| For several years, with the rapid development of embedded technology, the function of mobile intelligent terminal has becoming more and more rich. In addition, People are also raising demand for multimedia information. The video transmission in wireless channels is the hot spot of multi-media technology, and many scholars both at home and abroad are interested in the technology of coding and decoding the video information and the transmission of it.At present, the research for wireless video transmission have focused on the3G network, or use the WI-FI to build the broadband local area network to transmit videos. In recent years, people pay more attention to the development of the internet of things. But the main function of the internet of things technology is only to send the small data collected by the sensors. With the development of microelectronics and RF technology, the transmission rate of ZigBee has reached up to640kbps. H.264/AVC, the new generation video compression standard, has greatly improved the video compression performance. In the same visual quality, the compression efficiency of H.264improves about50%than the MPEG-4. Therefore, the low bit rate of video coded stream sent in ZigBee network is worth studying.Due to the wireless channel’s features in limited bandwidth and big fluctuation, this paper paid attention to the scheme of the rate control for the low bit rate video transmission in wireless channels. This method made the output bit rate of the H.264video coder more stable. Then transmission quality in wireless channels was increased. According to the rate control for JM software, this article proposed an algorithm for bits allocation in the frame level based on the gray histogram and computing the quantization parameter with the stabilizing factor. The experiment results turn out to show that the algorithm improved the accuracy of the rate control, and the output bit rate is more stable than the standard algorithm. Therefore, it is more acceptable used in the wireless channels. The algorithm we proposed has an average increase of0.25dB Signal-to-Noise to the standard rate control algorithm, so it also improved the quality of videos.In order to understand the transmission characteristics of the video in the ZigBee channel, we build a ZigBee network environment based on Network Simulator. The frequency band of the network environment is2.4GHz and the maximum transmission rate is250kbps. An intermediate connection has be established between the ZigBee environment and encoder, thus it made the H.264codec and ZigBee network composed of a video transmission model. By comparing the simulation results, when the bit rate is not more than128kbps, the video streams transmitted in a single hop network have low error rate, the decoded image can be accepted. Compared with the standard algorithm, the algorithm we proposed control the rate better in the transmission.In order to verify the performance of low bit rate video transmitted in the ZigBee channels, we build a single hop network using three ZigBee devices, design a receiver using the ARM11embedded platform, and also design a sender using a computer. So a real platform for the transmission is made by the three parts. Compared with the results, the error rate is3%to5%when the bit rate is128kbps and is1%to2%when the bit rate is64kbps. Specially, when the bit rate is more than256kbps, the error rate is more than50%. Therefore, the low bit rate video transmitted in ZigBee wireless network can be achieved. |
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