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