3GPP RELEASE 15+ · NEW RADIO · IMT-2020

5G NR in a Nutshell
Engineer's Quick Reference

New Radio architecture, numerology, massive MIMO, gNB/5GC, KPIs, and procedures — the complete 5G NR reference in one page.

20
Gbps peak DL
1 ms
URLLC latency
FR1+FR2
Frequency ranges
Rel-15
First NR spec
01 — OVERVIEW

What is 5G NR?

🚀
eMBB
Enhanced Mobile Broadband · 20 Gbps peak · HD video, AR/VR
⚡
URLLC
Ultra-Reliable Low-Latency · <1 ms · Autonomous vehicles, surgery
🌐
mMTC
Massive Machine-Type Comm · 10⁶ devices/km² · IoT sensors
WHAT'S NEW vs LTE
✦Flexible numerology (multiple SCS options)
✦mmWave support (FR2: 24–52 GHz)
✦Massive MIMO / beamforming (up to 256TRX)
✦Network slicing on 5GC
✦PDCCH / DMRS fully redesigned
✦SA (standalone) + NSA deployment modes
FREQUENCY RANGES
FR1 — Sub-6 GHz
450 MHz – 7.125 GHz · Max BW 100 MHz · Coverage-first
FR2 — mmWave
24.25 – 52.6 GHz · Max BW 400 MHz · Capacity-first
DEPLOYMENT OPTIONS (3GPP ARCHITECTURE)
NSA Opt.3x
LTE anchor + NR
SA Opt.2
5GC + gNB only
SA Opt.4/7
5GC + NR + LTE
Most operators begin with NSA Option 3x (LTE anchor, NR adds capacity). Migration to SA Option 2 enables full 5GC features: network slicing, edge compute, URLLC.
02 — ARCHITECTURE

5G System Architecture

5G SYSTEM (5GS) — SERVICE-BASED ARCHITECTURE
📱
UE
Uu
gNB 🗼
CU-CP
RRC/PDCP-C
CU-UP
PDCP-U/SDAP
DU
RLC/MAC/PHY
RU
RF/PHY-low
N1/N2/N3
5GC Network Functions
AMF
Access & Mobility
SMF
Session Mgmt
UPF
User Plane
UDM
Subscriber DB
PCF
Policy
NSSF
Network Slicing
N6
🌐
DN
Data Network
💡 Key difference from LTE: gNB splits into CU (Centralised Unit) + DU (Distributed Unit) + RU (Radio Unit). 5GC uses a Service-Based Architecture (SBA) where NFs communicate via REST APIs over the Service Bus (SBI). No more monolithic MME/SGW.
03 — AIR INTERFACE

NR Air Interface

FLEXIBLE NUMEROLOGY — µ (MU) PARAMETER
µ SCS (kHz) SLOT (ms) USE CASE RANGE
0 15 1.0 eMBB sub-6, backward compat FR1
1 30 0.5 eMBB, most deployed sub-6 FR1
2 60 0.25 URLLC / mmWave FR1 / FR2
3 120 0.125 mmWave eMBB FR2
4 240 0.0625 mmWave reference signals only FR2
MODULATION (NR extends LTE)
QPSK 2 bits/sym · Cell edge
16-QAM 4 bits/sym
64-QAM 6 bits/sym
256-QAM 8 bits/sym · High SINR
1024-QAM 10 bits/sym · Rel-16 mmWave
MASSIVE MIMO / BEAMFORMING
NR enables large antenna arrays. Beamforming steers energy toward UE, improving SINR and capacity.
Sub-6 GHz typical64T64R
mmWave typical256T256R
Beamforming typeAnalog + Digital
CSI-RS portsUp to 32
MU-MIMO layersUp to 8 DL
04 — PROTOCOL STACK

NR Protocol Stack

RRC
System info · RRC setup/reconfig · Measurement config · Beam management · Connection release · Paging
SDAP
NEW in NR · Maps QoS flows to DRBs · Reflective QoS mapping · Replaces LTE's QCI bearer model with flow-based QoS
PDCP
Header compression (ROHC) · Ciphering / integrity · Duplication for URLLC · Data split for CA / DC
RLC
Segmentation & reassembly · ARQ (AM mode) · UM for URLLC · TM for broadcast
MAC
HARQ (16-process DL, 8 UL) · Scheduling · BSR/PHR · BWP switching · Beam failure recovery
PHY
OFDM DL + UL (no SC-FDMA) · LDPC (data) / Polar codes (control) · Massive MIMO · Beam sweeping · SSB
LDPC
Replaces Turbo code for data channels. Lower complexity at high throughput.
POLAR CODES
Used for control channels (PBCH, DCI, UCI). First-ever polar code deployment.
SDAP (NEW)
5G introduces QoS flow IDs. SDAP maps flows → radio bearers based on 5QI.
05 — PERFORMANCE

Key Performance Indicators

KPI TARGET THRESHOLD FORMULA / NOTE
NR RRC Setup SR > 98% < 95% RRC Setup Success / Attempts
PDU Session Setup SR > 98% < 95% Replaces E-RAB from LTE
NR Call Drop Rate < 0.5% > 2% Abnormal PDU releases / Total PDUs
DL Throughput > 100 Mbps < 30 Mbps Avg cell DL (busy hour, NR only)
SS-RSRP > -100 dBm < -110 dBm Sync Signal Reference Signal Received Power
SS-SINR > 0 dB < -3 dB Measured from SSB reference signals
HO Success Rate > 99% < 97% Intra-NR + NR↔LTE (NSA)
PRB Utilisation < 70% > 85% Used PRBs / Available PRBs × 100
SS-RSRP RANGES (NR)
Excellent> -80 dBm
Good-80 to -95 dBm
Fair-95 to -105 dBm
Poor< -110 dBm
IMT-2020 REQUIREMENTS
Peak DL throughput20 Gbps
Peak UL throughput10 Gbps
User-plane latency4 ms (eMBB)
URLLC latency1 ms
Connection density10⁶/km²
06 — PROCEDURES

Key Procedures

INITIAL ACCESS (NR)
1
SSB Detection — UE detects Sync Signal Block (PSS/SSS/PBCH). Up to 64 beams swept per 20 ms.
2
MIB / SIB1 — UE decodes PBCH for MIB, then SIB1 for cell access parameters (RACH config).
3
RACH (4-step) — Msg1 preamble → Msg2 RAR → Msg3 RRC Setup Req → Msg4 Contention Resolution.
4
Registration — AMF authenticates, assigns 5G-GUTI, allocates PDU session via SMF/UPF.
NR HANDOVER
1
A3/A5 Trigger — UE L3 measurement report. Same events as LTE but with beam-level granularity.
2
Xn HO Request — Source gNB-CU sends Xn HO Request (Xn = X2 equivalent in NR).
3
RRC Reconfiguration — UE commanded to random access to target cell. Beam selection included.
4
Path Switch (AMF) — N2 path switch. UPF updated. Source gNB releases UE context.
07 — CHANNELS

NR Channel & Signal Structure

DOWNLINK
PDSCH Physical DL Shared Channel — user data (LDPC)
PDCCH DCI — scheduling grants, DCI formats 0_0–1_1
PBCH MIB carried every 20 ms inside SSB
SSB New: PSS+SSS+PBCH+DMRS — beam scanning signal
CSI-RS Channel estimation, beam management, RRM
UPLINK
PUSCH UL data — CP-OFDM and DFT-s-OFDM (PAPR reduction)
PUCCH UCI: HARQ-ACK, SR, CSI reports (Formats 0–4)
PRACH 4-step or 2-step RACH (2-step from Rel-16)
DMRS Front-loaded DMRS (slot position 2 or 3) — faster demod
SRS UL sounding, beam management, reciprocity calibration
SSB (SYNC SIGNAL BLOCK) — KEY NR CONCEPT
Periodicity
20 ms (default)
Max beams FR1
8 SSBs/burst
Max beams FR2
64 SSBs/burst
Bandwidth
20 RBs (FR1)
Symbols
4 OFDM symbols
Purpose
Cell search, beam selection, timing
08 — QUICK REFERENCE

Values & Parameters Cheatsheet

NR BANDWIDTH (FR1)
5 / 10 / 15 / 20 MHzSCS 15/30 kHz
25 / 30 / 40 / 50 MHzSCS 15/30 kHz
60 / 70 / 80 / 90 MHzSCS 30 kHz
100 MHzMax FR1
NR BANDWIDTH (FR2 mmWave)
50 / 100 MHzSCS 60/120 kHz
200 MHzSCS 60/120 kHz
400 MHzMax FR2
CA aggregationUp to 8 CC
RRC STATES (NR)
RRC_IDLE — DRX, no context, paging monitored
RRC_INACTIVE — New in NR: context stored at gNB + AMF, fast resume
RRC_CONNECTED — Active session, fully scheduled
INACTIVE enables faster resume (< 10 ms) vs IDLE (~100 ms)
TIMING VALUES (µ=1, SCS 30 kHz)
Frame10 ms
Subframe1 ms
Slot0.5 ms (14 symbols)
Mini-slot2 / 4 / 7 symbols
HARQ processes DL16 (vs 8 in LTE)
SLOT FORMATS (TDD)
DDDSU Config-0: 5-slot period
DDDSUDDSUU Config-1: 10-slot
D=DL, U=UL, S=Special (mixed). Flexible per-symbol TDD allocation in Rel-15+.
COMMON FAILURE CAUSES
⚠SSB detection failure → poor coverage / beam misalign
⚠RACH failure → contention / insufficient PRACH resources
⚠mmWave blockage → sudden link loss, beam failure
⚠NSA anchor drop → both LTE and NR sessions lost
⚠High PRB utilization → scheduler congestion, latency spike