As a user roams about his cell, he will at times reach {HEAD ~ the boundary} of {TAIL ~ good coverage} 
of
As a user roams about his cell , he will at times reach { HEAD ~ the boundary } of { TAIL ~ good coverage }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL