Wireless Video Communication Scheme Based on MIMO Technology and H.264 Code

Aiming at the problem of low reconstructed image quality in traditional video transmission, a new scheme of H.264 bitstream transmission is proposed. At the source end, according to the importance difference of H.264 code stream, it is divided into two parts. MIMO channel is used to transmit video signal. Under the condition of keeping the total transmission power constant, the transmission power is dynamically distributed on two antennas. Simulation results show that the proposed scheme effectively improves the reconstructed image quality at the receiver under the same channel conditions.

0 Introduction

In recent years, with the development and application of high-speed broadband wireless technology, wireless video communication is becoming a field of widespread concern. How to significantly improve the spectrum efficiency in wireless communication system to meet the increasing demand of communication capacity has become a widespread concern and urgent problem to be solved all over the world. Multiple input multiple output (MIMO) technology can effectively alleviate the above contradiction by increasing the number of antennas at the transmitter and receiver. The system uses multiple antenna arrays at the transmitter and receiver to obtain spatial multiplexing and diversity gain, and space-time code (STC) fully exploits the MIMO system capacity, which is an effective means to improve the bit error performance of the whole system. On the other hand, as a new generation of video compression coding standard, h.264/avc has high coding efficiency and good network performance

Complex affinity has been widely valued by scholars at home and abroad. The combination of MIMO technology and h.264/avc will greatly improve the reliability of wireless video communication.

1. Bitstream segmentation of H.264

H. The code stream of 264 is encapsulated by network abstraction layer (NAL unit). Each nal unit has a specific data type. It contains a byte nal unit header and an original byte sequence load. The importance of the current nal unit is indicated by the NRI in the nal unit header information. The higher its value, the more important the nal unit is. In the semantics of H.264 nal layer, nal is used_ ref_ IDC to indicate the priority of the current nal.

Based on this idea, for the H.264 code stream in annexb data format, the nal of I frame or IDR frame (immediate refresh frame), SPS (sequence parameter set) and PPS (image parameter set) in the sequence_ ref_ The IDE value of 3 indicates that the nal unit in which it is located has a high importance level. Once this kind of data is lost, it will have a fatal impact on video reconstruction. Because I frame is the intra coding mode and it is used as the reference frame of P frame, only its accurate transmission can ensure the complete decoding of the image. SPS and PPS are necessary parameters for decoding, and its loss is bound to have a fatal impact on the image. Based on the above considerations, the bitstream segmentation method in this paper is as follows: the data of I frame (or IDR frame), SPS and PPS which play an important role in video image reconstruction are regarded as a kind of data, and the high-level protection is adopted for this kind of data; The rest is class II data, which adopts low-level protection, and on this basis, unequal error protection scheme is designed to improve the quality of reconstructed image.

2 space time block coding (STBC)

Space-time code is a high reliability channel coding proposed to realize the channel capacity of MIMO system. According to the channel characteristics, it effectively integrates the technologies of transmit diversity, receive diversity, error correction coding and modulation. It can achieve high spectral efficiency communication with low transmission power and approach the performance of MIMO channel capacity. Compared with the system without space-time coding, space-time code can obtain better anti error performance under the same spectrum resources.

Space-time coding system not only provides full diversity gain, but also provides coding gain, and has linear detection complexity. For simplicity and generality, this paper adopts a STBC system with two transmitters and one receiver. This system is also the most classical space-time code at present. It not only provides full diversity gain, but also provides coding gain, and has linear detection complexity. This scheme is also the most classical space-time code, and its coding structure is

The received signal corresponding to two consecutive time slots on the receiving antenna can be expressed as

Where H1 and H2 are the channel fading coefficients from the two transmitting antennas to the receiving antenna respectively, W1 and W2 are the complex Gaussian white noise added to the receiving antenna, the mean value is 0 and the variance is N0. The detection can be completed by the maximum likelihood decoding criterion.

3 H.264 space-time coding scheme based on power allocation

3.1 power allocation strategy

Assuming that the total transmission power of the system is p, there are n transmission antennas, and the transmission power on each antenna is P0, so there is

In order to realize unequal error protection, for the STBC system with two transmitters and one receiver, it is assumed that antenna 1 transmits a high priority code stream and allocates a large transmission power to it, and the allocation coefficient is K1, (K1 > 1); Antenna 2 transmits low priority code stream and allocates small transmission power to it. Set the allocation coefficient as K2, (K2