5G NR Frame Structure
Numerology, Slots & Timing Scaling
The Analytics of Numerology ()
In 5G NR, the term Numerology refers to the configuration of subcarrier spacing (SCS) and cyclic prefix. The SCS is defined by the exponential scaling law:
Where is the numerology index. As increases, the symbol duration decreases proportionally, defined as . This is the fundamental mechanism that allows 5G to scale from wide-area coverage to ultra-responsive industrial control.
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 .
The slot count follows the scaling law:
For , there is 1 slot/subframe. For (mmWave), there are 8 slots/subframe, each lasting only 0.125ms.
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.
TDD Timing: Static vs. Dynamic
Most 5G deployments utilize Time Division Duplexing (TDD), where the same frequency is used for both Uplink (UL) and Downlink (DL) at different times.
Mini-Slots: The Preemption Mechanic
A standard slot contains 14 OFDM symbols. However, for Ultra-Reliable Low-Latency Communication (URLLC), 5G NR introduces Non-slot based scheduling.
The URLLC Preemption Flow
When an urgent packet arrives, the gNodeB can perform Preemption. It stops an ongoing eMBB (mobile data) transmission mid-slot, punctures the resource grid, and inserts a 2-symbol Mini-slot.
Latency Impact: 1ms (LTE) → 0.5ms (NR Slot) → 0.1ms (NR Mini-slot)
PRB Geometry: The Resource Grid
Regardless of numerology, a Physical Resource Block (PRB) consists of 12 consecutive subcarriers. In the frequency domain, the sub-carrier spacing determines the total bandwidth occupied. For example, at , a 100MHz carrier provides 273 PRBs, each spanning 360kHz.