[Tinyos-help] Can the synchronous ackowledgement of AM layer solve the hidden terminal problem?

[PolyUComp]

It has been documented that with synchronous ackowledgement, if the receiver gets a packet with no CRC error and addressed for the receiver or the broadcast address, then the receiver will transmit a short bit pattern indicating acknowledgment. 

My question is what happens when the receiver receives the packet with the presence interferences from a hidden terminal,  with such a mechanism? In my opinion, the receiver will not recognize the incoming packet well and refrain from sending the acknowledgement. Hence, the sender knows its failure of its message sending and the presence of a hidden terminal.

AMSendMsg.sendDone (TOS_MsgPtr msg, result_t result) {
   if (result == SUCCESS && msg->ack == 1)
      dbg(DBG_USR2, "successful message delivery detected by synchoronous acknowledgement!\n");
  else
      dbg(DBG_USR2, "failed message delivery detected by synchoronous acknowledgement!\n");
}

Does it means the synchronous ackowledgement can address the hidden terminal problem? 

My second question is that is this mechanism really applicable to broadcast? What if all the receivers of a broadcast packet sends their own acknowledgement? Will a collission happens therefore? What's the real semantics of the acknowledgement bit msg->ack to the sender, when sending a broadcast packet? Does it means at least one receiver sent out its acknowledgement?

thank your for your help.

shawn
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