. Figures 10.52 and 10.53 show the performance for short (0.14 ms) and long (1 ms) TTIs, considering both the case with low offered traffic and high offered traffic. One of the reported performance metrics is the smoothed RTT of TCP packets. It is observed that the best performance is achieved for a short transmis- sion time at a low offered load. This is due to the lower air interface latency that helps to quickly overcome the slow-start TCP phase. The higher control channel overhead from operating with a short transmission time is not a problem at the low offered load. Short TTI (mini-slot) Figure 10.50 Preemptive scheduling for LLC traffic with short TTI (LLC, Low Latency Communication; eMBB, enhanced Mobile BroadBand). Long TTI for eMBB traffic Preemptive scheduling Figure 10.51 Preemptive scheduling taking resources from eMBB users. Frequency (PRB) Time slots 10.8 Packet Scheduling Algorithms Figure 10.52 Smoothed median TCP level round trip time [ms] TCP packet round trip time for eMBB file download. Low load High load Mini-slot TTI, 0.14 ms Two slot TTI, 1 ms Figure 10.53 Median TCP level user TCP level user throughput [Mbps] throughput for eMBB file download. Low load High load Mini-slot TTI, 0.14 ms Two slot TTI, 1 ms However, at the high offered load case, the best performance is observed for the case with a long transmission time. This is due to the fact that using a longer transmission time results in higher average spectral efficiency with lower control channel overhead. The results clearly show the benefit of being able to dynamically adjust the transmission time size. Next, we present the downlink performance for a mixture of mobile broadband and LLC type of traffic. In this particular example, there are on average five active mobile broadband users per macrocell, performing a download of a 500 kB file size, using TCP. As soon as one of the mobile broadband users finishes its file download, the user is removed, and a new one is generated at a random location. In addition, there are on average 10 LL