5G will Radically Transform RAN Design and Topology as Multiple Spectrum Bands and Use Cases Converge

It has been difficult to avoid the hype surrounding the imminent arrival of the Fifth Generation (5G) of mobile networks. The most extensive change in mobile communications since the first handheld cellular call was made in 1973 by Motorola’s Marty Cooper, 5G promises to add billions to a country’s gross domestic product and to create millions of jobs—more than 4G has. As it is designed to pair with technologies like Artificial Intelligence (AI) and Cross Reality (XR) to enhance current services and applications, 5G should offer elevated levels of user experiences.

If one moves beyond this blue sky thinking, there is every reason to believe that the various promises of 5G will not occur simultaneously. Understanding the challenges and time lines behind 5G deployment is essential to getting beyond the hype and managing expectations for real-life deployments for both companies and consumers alike. Although there are many elements to consider in 5G deployments, in the Foresight we discuss the influence on RAN design of spectrum and use case choice.

Unlike previous cellular generations that tended to operate in sub-1 GHz spectrum (or at least a single band) for the most part, 5G encompasses three distinct spectrum bands. Spectrum for 5G is defined in low-band (sub-1 GHz), mid-band (1–6 GHz), and high-band (greater than 6 GHz) frequencies. The high band is generally considered to be Millimeter Wave (mmWave) at 28 GHz or 39 GHz. Low-band performance is expected to be roughly equivalent to the performance experienced from today’s Long-Term Evolution (LTE) Advanced Pro networks. Next up is mid-band; expectations are that 3.5 GHz or C-band spectrum will prove to be popular. These frequencies do not have the range of low band and consequently will be deployed in metropolitan areas (and not nationwide) as a small cell network. Also, the outdoor-to-indoor signal penetration will suffer, and this will drive more small cells or radio nodes indoors; as a result, this will be very expensive. Finally, mmWave deploys in dense urban areas as a hyper-dense small-cell Radio Active Network (RAN) with possible downlink throughputs of greater than 10 Gigabits per second (Gbps).

We expect that a low-band 5G RAN will appear first and that many MNOs and vendors will claim that a software change is all that is necessary to turn on 5G. Naturally, this will be a gradual process, since low-band frequencies are likely allocated to 4G; therefore, migrating users to 5G needs to be a steady progression. The experience will be equivalent to today’s LTE Advanced Pro. Mid-band will be the next frequency to be deployed in select locations, followed by mmWave.

As a result, many of the use cases which leverage 5G will rely on small cells or ultra-dense small cells placed near the subscriber; these will require a densification of fiber-based backhaul and provisioning of power to the RAN. Bringing together the Enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communications (URLLC), and Massive Machine Type Communication (mMTC) use cases across three distinct RANs encompassed in one network is a significant challenge for MNOs. The MNO cannot use the same connection for all use cases and must resort to network slicing to create new network device interfaces. Network slicing will enable 5G functionality by creating virtual networks using shared physical infrastructure to maximize network flexibility. The orchestration of many network characteristics will be among the complex challenges that MNOs face as 5G deploys. We believe that large-scale commercial network slicing will become significant around the year 2023, with (for example) a few customs and proprietary slices available sooner for MNO private use or public safety. We believe that 5G will reach 1 billion subscribers in 2026 for only 10% of the total number of worldwide subscribers at that time.

Unlike prior generations, 5G mobile networks will usher in 3 distinct types of RAN corresponding to each of the spectrum bands, and that the dense and ultra-dense RANs built for mid-band and high-band spectrum will need to interwork seamlessly with the low-band RAN for high QoS. Also, unlike preceding generations, network slicing will be used to create virtual networks for each business case on a shared physical infrastructure and that the orchestration of 5G networks will be among the most challenging tasks faced by an operator. Consequently, we expect the RAN build for full nationwide 5G coverage will be a gradual process as the service providers solve the complex challenges involved.