自己想弄明白的，在網上找到了:
複用和多址的聯繫和區別在Glossory of Telecommunication Terms中的解釋
multiplexing (MUXing): The combining of two or more information channels onto a common transmission medium.
multipoint(multiple) access: Access in which more than one terminal is supported by a single network termination.(比如一個基站支持多個移動臺的情況)。
duplex operation: Operating method in which transmission is possible simultaneously, in both directions of a telecommunication channel.
由此可見，multiplexing翻譯爲“複用”較好；deplexing翻譯爲“雙工”較好；multiple access翻譯爲“多址”不是很好，其實準確地講應當是“多點接入”。
Medium與Resource也是應當區分的。
A typical characteristic of wireless communications is that the medium, that is, the air interface, must be shared among different applications (e.g., radio and television, mobile cellular systems, LANs), and within a certain application between different users (radio and television stations, subscribers).
Generally, a medium offers a number of resources each of which or a combination of which can be subdivided into several channels by the process of multiplexing.
在無線通信中，the medium is the air interfaces,the resource is SPACE，TIME， 複用，漢語詞典意思是重複運用。把multiplex翻譯成複用，感覺有點不妥。multiplex並不是真正的重複使用。比如說FDM，並不是重複使用同一個頻率段，而是每個用戶佔據一定的帶寬，帶寬是不重疊的。可以說是複用了整個帶寬。但並不是頻率複用。
真正的頻率複用，比如說蜂窩系統，這個就是頻率的重複使用了~干擾足夠小的2個小區是使用相同的頻率段的~
可以把這種譯法當做是約定俗成。
就像Pulse Code Modulation（脈衝編碼調製），其實並不是一種調製方式，而是一種模擬到數字的轉換方法。
歡迎補充。 ^_^
注一：
空分複用(SDM，Space Division Multiplexing)即多對電線或光纖共用1條纜的複用方式。比如5類線就是4對雙絞線共用1條纜，還有市話電纜(幾十對)也是如此。能夠實現空分複用的前提條件是光纖或電線的直徑很小，可以將多條光纖或多對電線做在一條纜內，既節省外護套的材料又便於使用。