The asynchronous two-way point-to-point link setup protocol (LSU) is used to set up a link between two stations when one or both of them is scanning asynchronously. The asynchronous link setup protocol is the same as the synchronous one except for the following:
a. the call may be transmitted at any time.
b. the call is preceded by the “capture probe”
The capture probe, sent after the the LBT (Listen Before Transmit) interval, comprises repeated blocks of known symbols that will be recognized by the scanning receivers so that they will stop scanning and wait to receive the real call PDU (Protocol Data Unit) which immediately follows the capture probe section; the called station will reply sending a request confirm PDU. The capture probe must last long enough so that every scanning receiver will have a chance to receive it, thus its duration depends on the number of frequencies (N) in the scan set and on the minimum dwell time dmin: more precisely, it shall be ≥ dmin(N+2).
6,1,0,7,1,2,1,6,3,2,0,2,5,5,2,7,3,1,0,4,7,7,7,7,2,6,5,6,6,7,0,2,
0,1,2,5,6,1,7,7,4,0,4,7,4,5,4,4,1,4,2,2,2,4,6,7,3,4,5,5,1,0,3,0
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| Fig. 2 - ACF of the capture block section |
