  We study a problem of sequential frame synchronization for a frame
transmitted uniformly in $A$ slots. For a discrete memoryless channel (DMC),
Venkat Chandar et al showed that the frame length $N$ must scale with $A$ as
$e^{N \alpha(Q)} > A$ for the frame synchronization error to go to zero
(asymptotically with $A$). Here, $Q$ denotes the transition probabilities of
the DMC and $\alpha(Q)$, defined as the synchronization threshold,
characterizes the scaling needed of $N$ for asymptotic error free frame
synchronization. We show that the asynchronous communication framework permits
a natural tradeoff between the sync frame length $N$ and the channel (usually
parameterised by the input). For an AWGN channel, we study this tradeoff
between the sync frame length $N$ and the input symbol power $P$ and
characterise the scaling needed of the sync frame energy $E = N P$ for optimal
frame synchronisation.
