Considerations and Strategies for Maximizing C-band Deployment
The recently concluded C-band auction has created new opportunities to help mobile operators address the ever growing need for network capacity, spectral efficiency and a migration path to 5G and beyond. As with all mobile technology innovations, the benefits the new C-band spectrum provides will depend on how operators plan for and implement it into their existing legacy networks. There are a number of key challenges, including the integration of advanced beamforming technologies, the rise of massive and multi-user MIMO, site architecture issues, potential interference with fixed satellite services and use with small cells, to name a few. This white paper provides a wide angle perspective of some of the major challenges facing operators as they consider the strategies for deploying new C-band capabilities. It also shines a light on some of the innovative developments from leading network OEMs like CommScope.
As we begin 2021, the first commercial 5G networks are well over a year into operation. During the past year, 5G activities have accelerated and now outpace the growth rate of all past generations of mobile technology. While 5G global deployments have utilized a wide range of the spectrum, from 600 MHz to 40 GHz, special focus is being paid to mid-band frequencies in the 3.3–4.2 GHz range. Most European nations have now assigned 3.5 GHz spectrum to operators and several networks have progressed beyond initial build-out and commercial launch. Likewise, in Asia-Pacific and the Middle East, 5G at 3.5 GHz continues to expand and mature.
3.5 GHz allocations in the United States now include the 150 MHz CBRS band which is designated for shared use with limited transmit power. As such, it is not ideally suited for macro deployment on existing sites. In December 2020, the C-band auction added another 280 MHz. This latest addition to the spectrum is regulated by rules to enable its use as a capacity overlay on macro sites with coverage characteristics similar to mid-bands around 2 GHz. Using Time Division Duplex (TDD), C-band will operate as bands n77/n78 and be fully compatible with global 3.5 MHz 5G networks. Beyond C-band, an additional 100 MHz allocation at 3.45–3.55 GHz is planned for release in 2021.
The U.S. C-band 3.7–4.2 GHz is currently used primarily for Fixed Satellite Service (FSS) downlink from space to earth. FSS includes about 20,000 operational earth station receivers which cannot coexist in the same band as 5G. Fortunately, technology advancements enable these services to continue unimpaired using just 200 MHz of bandwidth at 4.0–4.2 GHz. FSS operators will relocate to this frequency range as part of C-band refarming. The transition will take place in two phases, with a first phase of 100 MHz bandwidth (3.7–3.8 GHz) expected to be cleared for 5G use in 46 major markets in late 2021. The remaining 180 MHz (3.8–3.98 GHz) will be added nationwide in a second phase on a timeline to be agreed upon by the parties in each market.
Propagation path loss increases with frequency and the loss at C-band is about 6–8 dB higher than at the mid-bands around 2 GHz. Building penetration loss also increases by some 4 dB but this varies with building materials. The building’s impact on signal loss is less severe for a wood framed home, but an industrial or office building can be left without C-band coverage throughout much of its interior. This is due to the larger building size and use of wall and window materials with higher RF attenuation characteristics.
To match the coverage at lower frequencies from existing sites, the C-band path loss deficit must be compensated. The solution to the coverage problem is beamforming. The 5G NR standard supports beamformed control channels and traffic channels; whereas, beamforming in LTE is limited to traffic channels. Downlink (DL) coverage is defined by the control (broadcast) channel. Beamforming allows C-band coverage to closely match that of LTE at 2 GHz. The C-band uplink (UL) budget is still more limited, however. It is sufficient for maintaining a connection (control plane signaling) but may need help with uplink traffic (user plane) around the cell edge. In these cases, a common solution is dual connectivity, where LTE at the lower bands complements the 5G UL. As lower bands migrate to 5G NR, the same or better improvement can be achieved with carrier aggregation.
Learn more about Beamforming, Site Architecture, Co-Existence with FSS, Supply Power, Small Cells, Fronthaul and Backhaul, the importance of putting plans and partnerships in place now instead of later by clicking here.
