中文摘要：

直升机应急起降中紫外光通信数据决定了助降过程的安全性，需要对数据码流中的重要数据提供更强保护。针对该问题，结合重复信息块方法对扩展窗函数（EWF）法，提出一种分步式非均等数据保护的LT码（SUEP—LT）。在二进制删除信道下对重复信息块方法、EWF方法和SUEP—LT进行仿真和对比，结果表明，SUEP-LT编码方式具有更强的非均等保护特性，在牺牲少量整体数据可靠性情况下可明显提高重要等级数据的可靠性，保障直升机起降中重要数据的优先可靠传输，增强直升机起降的安全性。

英文摘要：

Ultraviolet communication data determines the security of helicopter emergency landing. In order to provide greater protection for More Important Bits（ M IB）, a novel approach to provide Unequal Error Protection （UEP） based on the block duplication method and improved Expanding Window Fountain （EWF） codes over erasure channels, named SUEP-LT code, is developed and discussed. Block duplication method, EWF and SUEP-LT code are simulated and compared over binary erasure channel. Experimental results show that, the SUEP-LT code has better performance in UEP. It can yield lower Bit Error Rates （BER） for the MIB, sacrificing the least reliability of the whole data. Priority and reliability of the important data are guaranteed. Thus, the security of helicopter emergency landing is improved.