T-Mobile pursues a multi-band 5G spectrum strategy

The architecture and technology choices in a 5G network are about delivering the right connectivity where users need it, while maximizing the available spectrum assets. Most service providers around the globe initially launched 5G networks using mid-band spectrum, as it provides a balance between coverage and capacity for initial 5G use cases and deployment scenarios. A few service providers have already deployed their 5G networks in more than one spectrum band.

Understanding different spectrum bands’ characteristics and roles in carrying 5G services can be a challenge for consumers and businesses. This is partly because most existing 4G services perform well for both outdoor and indoor scenarios in fewer spectrum bands. 5G technologies use more spectrum bands, compared to 4G, to deliver a broader range of services with different network performance requirements.

Eventually, all three major spectrum bands will power the world’s 5G networks, but some service providers are already leading the way. This article examines the 5G deployment strategy of T-Mobile in the US, currently deploying a network on all three band types. For more information on 5G spectrum, see page 21.

T-Mobile’s strategy for 5G deployments

T-Mobile is deploying 5G on dedicated low-band spectrum (600MHz) as a base layer for coverage, which allowed it to launch the country´s first nationwide 5G network at the end of 2019. The target is to cover 300 million people (90 percent of people in the US) by the end of 2021 and 97 percent of the population in 2022.

T-Mobile has dedicated mid-band spectrum (2.5GHz), from its merger with Sprint, on which deployments started in mid-2020 and are ongoing. Mid-band spectrum can deliver more capacity and speed than low-band, with better reach and building penetration capabilities than high-band spectrum. The build-out of population coverage on this band reached 140 million (over 40 percent of people in the US) in early 2021, and is planned to grow to reach 200 million this year. This is the largest mid-band deployment to date in the US, with a target of reaching 300 million people (90 percent) by the end of 2023. In addition, acquired C-band spectrum will be used for deployment where helpful in urban areas, complementing the 2.5GHz layer.

The use of 5G mid-band spectrum, in proximity to mid-band spectrum for existing 4G services, allows for a network realization characterized by:

• urban and suburban coverage and capacity across large metropolitan areas
• networks leveraging existing 4G macro radio sites
• Massive MIMO radios at each site, software configurable to support the full spectrum available
• increases in coverage and capacity for mid-band services, when mid-band downlinks are combined with uplinks in low-band spectrum (inter-band carrier aggregation)
• significant performance increase for mid-band versus low-band services
• upgrade of backhaul capacity to support the leap in capacity enabled by powerful radios

The third part of T-Mobile US’s 5G deployment strategy is high-band spectrum (mmWave), where deployments started in parts of large metropolitan areas in the middle of 2019.

The combination of low- and mid-band spectrum delivers significant improvements over the 4G/5G average downlink speeds, as measured in drivetests performed by Umlaut (see Figure 20).

Network quality and differentiated services

T-Mobile’s 5G network build-out across all spectrum bands is expected to increase the available network capacity by a factor of 14 over the next few years, compared to the capacity in 2019. T-Mobile’s multi-layer 5G network will be fit for a range of services and applications that demand wide-area network coverage and mobility, enabling an increase in service revenue through customer adoption of multiple services.

Enhanced mobile broadband (eMBB) delivers the higher peak rates and low latencies required for rich media experiences. The tectonic shift in the entertainment sector towards streaming of video, music and games is exciting for mobile service providers to tap into. The targeted increase in network capacity through 2024 is the foundation to meet a growing demand for higher quality video services, AR/VR, cloud gaming and connected consumer wearables.

Fixed wireless access (FWA) is an attractive proposition where the business case for fiber is weak compared to the limited incremental investments needed to deploy FWA. T-Mobile targets the home broadband market with FWA over 5G as an alternative to older generations of copper, coax and non-cellular wireless network technologies. A dual play broadband offer, FWA and mobile broadband, is attractive for residential users, for meeting both private and remote working needs. According to the Organisation for Economic Cooperation and Development (OECD), 16.5 percent of US residential broadband connections were fiber-based by mid-2020. Providing 4G- and 5G-based home broadband is a fast way to secure digital inclusion for education and work. T-Mobile aims to serve 7–8 million customers by 2025.

The pandemic has also shown the potential for 5G in serving small and medium-sized businesses (SMBs) by connecting business locations with FWA for primary or secondary access. Fiber connections to large commercial buildings are well underway in the US, but only 12.8 percent of small commercial buildings were fiber-connected at the end of 2020. 5G has an important role to play in connecting SMBs in urban, suburban and rural areas.

Smaller markets and rural areas in the US are made up of 50 million households that are home to 130 million people, making it the largest geographic segment of the consumer market. T-Mobile wants to expand its addressable market by targeting this segment with fixed wireless and mobile broadband offerings.

Network architectural considerations to secure mid-band performance

The architecture and technology choices in a 5G network are about delivering the right connectivity where users need it, while maximizing the available spectrum assets.

• T-Mobile’s strategy relies on using dedicated spectrum for 5G services, in all three band types, while keeping its 4G services in existing bands.
• T-Mobile decided to adopt 5G standalone (SA) architecture when introducing 5G in the low-band spectrum to expand 5G coverage to areas with a low-band only signal. This decision was made to secure the integration from low- and mid-band services on the target architecture from the start. 5G SA brings significant benefits, with a simplified architecture, providing opportunities for a better end-user experience and enabling new use cases with low-latency requirements compared to non-standalone (NSA) architecture. It is also the only way to deploy 5G without dependencies on 4G coverage.
• Massive MIMO 64x64 deployed on mid-band spectrum (2.5GHz) further increases capacity and extends the cell edge, providing an improved user experience, as the performance in each sector can be maximized.
• The introduction of inter-band carrier aggregation allows T-Mobile to combine high-capacity downlinks in the mid-band spectrum with an uplink in the low-band to extend the mid-band coverage by up to 30 percent in suburban and rural areas. This combination is one of many examples of how additional 5G performance values are unlocked when using multiple spectrum bands together. This is also applicable for aggregating 5G high-band with low-band FDD, which can increase the high-band cell coverage area more than threefold. Carrier aggregation can also improve in-building performance in urban areas.
• Voice services will remain central in mobile networks. By introducing voice over NR (VoNR), T-Mobile can ensure users stay in the 5G domain as long as there is coverage, and only fall back on 4G when outside of 5G coverage.

T-Mobile’s strategy to build out 5G across all three bands exemplifies how to build a target architecture that unlocks a wide range of 5G use case possibilities, as well as how different 5G technologies can interwork to improve network performance.

Eventually, most 5G networks in the world will utilize low-, mid- and high-band spectrum to deliver the required network performance in different geographical areas, and to serve the evolving needs of consumers, society and businesses.

Diving into 5G spectrum

Different 5G spectrum bands provide different capabilities:

• Low-band 5G spectrum comes from a mix of re-farmed spectrum from early mobile generations (1G, 2G) and previously unused bands. This type of spectrum is suitable for building out a foundation for 5G coverage.
• Mid-band spectrum covers the 1–6GHz bands and includes existing 3G/4G bands, as well as new spectrum licensed for mobile services. The increase in capacity comes from the use of wider bands, and higher 5G coverage and capacity per band are enabled by new radio technologies.
• High-band spectrum is completely new for 5G and enables the launch of services with high performance in dedicated zones. The coverage for 5G services in this spectrum band is less than the coverage provided by low- and mid-band spectrum, but serves larger zones than Wi-Fi hotspots.

Services on low- and mid-bands can be delivered from existing macro towers and can also serve indoor environments from outdoor radios. Delivering services on high-bands relies on a combination of radios on towers and small cell poles to cover outdoor areas, while indoor coverage is achieved by deploying indoor small cell solutions. 5G services will be seamlessly delivered over all three bands as they become increasingly available over time.

Flavors of mid-band spectrum in the US

Spectrum allocation differs in the US from the rest of the world. The early spectrum auctions for 5G focused on providing high- and low-band spectrum to service providers. Three flavors of the mid-band spectrum are now through the auctioning phase and a fourth is coming up in the second half of 2021.

• 2.496–2.690GHz: Broadband Radio Service/Educational Broadband Service (BRS/EBS) is a pure licensed spectrum band with 194MHz allocated to serve both 4G (band 41) and 5G NR (band n41). The proximity to frequently used 4G bands makes it attractive for capacity expansion for both mobile and fixed wireless broadband.
• 3.55–3.70GHz: Citizens Broadband Radio Service (CBRS) consists of a mix of 80MHz of shared and 70MHz of licensed spectrum. The reach of CBRS is shorter as the power allowed is lower than licensed spectrum bands. CBRS spectrum can serve both 4G and 5G services.
• 3.70–3.98GHz: C-band is the most recently added spectrum in the largest auction in US history. The Federal Communications Commission (FCC) auctioned 280MHz of spectrum, with clearing to take place in two steps, the first by the end of 2021 and the second at the end of 2023.
• 3.45-3.55GHz: The next mid-band spectrum band to be auctioned in the US in 2021.

In addition, earlier licensed mid-band spectrum that today serves 3G and 4G services, can potentially be re-farmed for 5G services later.