Three use cases, one standard
5G NR was designed around three fundamentally different use cases, each demanding capabilities that a single optimised system could not simultaneously achieve in LTE. IMT-2020 (the ITU framework that 5G NR satisfies) defines them as:
These three use cases have contradictory requirements. eMBB needs wide channels and complex modulation. URLLC needs minimal latency and extreme reliability. mMTC needs tiny devices and multi-year battery life. NR's flexible numerology — configurable subcarrier spacing, slot structure, and channel coding — is the mechanism that allows one air interface to serve all three.
What is actually new in NR vs LTE
LTE (Long Term Evolution) was already a capable system. 5G NR is not a clean break — many design principles carry over. But several fundamental changes were made:
| Feature | LTE (4G) | 5G NR |
|---|---|---|
| Subcarrier spacing | Fixed 15 kHz | 5 numerologies: 15/30/60/120/240 kHz |
| Max channel BW | 20 MHz | 100 MHz (FR1), 400 MHz (FR2) |
| Channel coding (data) | Turbo codes | LDPC codes |
| Channel coding (control) | Tail-biting convolutional | Polar codes |
| Massive MIMO | Limited (up to 8 ports) | Up to 256 ports, full 3D beamforming |
| mmWave support | No | Yes (FR2: 24–52 GHz) |
| Self-contained slots | No | Yes — DL + UL in same slot (URLLC) |
| Standalone core | EPC | 5GC (5G Core) — service-based architecture |
| RRC_INACTIVE state | No | Yes — power-efficient IoT connectivity |
| Forward compatibility | Limited | Reserved fields, NR-U, sidelink built in |
3GPP Release history — what each one added
| Release | Date | Key 5G NR additions |
|---|---|---|
| Rel-15 | 2018 | First complete NR spec. NSA + SA. eMBB baseline. FR1 + FR2. |
| Rel-16 | 2020 | URLLC enhancements, NR-V2X, NR-U (unlicensed), IAB (backhaul), positioning, industrial IoT. |
| Rel-17 | 2022 | NR-Light (RedCap for IoT), sidelink enhancements, NTN (satellite), multi-SIM, 52–71 GHz FR2-2. |
| Rel-18 | 2024 | 5G-Advanced. AI/ML in RAN, XR optimisations, network energy efficiency, NTN IoT. |
| Rel-19 | 2025+ | 5G-Advanced continued. Foundation for 6G research items. |
Standalone vs Non-Standalone
When 5G first deployed, operators reused their existing LTE core network (EPC) as an anchor. The UE connects to LTE for control plane (signalling) and uses NR for data. This is Non-Standalone (NSA) — Option 3x in 3GPP terms.
Standalone (SA) uses the full 5G Core (5GC). NR handles both control and data. SA enables all 5G features — network slicing, URLLC, RRC_INACTIVE, and true end-to-end 5G QoS. This site covers SA operation throughout.
What this site covers
Every page on this site follows the same cell: a UE on band n78 (3.5 GHz), 100 MHz channel, 30 kHz SCS, connecting to a cell with PCI 442. The same numbers flow through every section — from the GSCN sweep that finds the SSB frequency, through PSS/SSS, MIB decoding, CORESET derivation, SIB1, RACH, RRC connection, scheduling, and beamforming.
This is not a summary of 5G. It is a derivation. Every number is computed from the 3GPP specifications cited on each page. If you follow every section, you will be able to decode a live 5G capture by hand.