A new solution for H.264 code stream transmission is proposed for the traditional video transmission to rebuild the quality of image quality. In the source end, according to the difference in importance of the H.264 code stream, it is divided into two parts. The video signal is transmitted using the MIMO channel, and the transmit power is dynamically allocated on the two antennas when maintaining a total transmit power constant. The simulation results show that under equivalent channel conditions, the proposed program effectively increases the reconstruction image quality of the receiving end.
0 Preface
In recent years, with the development and application of high-speed broadband wireless technology, wireless video communications is becoming a wide range of people. How to significantly improve the spectral efficiency in the wireless communication system to meet the needs of increasing communication capacity, which has become a worldwide concern and urgently needed. Multi-input Multiple Output (MIMO) technology can effectively alleviate the contradiction by increasing the number of antennas of the transmitting end and the receiving end, the system uses a multi-antenna array at the same time and the receiving end to obtain spatial multiplexing and diversity gain, empty time code ( STC) The MIMO system capacity is fully excavated, which is an effective means of improving the error performance of the entire system. On the other hand, H.264 / AVC is a new generation of video compression coding standard video due to its high coding efficiency and good network.
The affinity is widely valued by scholars at home and abroad. The combination of the world MIMO technology and H.264 / AVC will greatly improve the reliability of wireless video communication.
1 H.264 code stream segmentation
The code stream of H.264 is encapsulated by a network abstraction layer (NAL unit). Each NAL unit has a specific data type, which contains a byte NAL element head and an original byte sequence load, wherein in the NAL unit header information The NRI refers to the importance of the current NAL unit, the higher the value indicating that the NAL unit is, and in the H.264NAL layer semantics, with NAL_REF_IDC to indicate the priority of the current NAL.
Based on this idea, the I frame or IDR frame in the ANNEXB data format (immediately refresh frame), SPS (Sequence Parameter Set), PPS (Image Parameter Set), NAL_REF_IDE The value is 3, indicating that its NAL unit is highly important, and once the type of data is lost, it will cause a fatal impact on video reconstruction, because i frame is intra encoding mode, it is used as a reference frame of the P frame, so it is only guaranteed it Accurate transmission to ensure that the full decoding of the image, the SPS and PPS must be parameters for decoding, which must have a fatal impact on the image. Based on the above, the code stream division of this paper is: the I frame (or IDR frame), SPS, PPS data of the I frame (or IDR frame), SPS, and PPS data of the video image, using a higher level protection for the class data; The remaining is two-class data, using low-level protection, and designing non-waiting for error protection programs to improve the quality of the reconstructed image.
2 empty block encoding (STBC)
The empty time code is a highly reliable channel encoding proposed to implement the MIMO system channel capacity. According to the channel characteristics, it effectively combines transmission diversity, receiving diversity, error correction coding, and modulation, which can achieve higher spectrum efficiency with lower transmission power, and can achieve the performance of approximation MIMO channel capacity. The empty time code can achieve better anti-comment performance in the same spectrum resource conditions compared to the system that does not employ an empty time.
The empty coding system not only provides a total set of gain, but also provides encoding gain, and has a linear detection complexity. For the sake of simplicity, this paper uses a 2-handed STBC system, which is the current most classic time code, which not only provides a total set of gain, but also provides encoding gain, and has Linear detection complexity. This program is also an empty time code, which is the most classic code.
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The received signal corresponding to the two times on the receiving antenna can be expressed as
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In the formula, the channel fading coefficients, W1 and W2 of the two emission antennas, respectively, the W1 and W2 are added to the receiving antenna, and the average value is 0, and the variance is N0. The detection can be completed through the largest likelihood decoding criteria.
3 H.264 empty coding scheme based on power allocation
3.1 Power Allocation Strategy
Suppose the total transmit power of the system is p, there is N root transmit antenna, and the transmit power on each antenna is P0, so there is
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In order to achieve the unparalleled error protection, the two-to-1 STBC system is assumed that the antenna 1 transmits a high priority stream stream, which allocates a large transmit power, and the distribution coefficient is K1, (k1>1); antenna 2 transmission low The priority level stream is allocated to which the smaller transmit power is assigned, and the distribution coefficient is K2, (k2<1), in order to ensure the total transmit power P of the system, the allocated coefficient K1, K2 should meet the following relationship
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In the formula, N1, N2 is the number of symbols transmitted on both antennas of each time slot, and N1 = N2 in the empty transmission;
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The equation (6) is the power allocation of the two emission antennas in the empty time.
3.2 Algorithm implementation of the H.264 empty coding scheme based on power allocation
It is assumed that the codeword matrix transmitted on both transmit antennas is shown in the formula (6), first multiplied power distribution coefficients (K1 or K2), and then fed into the empty time packet encoder. When the empty is encoded, it is finally transmitted through the transmit antenna, and the model is generally transmitted by the empty system (Y = HS + W) can be, and the received signal can be expressed as
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4 simulation results and analysis
In order to verify the superiority of the proposed scheme, the number of cascading models with the H.264 encoder is used in the case of the empty time-free code system, and the system is compared with the traditional 2-time 1 STBC is being shipped. All modulation symbols are selected from the BPSK constellation. . The channel is quasi-static Rayleigh fading channel, noise is an additive. In the test, the antenna 1 transmits a high priority stream, and the antenna 2 transmits a low priority level stream. This paper uses EB / NO size to indicate the signal-to-noise ratio of the transmission system (usually EB / NO represents a bit of average power spectral density of a bit of signal average energy and noise). The test sequence is "fo-reman" sequence, the image format is QCIF, the encoding mode is IPPP, the frame rate is 30F / S; generates the H.264 source file with the X264 encoder. The average PSNR value of reconstructing images is used as an indicator of image quality.
4.1 Comparison of error performance curves
Figure 1 shows the bit error performance of the proposed power allocated STBC system with a power distributed STBC system compared to the system's error performance compared to the power distributed STBC system. It is known from the figure that the performance of the antenna 1 is superior to the conventional STBC system, and the anti-error performance of the antenna 2 is slightly lower than the conventional STBC system. Since the antenna 1 transmits high-priority stream streams, the improvement of its anti-comment performance is bound to increase the quality of the reconstruction image. Therefore, the proposed scheme can improve the anti-commentary performance of high-priority streams without improving the total transmission power of the system, it is clear that this result is consistent with theoretical reasoning, thus verifying the rationality and superiority of the improvement plan.
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4.2 Reconstructing image subjective effect comparison
Figure 2 shows the comparison of two programs from subjective visual effects. When EB / NO = 18dB, the sixth scheme will rebuild the image as shown in Figure 2: Figure 2 (a) is the original image, Figure 2 (b) is a reconstruction image under the improvement scheme, Figure 2 (C ) For the reconstructed image under the traditional (2, 1) STBC scheme, by comparing the reconstruction image quality of the present scheme than the traditional (2, 1) STBC scheme.
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5 Conclusion
In order to solve the problem of reconstructing image quality in traditional wireless video transmission, this paper proposes a power allocated H.264 empty coding scheme, which divides the H.264 code stream into two parts, while maintaining In case of constant rhyme, the transmit power is dynamically allocated on two antennas to enhance the error performance of high-priority stream streams, thereby increasing reconstruction image quality. The simulation results show that the proposed scheme has obtained a better reconstruction image quality compared to the traditional STBC system. , Reading the full text, the technology area
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