| 摘要 |
Improvements in the detection of TWACS outbound message signals. A first improvement involves matching some (or all) of the intermediate points in an outbound preamble occurring between bits of the preamble currently being detected. This reduces the possibility of a false synchronization and therefore decreases the probability of missing outbound message signals. A second improvement is to require some or all of the known preamble bits to exceed a predetermined threshold where both the thresh-old and which bits are adjustable. An additional approach is using 4-8 additional buffers in a transponder to detect preamble patterns in the outbound message. Each half cycle of the outbound message waveform requires entering a bit only into the buffers active for the particular frame of reference in which the message is being transmitted, since only buffers for that frame of reference are employed. The process continues until all bits specified to be sent, based on the length of the outbound message, are extracted. A CRC is then performed for the message. Using this method eliminates the problem of inbound messages being detected as outbound messages, and the resulting "blindness" of the transponder. It further makes the transponders less sensitive to noise which currently causes the transponder to detect a preamble when there is none, resulting in a valid outbound message being missed. |
