During a calibration phase {HEAD ~ a training signal} is injected digitally into {TAIL ~ the digital} to analog converter of the transmit path 
is injected digitally into
During a calibration phase { HEAD ~ a training signal } is injected digitally into { TAIL ~ the digital } to analog converter of the transmit path
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH