802.16d系统的视频跨层容错传输机制

Video error-resilient transmission mechanism using cross-layer design in 802.16d systems

为了提高IEEE 802.16d系统的吞吐量和无线信道的视频质量,提出了估计物理层正交频分复用(OFDM)符号错误程度的方法,设计了视频跨层容错传输机制。在物理层用幸存路径的平均量度实时估计OFDM符号错误程度,得到了数据错误级因子(Ef);MAC层根据容错门限和Ef值决定是否上传CRC校验出错的数据包。同时,应用层采用优化的分组级FEC算法恢复丢弃和出错的视频帧。实验结果表明,容错门限取值在0.02～0.06时可以达到用户可接受的视频峰值信噪比(PSNR)。与无容错传输功能的802.16d系统相比,本文设计的视频容错传输系统可在各种信道条件下获得更好的视频质量和更高的吞吐量。

In order to increase the throughput of IEEE 802.16d systems to improve the quality of video service,a method is proposed to evaluate the degree of error of Orthogonal Frequency Division Multiplexing（OFDM） symbols in the physical layer,and a cross-layer error resilient system for video transmission is designed.In the physical layer,the degree of error for OFDM symbols is calculated in the time domain from the mean metric of the survivor path and an error-level factor is defined.According to the error-level factor sent from physical layer and the threshold of error resilience,the MAC layer can decide whether or not the frame with CRC errors is passed to the upper layer.A packet-level FEC algorithm is designed to restore discarded and error affected video frames in the application layer.Experimental results indicate that the error-resilient system can guarantee the user acceptable video Peak Signal to Noise Ratio（PSNR）,when the error-resilient threshold value is within 0.02-0.06.Compared to the original IEEE802.16d,the error-resilient 802.16d proposed in this paper can support a larger throughput and a better quality video service.This conclusion also holds for different channel conditions.