| Nowadays, the transmission of audio, video and other multimedia data over wireless networks has become a hot topic. However, due to various defects of wireless channels, including high bit error rate, large transmission latency and limited actual transmission rate, it is a key and difficult problem to improve the video transmission reliability in wireless networks. Recently, as a kind of fault-tolerant technique, erasure codes are used for video transmission in wireless networks, which do not have retransmission latency, but have limited error-correction abilities and are very sensitive to wireless channels. On the other hand, reliable UDP is based on traditional UDP, which can guarantee transmission reliability and has strong channel adaptability but large retransmission latency. Therefore, the combination of erasure codes and reliable UDP will achieve their complementary advantages.First, we use UEP Raptor as the erasure code, which has advantages of standard Raptor code, including unlimited data rate, linear complexity and good error tolerance. Besides, by keeping the GOP (Group Of Pictures) redundancy invariant but increase the redundancy of the key frames in the GOP, UEP Raptor provides video transmission with unequal error protection. Secondly, we realize reliable UDP in the respects of connection mechanism, acknowledgement mechanism and retransmission mechanism as an application layer protocol, and use it for video transmission in wireless networks. Finally, we design the video sender to retransmit the lost data packets of key frames in the GOP, and adjust the data transmission rate and redundancy of Raptor code according to the feedback information of the video receiver. In this way, UEP Raptor and reliable UDP are combined to guarantee the reliable video transmission in wireless networks.We build a wireless video transmission system to test and analyze our proposed method. The results show that the combination of UEP Raptor and reliable UDP can effectively improve the real-time quality of video transmission over wireless networks. |
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