A symbol detector converts initial symbol estimates of {HEAD ~ received symbols} to soft estimates for {TAIL ~ decoding} 
A symbol detector converts initial symbol estimates of { HEAD ~ received symbols } to soft estimates for { TAIL ~ decoding }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL