To reduce the de⁃mapping complexity of cross⁃constellation QAM in G. HN standard, we first introduce a novel concept of contribution weight to evaluate the contribution of given constellation to the log⁃likelihood ratio. With its help, a low complexity de⁃mapping algorithm within shrunk search range is proposed. And then, some boundary conditions are analyzed and solved. Furthermore, an adaptive configuration of search range is also presented with the assistance of channel estimation. The simulation result validates that the proposed algorithm downsizes the search range without any sacrifice of performance. 2 048⁃QAM and 512⁃QAM shrink their average of searching constellations to 1�9% and 5�7% respectively of the whole constellations. Therefore, the proposed algorithm makes good tradeoffs between performance and complexity, and is expected to have important engineering value and widely application foreground.%为降低G．HN标准中十字星座QAM解映射的复杂度，首先引入对数似然比贡献权值，衡量参考星座点对解映射的贡献；提出十字星座QAM低复杂度解映射算法，搜索范围缩小为对数似然比贡献权值较大的参考星座点；讨论算法边界情况的搜索范围确定方法；研究信道估计辅助的自适应搜索范围选择方案．仿真结果表明，本文所提算法在获得与全搜索范围相同的误码性能前提下，减小平均搜索星座点数，2048⁃QAM和512⁃QAM解映射平均搜索星座点数仅为全搜索范围的1�9％和5�7％．简化算法较好的平衡性能和解映射复杂度，具有较大的工程应用前景．
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