111 inuriy practical t a&, the aim i s to iecognise knoRii signal for 1115, which irieaiii identifying wliat point in t irirc thry emir and distinguishing ti-tein irorri otlirr signal fo
Trang 1111 inuriy practical t a&, the aim i s to iecognise knoRii signal for 1115, which irieaiii identifying wliat point in t irirc thry emir and distinguishing ti-tein irorri otlirr signal forrrrs Exainplcs of thcse tasks are sp 11 recognition objcrt recognition
sinciple: In tlre sirnpleist rase wc \\rilnt to recogni5e when a sigiial corrrponent
7 r r ( t ) occiirs That niearrs we :ale dealiirg with B sigiiA of t h t forni
r ( f ) = m(t - t o ) j8.72) wlierr the f m r t i o i r m ( t ) i s known hut thc lime l o by ~ l r i c h nr(t) is drifted i5 iiot ltnown For exarnple, we could trarrsiriit wri izconsttc~ 51gi-1al ? i t ( t ) , a i d with
r ( l ) , tlrteimiiiih tlie ~inlrnc~wri time taken for it to retiirn
To achieve Iliis, the ieerivrtl signal s(2) is filtcwd with a n LTI-sy
a11 irripulsc response derived from the signal forin ) U ( 1):
The rniiius sign in m( -t) cancels out) the reversal of the signal ii-i convolution, so t,he o i t t p t signal is
(S.75)
The integral owr thc always positive d u e m2( r - to) must be at It-
than y ( t ) cxccpt a t f - t o Suilable choice of thc sigrial m ( l ) can nialtc thc w l u r
of y(t0) iiiix*h greater than all other vahes o f ~ ( t ) , and thcn the unkiiowii tiiiic
ognised as the peak in tlie sign;d y ( / ) Figiire 6.31 shows the
( 8 7 3 ) arid a pc->ak igerneiit of a filtcr with ilnpnlsr respo
this kind is c;tllcv~ i~ m i z t ~ k e d filter