SCS
Subcarrier Spacing: the frequency separation between OFDM subcarriers in NR. Values are 15, 30, 60, 120, or 240 kHz (2^mu x 15 kHz), selected based on the deployment scenario.
Subcarrier spacing is the knob that defines an NR numerology — every other timing parameter follows from it. The values scale as 2^mu × 15 kHz: 15, 30, 60, 120, 240 kHz. Widen the spacing and the OFDM symbol gets proportionally shorter, so the slot duration shrinks too. That's the lever behind NR's flexible latency.
What an engineer needs to remember is which spacings are allowed where. In FR1 you use 15, 30, or 60 kHz; in FR2, data uses 60 or 120 kHz (120 kHz is the common choice) and SSB runs at 120 or 240 kHz. The choice is a balancing act. Narrow spacing gives long symbols with a roomy cyclic prefix — better for delay spread in big cells and lower bands. Wide spacing shortens slots for lower latency and survives the Doppler and phase noise that worsen at high frequency, but the cyclic prefix shrinks with it, so it tolerates less delay spread. There's no universally "best" SCS; it's matched to band and scenario.
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