A novel solution to improve uplink synchronization control in OFDM-based mobile networks

In OFDM-based mobile networks, uplink synchronization is essential in order for an eNB (evolved Node Base station) to handle a variety of interference issues. To guarantee uplink synchronization control, the HARQ (Hybrid Automatic Repeat-reQuest) mechanism is applied into the process of its TAC (Timing Advance Command) transmission in current standards. But HARQ conflicts with the TAC scheduling mechanism in nature, because TAC control information is typically scheduled for transmission at the end of a synchronization period in order to save signaling overhead by reducing TAT (Time Alignment Timer) restart frequency. To handle the conflict between the extra HARQ retransmission delay and TAC scheduling mechanism, we propose a novel TO (Time Offset)-TAC solution that can remove the side effects from TAC information delivery caused by the extra delay of HARQ retransmission. We conduct system-level simulation experiments to evaluate our proposal's performance gain. Results demonstrate that our solution can avoid losing synchronization due to its TAT expiration, at a slight penalty of signaling overhead. This study is the first effort at addressing how to guarantee uplink time alignment in the control layer, which is the basis for suppressing interference from "time-staggered symbols" among multiple paths.