Dynamic Spectrum Sharing (DSS): How LTE and 5G Share the Same Frequency Band

Spectrum is one of the most valuable and contested resources in wireless communications. Governments auction it, operators pay billions for it, and engineers spend years figuring out how to squeeze every last bit of efficiency out of it. When 5G arrived, it created a problem that no amount of engineering enthusiasm could easily solve: where do you find the spectrum to launch 5G when most of your usable low-band frequencies are already occupied by millions of active LTE subscribers?

Dynamic Spectrum Sharing (DSS) became the solution most operators reached for.

Key Takeaways

• What DSS Is: Dynamic Spectrum Sharing allows LTE and 5G NR to coexist and share the same frequency band simultaneously, with resources allocated dynamically based on real-time traffic demand.
• Why It Matters: Spectrum is a finite and expensive resource. DSS allows operators to launch 5G on existing LTE spectrum without waiting years for new spectrum allocation or disrupting existing 4G subscribers.
• The Trade-Off: DSS is not a free lunch. Running two systems on the same carrier introduces overhead – typically a 25% reduction in LTE performance and around 15% reduction in 5G NR performance compared to dedicated spectrum deployments.
• Coverage vs. Capacity: DSS is primarily a coverage tool, not a capacity tool. It is most useful for getting 5G signals into rural and suburban areas quickly, not for delivering peak 5G throughput in dense urban environments.
• What Comes Next: As operators refarm spectrum from LTE to 5G and acquire dedicated mid-band spectrum, DSS becomes less critical – but the concept of spectrum sharing is evolving toward 5G and 6G coexistence with Multi-RAT Spectrum Sharing (MRSS).

What is Dynamic Spectrum Sharing?

Dynamic Spectrum Sharing is a technology that allows LTE and 5G NR to share the same frequency band at the same time. Instead of dedicating a separate carrier for 5G – which would require either new spectrum or refarming existing LTE spectrum (and potentially disrupting service for 4G users) – DSS allows both technologies to operate on a single carrier, with the network dynamically allocating resources between them based on real-time traffic demand.

The key idea here is dynamic allocation. The allocation is not fixed. If there are more 5G users active at a given moment, the network assigns more resources to 5G. If 4G demand spikes, more resources shift back to LTE. This happens in real time, at the subframe level, invisibly to the end user.

DSS is standardised in 3GPP Release 15 and Release 16, and it operates on the principle of MBSFN (Multicast Broadcast Single Frequency Network) subframes in LTE – a mechanism that was originally designed for broadcast services but turns out to be a convenient way to carve out time slots for 5G NR transmission within an LTE carrier.

How Does DSS Work? A Simple Example

Imagine a highway with four lanes. Historically, all four lanes were reserved for cars (LTE). One day, motorcycles (5G NR) are allowed to use the same highway, but there is no additional space to build new lanes. DSS is the traffic management system that decides, in real time, how many lanes are available for cars and how many for motorcycles – based on how many vehicles of each type are currently on the road.

An operator has a 10 MHz carrier in the 850 MHz band, currently used entirely for LTE. They want to launch 5G but have no additional low-band spectrum. With DSS enabled, the base station broadcasts both an LTE cell and a 5G NR cell on the same 10 MHz carrier. When a 4G device connects, it sees an LTE cell and operates normally. When a 5G device connects, it sees a 5G NR cell and gets 5G service. The network dynamically decides which subframes carry LTE traffic and which carry 5G NR traffic, based on demand at that moment.

Both technologies get access to the same spectrum – just not always at the same time, and not always in equal measure.

Why Do Operators Need DSS?

The 5G rollout created a fundamental spectrum problem. The most desirable 5G frequencies – mid-band C-band spectrum around 3.5 GHz – offer an excellent balance of coverage and capacity. But acquiring mid-band spectrum takes time. Regulators need to identify it, operators need to bid for it in auctions, and existing users of that spectrum need to be cleared out. In many markets, this process takes years.

Meanwhile, operators were under commercial and competitive pressure to launch 5G as quickly as possible. The solution was to use the low-band spectrum they already owned – frequencies like 700 MHz, 850 MHz, and 1800 MHz – which already had excellent coverage, existing infrastructure, and a large installed base of LTE subscribers.

DSS allowed operators to do exactly this: flip on 5G in their existing low-band spectrum without decommissioning LTE service. T-Mobile in the United States used DSS extensively to cover large parts of its 600 MHz band with 5G while maintaining LTE service for the majority of its subscribers who still had 4G devices. Several European operators followed a similar path with their 700 MHz and 1800 MHz holdings.

Advantages of Dynamic Spectrum Sharing

Faster 5G rollout: DSS eliminates the need to wait for new spectrum allocation. Operators can activate 5G in their existing low-band carriers with a software upgrade to the base station, in many cases without new hardware. This dramatically compresses the time from 5G launch to broad geographic coverage.

No disruption to LTE subscribers: Because resources are shared dynamically, existing 4G users continue to receive service on the same carrier. The network manages the coexistence transparently without requiring operators to migrate subscribers or reduce LTE coverage.

Cost-effective deployment: In many cases, enabling DSS is a software upgrade to existing radio hardware. This avoids the capital expenditure of deploying an entirely separate 5G carrier on new spectrum – a significant advantage for operators with tight infrastructure budgets.

Wide-area 5G coverage: Low-band spectrum has inherently better propagation characteristics than mid-band or mmWave. By deploying 5G on 700 MHz or 850 MHz bands via DSS, operators can achieve 5G coverage across rural and suburban areas where higher frequency 5G signals would not reach.

Coexistence with legacy systems: DSS is designed to work alongside existing 2G, 3G, and LTE deployments, including vertical services like NB-IoT and LTE-M. Operators do not need to shut down legacy systems to enable DSS.

Limitations of Dynamic Spectrum Sharing

DSS is a practical compromise, and it comes with real costs.

Performance overhead: This is the most significant limitation. Running two systems on the same carrier introduces signalling overhead. The widely cited figures are approximately a 25% reduction in LTE throughput and around a 15% reduction in 5G NR throughput compared to what each technology would achieve on its own dedicated carrier. For subscribers in areas where DSS is the only available 5G coverage, this means 5G speeds that are only marginally better than LTE in many real-world conditions.

This is one reason many early low-band DSS deployments were criticised as 5G in name more than performance, despite delivering excellent geographic coverage.

Not a capacity solution: DSS is designed to extend 5G coverage – it is not designed to deliver the high capacity and peak throughput that 5G promises. For high-density environments like stadiums, city centres, and transport hubs, dedicated mid-band or mmWave spectrum is required. Trying to serve dense urban traffic with DSS results in a poor experience for both LTE and 5G users.

Device compatibility complexity: The behaviour of DSS varies depending on the specific release capabilities of the device. Some DSS scenarios require Release 16 or Release 17 compliant devices to function correctly, which adds complexity in networks where a large proportion of connected devices are older models.

FDD-centric design: Early DSS implementations focused primarily on FDD (Frequency Division Duplex) bands. TDD (Time Division Duplex) scenarios involve additional complexity, and performance in TDD-based DSS deployments is typically more variable.

Scheduling complexity: Because the base station must simultaneously manage LTE and 5G NR scheduling on the same carrier, the scheduling algorithms become significantly more complex. This places additional demands on the baseband processing capability of the base station hardware.

DSS and Its Significance in 5G

DSS did not get much attention publicly, but it solved one of the most critical problems of the early 5G rollout. Without it, operators in markets where mid-band spectrum was not yet available would have faced a choice between launching 5G with very limited geographic coverage or waiting years for spectrum auctions to conclude.

DSS gave operators a third option: launch 5G now with broad coverage, even if the performance is not at peak 5G capability, while continuing to build out dedicated mid-band and mmWave capacity in parallel. This allowed 5G subscriber numbers to grow, 5G-capable devices to ship in volume, and the overall ecosystem to develop – even before the dedicated 5G spectrum infrastructure was fully in place.

In markets like the United States, where the 600 MHz band DSS rollout preceded the major C-band auction, DSS was the reason millions of consumers first experienced 5G connectivity on their devices. The coverage was broad, even if the speeds did not always reflect the full potential of 5G NR.

Moving Forward – From DSS to MRSS

As 5G networks mature and operators acquire dedicated mid-band spectrum, the role of DSS naturally diminishes. Once an operator has sufficient C-band or 3.5 GHz spectrum for 5G, there is less incentive to run LTE and 5G NR on the same low-band carrier with the associated overhead.

But the concept of spectrum sharing is not going away – it is evolving.

Ericsson published research in April 2026 outlining Multi-RAT Spectrum Sharing (MRSS) – the next generation of the DSS concept, designed to enable coexistence between 5G and 6G on the same FR1 spectrum. MRSS differs from DSS in two important ways: it supports both FDD and TDD (DSS primarily focused on FDD), and it achieves significantly lower overhead thanks to the ultra-lean design of 5G NR, which relies far less on always-on reference signals than LTE did.

The principle is the same – multiple radio technologies sharing finite and valuable low-band spectrum efficiently – but the implementation is cleaner, and the performance penalty is lower. As 6G standardisation progresses through the late 2020s, MRSS is likely to play the same role for the 5G-to-6G transition that DSS played for the LTE-to-5G transition.

In parallel, AI-driven spectrum management frameworks are being developed for 6G bands. Research programmes like the POST (Programmable Open Spectrum Twin) framework combine Open RAN and Digital Twin technologies to enable real-time spectrum sensing, prediction, and dynamic allocation – taking the core idea of DSS and scaling it to a far more intelligent and automated level.

DSS was not the most glamorous technology to come out of the early 5G era. It did not deliver the headline speeds that 5G promised, and it was always understood as a transitional tool rather than a long-term architecture. It solved a real problem at exactly the right time – and the lessons learned from deploying it at scale are directly shaping how the industry thinks about spectrum sharing for the next generation of wireless networks.

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