What TDD frame structures are used on Band n78?

The most common TDD frame structure on Band n78 is DDDSU (4:1 DL/UL ratio) with 30 kHz subcarrier spacing and 5 ms periodicity. This provides 80% downlink capacity. Some operators use DDDDDDDSUU (7:2) for higher downlink ratio or DDSUU (2:2) for lower latency and better uplink. The 'S' slot contains a DL portion, guard period, and UL portion. Japan uses a unique DDDDDDDSUUUUU (7:5) pattern for balanced DL/UL. TDD synchronization between operators is critical to prevent cross-link interference.

How does SUL extend Band n78 coverage?

Supplemental Uplink (SUL) uses a low-band carrier (n20 at 800 MHz or n28 at 700 MHz) for uplink transmission while the device receives on n78 downlink (3.5 GHz). Since mobile devices are power-limited (23 dBm), the uplink link budget determines cell edge. At 800 MHz, the uplink link budget is 12 dB better than 3.5 GHz, extending n78 coverage by approximately 3 dB per doubling. This translates to 30-50% more coverage area per cell. SUL is mandatory for rural n78 deployment where site spacing exceeds 2 km.

What is the relationship between Band n77 and n78?

Band n78 (3300-3800 MHz) is a subset of Band n77 (3300-4200 MHz). A device supporting n77 can operate on n78 frequencies, but not vice versa. In practice, n78 is used in Europe, China, and Korea (3.3-3.8 GHz allocations), while n77 is used in the US and Japan (allocations extend above 3.8 GHz). The distinction matters for device certification: a global device must support n77 to work everywhere, while a Europe-only device can support n78 alone.

Deployment Guide

Band n78 (3.5 GHz) Deployment Guide

/three-point-five gig/

Technical deployment reference for 5G NR Band n78 (3300 to 3800 MHz TDD), the most deployed 5G TDD band globally. Covers TDD frame structures (DDDSU, DDDDDDDSUU), slot format configuration, Supplemental Uplink (SUL) with low-band anchors for coverage extension, and the n77/n78 subset relationship for global device certification.

Band: n78 (3300 – 3800 MHz)

Superset: n77 (3300 – 4200 MHz)

Focus: TDD Frame & SUL Design

TDD Frame Structure Design

The TDD frame structure on Band n78 determines the DL/UL capacity split, latency, and inter-operator synchronization requirements. European operators have harmonized on DDDSU (4:1) with 30 kHz SCS, providing a good balance of downlink throughput and acceptable uplink latency. The choice of frame structure is one of the most consequential deployment decisions for TDD 5G networks.

Cross-link interference is the critical constraint: if adjacent operators use different TDD patterns, their uplink and downlink transmissions interfere with each other. This requires regulatory coordination, typically mandating a common frame structure within each country. Japan's unique DDDDDDDSUUUUU pattern provides more uplink slots but requires all operators to synchronize.

TDD Frame Structure Comparison

DDDSU (Europe standard):
DL ratio: 75% (slots 0-2 DL, slot 3 special, slot 4 UL)
Periodicity: 5 ms | Latency: 4.5 ms UL

DDDDDDDSUU (high DL):
DL ratio: 80% | More DL throughput
UL latency: 8 ms (longer wait for UL slot)

DDSUU (low latency):
DL ratio: 50% | Balanced DL/UL
UL latency: 2.5 ms | Best for URLLC

SUL Coverage Extension

Configuration	DL Band	UL Band	Coverage Gain	Use Case
n78 only	3.5 GHz	3.5 GHz	Baseline	Urban dense
n78 DL + n20 SUL	3.5 GHz	800 MHz	+30-50%	Suburban/rural EU
n78 DL + n28 SUL	3.5 GHz	700 MHz	+40-60%	Rural APAC

Common Questions

Frequently Asked Questions

What TDD frame structures are used on n78?

DDDSU (4:1, Europe standard, 75% DL, 5 ms). DDDDDDDSUU (7:2, high DL, 80%). DDSUU (2:2, balanced, 50%, best for URLLC). Japan: DDDDDDDSUUUUU (7:5, balanced). Inter-operator synchronization is mandatory to prevent cross-link interference.

How does SUL extend n78 coverage?

Low-band UL (n20 at 800 MHz or n28 at 700 MHz) while receiving n78 DL (3.5 GHz). 12 dB better UL link budget at low-band. +30 to 50% coverage area per cell. Mandatory for rural n78 where site spacing exceeds 2 km.

What is the n77/n78 relationship?

n78 (3300 to 3800 MHz) is a subset of n77 (3300 to 4200 MHz). n77 devices work on n78 frequencies, not vice versa. n78 for Europe/China/Korea. n77 for US/Japan. Global devices must support n77 for universal compatibility.

Related Terms

← Band n77 Detail Band n79 Detail →

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