The receiver compares the difference between {HEAD ~ the phase sector} of {TAIL ~ the present symbol} and the phase sector of a preceding symbol 
of
The receiver compares the difference between { HEAD ~ the phase sector } of { TAIL ~ the present symbol } and the phase sector of a preceding symbol
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH