5G NR Frame Structure
Numerology, Slots & Timing Scaling
The Concept of Numerology ($\mu$)
In 5G NR, the term Numerology refers to the configuration of subcarrier spacing (SCS) and cyclic prefix. The SCS is defined as $15 \times 2^\mu$ kHz, where $\mu$ is an integer ranging from 0 to 4.
The 10ms Radio Frame
Despite the flexible numerology, the top-level timing remains constant: A Radio Frame is always 10ms, divided into ten 1ms Subframes. The number of Slots per subframe, however, scales with $\mu$. For $\mu=0$, there is 1 slot/subframe. For $\mu=3$ (mmWave), there are 8 slots/subframe.
Flexible Numerology Simulator
Subframe (1ms) Slot Scaling Analysis
Scientific Context: As Carrier Spacing (SCS) doubles, the slot duration halves. In mmWave ($\mu=3$), we have 8 slots per millisecond, allowing the gNodeB to make scheduling decisions every 125 microseconds—essential for self-driving vehicles and high-speed industrial robotics.
Mini-Slots and URLLC
For mission-critical latency, 5G NR introduces Non-slot based scheduling (Mini-slots). A mini-slot can be as short as 2 OFDM symbols, allowing the gNodeB to preempt ongoing data transfers to transmit urgent control or telemetry data with sub-millisecond turnarounds.
Resource Blocks (PRB)
Regardless of numerology, a Physical Resource Block (PRB) consists of 12 consecutive subcarriers. In the frequency domain, a 100MHz carrier at 30kHz SCS provides approximately 273 PRBs. This grid is the atomic unit of the 5G air interface.