》;20080102;147-150 * |
| Layer-based RED-FEC (L-RED-FEC) method for wireless scalable video streaming;H. Ha等;《IEEE ELECTRONICS LETTERS》;20141225;第50卷(第20期);1438-1440 * |
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