LTE Uplink Coverage Enhancement Techniques Based on Enhanced TTI Bundling

In the Long Term Evolution (LTE) system, there is limited on uplink average data rate the cell edge users for the power limitation and the inherent short Transmission Time Interval (TTI) length of the cell edge users. TTI bundling scheme was presented for the VoIP service in the LTE Release 8 specifications to solve the cell coverage problem. But the R8 TTI bundling is restricted to bundles of 4 TTIs, QPSK modulation and allocations up to 3 PRBs, which impose restrictions on the support of the medium data rate service. In this paper, several TTI bundling enhancement schemes with different RTT, HARQ process number, TTI bundled size and the maximum number of HARQ retransmission are discussed in detail and evaluated by the link-level simulation. The simulation analysis proves that TTI bundling enhancement schemes can effectively improve uplink coverage performance in LTE system.