说明：  针对译码转发系统中传统的用户选择策略复杂度过高的问题，提出一种半分布式用户选择策略(SDUS策略)．协作分集；用户选择；中断性能；运算复杂度
(A semi—distributed user selection scheme(SDUS scheme)is proposed to reduce the high compleXity in conventional user selection schemes in decodPand—forward(DF)systems．cooperative diversity；user selection；outage perfornlance；computational complexity)