Summary
Dynamic Spectrum Sharing is a way to use one frequency range for LTE and 5G at the same time. Important technical foundations were introduced in 3GPP Release 15, the first 5G release. Resources are assigned dynamically according to user demand. An operator can keep serving LTE devices on a carrier while adding 5G NR devices, rather than reserving the whole carrier permanently for one technology. Efficiency depends on load and implementation. [1]
DSS: making better use of spectrum during a technology transition
Each transition to a new mobile generation raises the question of which technology should use which frequencies. Traditionally, new generations have been deployed in separate frequency blocks, as with 2G, 3G and 4G. These decisions have consequences for years because changing a frequency range's use takes planning. Refarming reallocates existing spectrum to another technology. The split is especially important in lower bands, where spectrum is comparatively limited.
The LTE/NR coexistence capabilities introduced in Release 15 simplify this transition. DSS initially allows both technologies to share the carrier. As more traffic moves to NR, the operator can later dedicate it entirely to NR. [1]
DSS takes advantage of the fact that both 4G LTE and 5G NR use OFDM-based technology. Scheduler algorithms coordinate radio resources between the two as the balance of 4G and 5G devices changes over time. LTE and NR users can therefore coexist on one carrier, with its resources allocated dynamically between them.
What simultaneous use means in DSS
The scheduler coordinates LTE and NR allocations in time and frequency. Some signals are also required independently of current user traffic. One important example is LTE Cell-specific Reference Signals (CRS). In a common DSS implementation, NR data transmission accounts for their positions through rate matching, avoiding the resource elements they occupy. This coordinates both systems' use of the shared carrier. [2]
DSS can open existing LTE frequencies to additional NR use. Radio equipment, software, supported bands and device capabilities must be compatible. LTE devices continue to use LTE on the shared carrier, while suitable NR devices use 5G NR.
The technology is often considered for broad 5G coverage at low frequencies. These frequency ranges can cover large areas. Data rates depend on the available radio resources and their allocation between LTE and NR.
How DSS affects usable capacity
DSS uses resources for both technologies' signalling. Its effect on usable capacity depends on reference signals, control channels, configuration and traffic distribution, among other factors. Operators weigh shared use against separate carriers or refarming for each site. [1]
DSS describes spectrum use over the radio link. Integrated Access Backhaul (IAB) explains how a small mobile cell forwards its data to the rest of the network. In that context, in-band and out-of-band refer to access and backhaul.
DSS in the 700 MHz band
The 700 MHz range can support shared LTE and NR use. Germany auctioned the relevant mobile frequencies in 2015. Low frequencies suit rural coverage because, under comparable conditions, they provide favourable conditions for long radio range. Terrain, antennas and buildings also determine the usable range. [7]
NR supports FDD and TDD. The 700 MHz band n28 uses FDD, while n78 uses TDD. Check a device's specifications for the bands and combinations it supports. [3]
An operator can use suitable 700 MHz spectrum jointly for LTE and NR or dedicate it to NR. The network configuration determines which approach is used.
DSS and 5G Standalone describe different aspects of a network
Low-frequency coverage can provide a base layer for wide-area 5G. DSS describes shared spectrum use; Standalone (SA) and Non-Standalone (NSA) describe network connectivity and architecture. With appropriate support, DSS can be used in either architecture. [4]
Depending on configuration and device support, the network can add other carriers, for example through NR Carrier Aggregation. Each carrier carries the signals needed for its operation. Carrier Aggregation, LTE/NR Dual Connectivity and DSS are distinct techniques. [4]
5G DSS and voice calls
Ericsson and Qualcomm demonstrated an early 5G DSS data call in 2019. It used low-band frequency division duplex (FDD) spectrum, Ericsson Radio System hardware and software, and a mobile test device with the Qualcomm Snapdragon X55 5G Modem-RF System.
The laboratory test took place in Ottawa, Canada. An LTE smartphone and the 5G test device used the same FDD spectrum for their data connections. Here, a data call means establishing a data connection. Voice transmission depends on the voice services supported by the network and device. [6]
How voice calls are carried
Whether a smartphone carries a call over LTE or NR depends on the network's voice solution and device support. The following approaches are used:
- VoLTE: Voice travels over LTE. This is also the usual basis for calls in common 5G NSA deployments.
- VoNR: Voice travels over NR and the 5G core network. Both network and device must support it.
- EPS Fallback: A device on an SA network moves to LTE for the call and uses VoLTE there.
These voice services also require the relevant IMS support. Call quality depends on the voice solution and radio conditions. [5]
Sources and editorial review
Originally published on 17 January 2020. Technically reviewed and selectively updated on 26 October 2026. The original illustration was retained. Historical laboratory trials are identified as such; this article contains no original capacity measurements.
- [1] Samsung Networks: Dynamic Spectrum Sharing – Technical White Paper, January 2021
- [2] MediaTek: Practical Evaluation of Dynamic Spectrum Sharing, 2022
- [3] ETSI / 3GPP: TS 38.101-1 V18.5.0, Table 5.2-1: NR bands and duplex modes
- [4] MediaTek: 5G NR and 4G LTE Coexistence – DSS Deployment Guide, March 2020
- [5] Ericsson: Voice and communication services in 4G and 5G networks
- [6] Ericsson GmbH, press release on Presseportal: Ericsson, Swisscom and Qualcomm enable an efficient 4G-to-5G transition in Switzerland with Spectrum Sharing, 11 November 2019
- [7] Bundesnetzagentur: Completed spectrum award procedures – 2015 auction