  Calibration of the polarization basis between the transmitter and receiver is
an important task in quantum key distribution (QKD). An effective
polarization-basis tracking scheme will decrease the quantum bit error rate
(QBER) and improve the efficiency of a polarization encoding QKD system. In
this paper, we proposed a polarization-basis tracking scheme using only
unveiled sifted key bits while performing error correction by legitimate users,
rather than introducing additional reference light or interrupting the
transmission of quantum signals. A polarization-encoding fiber BB84 QKD
prototype was developed to examine the validity of this scheme. An average QBER
of 2.32% and a standard derivation of 0.87% have been obtained during 24 hours
of continuous operation.
