essing time requirements in downlink reception [5]. UE capability 15 kHz 30 kHz 60 kHz 120 kHz Capability 1 for 8 symbols 10 symbols 17 symbols 20 symbols mobile = 0.57 ms = 0.36 ms = 0.30 ms = 0.17 ms broadband UE Capability 2 for 3 symbols 4.5 symbols 9 symbols low latency UE = 0.21 ms = 0.186 ms = 0.186 ms by the transmission network and by the core network. We assume 1 ms transport latency in LTE. The assumption for 5G is local content close to the base station, which makes the transport latency close to zero. These estimates show that HSPA can achieve a round trip time (RTT) of approximately 20 ms, LTE with pre-allocated scheduling can achieve 11 ms RTT, and 5G even below 1 ms RTT with these processing time assumptions. These latencies are optimistic val- ues without retransmission and with minimum transport delays. The RTT evolution is illustrated in Figure 10.8. Example live network measurements with smartphones in Helsinki are shown in Figure 10.9, with HSPA showing 19 ms average latency and LTE showing 11 ms average latency. These measurements illustrate that it is possible to get close to the estimated RTTs also in live networks when the core network gateway and server are close to the base station (Tables 10.6 and 10.7). UE processing time is one of the contributing factors in the latency. 5G UE require- ments for PDSCH decoding are defined in 3GPP for mobile broadband UE called Processing Capability 1 and for low latency services called Processing Capability 2. The processing time is dependent on the subcarrier spacing. For low latency UE, 10.4 Latency Round trip time Downlink transmission Uplink transmission Frame alignment Scheduling UE processing BTS processing Transport and core Figure 10.8 Round trip time evolution. Figure 10.9 Round trip time HSPA 19 ms LTE 11 ms measurements in live network. Ping 19 ms Jitter 5 ms + Ping 11 ms Jitter 2 ms Table 10.7 UE processing time requirements in uplink transmission [5]. UE capability 15kHz 30 kHz 60 kHz 120 kHz Capability 1 for 10 symbols 12 symbols 23 sym