2.1 Frame Structure/Duplex Mode
- Support for New Subcarrier Spacings NR adopts a radio access scheme called Orthog- onal Frequency Division Multiplexing (OFDM)( OFDM: A multi-carrier modulation format where information signals are modulated with orthogonal subcarriers. A type of digital modulation scheme where information is split across multiple orthogonal carriers and transmitted in parallel. It can transmit data with high spectral efficiency), which is the same scheme used in To adapt to services requiring low latency and to enable the use of higher frequencies (including millime- ter-wave (Millimeter waves: Radio frequency band with wavelengths inthe range of 1 to 10 mm) frequencies), NR supports higher sub- carrier ( Subcarrier: Each carrier in a multi-carrier modulation system that transmits bits of information in parallel over multiple carriers) spacings of 30, 60, 120, and 240 kHz based on the LTE subcarrier spacing of 15 kHz. Note that a subcarrier spacing of 240 kHz is only used for Synchronization Signal (SS) (SS: A physical signal enabling the mobile station to detect)/Physical Broad- cast CHannel (PBCH) blocks, as described later (In addition, the SS/PBCH block does not support
a subcarrier spacing of 60 kHz).
When user equipment initially accesses the net- work, it detects an SS/PBCH block by assuming a subcarrier spacing that can be set in this carrier,
and based on the PBCH detected in this block, it identifies the subcarrier spacings of the control/ data channels, etc.
2.2 Frame Structure
In NR, multiple OFDM symbols are used to construct slots, subframes, and frames. A slot consists of 14 OFDM symbols for the given sub- carrier spacing, a subframe is defined as a 1 ms interval, and a frame is defined as 10 subframes. These relationships are shown in Figure 1. In the frequency domain, a resource block con- sists of 12 consecutive subcarriers for the given subcarrier spacing. In NR, unlike LTE, the frame structure is not dependent on the duplex mode . In other words, it uses a common frame structure regardless of the duplex mode.
NR provides much greater flexibility than LTE in the uplink and downlink patterns of Time Divi- sion Duplex (TDD) communication. It is possibleto semi-statically or dynamically set various up- link/downlink patterns by the system information and/or by user-specific higher layer signalingand/or L1 signaling It is also possible to perform TDD communica- tion without using higher layer/L1 signaling to indi- cate the uplink/downlink patterns. The user equip- ment can recognize the direction of uplink/downlink communication based on periodic transmission and reception that are configured by higher layer sig- naling and/or indicated by dynamic signaling in the physical layer.