Numerology — From Fixed to Flexible
LTE: fixed 15 kHz subcarrier spacing, 1 ms TTI, 14 OFDM symbols/slot, no choice. 5G NR: 7 numerologies (μ=0..6) with SCS = 2^μ × 15 kHz, slot length scales 1 ms / 2^μ — from 1 ms (μ=0) down to 15.625 μs (μ=6). The same hardware can serve both extremes.
Channel Coding — LDPC + Polar Replace Turbo + Convolutional
LTE used Turbo codes for data and tail-biting Convolutional codes for control. NR uses LDPC for data (PDSCH, PUSCH) and Polar codes for control (PDCCH, PBCH). LDPC decodes ~10× faster than Turbo (parallel belief propagation vs serial component decoders), enabling URLLC sub-ms latency. Polar achieves Shannon-bound performance at small block sizes.
Bandwidth — 20 MHz Cap to 400 MHz
LTE max single-carrier bandwidth: 20 MHz. NR: 100 MHz in FR1, 400 MHz in FR2. Carrier aggregation extends both, but NR's native single-carrier already covers 5× the bandwidth.
MIMO — From 4×4 to 256×256
LTE supported up to 8×8 MIMO. NR supports 256×256 in FR2 (massive MIMO with full-dimension beamforming). The codebook structure is also entirely new (Type I, Type II, eType II) with explicit beam-index reporting.
Beam Management — Implicit to Explicit
LTE assumed roughly omnidirectional UE antennas; no explicit beam concept. NR introduces SSB beam-sweeping (up to 64 beams), TCI states for beam binding, QCL Type D for spatial-Rx beam reuse, and BFR (beam failure recovery) as a first-class procedure.
Resource Grid — BWPs Replace Full-Carrier Operation
LTE: UE always operates across the entire carrier. NR: UE monitors a Bandwidth Part (≤ 275 PRBs), can have up to 4 DL + 4 UL BWPs configured, switches via DCI/timer. Saves UE battery by 30-50%.
Frame Structure — 10 ms Same, Everything Else Different
Frame stays 10 ms (backward compatibility). But within the frame: NR slots are flexible (1 ms / 2^μ); mini-slots (2/4/7 sym) enable URLLC; TDD is symbol-level configurable (D/U/F per symbol via DCI 2_0); 56 predefined TDD formats vs LTE's 7.
Reference Signals — UE-specific to UE-specific Beam-specific
LTE used cell-specific RS (CRS) — every UE saw the same pilot. NR uses UE-specific DMRS — each scheduled UE gets its own pilots, on its own beam. Plus NR adds CSI-RS (channel sounding), PT-RS (phase tracking), TRS (tracking), PRS (positioning).
What Stayed Compatible
10 ms frame · 14 symbols/slot (Normal CP) · 1 ms subframe (always) · OFDM modulation · 1024-QAM ceiling (LTE Rel-15 introduced too) · κ = 64 (T_s/T_c ratio bridges LTE timing).
Frequently Asked Questions
Is 5G NR backward compatible with LTE at the physical layer?
Frame timing is identical (10 ms), but PHY procedures are not interoperable. EN-DC (E-UTRA-NR Dual Connectivity) lets a UE camp on LTE and use NR as a secondary leg, but the radios run independently.
Why did 3GPP replace Turbo with LDPC for 5G data?
LDPC enables parallel decoding (sub-ms latency for URLLC) and has no error floor at high SNR. Turbo decoders are inherently serial because of the interleaver, capping their throughput.
Can I use my LTE PHY skills for 5G NR?
Most concepts transfer (OFDM, scheduling, MIMO, HARQ). What's new: numerology flexibility, LDPC/Polar coding, BWPs, QCL/TCI states, mini-slots, and beam management. The CafeTele 5G NR PHY Advanced course is designed to build directly on LTE knowledge.