求翻译：圖4(a)所示為一個16-QAM訊號星座圖，且每一符元皆有唯一映對的資料位元內容，反觀16-QAM延伸星座圖方案，則是部分符元具有二個可映對的資料位元內容是什么意思？

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Figure 4 (a) are shown in a 16-QAM SIGNAL constellation figure, and each of the operator dollar are only image of the information bit, on the contrary 16-QAM extended constellation figure program, is that some operators dollar has two image of the information bit content

Chart 4(a) shows is a 16-QAM signal star map, also each Fu Yuanjie has only reflects to the material element content, instead observes 16-QAM to extend the star map plan, then is the partial symbol Yuan has two may reflect to the material element content

Figure 4 (a) a 16-QAM signal constellation diagram are shown in, and every Fu Yuan is the only map data content, looking back at extension 16-QAM constellation programme, it is part of Fu Yuan has two enantiomers on data contents

4 (a) one 16 - QAM訊號 constellations shown, and every incantation yuan all have only 資 material location yuan reflected to hold, extend the constellation scheme against ?6 - QAM, agreeing with yuan two 資 material location yuan that can be reflected holds partly