| Summary: | 碩士 === 國立中央大學 === 通訊工程學系 === 101 === In Long Term Evolution (LTE) Time-division Duplexing (TDD), some configurations which assign more subframes for Downlink (DL) are designed for heavy DL traffic. In such case, multiple Hybrid Automatic Repeat reQuest (HARQ) ACK/NACKs for different DL subframes shall be transmitted in a given Uplink (UL) subframe. This situation will become worse while Machine Type Communication (MTC) User Equipments (UEs) come into the LTE network because the number of the MTC UEs is very large, and MTC UEs have several particular features. Furthermore, in LTE-Advanced (LTE-A) TDD, the system supports the Carrier Aggregation (CA) which also makes the asymmetry problem of DL and UL subframes even worse. Indeed, to efficiently reduce the UL overhead caused by control signallings, the time bundling is adopted to combine multiple HARQ ACK/NACKs into an ACK/NACK by AND operation.
However, the time bundling increases the number of transmission times of each Transport Blocks (TBs) and also degrades the overall system throughput. This thesis proposes the Window-based Time Bundling (WBTB) to decrease the number of retransmission times and to increase the system throughput by strategically mixing the portion of TBs waiting for retransmission and the portion of newly coming TBs. These two kinds of portions are controlled by a so called moving window. The numerical analysis is also provided to prove that the simulation results match the results of the numerical analysis. The simulation results show that the WBTB can significantly improve the efficiency of HARQ feedback operation in LTE and LTE-A TDD. In other words, the overall throughput performance and the number of transmission times per TB are improved especially for a large number of MTC UEs existing in LTE and LTE-A TDD network.
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