TTI bundling enhancements for medium data rate PUSCH in LTE-Advanced systems

In order to improve network performance and cell-edge UE experience, a study item (SI) on "LTE coverage enhancements" has been proposed and approved for LTE-Advanced. In this SI, it was concluded that the coverage of medium data rate PUSCH (Physical uplink shared channel) is poorer than other LTE channels, with significant gap observed. Therefore, coverage improvement for medium data rate PUSCH is greatly desired for LTE operators. TTI bundling was first specified in LTE Release 8 to improve uplink coverage, especially for low rate data transmission. However, it cannot be applied to medium rate data transmission. In this paper, we propose an enhanced TTI (Transmission time interval) bundling scheme for medium data rate PUSCH. The proposed scheme can enable TTI bundling for PUSCH transmission with medium rate data, and achieve higher scheduling flexibility as well as larger turbo encoding gain. Link-level simulations validate that compared with PUSCH transmission without TTI bundling, TTI bundling enhancements can obtain 1.1-1.9 dB gain in terms of required SNR, and improve UE throughput by 24%-35%.