A Go-back-N HARQ time bundling for Machine Type Communication devices in LTE TDD

In LTE TDD, some configurations which assign more subframes for Downlink (DL) are designed for heavy DL traffic. In such case, multiple HARQ ACK/NACKs for different DL subframes shall be transmitted in a given Uplink (UL) subframe. This situation will become worse while the Machine Type Communication (MTC) User Equipments (UEs) come into the LTE network because the number of the MTC UEs is very large and with several particular features. Indeed, to efficiently reduce the UL overhead caused by control signalling, 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 transmissions and also degrades the overall system throughput. In this paper, we propose the Go-back-N (GBN) time bundling to decrease the number of transmissions and to increase the system throughput by strategically mixing the transmitted Transport Blocks (TBs) and the new coming TBs controlled by the transmit window. The simulation results show that the GBN time bundling can significantly improve the efficiency of HARQ feedback operation in LTE TDD. In other words, the overall throughput performance and the number of transmissions are improved especially for a large number of MTC UEs in LTE TDD network.