 sessions simultaneously on two different UPF functions. The mobile temporarily has two IP addresses for an IP session. SSC Mode 1 SSC Mode 2 SSC Mode 3 @IP @IP1 Before handover After handover Before handover After handover Before handover After handover Figure 3.16. Service continuity. For a color version of this figure, see www.iste.co.uk/launay/5g.zip 3.3. References All standards can be downloaded from the ETSI website: https://www.etsi.org/ standards. 3GPP TS 23.502 5G - Procedure for the 5G System; Version 15.3.0 Release 15 NG-RAN and 5G-NR 3GPP TS 37.340 5G NR - Multi-connectivity; Overall description; Stage-2 Version 15.8.0 Release 15 3GPP TS 38.211 5G NR - Physical Channels and modulation; Version 15.8.0 Release 15 3GPP TS 38.321 5G, NR - Medium Access Control (MAC) protocol specification; Version 15.6.0 Release 15 3GPP TS 38.331 5G, NR - Radio Resource Control (RRC); Protocol specification; Version 15.6.0 Release 15 3GPP TS 38.413 5G, NG-RAN - NG Application Protocol (NGAP); Version 15.6.0 Release 15 Campos, J. (2017). Keysight: Understanding the 5G NR physical layer [Online]. Available at: https://www.keysight.com/upload/cmc_upload/All/Understanding_the_5G_NR_Physical, Layer.pdf. 5G-NR Radio Interface - The Physical Layer 4.1. 5G-NR radio interface 4.1.1. OFDM waveform OFDM modulation consists of modulating orthogonal subcarriers (Figure 4.1). f1 f2 f3 Figure 4.1. OFDM modulation on three subcarriers The two subcarriers c1(t) and c2(t) are orthogonal if and only if their scalar product is null: Orthogonality conditions impose that 1-1/1 where of is the subcarrier spacing and T represents the duration of a symbol. For a color version of all the figures in this chapter, see www.iste.co.uk/launay/5g.zip NG-RAN and 5G-NR: 5G Radio Access Network and Radio Interface, First Edition. Frédéric Launay. C ISTE Ltd 2021. Published by ISTE Ltd and John Wiley & Sons, Inc. NG-RAN and 5G-NR Thanks to orthogonality, OFDM modulation offers good spectral efficiency and provides resilience to the frequency selective fadi