We experimentally investigate a highly integrated, polarization qubit based quantum key distribution system
over a real-world, 12.4 km fiber link. Our system implements quantum frames, i.e. alternating sequences of
high intensity optical pulses (classical data) and faint ones (qubits or quantum data). The classical data enables
compensation of time-varying birefringence in the fiber link, and will facilitate synchronization, time tagging,
and allow extending point-to-point quantum key distribution systems to networks. Our system can be clocked
at 980 MHz, and has demonstrated good stability over 37 hours operation. We also discuss high rate error
correction using a low-density parity-check code.