lexity. The latency components in HSPA, LTE, and 5G networks are shown in Table 10.5. The main solution for minimizing latency is a shorter transmis- sion time interval (TTI). A shorter TTI makes the transmission time shorter, and it also makes the buffering and processing times shorter. 5G supports the shortest TTI 0.125 ms, while LTE Release 8 has 1 ms TTI and HSPA has 2 ms TTI. 5G latency can be decreased further by using mini-slot transmission. It is considered later in this section. Uplink and downlink transmission takes one TTI. There is also a frame alignment time needed in the transmission buffer until the next TTI starts. The average buffering time is half TTI both in the uplink and downlink. We assume that at a minimum, PDCCH transmission and waiting time until Physical Uplink Shared Channel (PUSCH) is needed in LTE with a 3 ms delay. We assume that 5G can use grant-free transmission without any scheduling delay. Scheduling delay would be greater if the UE must send a capacity request and the base station must run a packet scheduling decision. Data encoding and decoding take some time in the transmitter and receiver. Processing times will decrease in 5G simply because of the shorter TTI. The UE processing time requirement in LTE is more than 2 ms, and in 5G it is as low as below 0.2 ms. We also assume that the base sta- tion processing time correspondingly decreases. In practice, some latency is also caused 10 5G Performance Table 10.5 HSPA, LTE, and 5G two-way latency (=round trip time) components. 5G with short Delay component LTE Release 8 TTI transmission Downlink transmission (ms) 0.125 Uplink transmission (ms) 0.125 Downlink frame alignment (ms) Uplink frame alignment (ms) 0.0625 Scheduling (ms) 3-18b) UE processing (ms) BTS processing (ms) Transport and core (ms) 2 (including RNC) 0.1 (for local content) Total (ms) 11-28 RNC, Radio Network Controller. a) Shared Control Channel (SCCH) transmissions. b) Scheduling period + capacity request + scheduling decision + PDCCH signaling. Table 10.6 UE proc