6.2 Design and Analysis of FSA

6.2.1 Design of FSA

The main objective of FSA is to achieve an agreement among multiple candidates with lower coordination delay than SA and CSA. At the same time, FSA must be robust enough to deal with potential collision and unnecessary retransmission. Since all the inefficiencies in SA and CSA are mainly due to the use of multiple ACKs, we adopt a single ACK in FSA, which will be sent by the highest priority candidate in the set of successful receivers. This single ACK plays two roles. On one hand, it informs the sender that reception has been successful, which is the same as SA and CSA; On the other hand, it suppresses all the other lower priority candidates' attempts to forward the data packet. This is different from the ACKs in SA and CSA schemes, which are to help candidates share the information about the reception status. Accordingly, we also choose to use the channel assessment technique to detect the appearance of ACK.

The FSA works as follows. Each candidate waits for images/c06_I0006.gif before deciding whether it should broadcast ACK, where n is its priority order in the candidate set. So with a time delay of SIFS after the data packet was received, the highest priority candidate sends out an ACK. From that point in time, all the other candidates detect the channel for a time to tell whether they detect this ACK. If the answer is positive, they stop detecting ...

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