3GPP Release 17 & Release 18: 5G NR Subcarrier Spacing (SCS) and Frame Structure

The 5G NR (New Radio) framework is designed with a flexible and scalable Subcarrier Spacing (SCS) and frame structure to support diverse deployment scenarios and diverse end-user applications.

5G NR Subcarrier Spacing (SCS)

  • The Subcarrier Spacing (SCS) in 5G NR is a crucial component of the 5G network that allows for the accommodation of various use cases by adjusting the frequency domain’s subcarrier spacing. The SCS is designed to be scalable to support different deployment scenarios, frequency bands, and use cases, ranging from low-bandwidth, wide-area coverage to high-bandwidth, low-latency.
  • 3GPP has specified subcarrier spacing of 15, 30, 60, 120 ,240, 480 and 960 KHz.
    • Larger SCS allows for lower latency and supports higher-frequency bands, suitable for use cases requiring quick data transmission, like autonomous vehicles or real-time gaming.
    • Smaller SCS is ideal for lower-frequency bands and increased coverage, which benefits use cases like IoT deployments where a wide area needs to be covered.
  • 3GPP introduced the SCS of 480 and 960 KHz in release 17 and the SCS of 960 KHz also represents the highest SCS in release 18. A new NR mmwave frequency band (n263: 57–71GHz) has been specified in release 17 to utilize two new SCS of 480 and 960 KHz which support extremely high data rates and very low latency communications. The new NR frequency band n263) is for unlicensed operation and subject to regional and/or country specific regulatory requirements.

5G NR Frame Structure

  • The frame structure in 5G NR is designed to be highly adaptable, supporting different bandwidths, to cater diverse service requirements. The 5G NR radio frame has а fixed duration of 10 ms, which are divided into subframes, slots and OFDM symbols. The 5G NR subframe has а fixed duration of 1 ms so there are always 10 subframes within each radio frame.

  • The 5G NR slot duration and OFDM symbol duration depend upon the Subcarrier Spacing (SCS). This means that the number of slots per subframe and the number of OFDM symbols per subframe also depends upon the Subcarrier Spacing (SCS) .

    • For instance, the 5G NR slot duration for SCS of 15 KHz is 1 ms, while it is 15.625 μs for SCS of 960 KHz specified in release 17.
  • The number of OFDM symbols per slot is always 14 when using the Normal Cyclic Prefix NCP) and is always 12 when using the Extended Cyclic Prefix(ECP).

  • Here I try to depict the 5G NR frame structure based upon the different Subcarrier Spacing (SCS) covering 3GPP release 15 to 18.

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