n78 / 3.5 GHz Mid-Band 5G — What Operators Actually Configure

n78 is the workhorse band of mid-band 5G — 3.3 to 3.8 GHz, deployed in India, Europe, China, US C-band. What does an actual production cell look like under the hood? Here's the config that ships in 2026.

Channel Bandwidth & Numerology

Default: 100 MHz channel @ 30 kHz SCS (μ=1). 273 PRBs. Single carrier (no CA needed at this BW).

Why 30 kHz: short enough slot (500 μs) for low latency; long enough CP (2.34 μs) for typical urban delay spread.

TDD Pattern

India / EU typical: DDDDDDDDDDDDFU (Format 28: 12 DL + 1 Flexible + 1 UL per slot). At 30 kHz SCS, 2 slots per ms = 1 ms TDD cycle. Strongly DL-biased, suiting consumer streaming.

Industrial / private 5G: DDDDDFUUUU (5 DL + 1 F + 4 UL) — more uplink for sensor data, robot control.

Operator-specific: some use 7DL+1F+2UL @ 5 ms cycle; others use 4DL+1F+5UL for fixed wireless access (FWA) where UL bottleneck matters.

BWP Configuration

Typically 2-3 BWPs configured:

• Initial BWP: 20-50 MHz centered on Point A — for cell-search and idle UEs.
• Default BWP: 50-100 MHz — UE fallback after timer.
• Active BWP: 100 MHz wideband — for active downloads.

UE switches initial→active when first data DCI arrives; switches active→default after bwp-InactivityTimer (typically 100-200 ms).

MCS Table Selection

MCS Table 2 (256-QAM) almost always enabled for n78. Most modern UEs support it; cell-edge UEs fall back to Table 1 (64-QAM) automatically via link adaptation.

Typical observed MCS distribution at city scale:

• MCS 0-7 (QPSK / 16-QAM): ~15% of UEs (cell-edge, high path loss)
• MCS 8-15 (16-QAM / 64-QAM): ~30% of UEs (mid-cell)
• MCS 16-23 (64-QAM / 256-QAM): ~40% of UEs (good signal)
• MCS 24-27 (256-QAM): ~15% of UEs (close to gNB, high SINR)

Beam Configuration

Massive MIMO: typical 32 or 64 element AAU. Number of SSB beams: 8 (FR1 default for 3.5 GHz). UE sees up to 8 SSB-level beams; finer CSI-RS beams come during P2 refinement.

Beam-tracking period: 5-10 ms typical (every 5-10 SS bursts). For mobile UEs, beam recalibration via CSI-RS happens every ~1 ms.

HARQ Configuration

16 parallel HARQ processes per UE. k1 timing: 4-7 slots typical (PUCCH ACK 2-3.5 ms after PDSCH). k2 timing: 1-3 slots (UL grant → PUSCH).

HARQ-ACK codebook: typically dynamic Type 2 (better at sparse scheduling). Type 1 semi-static used for predictable URLLC traffic.

Power & EIRP

Sub-6 GHz n78 typical EIRP: 60-70 dBm (~1-10 kW EIRP) for macro cells. Many countries cap EIRP to 78 dBm for 64T64R massive MIMO.

UE max output: 23 dBm (Power Class 3) for typical phones; 26 dBm (Power Class 2) for high-power UE / FWA CPE; 31 dBm (Power Class 1.5) for premium FWA.

Real Throughput on n78

Peak DL: 1.2-1.5 Gbps (4×4 MIMO, 256-QAM, MCS 27). Typical user DL at mid-cell: 200-500 Mbps. Peak UL: 200-300 Mbps (single layer).

5G NR n78 in real deployment vs spec peak: ~70-80% achievable on a clean cell, dropping to 30-40% in congested traffic.

If you're tuning n78 cells, the CafeTele 5G NR PHY Advanced course covers MCS Table 2, BWP switching, dynamic TDD, and beam tracking in detail. $29 lifetime.