关于CSMA/CA与Wi-Fi中继器同信道干扰的疑问

嘿，这个问题提得太到位了！我之前看到过一篇挺有意思的文章《Why Don't Wi-Fi Repeaters Work Very Well - OK, Why Do They Suck?》，里面作者聊到的中继器同信道干扰的点，当时也让我停下来琢磨了好久。

作者原文里这段描述特别直观：

'However - when the repeater is talking to one of its own clients, then the root AP can take that opportunity to talk to one of its own clients too. So now you have both the root AP and the repeater talking to a separate client at the same time...on the same channel - and there is no coordination going on between the repeater and the root AP...they will both transmit/receive with their client as they see fit. That's like two sets of conversations going on between two groups of people at the same time in close proximity (i.e. overlapping)....and the conversation for one group is just noise for the other group and vice-versa.....thats your interference.'

你问的正好是我当时的疑惑：CSMA/CA不就是用来避免这种冲突情况的吗？

其实问题出在「协同缺失」上。CSMA/CA的核心是「先听后说」——设备发送数据前会先检测信道是否空闲，确认没人用再发。但中继器和主AP是两个独立的设备，它们各自执行自己的CSMA/CA逻辑，却没有任何机制来同步彼此的通信计划。

举个生活化的例子：就像两个小组在同一个房间里聊天，每个人都遵守「别人说话时我不插嘴」的规则，但两个小组之间没有约定谁先聊、谁后聊。结果就是A组刚停下，A组的人开始说，同时B组的人也觉得现在没人说话，也开始说——这下就撞在一起了，两边的话都变成了对方的噪音。

放到Wi-Fi场景里，主AP和中继器各自检测信道状态，当其中一方和自己的客户端通信时，另一方可能刚好检测到信道「暂时空闲」（或者信号强度没达到触发载波侦听的阈值），就直接开始发送数据，最终导致同信道的信号互相干扰。CSMA/CA管得了单个设备的行为，管不了两个独立设备之间的协同调度，这就是中继器容易出现干扰的关键原因。

备注：内容来源于stack exchange，提问作者Nevesja