Study on Flexible TTI Scheduling for LAA Systems

In this paper, we investigate the designation of transmission time intervals (TTls) in a LAA system. With considerations of backward compatibility and feasibility, two shortened TTI schemes are proposed to increase the flexibility of frame structure in the unlicensed spectrum. Additionally, the advantage of the designed shortened TTI schemes on the DL transmission performance is also studied for different cases of packet size. More specially, it is found that the system using the proposed shortened TTI schemes is able to reach the start point of a transmission more quickly when sending small packets. Therefore, the performance of small packets can be improved. Differently, the proposed shortened TTI schemes are able to reduce the padding time when transmitting large packets, so that the performance, especially the utilization of the maximum channel occupancy time (MCOT), can be improved. The simulation results verify that remarkable performance gain can be achieved under the proposed shortened TTI schemes. In addition, based on the analysis in this paper, it is suggested that shortened TTI should be included in the future designation of LAA systems in order to achieve better performance.