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