Enabling the Potential of 5G: Solutions to the Technical Challenges of the Diverse 5G Bands

During recent years, the 3GPP ecosystem has developed a fifth generation of wireless technology known as new radio (NR). The next generation specification aims to both improve the performance of mobile broadband and to expand the scope of mobile communications to encompass new so-called verticals (i.e., use cases related to specific industries). Examples of potential new areas include industry and automation, the evolving automobile industry, environmental technologies, the medical industry, and harnessing the potential of artificial intelligence systems (more details in [1] for interested readers). In the mobile broadband sphere, the emergence of applications such as virtual reality and augmented reality drive continuing growth in both traffic and subscribers, and network quality demands such as latency performance. To enable 5G growth, it is thus essential to be able to exploit newly available spectrum resources in addition to currently used spectrum under 4G systems. In this column, we refer to 2.6–7.125 GHz as “mid band” and above 24 GHz as “high band.” Providing mobile broadband services in this spectrum has presented new challenges that needed to be solved both in specifications and in implementation, as described herein. Although the core waveform in 5G NR specification is cyclic prefix orthogonal frequency-division multiplexing (CP-OFDM)based like LTE, the design of NR allows for a very high degree of flexibility in allocating different bandwidth and different numerologies, including decoupling of the total bandwidth supported by the BS and the bandwidths used for communication toward and from different user equipments (UEs). This, combined with advanced carrier aggregation and dual connectivity features, enables tailored support for complex and fragmented spectrum allocations. At medium and high bands, path loss is greater than low bands, which is compensated by beamforming using advanced antenna array technologies. The NR specification includes a large number of features intended to support beamforming processing, ranging from support of a diverse set of MIMO schemes to the development of over-the-air (OTA)-based conformance requirements, which enables tight integration of radio and antennas in large advanced antenna arrays. Even with array processing, uplink coverage with reasonable data rates may be restricted in medium and high bands. To enable flexible utilization of the available spectrum, the 3rd Generation Partnership Project (3GPP) has standardized solutions for sharing the same carriers in regular bands between LTE and NR, while operating CA between regular and mid/ high bands for NR. With such solutions, the high bands can be used close to the base station (BS), while further from the BS the uplink (UL) is provided mainly by the low band part of the NR CA pair, and the downlink (DL) is provided in the high band. The sharing solutions also provide a very effective path for migration from LTE to NR. Studies are ongoing into the usage scenarios and potential for further spectrum between 7 and 24 GHz and above 52 GHz in future 3GPP Releases. The existing LTE spectrum is also being refarmed for NR operation in low and mid bands (450 MHz–3.8 GHz). The status of the NR spectrum in the Release 15 specifications is shown in Fig. 1. Once the standardization aspects were settled, harnessing the new spectrum with the 5G standard presented new challenges in network and UE implementation and testing. The success in both standardization and implementation means that deployment of both mid band and high band has commenced in some markets and can be expected to grow significantly. In the remainder of the column, we summarize the challenges relating to implementing 5G in new spectrum and demonstrating compliance with radio and radio resource management (RRM) specifications in a satisfactory manner, which has been of crucial importance in getting to commercial grade hardware.