Transmission Diversity Schemes for Downlink Control Channel in 5G

The 5th generation(5G) cellular network could provide ever best performance to mobile customers, with higher system capacity, massive connections and lower transmission latency. Physical downlink control channel(CCH) is a core element due to its crucial function to the data transmission in the whole system. In particular, the transmission diversity scheme for downlink control channel is one fundamental aspect to influence the coverage and spectral efficiency. Considering the amount of resources to be used for reference signal will be greatly compressed compared with long term evolution (LTE) system, the existing transmission diversity schemes for CCH, such as spatial frequency block codes (SFBC) and resource element (RE)-based random beamforming would suffer severe block error rate (BLER) loss due to their sensitivity to channel estimation error. To improve the BLER performance, this paper proposes the resource element group (REG) bundle-level random beamforming with the adaptive size of the REG bundle to the aggregation levels of CCH. Moreover, corresponding search space design is further proposed to prevent increase of the CCH blocking. The effectiveness of the proposed methods is validated by link level simulation and numerical analysis.